Tagged: Ethan Siegel Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 2:09 pm on June 23, 2018 Permalink | Reply
    Tags: , , , , Could The Energy Loss From Radiating Stars Explain Dark Energy?, Ethan Siegel   

    From Ethan Siegel: “Could The Energy Loss From Radiating Stars Explain Dark Energy?” 

    From Ethan Siegel
    June 23, 2018

    1
    An artist’s conception of what the Universe might look like as it forms stars for the first time. As they shine and merge, radiation will be emitted, both electromagnetic and gravitational. But will the conversion of matter into energy be able to generate an anti-gravitational force? NASA/ESA/ESO/Wolfram Freudling et al. (STECF)

    When it comes to our quest to understand the Universe, there are mysteries out there that no one knows the solution to. Dark matter, dark energy, and cosmic inflation, for example, are all incomplete ideas, where we don’t know which type(s) of particles or fields are responsible for them. It’s even possible, although most of the top professionals don’t think it’s likely, that one or more of these puzzles might have an unconventional solution that isn’t what we’re expecting at all.

    For the first time in Ask Ethan history, we’ve got a question from a Nobel Laureate — John Mather — who wants to know if stars, by virtue of converting mass into energy, might be responsible for the effects we attribute to dark energy:

    What happens to the gravity produced by the mass that is lost, when it’s converted by nuclear reactions in stars and goes out as light and neutrinos, or when mass accretes into a black hole, or when it’s converted into gravitational waves? […] In other words, are the gravitational waves and EM waves and neutrinos now a source of gravitation that exactly matches the prior mass that was converted, or not?

    This is a fascinating idea. Let’s take a look at why.

    2
    Artist’s illustration of two merging neutron stars. The rippling spacetime grid represents gravitational waves emitted from the collision, while the narrow beams are the jets of gamma rays that shoot out just seconds after the gravitational waves (detected as a gamma-ray burst by astronomers). Mass, in an event like this, gets converted into two types of radiation. NSF / LIGO / Sonoma State University / A. Simonnet

    In Einstein’s theory of General Relativity, there are only a few ways we can model the Universe that give us exact solutions. Make a Universe with nothing in it? We can describe spacetime exactly. Put down a single mass anywhere in that otherwise empty Universe? It’s much more complicated, but we can still write down a solution. Put down a second mass somewhere else in that Universe? It’s unsolvable. All you can do is make estimates, and try and arrive at a numerical answer. This maddeningly difficult property of spacetime, that it’s so hard to characterize exactly, is why it’s taken such tremendous computing power, theoretical work, and so much time in order to properly model the merging black holes and neutron stars that LIGO has seen.

    UC Santa Cruz

    UC Santa Cruz

    14

    A UC Santa Cruz special report

    Tim Stephens

    Astronomer Ryan Foley says “observing the explosion of two colliding neutron stars” [see https://sciencesprings.wordpress.com/2017/10/17/from-ucsc-first-observations-of-merging-neutron-stars-mark-a-new-era-in-astronomy ]–the first visible event ever linked to gravitational waves–is probably the biggest discovery he’ll make in his lifetime. That’s saying a lot for a young assistant professor who presumably has a long career still ahead of him.

    2
    The first optical image of a gravitational wave source was taken by a team led by Ryan Foley of UC Santa Cruz using the Swope Telescope at the Carnegie Institution’s Las Campanas Observatory in Chile. This image of Swope Supernova Survey 2017a (SSS17a, indicated by arrow) shows the light emitted from the cataclysmic merger of two neutron stars. (Image credit: 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

    Carnegie Institution Swope telescope at Las Campanas, Chile, 100 kilometres (62 mi) northeast of the city of La Serena. near the north end of a 7 km (4.3 mi) long mountain ridge. Cerro Las Campanas, near the southern end and over 2,500 m (8,200 ft) high, at Las Campanas, Chile

    A neutron star forms when a massive star runs out of fuel and explodes as a supernova, throwing off its outer layers and leaving behind a collapsed core composed almost entirely of neutrons. Neutrons are the uncharged particles in the nucleus of an atom, where they are bound together with positively charged protons. In a neutron star, they are packed together just as densely as in the nucleus of an atom, resulting in an object with one to three times the mass of our sun but only about 12 miles wide.

    “Basically, a neutron star is a gigantic atom with the mass of the sun and the size of a city like San Francisco or Manhattan,” said Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz.

    These objects are so dense, a cup of neutron star material would weigh as much as Mount Everest, and a teaspoon would weigh a billion tons. It’s as dense as matter can get without collapsing into a black hole.

    THE MERGER

    Like other stars, neutron stars sometimes occur in pairs, orbiting each other and gradually spiraling inward. Eventually, they come together in a catastrophic merger that distorts space and time (creating gravitational waves) and emits a brilliant flare of electromagnetic radiation, including visible, infrared, and ultraviolet light, x-rays, gamma rays, and radio waves. Merging black holes also create gravitational waves, but there’s nothing to be seen because no light can escape from a black hole.

    Foley’s team was the first to observe the light from a neutron star merger that took place on August 17, 2017, and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Now, for the first time, scientists can study both the gravitational waves (ripples in the fabric of space-time), and the radiation emitted from the violent merger of the densest objects in the universe.

    3
    The UC Santa Cruz team found SSS17a by comparing a new image of the galaxy N4993 (right) with images taken four months earlier by the Hubble Space Telescope (left). The arrows indicate where SSS17a was absent from the Hubble image and visible in the new image from the Swope Telescope. (Image credits: Left, Hubble/STScI; Right, 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

    It’s that combination of data, and all that can be learned from it, that has astronomers and physicists so excited. The observations of this one event are keeping hundreds of scientists busy exploring its implications for everything from fundamental physics and cosmology to the origins of gold and other heavy elements.


    A small team of UC Santa Cruz astronomers were the first team to observe light from two neutron stars merging in August. The implications are huge.

    ALL THE GOLD IN THE UNIVERSE

    It turns out that the origins of the heaviest elements, such as gold, platinum, uranium—pretty much everything heavier than iron—has been an enduring conundrum. All the lighter elements have well-explained origins in the nuclear fusion reactions that make stars shine or in the explosions of stars (supernovae). Initially, astrophysicists thought supernovae could account for the heavy elements, too, but there have always been problems with that theory, says Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz.

    4
    The violent merger of two neutron stars is thought to involve three main energy-transfer processes, shown in this diagram, that give rise to the different types of radiation seen by astronomers, including a gamma-ray burst and a kilonova explosion seen in visible light. (Image credit: Murguia-Berthier et al., Science)

    A theoretical astrophysicist, Ramirez-Ruiz has been a leading proponent of the idea that neutron star mergers are the source of the heavy elements. Building a heavy atomic nucleus means adding a lot of neutrons to it. This process is called rapid neutron capture, or the r-process, and it requires some of the most extreme conditions in the universe: extreme temperatures, extreme densities, and a massive flow of neutrons. A neutron star merger fits the bill.

    Ramirez-Ruiz and other theoretical astrophysicists use supercomputers to simulate the physics of extreme events like supernovae and neutron star mergers. This work always goes hand in hand with observational astronomy. Theoretical predictions tell observers what signatures to look for to identify these events, and observations tell theorists if they got the physics right or if they need to tweak their models. The observations by Foley and others of the neutron star merger now known as SSS17a are giving theorists, for the first time, a full set of observational data to compare with their theoretical models.

    According to Ramirez-Ruiz, the observations support the theory that neutron star mergers can account for all the gold in the universe, as well as about half of all the other elements heavier than iron.

    RIPPLES IN THE FABRIC OF SPACE-TIME

    Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity, but until recently they were impossible to observe. LIGO’s extraordinarily sensitive detectors achieved the first direct detection of gravitational waves, from the collision of two black holes, in 2015. Gravitational waves are created by any massive accelerating object, but the strongest waves (and the only ones we have any chance of detecting) are produced by the most extreme phenomena.

    Two massive compact objects—such as black holes, neutron stars, or white dwarfs—orbiting around each other faster and faster as they draw closer together are just the kind of system that should radiate strong gravitational waves. Like ripples spreading in a pond, the waves get smaller as they spread outward from the source. By the time they reached Earth, the ripples detected by LIGO caused distortions of space-time thousands of times smaller than the nucleus of an atom.

    The rarefied signals recorded by LIGO’s detectors not only prove the existence of gravitational waves, they also provide crucial information about the events that produced them. Combined with the telescope observations of the neutron star merger, it’s an incredibly rich set of data.

    LIGO can tell scientists the masses of the merging objects and the mass of the new object created in the merger, which reveals whether the merger produced another neutron star or a more massive object that collapsed into a black hole. To calculate how much mass was ejected in the explosion, and how much mass was converted to energy, scientists also need the optical observations from telescopes. That’s especially important for quantifying the nucleosynthesis of heavy elements during the merger.

    LIGO can also provide a measure of the distance to the merging neutron stars, which can now be compared with the distance measurement based on the light from the merger. That’s important to cosmologists studying the expansion of the universe, because the two measurements are based on different fundamental forces (gravity and electromagnetism), giving completely independent results.

    “This is a huge step forward in astronomy,” Foley said. “Having done it once, we now know we can do it again, and it opens up a whole new world of what we call ‘multi-messenger’ astronomy, viewing the universe through different fundamental forces.”

    IN THIS REPORT

    Neutron stars
    A team from UC Santa Cruz was the first to observe the light from a neutron star merger that took place on August 17, 2017 and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO)

    5
    Graduate students and post-doctoral scholars at UC Santa Cruz played key roles in the dramatic discovery and analysis of colliding neutron stars.Astronomer Ryan Foley leads a team of young graduate students and postdoctoral scholars who have pulled off an extraordinary coup. Following up on the detection of gravitational waves from the violent merger of two neutron stars, Foley’s team was the first to find the source with a telescope and take images of the light from this cataclysmic event. In so doing, they beat much larger and more senior teams with much more powerful telescopes at their disposal.

    “We’re sort of the scrappy young upstarts who worked hard and got the job done,” said Foley, an untenured assistant professor of astronomy and astrophysics at UC Santa Cruz.

    7
    David Coulter, graduate student

    The discovery on August 17, 2017, has been a scientific bonanza, yielding over 100 scientific papers from numerous teams investigating the new observations. Foley’s team is publishing seven papers, each of which has a graduate student or postdoc as the first author.

    “I think it speaks to Ryan’s generosity and how seriously he takes his role as a mentor that he is not putting himself front and center, but has gone out of his way to highlight the roles played by his students and postdocs,” said Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz and the most senior member of Foley’s team.

    “Our team is by far the youngest and most diverse of all of the teams involved in the follow-up observations of this neutron star merger,” Ramirez-Ruiz added.

    8
    Charles Kilpatrick, postdoctoral scholar

    Charles Kilpatrick, a 29-year-old postdoctoral scholar, was the first person in the world to see an image of the light from colliding neutron stars. He was sitting in an office at UC Santa Cruz, working with first-year graduate student Cesar Rojas-Bravo to process image data as it came in from the Swope Telescope in Chile. To see if the Swope images showed anything new, he had also downloaded “template” images taken in the past of the same galaxies the team was searching.

    9
    Ariadna Murguia-Berthier, graduate student

    “In one image I saw something there that was not in the template image,” Kilpatrick said. “It took me a while to realize the ramifications of what I was seeing. This opens up so much new science, it really marks the beginning of something that will continue to be studied for years down the road.”

    At the time, Foley and most of the others in his team were at a meeting in Copenhagen. When they found out about the gravitational wave detection, they quickly got together to plan their search strategy. From Copenhagen, the team sent instructions to the telescope operators in Chile telling them where to point the telescope. Graduate student David Coulter played a key role in prioritizing the galaxies they would search to find the source, and he is the first author of the discovery paper published in Science.

    10
    Matthew Siebert, graduate student

    “It’s still a little unreal when I think about what we’ve accomplished,” Coulter said. “For me, despite the euphoria of recognizing what we were seeing at the moment, we were all incredibly focused on the task at hand. Only afterward did the significance really sink in.”

    Just as Coulter finished writing his paper about the discovery, his wife went into labor, giving birth to a baby girl on September 30. “I was doing revisions to the paper at the hospital,” he said.

    It’s been a wild ride for the whole team, first in the rush to find the source, and then under pressure to quickly analyze the data and write up their findings for publication. “It was really an all-hands-on-deck moment when we all had to pull together and work quickly to exploit this opportunity,” said Kilpatrick, who is first author of a paper comparing the observations with theoretical models.

    11
    César Rojas Bravo, graduate student

    Graduate student Matthew Siebert led a paper analyzing the unusual properties of the light emitted by the merger. Astronomers have observed thousands of supernovae (exploding stars) and other “transients” that appear suddenly in the sky and then fade away, but never before have they observed anything that looks like this neutron star merger. Siebert’s paper concluded that there is only a one in 100,000 chance that the transient they observed is not related to the gravitational waves.

    Ariadna Murguia-Berthier, a graduate student working with Ramirez-Ruiz, is first author of a paper synthesizing data from a range of sources to provide a coherent theoretical framework for understanding the observations.

    Another aspect of the discovery of great interest to astronomers is the nature of the galaxy and the galactic environment in which the merger occurred. Postdoctoral scholar Yen-Chen Pan led a paper analyzing the properties of the host galaxy. Enia Xhakaj, a new graduate student who had just joined the group in August, got the opportunity to help with the analysis and be a coauthor on the paper.

    12
    Yen-Chen Pan, postdoctoral scholar

    “There are so many interesting things to learn from this,” Foley said. “It’s a great experience for all of us to be part of such an important discovery.”

    13
    Enia Xhakaj, graduate student

    IN THIS REPORT

    Scientific Papers from the 1M2H Collaboration

    Coulter et al., Science, Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source

    Drout et al., Science, Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis

    Shappee et al., Science, Early Spectra of the Gravitational Wave Source GW170817: Evolution of a Neutron Star Merger

    Kilpatrick et al., Science, Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger

    Siebert et al., ApJL, The Unprecedented Properties of the First Electromagnetic Counterpart to a Gravitational-wave Source

    Pan et al., ApJL, The Old Host-galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational-wave Source

    Murguia-Berthier et al., ApJL, A Neutron Star Binary Merger Model for GW170817/GRB170817a/SSS17a

    Kasen et al., Nature, Origin of the heavy elements in binary neutron star mergers from a gravitational wave event

    Abbott et al., Nature, A gravitational-wave standard siren measurement of the Hubble constant (The LIGO Scientific Collaboration and The Virgo Collaboration, The 1M2H Collaboration, The Dark Energy Camera GW-EM Collaboration and the DES Collaboration, The DLT40 Collaboration, The Las Cumbres Observatory Collaboration, The VINROUGE Collaboration & The MASTER Collaboration)

    Abbott et al., ApJL, Multi-messenger Observations of a Binary Neutron Star Merger

    PRESS RELEASES AND MEDIA COVERAGE


    Watch Ryan Foley tell the story of how his team found the neutron star merger in the video below. 2.5 HOURS.

    Press releases:

    UC Santa Cruz Press Release

    UC Berkeley Press Release

    Carnegie Institution of Science Press Release

    LIGO Collaboration Press Release

    National Science Foundation Press Release

    Media coverage:

    The Atlantic – The Slack Chat That Changed Astronomy

    Washington Post – Scientists detect gravitational waves from a new kind of nova, sparking a new era in astronomy

    New York Times – LIGO Detects Fierce Collision of Neutron Stars for the First Time

    Science – Merging neutron stars generate gravitational waves and a celestial light show

    CBS News – Gravitational waves – and light – seen in neutron star collision

    CBC News – Astronomers see source of gravitational waves for 1st time

    San Jose Mercury News – A bright light seen across the universe, proving Einstein right

    Popular Science – Gravitational waves just showed us something even cooler than black holes

    Scientific American – Gravitational Wave Astronomers Hit Mother Lode

    Nature – Colliding stars spark rush to solve cosmic mysteries

    National Geographic – In a First, Gravitational Waves Linked to Neutron Star Crash

    Associated Press – Astronomers witness huge cosmic crash, find origins of gold

    Science News – Neutron star collision showers the universe with a wealth of discoveries

    UCSC press release
    First observations of merging neutron stars mark a new era in astronomy

    Credits

    Writing: Tim Stephens
    Video: Nick Gonzales
    Photos: Carolyn Lagattuta
    Header image: Illustration by Robin Dienel courtesy of the Carnegie Institution for Science
    Design and development: Rob Knight
    Project managers: Sherry Main, Scott Hernandez-Jason, Tim Stephens

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

    Noted in the vdeo but not in te article:

    NASA/Chandra Telescope

    NASA/SWIFT Telescope

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

    Prompt telescope CTIO Chile

    NASA NuSTAR X-ray telescope

    See the full article UCSC article here

    3
    It isn’t just the locations and magnitudes of masses that determine how gravity works and spacetime evolves, but rather how those masses move relative to one another and accelerate through a changing gravitational field over time. In General Relativity, a system with more than one mass is not exactly solvable. David Champion, Max Planck Institute for Radio Astronomy

    One of the few cases we can solve exactly is where the Universe is filled with an even amount of “stuff” everywhere and in all directions. It doesn’t matter what that “stuff” is. It could be a collection of particles, a fluid, radiation, a property inherent to space itself, or a field with the right properties. It could be a mix of a bunch of different things, such as normal matter, antimatter, neutrinos, radiation, and even the mysterious dark matter and dark energy.

    If this describes your Universe, and you know how much of each of these different quantities there are, all you need to do is measure the expansion rate of the Universe. Do that, and you immediately know how the Universe expanded over its entire history, including its future history. If you know what the Universe is made of and how it’s expanding today, you can figure out the fate of the entire Universe.

    4
    The expected fates of the Universe (top three illustrations) all correspond to a Universe where the matter and energy fights against the initial expansion rate. In our observed Universe, a cosmic acceleration is caused by some type of dark energy, which is hitherto unexplained. All of these Universes are governed by the Friedmann equations. E. Siegel / Beyond the Galaxy

    When we do this figuring based on the Universe we observe today, we arrive at a Universe that’s made of:

    68% dark energy,
    27% dark matter,
    4.9% normal matter,
    0.1% neutrinos,
    0.01% radiation,

    and a negligible amount of everything else: curvature, antimatter, cosmic strings, and anything else you can imagine. The total uncertainty on all of these, combined, is less than 2%. We also learn the fate of the Universe — that it will expand forever — and the age of the Universe: 13.8 billion years since the Big Bang. It’s a remarkable achievement of modern cosmology.

    4
    An illustrated timeline of the Universe’s history. If the value of dark energy is small enough to admit the formation of the first stars, then a Universe containing the right ingredients for life is pretty much inevitable. We are, thankfully, here to confirm that this occurred where we live. European Southern Observatory (ESO)

    But this assumes that we can approximate the Universe the way we modeled it: with a smooth, even amount of stuff everywhere and in all directions. The real Universe, as you probably noticed, is clumpy. There are planets, stars, clumps of gas and dust, plasmas, galaxies, clusters of galaxies and great cosmic filaments connecting them. There are enormous cosmic voids, sometimes stretching billions of light years across. The mathematical word for a perfectly smooth Universe is homogeneous, and yet our Universe is remarkably inhomogeneous. It’s possible that our assumption that led us to this conclusion is all wrong.

    5
    Both simulations (red) and galaxy surveys (blue/purple) display the same large-scale clustering patterns. The Universe, particularly on smaller scales, is not perfectly homogeneous.
    Gerard Lemson and the Virgo Consortium

    On the largest scales, though, the Universe is homogeneous. If you look at a small scale, like that of a star, galaxy, or even a cluster of galaxies, you’ll find that you have regions that are both way below and way above the average density. But if you look at scales that are closer to 10 billion light years (or more) on a side, the Universe appears roughly the same everywhere, on average. On the largest scales, the Universe is over 99% homogeneous.

    Thankfully, we can quantify how good (or not good) our assumption is by calculating the effects of the inhomogeneities atop this large-scale homogeneous background. I did this for myself back in 2005, and found that the inhomogeneities contribute less than 0.1% to the expansion rate, and they don’t behave like dark energy. You can see this for yourself if you like.

    6
    Fractional contributions of gravitational potential energy W (long-dashed line) and kinetic energy K (solid line) to the total energy density of the universe, plotted as a function of past and future expansion factor for a Universe with matter but no dark energy. The short-dashed line is the sum of contributions from inhomogeneities. The dotted lines show results from linear perturbation theory. E.R. Siegel and J.N. Fry, ApJ, 628, 1, L1-L4.

    But a related possibility is that certain types of energy can transform from one type into another over time. In particular, owing to the

    burning of nuclear fuel inside stars,
    gravitational collapse of clouds into contracted objects,
    mergers of neutron stars and black holes,
    and the inspiraling action of many gravitational systems,

    matter, or mass, can transform into radiation, or energy. In other words, it’s possible to change how the Universe gravitates, and therefore, how it expands (or contracts) over time.

    7
    Although we’ve seen black holes directly merging many separate times in the Universe, we know many more exist. When supermassive black holes merge together, LISA will allow us to predict, up to years in advance, exactly when the critical event will occur. LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)

    When two black holes merge together, for example, a significant fraction of mass can be converted into energy: up to about 5%. In the first black hole-black hole merger detected by LIGO, a black hole of 36 solar masses and a black hole of 29 solar masses merged together, but produced a single black hole whose final mass was only 62 solar masses. What happened to the other 3 solar masses? They were converted into pure energy, in the form of gravitational waves, by Einstein’s E = mc2.

    The question, then, becomes how a change from mass into radiation affects the expansion of the Universe? According to a recent paper by Nick Gorkavyi and Alexander Vasilkov, they claim that it can generate a repulsive, anti-gravitational force.

    8
    Computer simulation of two merging black holes producing gravitational waves. When mass converts into radiation, is it possible that we can generate a repulsive force? Werner Benger, cc by-sa 4.0

    Unfortunately, this claim is based in what only appears to be anti-gravity. When you have a certain amount of mass, you experience a certain amount of gravitational attraction towards that mass: this is equally true in both Einstein’s and Newton’s theory of gravity. If you transform that mass into energy and it radiates outward at the speed of light, like all massless radiation, then when that radiation passes by you, you’ll suddenly see less mass to be attracted to.

    The curvature of spacetime changes, and where you once experienced gravitational attraction of a certain amount, you’ll now experience attraction that’s 5% less. It’s equivalent, mathematically, to adding a repulsive, anti-gravitational force to your system. But in reality, you’re experiencing the reduced attraction because you turned mass into energy, and radiation gravitates differently (especially once it passes you by) than matter does.. This has been stated quite clearly.

    9
    Any object or shape, physical or non-physical, would be distorted as gravitational waves passed through it. Whenever one large mass is accelerated through a region of curved spacetime, gravitational wave emission is an inevitable consequence. However, we can compute the effects of this radiation on space, and it doesn’t cause a repulsion or an accelerated expansion. NASA/Ames Research Center/C. Henze

    In fact, we can go a step further and calculate how this transformation affects the entire Universe! We can quantify both how gravitational waves contribute to the energy density of the Universe and how much of the Universe’s energy is in the form of radiation of all types. Like mass, radiation is quantized, so that as the volume of the Universe increases (by a factor of distance cubed), the particle density decreases (by a factor of one over the distance cubed). But unlike mass, radiation has a wavelength, and as space expands, that wavelength drops as one over the distance as well; radiation becomes less gravitationally important faster than matter does.

    Another thing that you’d need to do is have the correct equation-of-state. Matter and radiation both evolve over time as stated above, but dark energy keeps a constant density throughout all of space as the Universe expands. As we move forward in time, this problem only gets worse; dark energy becomes more dominant while matter and radiation both become less and less important.

    Not only do matter and radiation both result in an attractive force and a decelerating Universe, but neither one can come to dominate the energy density of the Universe so long as it keeps expanding.

    10
    The blue “shading” represent the possible uncertainties in how the dark energy density was/will be different in the past and future. The data points to a true cosmological “constant,” but other possibilities are still allowed. Unfortunately, the conversion of matter into radiation cannot mimic dark energy; it can only cause what was once behaving as matter to now behave as radiation. Quantum Stories.

    If you want to create a Universe where you have an accelerated expansion, to the best of our knowledge, you require a new form of energy over the ones we presently know about. We have given a name to it, dark energy, even though we aren’t 100% sure what the nature of dark energy truly is.

    However, despite our ignorance in that realm, we can very clearly state what dark energy isn’t. It isn’t stars burning through their fuel; it isn’t matter emitting gravitational waves; it isn’t due to gravitational collapse; it isn’t due to mergers or inspirals. It’s possible that there’s a new law of gravity that will eventually replace Einstein, but in the context of General Relativity, there’s no way to explain what we observe with the physics we know today. There’s something truly new to discover out there.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

    Advertisements
     
  • richardmitnick 2:19 pm on June 20, 2018 Permalink | Reply
    Tags: , , , , Ethan Siegel, The Surprising Reason Why Neutron Stars Don’t All Collapse To Form Black Holes   

    From Ethan Siegel: “The Surprising Reason Why Neutron Stars Don’t All Collapse To Form Black Holes” 

    From Ethan Siegel
    June 20, 2018

    1
    In the aftermath of the creation of a neutron star, it can have a variety of masses, many of which are far in excess of the most massive white dwarf. But there is a limit to how massive they can get before becoming a black hole, and a simple nuclear physics experiment on a single proton may have just discovered why. (NASA)

    There’s something very special inside a proton and neutron that holds the key.

    There are few things in the Universe that are as easy to form, in theory, as black holes are. Bring enough mass into a compact volume and it gets more and more difficult to gravitationally escape from it. If you were to gather enough matter in a single spot and let gravitation do its thing, you’d eventually pass a critical threshold, where the speed you’d need to gravitationally escape would exceed the speed of light. Reach that point, and you’ll create a black hole.

    But real, normal matter will very much resist getting there. Hydrogen, the most common element in the Universe, will fuse in a chain reaction at high temperatures and densities to create a star, rather than a black hole. Burned out stellar cores, like white dwarfs and neutron stars, can also resist gravitational collapse and stave off becoming a black hole. But while white dwarfs can reach only 1.4 times the mass of the Sun, neutron stars can get twice as massive. At long last, we finally understand why [Nature].

    2
    Sirius A and B, a normal (Sun-like) star and a white dwarf star. Even though the white dwarf is much lower in mass, its tiny, Earth-like size ensures its escape velocity is many times larger. For a neutron stars, masses can be even larger, with physical sizes in the tens of kilometers. (NASA, ESA and G. Bacon (STScI))

    In our Universe, the matter-based objects we know of are all made of just a few simple ingredients: protons, neutrons, and electrons. Each proton and neutron is made up of three quarks, with a proton containing two up and one down quark, and a neutron containing one up and two downs. On the other hand, electrons themselves are fundamental particles. Although particles come in two classes — fermions and bosons — both quarks and electrons are fermions.

    3
    The Standard Model of particle physics accounts for three of the four forces (excepting gravity), the full suite of discovered particles, and all of their interactions. Quarks and leptons are fermions, which have a host of unique properties that the other (bosons) particles do not possess. (Contemporary Physics Education Project / DOE / NSF / LBNL)

    Standard Model of Particle Physics from Symmetry Magazine

    Why should you care? It turns out that these classification properties are vitally important when it comes to the question of black hole formation. Fermions have a few properties that bosons don’t, including:

    they have half-integer (e.g., ±1/2, ±3/2, ±5/2, etc.) spins as opposed to integer (0, ±1, ±2, etc.) spins,
    they have antiparticle counterparts; there are no anti-bosons,
    and they obey the Pauli Exclusion Principle, whereas bosons don’t.

    That last property is the key to staving off collapse into a black hole.

    4
    The energy levels and electron wavefunctions that correspond to different states within a hydrogen atom. Because of the spin = 1/2 nature of the electron, only two (+1/2 and -1/2 states) electrons can be in any given state at once. (PoorLeno / Wikimedia Commons)

    The Pauli exclusion principle, which only applies to fermions, not bosons, states, explicitly, that in any quantum system, no two fermions can occupy the same quantum state. It means that if you take, say, an electron and put it in a particular location, it will have a set of properties in that state: energy levels, angular momentum, etc.

    If you take a second electron and add it to your system, however, in the same location, it is forbidden from having those same quantum numbers. It must either occupy a different energy level, have a different spin (+1/2 if the first was -1/2, for example), or occupy a different location in space. This principle explains why the periodic table is arranged as it is.

    This is why atoms have different properties, why they bind together in the intricate combinations that they do, and why each element in the periodic table is unique: because the electron configuration of each type of atom is unlike any other.

    Periodic table Sept 2017. Wikipedia

    5
    The three valence quarks of a proton contribute to its spin, but so do the gluons, sea quarks and antiquarks, and orbital angular momentum as well. The electrostatic repulsion and the attractive strong nuclear force, in tandem, are what give the proton its size.(APS/Alan Stonebraker)

    Protons and neutrons are similar. Despite being composite particles, made up of three quarks apiece, they behave as single, individual fermions themselves. They, too, obey the Pauli Exclusion Principle, and no two protons or neutrons can occupy the same quantum state. The fact that electrons are fermions is what keeps white dwarf stars from collapsing under their own gravity; the fact that neutrons are fermions prevents neutron stars from collapsing further. The Pauli exclusion principle responsible for atomic structure is responsible for keeping the densest physical objects of all from becoming black holes.

    6
    A white dwarf, a neutron star or even a strange quark star are all still made of fermions. The Pauli degeneracy pressure helps hold up the stellar remnant against gravitational collapse, preventing a black hole from forming. (CXC/M. Weiss)

    And yet, when you look at the white dwarf stars we have in the Universe, they cap out at around 1.4 solar masses: the Chandrasekhar mass limit. The quantum degeneracy pressure arising from the fact that no two electrons can occupy the same quantum state is what prevents black holes from forming until that threshold is crossed.

    In neutron stars, there should be a similar mass limit: the Tolman-Oppenheimer-Volkoff limit. Initially, it was anticipated that this would be about the same as the Chandrasekhar mass limit, since the underlying physics is the same. Sure, it’s not specifically electrons that are providing the quantum degeneracy pressure, but the principle (and the equations) are pretty much the same. But we now know, from our observations, that there are neutron stars much more massive than 1.4 solar masses, perhaps rising as high as 2.3 or 2.5 times the mass of our Sun.

    7
    A neutron star is one of the densest collections of matter in the Universe, but there is an upper limit to their mass. Exceed it, and the neutron star will further collapse to form a black hole. (ESO/Luís Calçada)

    And yet, there are reasons for the differences. In neutron stars, the strong nuclear force plays a role, causing a larger effective repulsion than for a simple model of degenerate, cold gases of fermions (which is what’s relevant for electrons). For the past 20+ years, calculations of the theoretical mass limit for neutron stars have varied tremendously: from about 1.5 to 3.0 solar masses. The reason for the uncertainty has been the unknowns surrounding the behavior of extremely dense matter, like the densities you’ll find inside an atomic nucleus, are not well known.

    Or rather, these unknowns plagued us for a long time, until a new paper last month changed all of that. With the publication of their new paper in Nature, The pressure distribution inside the proton, coauthors V. D. Burkert, L. Elouadrhiri, and F. X. Girod may have just achieved the key advance needed to understand what’s happening inside neutron stars.

    8
    A better understanding of the internal structure of a proton, including how the “sea” quarks and gluons are distributed, has been achieved through both experimental improvements and new theoretical developments in tandem. These results apply to neutrons as well. (Brookhaven National Laboratory)

    Our models of nucleons like protons and neutrons have improved tremendously over the past few decades, coincident with improvements in both computational and experimental techniques. The latest research uses an old technique known as Compton scattering, where electrons are fired at the internal structure of a proton to probe its structure. When an electron interacts (electromagnetically) with a quark, it emits a high-energy photon, along with a scattered electron and leads to nuclear recoil. By measuring all three products, you can calculate the pressure distribution experienced by the quarks inside the atomic nucleus. In a shocking find, the average peak pressure, near the center of the proton, comes out to 10³⁵ pascals: a greater pressure than neutron stars experience anywhere.

    9
    At large distances, quarks are confined within a nucleon. But at short distances, there’s a repulsive pressure that prevents other quarks-and-nuclei from getting too close to each individual proton (or, by extension, neutron). (The quark-confinement-induced pressure distribution in the proton by V.D. Burkert, L. Elouadrhiri, and F.X. Girod)

    In other words, by understanding how the pressure distribution inside an individual nucleon works, we can calculate when and under what conditions that pressure can be overcome. Although the experiment was only done for protons, the results should be analogous for neutrons, too, meaning that, in the future, we should be able to calculate a more exact limit for the masses of neutron stars.

    10
    The masses of stellar remnants are measured in many different ways. This graphic shows the masses for black holes detected through electromagnetic observations (purple); the black holes measured by gravitational-wave observations (blue); neutron stars measured with electromagnetic observations (yellow); and the masses of the neutron stars that merged in an event called GW170817, which were detected in gravitational waves (orange). The result of the merger was a neutron star, briefly, that swiftly became a black hole. (LIGO-Virgo/Frank Elavsky/Northwestern)

    The measurements of the enormous pressure inside the proton, as well as the distribution of that pressure, show us what’s responsible for preventing the collapse of neutron stars. It’s the internal pressure inside each proton and neutron, arising from the strong force, that holds up neutron stars when white dwarfs have long given out. Determining exactly where that mass threshold is just got a great boost. Rather than solely relying on astrophysical observations, the experimental side of nuclear physics may provide the guidepost we need to theoretically understand where the limits of neutron stars actually lie.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 10:21 pm on June 19, 2018 Permalink | Reply
    Tags: , , , , Ethan Siegel, , NASA's Next Flagship Mission May Be A Crushing Disappointment For Astrophysics   

    From Ethan Siegel: “NASA’s Next Flagship Mission May Be A Crushing Disappointment For Astrophysics” 

    From Ethan Siegel
    Jun 19, 2018

    1
    Various long-exposure campaigns, like the Hubble eXtreme Deep Field (XDF) shown here, have revealed thousands of galaxies in a volume of the Universe that represents a fraction of a millionth of the sky. Ambitious, flagship-class observatories are needed to take the next great leap forward for science. NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)

    Every ten years, the field of astronomy and astrophysics undergoes a Decadal Survey. This charts out the path that NASA’s astrophysics division will follow for the next decade, including what types of questions they’ll investigate, which missions will be funded, and what won’t be chosen. The greatest scientific advances of all come when we invest a large amount of resources in a single, ultra-powerful, multi-purpose observatory, such as the Hubble Space Telescope.

    NASA/ESA Hubble Telescope

    These are high-risk, high-reward propositions. If the mission succeeds, we can learn an unprecedented amount about the Universe as never before.

    2
    Star birth in the Carina Nebula, in the optical (top) and the infrared (bottom). Our willingness to invest in fundamental science is directly related to how much we can learn about the Universe. NASA, ESA and the Hubble SM4 ERO Team

    Even though the mission proposals go through NASA, its the National Research Council and the National Academy of Sciences that ultimately make the recommendations. Since the inception of NASA in the 1960s, these Decadal Surveys have shaped the field of astronomy and astrophysics research. They brought us our greatest ground-based and space-based observatories. On the ground, radio arrays like the Very Large Array and the Very Long Baseline Array, as well as the Atacama Large Millimeter Array, owe their origins to the decadal surveys.

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    NRAO VLBA

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    Space-based missions include NASA’s great observatories: the Hubble Space Telescope, the Chandra X-ray observatory, the Spitzer Space Telescope, and the Compton Gamma-Ray Observatory Even though the mission proposals go through NASA, its the National Research Council and the National Academy of Sciences that ultimately make the recommendations. Since the inception of NASA in the 1960s, these Decadal Surveys have shaped the field of astronomy and astrophysics research. They brought us our greatest ground-based and space-based observatories. On the ground, radio arrays like the Very Large Array and the Very Long Baseline Array, as well as the Atacama Large Millimeter Array, owe their origins to the decadal surveys. Space-based missions include NASA’s great observatories: the Hubble Space Telescope, the Chandra X-ray observatory, the Spitzer Space Telescope, and the Compton Gamma-Ray Observatory in the 1990s and early 2000s.

    NASA/Chandra X-ray Telescope


    NASA/Spitzer Infrared Telescope

    NASA Compton Gamma Ray Observatory

    4
    NASA’s Fermi Satellite has constructed the highest resolution, high-energy map of the Universe ever created. Without space-based observatories such as this one, we could never learn all that we have about the Universe. NASA/DOE/Fermi LAT Collaboration

    NASA/Fermi LAT


    NASA/Fermi Gamma Ray Space Telescope

    More recent Decadal Surveys, conducted this millennium, will bring us the James Webb Space Telescope, the WFIRST observatory designed to probe dark energy and exoplanets, and the Large Synoptic Survey Telescope (LSST), among others.

    NASA/ESA/CSA Webb Telescope annotated

    NASA/WFIRST

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    They’ve identified the major, most important science goals of astronomy and astrophysics, including dark energy, exoplanets, supernovae, mergers of extreme objects, and the formation of the first stars and the large-scale structure of the Universe. But there was a warning issued in 2001’s report that hasn’t been heeded, and now it’s creating an enormous problem.

    5
    The 2010 NASA mission timeline doesn’t just show a planned James Webb, but an enormous suite of missions that require ongoing funding. Without a commensurate increase in funds, that means fewer resources available for new missions. NASA Astrophysics Division.

    While a robust astronomy program has many benefits for the nation and the world, it’s vital to have a diverse portfolio of missions and observatories. Prior Decadal Surveys have simultaneously stressed the importance of the large flagship missions that drive the field forward like no other type of mission can, while warning against investing too much in these flagships at the expense of other small and medium-sized missions.

    They’ve also stressed the importance of providing additional funding or securing external funding to support ongoing missions, facilities, and observatories. Without it, the development of new missions is hamstrung by the need to continually fund the existing ones.

    6
    As a percentage of the federal budget, investment in NASA is at a 58 year low; at only 0.4% of the budget, you have to go back to 1959 to find a year where we invested a smaller percentage in our nation’s space agency. Office of Management & Budget.

    Many austerity proponents and budget-hawks — both in politics and among the general public — will often point to the large cost of these flagship missions, which can balloon if unexpected problems arise. The far greater problem, however, would arise if one of these flagship missions failed.

    When Hubble launched with its flawed mirror, unable to properly focus the light it gathered, fixing it became mandatory [Soon after Hubble began sending images from space, scientists discovered that the telescope’s primary mirror had a flaw called spherical aberration. The outer edge of the mirror was ground too flat by a depth of 4 microns (roughly equal to one-fiftieth the thickness of a human hair). The flaw resulted in images that were fuzzy because some of the light from the objects being studied was being scattered.After this discovery, scientists and engineers developed COSTAR, corrective optics that functioned like eyeglasses to restore Hubble’s vision. By placing small and carefully designed mirrors in front of the original Hubble instruments, COSTAR –installed during the 1993 First Servicing Mission — successfully improved their vision to their original design goals (Thank you, Sandy Faber)]. Yes, it was expensive, but the far greater cost — to science, to society, and to humanity — would have been not to fix it. Our choice to invest in repairing (and upgrading) Hubble directly led to some of our greatest discoveries of all-time.

    James Webb, similarly, is now over budget, and will require additional funds to complete. But the small, additional cost to get it right enormously outweighs the cost we’d all bear if we cheated ourselves and didn’t finish this incredible investment. [Also, here, we have commitments from CSA and ESA]

    7
    The science instruments aboard the ISIM module being lowered and installed into the main assembly of JWST in 2016. The telescope must be folded and properly stowed in order to fit aboard the Ariane 5 rocket which will launch it, and all its components must work together, correctly, to deliver a successful mission outcome. NASA / Chris Gunn.

    Now, the 2020 Decadal Survey approaches. The future course of astronomy and astrophysics will be charted, and one flagship mission will be selected as the top priority for a premiere mission of the 2030s. (James Webb was that mission for the 2010s; WFIRST will be it for the 2020s.) Unfortunately, a memorandum was just released by the astronomy & astrophysics director, Paul Hertz, of NASA’s Science Mission Directorate. In it, each of the four finalist teams were instructed to develop a second architechture: a lower-cost, scientifically-inferior option.

    8
    This figure shows the real stars in the sky for which a planet in the habitable zone can be observed. The color coding shows the probability of observing an exoEarth candidate if it’s present around that star (green is a high probability, red is a low one). Note how the size of your telescope/observatory in space impacts what you can see. C. Stark and J. Tumlinson, STScI.

    It flies in the face of what a flagship mission actually is. Speaking at this year’s big American Astronomical Society meeting, NASA Associate Administrator Thomas Zurbuchen said,

    “What we learn from these flagship missions is why we study the Universe. This is civilization-scale science… If we don’t do this, we aren’t NASA.”

    8
    A simulated view of the same part of the sky, with the same observing time, with both Hubble (L) and the initial architecture of LUVOIR (R). The difference is breathtaking, and represents what civilization-scale science can deliver. G. Snyder, STScI /M. Postman, STScI.

    And yet, these scaled-down architectures are by definition not as ambitious. It’s an indication from NASA that, unless the budget is increased to accommodate the actual costs of doing civilization-scale science, we won’t be doing it. Each of the four finalists has been instructed to propose an option with a total cost of below $5 billion, which will severely curtail the capabilities of such an observatory.

    9
    The concept design of the LUVOIR space telescope would place it at the L2 Lagrange point, where a 15.1-meter primary mirror would unfold and begin observing the Universe, bringing us untold scientific and astronomical riches. NASA / LUVOIR concept team; Serge Brunier (background)

    As an example, one of the proposals, LUVOIR, was designed to be the ultimate successor to Hubble: 40 times as powerful with a diameter of up to ~15 meters. It was designed to tackle problems in our Solar System, measure molecular biosignatures on exoplanets, to perform a cosmic census of stars in every type of galaxy in the Universe, to achieve the sensitivity capable of seeing every galaxy in the Universe, to directly image and map the gas in galaxies everywhere, and to measure the rotation of galaxies (and better understand dark matter) for every galaxy in the Universe.

    But the new architecture would be only half the diameter, half the resolution, and with a quarter of the light-gathering power of the original design. It would basically be an optical version of the James Webb Space Telescope. The sweeping ambition of the original project, with the potential to revolutionize our view of the Universe, would be lost.

    9
    A simulated image of what Hubble would see for a distant, star-forming galaxy (L), versus what a 10-15 meter class telescope would see for the same galaxy (R). With a telescope of half the size, the resolution would be halved, and the light-gathering time would need to be four times as great to create that inferior image. NASA / Greg Snyder / LUVOIR-HDST concept team.

    The other three proposals are more easily scaled-down, but again lose their power. HabEx, designed to directly image Earth-like planets around other stars, loses 87.5% of the interesting planets it can survey if its size is reduced in half. It might not offer much more than the other suites of missions that will fly, like WFIRST (especially if WFIRST gets a starshade), to justify being the flagship mission with such a reduction. LYNX, designed to be a next-generation X-ray observatory that’s vastly superior to Chandra and XMM-Newton, might not be much superior to the ESA’s upcoming Athena mission on such a budget. Its spatial and energy resolution were supposed to be its big selling points; on a reduced budget, it’s hard to see how it will achieve those.

    10
    An artist’s concept of the Origins Space Telescope, with the (architecture 1) 9.1 meter primary mirror. At lower resolutions and sizes, it still offers a tremendous improvement over current-and-previous far-IR observatories. NASA/GSFC

    The best bet might be OST: the Origins Space Telescope, which would represent a huge upgrade over Spitzer: the only other far-infrared observatory NASA’s ever sent to space. Its 9.1 meter design is likely impossible at that price point, but a reduction in size is less devastating to this mission. At a lower price tag, it can still teach us a huge amount about space, from our Solar System to exoplanets to black holes to distant, early galaxies. There is no NASA or European counterpart to compete with, and unlike the optical part of the spectrum, it’s notoriously challenging to attempt astronomy in this wavelength from the ground. The closest we have is the airplane-borne SOFIA, which is fantastic, but has a number of limitations.

    11
    NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) with open telescope doors. This joint partnership between NASA and the German organization DLR enables us to take a state-of-the-art infrared telescope to any location on Earth’s surface, allowing us to observe events wherever they occur. NASA / Carla Thomas

    This is NASA. This is the pre-eminent space agency in the world. This is where science, research, development, discovery, and innovation all come together. The spinoff technologies alone justify the investment, but that’s not why we do it. We are here to discover the Universe. We are here to learn all that we can about the cosmos and our place within it. We are here to find out what the Universe looks like and how it came to be the way it is today.

    It’s time for the United States government to step up to the plate and invest in fundamental science in a way the world hasn’t seen in decades. It’s time to stop asking the scientific community to do more with less, and give them a realistic but ambitious goal: to do more with more. If we can afford an ill-thought-out space force, perhaps we can afford to learn about the greatest unexplored natural resource of all. The Universe, and the vast unknowns hiding in the great cosmic ocean.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 11:19 am on May 28, 2018 Permalink | Reply
    Tags: , , , , , Ethan Siegel, ,   

    From Ethan Siegel: “This Is Why The Event Horizon Telescope Still Doesn’t Have An Image Of A Black Hole” 

    From Ethan Siegel
    May 28, 2018

    1
    The black hole at the center of our Milky Way, simulated here, is the largest one seen from Earth’s perspective. The Event Horizon Telescope should, this year, come out with their first image of what this central black hole’s event horizon looks like. The white circle represents the Schwarzschild radius of the black hole. Ute Kraus, Physics education group Kraus, Universität Hildesheim; background: Axel Mellinger

    Across multiple continents, including Antarctica, an array of radio telescopes observe the galactic center.

    EHT APEX, IRAM, G. Narayanan, J. McMahon, JCMT/JAC, S. Hostler, D. Harvey, ESO/C. Malin


    A view of the different telescopes contributing to the Event Horizon Telescope’s imaging capabilities from one of Earth’s hemispheres. The data taken from 2011 to 2017 should enable us to now construct an image of Sagittarius A*.

    This network, the Event Horizon Telescope (EHT), is imaging, for the first time, a black hole’s event horizon.

    SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory


    SgrA* NASA/Chandra


    Sgr A* from ESO VLT

    2
    The most-visualized black hole of all, as illustrated in the movie Interstellar, shows a predicted event horizon fairly accurately for a very specific class of rotating black holes. Interstellar / R. Hurt / Caltech

    Of all the black holes visible from Earth, the largest is at the galactic center: 37 μas [Microarc-second].

    4
    This multiwavelength view of the Milky Way’s galactic center goes from the X-ray through the optical and into the infrared, showcasing Sagittarius A* and the intragalactic medium located some 25,000 light years away. Using radio data, the EHT will resolve the event horizon of the central black hole. X-ray: NASA/CXC/UMass/D. Wang et al.; Optical: NASA/ESA/STScI/D.Wang et al.; IR: NASA/JPL-Caltech/SSC/S.Stolov

    NASA/Chandra X-ray Telescope

    NASA/ESA Hubble Telescope

    With a theoretical resolution of 15 μas, the EHT should resolve it.

    Despite the incredible news that they’ve detected the black hole’s structure at the galactic center, however, there’s still no direct image.

    5
    A plot of the coverage in space of the area around the galactic center’s black hole from the telescopes whose data has been brought together so far. Additional telescopes will further constrain the black hole’s size, shape and orientation. R.-S. Lu et al, ApJ 859, 1

    They found evidence for an asymmetric source, about 3 Schwarzschild radii large: consistent with Einstein’s prediction of 2.5.

    66
    Two of the possible models that can successfully fit the Event Horizon Telescope data thus far. Both show an off-center, asymmetric event horizon that’s enlarged versus the Schwarzschild radius, consistent with the predictions of Einstein’s General Relativity. R.-S. Lu et al, ApJ 859, 1

    But before the South Pole data, delivered five months ago, can be added, all error sources must be identified.

    South Pole Telescope SPTPOL. The SPT collaboration is made up of over a dozen (mostly North American) institutions, including the University of Chicago, the University of California, Berkeley, Case Western Reserve University, Harvard/Smithsonian Astrophysical Observatory, the University of Colorado Boulder, McGill University, The University of Illinois at Urbana-Champaign, University of California, Davis, Ludwig Maximilian University of Munich, Argonne National Laboratory, and the National Institute for Standards and Technology. It is funded by the National Science Foundation.


    The South Pole Telescope, a 10 meter radio telescope located at the South Pole, will be the most important addition to the EHT as far as resolving the central black hole goes.

    Earth’s atmospheric turbulence, instrumentation noise, and spurious signals require identification, obtainable through additional imaging.

    8
    A map of the 7 million second exposure of the Chandra Deep Field-South. This region shows hundreds of supermassive black holes, each one in a galaxy far beyond our own. There should be hundreds of thousands of times as many stellar-mass black holes; we’re just waiting for the capability of detecting them. NASA/CXC/B. Luo et al., 2017, ApJS, 228, 2

    Although the data has been combined, novel algorithms must be developed to process them into an image.

    9
    Five different simulations in general relativity, using a magnetohydrodynamic model of the black hole’s accretion disk, and how the radio signal will look as a result. Note the clear signature of the event horizon in all the expected results. GRMHD simulations of visibility amplitude variability for Event Horizon Telescope images of Sgr A*, L. Medeiros et al., arXiv:1601.06799

    Only two black holes, Sagittarius A* and Messier 87, could have event horizon “silhouettes” imaged.

    10
    The second-largest black hole as seen from Earth, the one at the center of the galaxy Messier 87, is shown in three views here. Despite its mass of 6.6 billion Suns, it is over 2000 times farther away than Sagittarius A*. It may not be resolvable by the EHT.Top, optical, Hubble Space Telescope / NASA / Wikisky; lower left, radio, NRAO / Very Large Array (VLA); lower right, X-ray, NASA / Chandra X-ray telescope

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    New data will be taken annually, improving the future, overall pictures through subsequent analysis.

    Event Horizon Telescope Array

    Arizona Radio Observatory
    Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

    ESO/APEX
    Atacama Pathfinder EXperiment

    CARMA Array no longer in service
    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    Atacama Submillimeter Telescope Experiment (ASTE)
    Atacama Submillimeter Telescope Experiment (ASTE)

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

    IRAM NOEMA interferometer
    Institut de Radioastronomie Millimetrique (IRAM) 30m

    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA
    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    NSF CfA Greenland telescope

    Greenland Telescope

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    Over the coming months, preliminary images will show the:

    size,
    shape,
    changes,
    and surrounding environment,

    of our first directly-observed black holes.

    11
    High-Angular-Resolution and High-Sensitivity Science Enabled by Beamformed ALMA, V. Fish et al., arXiv:1309.3519

    Some of the possible profile signals of the black hole’s event horizon as simulations of the Event Horizon Telescope indicate.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.
    stem
    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 11:58 am on April 27, 2018 Permalink | Reply
    Tags: 000 Black Hole Mergers A Year..., , , , , , Ethan Siegel, , LIGO Misses 100   

    From Ethan Siegel: “LIGO Misses 100,000 Black Hole Mergers A Year…” 

    Ethan Siegel
    Apr 26, 2018

    …but if a radical new idea comes to fruition, maybe we can find them after all.

    1
    The General Relativity picture of curved spacetime, where matter and energy determine how these systems evolve over time, has made successful predictions that no other theory can match, including for the existence and properties of gravitational waves: ripples in spacetime. (LIGO)

    After decades of planning, building, prototyping, upgrading, and calibrating, the Laser Interferometer Gravitational-wave Observatory (LIGO) finally achieved it’s ultimate goal just a little over two years ago: the first direct detection of gravitational waves.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Since 2015, LIGO has seen the ripples in spacetime or gravitational waves from no fewer than six separate events. Five (and possibly more) black hole-black hole pairs and one neutron star-neutron star inspiral-and-merger had their unique, unmistakable signatures detected by multiple gravitational wave detectors simultaneously, enabling us to confirm a key prediction of Einstein’s General Relativity that had eluded experimentalists for a century. But in theory, black hole-black hole mergers should occur every few minutes somewhere in the Universe; LIGO is missing more than 100,000 of these annually. For the first time, a team of scientists may just have figured out how to detect all the mergers that LIGO is currently missing.

    When two black holes orbit one another, they’re both radiating energy away, and doing so constantly. According to Einstein’s General Relativity, any time a mass moves and accelerates through a changing gravitational field, itself changing its momentum, it has to emit radiation inherent to space itself: gravitational radiation. Each of the two masses in their gravitational dance emits them, and part of the theoretical work behind LIGO was calculating in excruciating detail what the magnitude, duration, amplitude, and frequencies of gravitational waves would be emitted for any two arbitrary black hole masses and orientations.

    2
    The gravitational wave signal from the first pair of detected, merging black holes from the LIGO collaboration. Although a large amount of information can be extracted, no images or the presence/absence of an event horizon can be gleaned. (B. P. Abbott et al., (LIGO Scientific Collaboration and Virgo Collaboration), Physical Review Letters 116, 061102 (2016))

    It was only from that sort of template creation and matching that we were able to detect these events at all. It was incredibly successful as well; the confirmations, when they occurred, were spectacular in their agreement with the predictions. But LIGO is only sensitive to those final few moments of a merger, where the amplitude of these gravitational waves is sufficient to contract-and-expand these enormous arms by a tiny fraction of a wavelength of light, enough so that after a thousand reflections, the light shifts by a barely-perceptible amount.

    3
    The masses of stellar remnants are measured in many different ways. This graphic shows the masses for black holes detected through electromagnetic observations (purple); the black holes measured by gravitational-wave observations (blue); neutron stars measured with electromagnetic observations (yellow); and the masses of the neutron stars that merged in an event called GW170817, which were detected in gravitational waves (orange).(LIGO-Virgo/Frank Elavsky/Northwestern)

    Over the time that LIGO’s been operational, it has seen six robust events: about 0.001% of the total number of mergers expected in the Universe. Sure, most of them are anticipated to be far away, oriented non-optimally, or to occur between low-mass, low-amplitude black holes. There’s a good reason LIGO hasn’t seen them; the current generation of ground-based gravitational wave detectors are severely limited in sensitivity and range.

    4
    Illustrated here is the range of Advanced LIGO and its capability of detecting merging black holes. Merging neutron stars may have only one-tenth the range and 0.1% the volume, but if neutron stars are abundant enough, LIGO may have a chance at those, too. (LIGO Collaboration / Amber Stuver / Richard Powell / Atlas of the Universe)

    But with 100,000 black hole-black hole mergers occurring annually in the observable Universe, these gravitational wave signals are constantly passing through Earth and our detectors. They’re simply below the detectable threshold, meaning that they have an impact on an apparatus like LIGO or Virgo, but not one we can pull out and identify as a unique, unambiguous gravitational wave event. You may not be able to detect them individually, but with so many of them occurring, it may be possible to extract an aggregate signal. Rather than an individual chirp, these combined mergers should produce a gravitational wave background hum. These mergers are quick and shouldn’t overlap with one another, meaning that the background should look like a series of disconnected signals that are too faint to detect.

    5
    The noise (top), the strain (middle), and the reconstructed signal (bottom) in a bona fide gravitational wave event seen in all three detectors. For most of the mergers, they’re simply too far away for their amplitude in order for LIGO/Virgo to detect them. (The LIGO Scientific Collaboration and The Virgo Collaboration)

    That is, they’re too faint to detect individually! But if you know what your signal looks like and you both build up enough statistics and apply enough computational power, you just might be able to tease it out of the noise. It won’t tell you how many individual events you have, but it can tell you how many total events there are over the time you observe it. In other words, rather than say, “we expect 100,000 of these a year,” we can actually observe the overall black hole-black hole merger rate in the Universe. More importantly, we can learn, for the first time, what the total number-and-mass density of black holes in the Universe actually is.

    6
    A map of the 7 million second exposure of the Chandra Deep Field-South. This region shows hundreds of supermassive black holes, each one in a galaxy far beyond our own. There should be hundreds of thousands of times as many stellar-mass black holes; we’re just waiting for the capability of detecting them. (NASA/CXC/B. Luo et al., 2017, ApJS, 228, 2)

    NASA/Chandra X-ray Telescope

    In a new paper entitled Optimal Search for an Astrophysical Gravitational-Wave Background [PHYSICAL REVIEW X], scientists Rory Smith and Eric Thrane propose to do exactly that. For every problem like this, there’s a computationally optimal way to approach it, and Smith and Thrane worked hard to come up with the answer. There are a number of interesting things the authors deduce they can learn from this computational exercise:

    You can derive the most sensitive possible search for this background of unresolved black holes.
    You can learn about the populations of black holes at earlier times in the Universe compared to the modern, nearby Universe.
    You can combine the results of this search with both confirmed detections and marginal, candidate detections to remove the bias inherent in seeing the largest-amplitude signals the most easily.
    If it’s successful, this method can be generalized to neutron stars, non-merging masses, and even potentially the gravitational wave background left over from the Universe’s birth.

    7
    The final prediction of cosmic inflation is the existence of primordial gravitational waves. It is the only one of inflation’s predictions to not be verified by observation… yet. (National Science Foundation (NASA, JPL, Keck Foundation, Moore Foundation, related) — Funded BICEP2 Program; modifications by E. Siegel)

    Best of all, their conclusions are incredibly optimistic for what the future holds for applying this supercomputer-based technique to the LIGO and Virgo data sets. Writing in the journal Physical Review X, they state:

    “…Preliminary estimates suggest that advanced detectors, operating at design sensitivity, can detect a stochastic background from binary black holes in about 1 day. These estimates rely on extrapolation using Gaussian mixture modeling of our Bayesian evidence distributions. The next step is to carry out a mock data challenge in which we demonstrate the safety and efficacy of the search using ≈1 day of design sensitivity Monte Carlo data. Such a demonstration would allow us to verify the extrapolations made here with a modest computational cost ≈500 000 core hours….”

    In other words, they plan to demonstrate that this signal can be extracted from a noisy background by simulating it, blinding the computer, and then proving that the supercomputer, alone, can identify it.

    8
    By simulating both data sets with (left) and without (right) a signal, the researchers anticipate that a realistic astrophysical background should be detected with a supercomputer time of approximately 20 hours, compared to more than year using existing methods. (R. Smith and E. Thrane, Phys. Rev. X 8, 021019 (2018)[link is above])

    The era of gravitational wave astronomy is now upon us. Owing to the incredible capabilities of ground-based detectors like LIGO and Virgo, we have now detected six robust events over the past 2+ years, from black holes to merging neutron stars. But huge questions surrounding the black holes in the Universe, such as how many there are, what their masses are early on compared to today, and what percent of the Universe is made of black holes, still remain to be answered. The direct efforts have gotten us a very long way, but the indirect signals matter, too, and can potentially teach us even more if we’re willing to make inferences that follow the physics and math. LIGO may be missing upwards of 100,000 black hole-black hole mergers a year. But with this new proposed technique, we might finally learn what else is out there, with the potential to apply this to neutron stars, non-merging black holes, and even the leftover ripples from our cosmic birth. It’s an incredible time to be alive.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 4:41 pm on April 24, 2018 Permalink | Reply
    Tags: , , , , Ethan Siegel, , One Galaxy Cluster Through Hubble’s Eyes Can Show Us The Entire Universe   

    From Ethan Siegel: “One Galaxy Cluster, Through Hubble’s Eyes, Can Show Us The Entire Universe… 

    From Ethan Siegel

    Apr 23, 2018

    …the picture itself is breathtaking. But what we learn is truly eye-opening.

    Galaxy clusters, like the massive one captured here by Hubble, PLCK G004.5–19.5, impress not just for their looks, but for their science.

    1
    In this Hubble Space Telescope image, the many red galaxies are members of the massive MACS J1149.6+2223 cluster, which creates distorted and highly magnified images of the galaxies behind it. A large cluster galaxy (centre of the box) has split the light from an exploding supernova in a magnified background galaxy into four yellow images (arrows), whose arrival time was delayed relative to one another owing to the bending of spacetime by mass. (Hubble Space Telescope / ESA and NASA)

    NASA/ESA Hubble Telescope

    Out there in the depths of space, collections of thousands of galaxies have formed over billions of years from gravity’s relentless pull.

    Laniakea supercluster. From Nature The Laniakea supercluster of galaxies R. Brent Tully, Hélène Courtois, Yehuda Hoffman & Daniel Pomarède at http://www.nature.com/nature/journal/v513/n7516/full/nature13674.html. Milky Way is the red dot.

    These are the largest bound structures of all, as dark energy will drive the apparently larger “superclusters” apart.

    2
    Our local supercluster, Laniakea, contains the Milky Way, our local group, the Virgo cluster, and many smaller groups and clusters on the outskirts. However, each group and cluster is bound only to itself, and will be driven apart from the others due to dark energy and our expanding Universe. (Andrew Z. Colvin / Wikimedia Commons)

    If you map out the motions of the galaxies inside the cluster, you can derive the total cluster mass.

    3
    The mass distribution of cluster Abell 370. reconstructed through gravitational lensing, shows two large, diffuse halos of mass, consistent with dark matter with two merging clusters to create what we see here. Around and through every galaxy, cluster, and massive collection of normal matter exists 5 times as much dark matter, overall. (NASA, ESA, D. Harvey (École Polytechnique Fédérale de Lausanne, Switzerland), R. Massey (Durham University, UK), the Hubble SM4 ERO Team and ST-ECF)

    Most of the mass is in between the galaxies, proving that there’s unseen matter in the cluster.

    4
    A galaxy cluster can have its mass reconstructed from the gravitational lensing data available. Most of the mass is found not inside the individual galaxies, shown as peaks here, but from the intergalactic medium within the cluster, where dark matter appears to reside. (A. E. Evrard. Nature 394, 122–123 (09 July 1998))

    We find these clusters from the hot, intergalactic gas that shifted the background light left over from the Big Bang [Astronomy and Astrophysics].

    5
    Shown here at frequencies above 220 GHz, the light from the cosmic microwave background gets shifted to higher energies from the presence of heated gas. This gas is found in galaxy clusters, and allows us to infer how much normal matter is present: about 15% of the total mass needed from gravitational lensing. (ESA/Planck Collaboration)

    ESA/Planck 2009 to 2013

    There’s more gravity than the gas can provide, showing the presence of non-baryonic dark matter.

    6
    The smallest, faintest, most distant galaxies identified in the deepest Hubble image ever taken. A 2017 study, by Livermore et al., has them beat, by perhaps two orders of magnitude, thanks to stronger gravitational lenses. The RELICS collaboration hopes to identify even better targets for James Webb. (Credit: NASA, ESA, R. Bouwens and G. Illingworth (UC, Santa Cruz))

    But all the mass, combined, contributes to gravitational lensing.

    Gravitational Lensing NASA/ESA

    7
    An illustration of gravitational lensing showcases how background galaxies — or any light path — is distorted by the presence of an intervening mass, such as a foreground galaxy cluster. (NASA/ESA)

    The bending of space stretches and magnifies the light from galaxies behind the cluster.

    8
    The streaks and arcs present in Abell 370, a distant galaxy cluster some 5–6 billion light years away, are some of the strongest evidence for gravitational lensing and dark matter that we have. The lensed galaxies are even more distant, with some of them making up the most distant galaxies ever seen. (NASA, ESA/Hubble, HST Frontier Fields)

    This is the whole purpose of the joint Hubble/Spitzer RELICS program, highlighted by this galaxy cluster.

    9
    From the distant Universe, light has traveled for some 10.7 billion years from distant galaxy MACSJ2129–1, lensed, distorted and magnified by the foreground clusters imaged here. The most distant galaxies appear redder because their light is redshifted by the expansion of the Universe, which helps explain what we measure as Hubble’s law. (NASA, ESA, and S. Toft (University of Copenhagen) Acknowledgment: NASA, ESA, M. Postman (STScI), and the CLASH team)

    Gravitationally lensed galaxies are the most distant ever identified.

    10
    The galaxy cluster MACS 0416 from the Hubble Frontier Fields, with the mass shown in cyan and the magnification from lensing shown in magenta. Mapping out the cluster mass allows us to identify which locations should be probed for the greatest magnifications and ultra-distant candidates of all. (STScI/NASA/CATS Team/R. Livermore (UT Austin))

    Through this process, RELICS can reveal the perfect observing targets for the James Webb Space Telescope.

    NASA/ESA/CSA Webb Telescope annotated

    11
    The GOODS-N field, with galaxy GN-z11 highlighted: the presently most-distant galaxy ever discovered. With the power of gravitational lensing and its advanced equipment, the James Webb Space Telescope will break this record. (NASA, ESA, P. Oesch (Yale University), G. Brammer (STScI), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz))

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 10:20 am on April 18, 2018 Permalink | Reply
    Tags: , , , , Ethan Siegel, , Turning Pixels Into Planets   

    From Ethan Siegel- “NASA Kepler’s Scientists Are Doing What Seems Impossible: Turning Pixels Into Planets” 

    From Ethan Siegel

    Apr 18, 2018

    1
    This highly pixelated view of TRAPPIST-1 shows the amount of light detected by each pixel in a small section of Kepler’s onboard camera. The light collected from TRAPPIST-1 is visible at the center of the image. Not directly visible are the planets that orbit TRAPPIST-1. NASA Ames/W. Stenzel.

    When you think of what’s out there in the vast recesses of space, glorious images of galaxies, stars, and new worlds probably leap to mind. A combination of the greatest images from Hubble and some gorgeous artistic renderings are how we visualize the Universe, but that’s not what most telescopes or observatories see, and that’s certainly not where most of the science gets done. NASA’s Kepler mission, famous for discovering thousands of planets outside of our Solar System, never actually images a planet.

    NASA/Kepler Telescope

    Instead, they simply image an unresolved star, or more accurately, around 100,000 stars at once. After doing that for weeks, months, or years, they announce the discovery of candidate planets, including properties like their radius and orbital period. A raw image shows nothing but pixels of a saturated star, but it’s what you do with the data that counts. Here’s the science of how a few pixels become an entire solar system.

    2
    This artist’s impression displays TRAPPIST-1 and its planets reflected in a surface. The potential for water on each of the worlds is also represented by the frost, water pools, and steam surrounding the scene. However, it is unknown whether any of these worlds actually still possess atmospheres, or if they’ve been blown away by their parent star. NASA/R. Hurt/T. Pyle.

    TRAPPIST-1 is perhaps the most exciting of the recent discoveries made with the Kepler spacecraft. Although it’s a small, low-mass star that’s red and dim, we’ve discovered an incredibly prolific solar system: 7 planets, all of which are approximately Earth-sized, including three that might have the right temperatures and conditions for liquid water on their surface. Best of all, it’s only 40 light years away, meaning that on a galactic scale, it’s right in our own backyard. But when you look at it through NASA’s Kepler telescope, which is where the best data on this planetary system comes from, this is what you see.

    3
    The viewing area of the Kepler satellite’s K2 Campaign 12, which includes TRAPPIST-1 in the region indicated above. NASA Ames/W. Stenzel.

    You don’t see planets, you don’t see orbits, you don’t even see anything that tells you about the properties of the star or its solar system. All you see is a set of pixels, indicating you have a light source of some type. There are other light sources nearby — space is a busy place — and Kepler is imaging all of them at once, continuously. Those two facts:

    that Kepler is imaging thousands upon thousands of stars at once,
    and that it’s imaging all of these stars continuously, over long periods of time,

    is what enables us to do the incredible science we’re doing. Take a look at this animation of the raw data over an interestingly long period of time.

    3
    When you apply a mask to TRAPPIST-1, as viewed by Kepler, and take a look at how the light evolves over time, a huge amount of information can be gleaned from a seemingly noisy few pixels. NASA / Kepler / K2 Campaign 12 team / Geert Barentsen.

    You’ll notice that the brightness of the star appears to change with time. But you’ll also notice, if you’re careful, that the background brightness of everything else — both other objects and the background “noise” of space itself — changes with time, too. If you’re looking at the raw data itself, there are things you need to know about it before you attempt to make any use of it. There are no corrections for smearing of data across multiple pixels in the raw data. There are no bias subtractions included in the raw data. The field (where there are no stars) isn’t flat, and so this introduces noise into the raw data. There are no flags for the time where the data is of poor quality, such as when the spacecraft’s thrusters fire. And there is no flagging of cosmic rays, which can influence the spacecraft’s software.

    Still, when you take all of this into account, the raw data itself (individual red points, below) still shows some remarkable features that are worth looking at.

    4
    A quick-look lightcurve of the long cadence data for TRAPPIST-1, derived from the raw data itself, reveals sinusoidal patterns due to star spots and at least 6 planets. NASA / Kepler / K2 Campaign 12 team / Geert Barentsen.

    There are sinusoidal (periodioc up-and-down) patterns, which tell you there are sunspots on the main star: some portions of the star are fainter than average. Also, there are a few big dips in the total amount of light in the long-cadence data, where between 0.5% and 1% of the light is temporarily blocked/dimmed over the course of approximately 30 minutes. When you normalize the data and make all the corrections that the raw data doesn’t possess, and then add in follow-up data from other telescopes and observatories, you can clearly see the periodic nature of the planets. When a world transits, or passes in front of the star, it blocks a portion of the light, making the star appear dimmer. Over time, these dips appear periodically, teaching us about the orbits of these worlds.

    5
    This diagram shows the changing brightness of the ultra cool dwarf star TRAPPIST-1 over a period of 20 days in September and October 2016 as measured by NASA’s Spitzer Space Telescope and many other telescopes on the ground. On many occasions the brightness of the star drops for a short period and then returns to normal. These events, called transits, are due to one or more of the star’s seven planets passing in front of the star and blocking some of its light. The lower part of the diagram shows which of the system’s planets are responsible for the transits. ESO/M. Gillon et al.

    This gives us all the information we need to deduce many of the properties of these worlds.

    Because we know the size and brightness of the star, we can deduce the radius of each transiting world.
    Because we know the mass of the star and how orbits work, we can figure out the distance of each planet from the star.
    Because we know the temperature of the star, we can figure out which worlds would have the right conditions for liquid water if they had Earth-like atmospheres.
    And because these worlds mutually tug on each other, inducing subtle shifts in one another’s orbits, we can infer what their masses ought to be.

    When you put all of this together, here’s how these worlds look, compared to the inner, rocky worlds of our own Solar System.

    6
    When all the information obtained from Kepler, Spitzer, and ground-based telescopes that have observed the TRAPPIST-1 are compiled, we can deduce the masses, radii, and orbital parameters of each of the discovered worlds. They are not so different from the four rocky worlds in our own solar system. We’re dying to know more. No image credit.

    NASA/Spitzer Infrared Telescope

    If you’re looking for the most Earth-like world among them all, your best bet is the fourth rock from the star: TRAPPIST-1e. Sure, it’s much closer to its star at just a distance of 3% our distance from the Sun and with an orbital period of 6 days, but its star is much smaller, dimmer and cooler. It’s only 9% smaller than Earth and, within the errors, the same density as our world. You’d weigh 93% of what you’d weigh on Earth on TRAPPIST-1e, as its gravity is almost identical to our own. Most impressively, it has properties consistent with being a dense, rocky world with a thin atmosphere encircling it. Of all the worlds we’ve found orbiting stars beyond the Sun, TRAPPIST-1e, may yet be the most Earth-like of all.

    7
    The various planets orbiting around TRAPPIST-1, seven of which have been found so far, all have unique properties that we can infer from their sizes, masses, and orbital parameters. The fourth planet from this star, TRAPPIST-1e, may be the most Earth-like of all. NASA / JPL-Caltech.

    Despite being around a red dwarf and likely locked to its star, the exoplanets orbiting TRAPPIST-1 are incredibly promising for life-giving conditions. They range from roasting to temperate to frozen with sub-surface oceans to potentially light and fluffy, with outer gas envelopes. All of this information — about the worlds around this star, their sizes, their orbits, and even their masses — can all be derived from those tiny, saturated pixels of light that Kepler picked up. And it isn’t just this one system; every star that experiences transits that have been observed by Kepler shows this.

    8
    A visualization of the planets found in orbit around other stars in a specific patch of sky probed by the NASA Kepler mission. As far as we can tell, practically all stars have planetary systems around them.
    ESO / M. Kornmesser.

    It isn’t the image itself that gives you this information, but rather how the light from image changes over time, both relative to all the other stars and relative to itself. The other stars out there in our galaxy have sunspots, planets, and rich solar systems all their own. As Kepler heads towards its final retirement and prepares to be replaced by TESS, take a moment to reflect on just how it’s revolutionized our view of the Universe. Never before has such a small amount of information taught us so much.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 9:13 pm on April 17, 2018 Permalink | Reply
    Tags: And yet - here we are, , , , , Dark Energy and Dark Matter, Ethan Siegel, What Astronomers Wish Everyone Knew About Dark Matter And Dark Energy   

    From Ethan Siegel: “What Astronomers Wish Everyone Knew About Dark Matter And Dark Energy” 

    From Ethan Siegel
    Apr 17, 2018

    1
    One way of measuring the Universe’s expansion history involves going all the way back to the first light we can see, when the Universe was just 380,000 years old. The other ways don’t go backwards nearly as far, but also have a lesser potential to be contaminated by systematic errors. (European Southern Observatory).

    Among the general public, people compare it to the aether, phlogiston, or epicycles. Yet almost all astronomers are certain: dark matter and dark energy exist. Here’s why.

    If you go by what’s often reported in the news, you’d be under the impression that dark matter and dark energy are houses of cards just waiting to be blown down. Theorists are constantly exploring other options; individual galaxies and their satellites arguably favor some modification of gravity to dark matter; there are big controversies over just how fast the Universe is expanding, and the conclusions we’ve drawn from supernova data may need to be altered. Given that we’ve made mistaken assumptions in the past by presuming that the unseen Universe contained substances that simply weren’t there, from the aether to phlogiston, isn’t it a greater leap-of-faith to assume that 95% of the Universe is some invisible, unseen form of energy than it is to assume there’s just a flaw in the law of gravity?

    The answer is a resounding, absolute no, according to almost all astronomers, astrophysicists, and cosmologists who study the Universe. Here’s why.

    Cosmology is the science of what the Universe is, how it came to be this way, what its fate is, and what it’s made up of. Originally, these questions were in the realms of poets, philosophers and theologians, but the 20th century brought these questions firmly into the realm of science. When Einstein put forth his theory of General Relativity, one of the first things that was realized is if you fill the space that makes up the Universe with any form of matter or energy, it immediately becomes unstable. If space contains matter and energy, it can expand or contract, but all static solutions are unstable. Once we measured the Hubble expansion of the Universe and discovered the leftover glow from the Big Bang in the form of the Cosmic Microwave Background, cosmology became a quest to measure two numbers: the expansion rate itself and how that rate changed over time. Measure those, and General Relativity tells you everything you could want to know about the Universe.

    COBE CMB

    NASA/COBE 1989 to 1993.

    Cosmic Microwave Background NASA/WMAP

    NASA WMAP 2001 to 2010

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    3
    A plot of the apparent expansion rate (y-axis) vs. distance (x-axis) is consistent with a Universe that expanded faster in the past, but is still expanding today. This is a modern version of, extending thousands of times farther than, Hubble’s original work. Note the fact that the points do not form a straight line, indicating the expansion rate’s change over time. (Ned Wright, based on the latest data from Betoule et al. (2014))

    These two numbers, known as H_0 and q_0, are called the Hubble parameter and the deceleration parameter, respectively. If you take a Universe that’s filled with stuff, and start it off expanding at a particular rate, you’d fully expect it to have those two major physical phenomena — gravitational attraction and the initial expansion — fight against each other. Depending on how it all turned out, the Universe ought to follow one of three paths:

    The Universe expands fast enough that even with all the matter and energy in the Universe, it can slow the expansion down but never reverse it. In this case, the Universe expands forever.
    The Universe begins expanding quickly, but there’s too much matter and energy. The expansion slows, comes to a halt, reverses, and the Universe eventually recollapses.
    Or, perhaps, the Universe — like the third bowl of porridge in Goldilocks — is just right. Perhaps the expansion rate and the amount of stuff in the Universe are perfectly balanced, with the expansion rate asymptoting to zero.

    That last case can only occur if the energy density of the Universe equals some perfectly balanced value: the critical density.

    4
    The expected fates of the Universe (top three illustrations) all correspond to a Universe where the matter and energy fights against the initial expansion rate. In our observed Universe, a cosmic acceleration is caused by some type of dark energy, which is hitherto unexplained. (E. Siegel / Beyond the Galaxy)

    This is actually a beautiful setup, because the equations you derive from General Relativity are completely deterministic here. Measure how the Universe is expanding today and how it was expanding in the past, and you know exactly what the Universe must be made out of. You can derive how old the Universe has to be, how much matter and radiation (and curvature, and any other stuff) has to be in it, and all sorts of other interesting information. If we could know those two numbers exactly, H_0 and q_0, we would immediately know both the Universe’s age and also what the Universe is made out of.

    5
    Three different types of measurements, distant stars and galaxies, the large scale structure of the Universe, and the fluctuations in the CMB, tell us the expansion history of the Universe. (NASA/ESA HUbble, Sloan Digital Sky Survey, ESA and the Planck Collaboration [ESA/Planck pictured above)

    NASA/ESA Hubble Telescope


    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

    Now, we had some preconceptions when we started down this path. For aesthetic or mathematically prejudicial reasons, some people preferred the recollapsing Universe, while others preferred the critical Universe and still others preferred the open one. In reality, all you can do, if you want to understand the Universe, is examine it and ask it what it’s made of. Our laws of physics tell us what rules the Universe plays by; the rest is determined by measurement. For a long time, measurements of the Hubble constant were highly uncertain, but one thing became clear: if the Universe were made 100% of normal matter, the Universe turned out to be very young.

    6
    Measuring back in time and distance (to the left of “today”) can inform how the Universe will evolve and accelerate/decelerate far into the future. We can learn that acceleration turned on about 7.8 billion years ago with the current data, but also learn that the models of the Universe without dark energy have either Hubble constants that are too low or ages that are too young to match with observations. (Saul Perlmutter, Nobel Laureate, of Berkeley)

    If the expansion rate, H_0, was fast, like 100 km/s/Mpc, the Universe would only be 6.5 billion years old. Given that the ages of stars in globular clusters — admittedly, some of the oldest stars in the Universe — were at least 12 billion years old (and many cited numbers closer to 14–16 billion), the Universe couldn’t be this young. While some measurements of H_0 were significantly lower, like 55 km/s/Mpc, that still gave a Universe that was 11-and-change billion: still younger than the stars we found within it. Moreover, as more and more measurements came in during the 1970s, 1980s and beyond, it became clear that an abnormally low Hubble constant in the 40s or 50s, simply didn’t line up with the data.

    7
    The globular cluster Messier 75, showing a huge central concentration, is over 13 billion years old. Many globular clusters have stellar populations that are in excess of 12 or even 13 billion years, a challenge for ‘matter-only’ models of the Universe. (HST / Fabian RRRR, with data from the Hubble Legacy Archive)

    At the same time, we were beginning to measure to good precision how abundant the light elements in the Universe were. Big Bang Nucleosynthesis is the science of how much relative hydrogen, helium-4, helium-3, deuterium, and lithium-7 ought to be left over from the Big Bang. The only parameter that isn’t derivable from physical constants in these calculation is the baryon-to-photon ratio, which tells you the density of normal matter in the Universe. (This is relative to the number density of photons, but that is easily measurable from the Cosmic Microwave Background.) While there was some uncertainty at the time, it became clear very quickly that 100% of the matter couldn’t be “normal,” but only about 10% at most. There is no way the laws of physics could be correct and give you a Universe with 100% normal matter.

    8
    The predicted abundances of helium-4, deuterium, helium-3 and lithium-7 as predicted by Big Bang Nucleosynthesis, with observations shown in the red circles. This corresponds to a Universe where the baryon density (normal matter density) is only 5% of the critical value. (NASA / WMAP Science Team)

    By the early 1990s, this began to line up with a slew of observations that all pointed to pieces of this cosmic puzzle:

    The oldest stars had to be at least 13 billion years old,
    If the Universe were made of 100% matter, the value of H_0 could be no bigger than 50 km/s/Mpc to get a Universe that old,
    Galaxies and clusters of galaxies showed strong evidence that there was lots of dark matter,
    X-ray observations from clusters showed that only 10–20% of the matter could be normal matter,
    The large-scale structure of the Universe (correlations between galaxies on hundreds-of-millions of light year scales) showed you need more mass than normal matter could provide,
    but the deep source counts, which depend on the Universe’s volume and how that changes over time, showed that 100% matter was far too much,
    Gravitational lensing was starting to “weigh” these galaxy clusters, and found that only about 30% of the critical density was total matter,
    and Big Bang Nucleosynthesis really seemed to favor a Universe where just ~1/6th of the matter density was normal matter.

    So what was the solution?

    9
    The mass distribution of cluster Abell 370. reconstructed through gravitational lensing, shows two large, diffuse halos of mass, consistent with dark matter with two merging clusters to create what we see here. Around and through every galaxy, cluster, and massive collection of normal matter exists 5 times as much dark matter, overall. This still isn’t enough to reach the critical density, or anywhere close to it, on its own. (NASA, ESA, D. Harvey (École Polytechnique Fédérale de Lausanne, Switzerland), R. Massey (Durham University, UK), the Hubble SM4 ERO Team and ST-ECF)

    Gravitational Lensing NASA/ESA

    Most astronomers had accepted dark matter by this time, but even a Universe that was made exclusively of dark and normal matter would still be problematic. It simply wasn’t old enough for the stars in it! Two pieces of evidence in the late 1990s that came together gave us the way forward. One was the cosmic microwave background, which showed us that the Universe was spatially flat, and therefore the total amount of stuff in there added up to 100%. Yet it couldn’t all be matter, even a mix of normal and dark matter! The other piece of evidence was supernova data, which showed that there was a component in the Universe causing it to accelerate: this must be dark energy. Looking at the multiple lines of evidence even today, they all point to that exact picture.

    11

    Constraints on dark energy from three independent sources: supernovae, the CMB, and BAO (which are a feature in the Universe’s large-scale structure). Note that even without supernovae, we’d need dark energy, and that only 1/6th of the matter found can be normal matter; the rest must be dark matter. (Supernova Cosmology Project, Amanullah, et al., Ap.J. (2010))

    So either you have all these independent lines of evidence, all pointing towards the same picture: General Relativity is our theory of gravity, and our Universe is 13.8 billion years old, with ~70% dark energy, ~30% total matter, where about 5% is normal matter and 25% is dark matter. There are photons and neutrinos which were important in the past, but they’re just a small fraction-of-a-percent by today. As even greater evidence has come in — small-scale fluctuations in the cosmic microwave background, the baryon oscillations in the large-scale structure of the Universe, high-redshift quasars and gamma-ray bursts — this picture remains unchanged. Everything we observe on all scales points to it.

    12
    The farther away we look, the closer in time we’re seeing towards the Big Bang. The newest record-holder for quasars comes from a time when the Universe was just 690 million years old. These ultra-distant cosmological probes also show us a Universe that contains dark matter and dark energy. (Jinyi Yang, University of Arizona; Reidar Hahn, Fermilab; M. Newhouse NOAO/AURA/NSF)

    It wasn’t always apparent that this would be the solution, but this one solution works for literally all the observations. When someone puts forth the hypothesis that “dark matter and/or dark energy doesn’t exist,” the onus is on them to answer the implicit question, “okay, then what replaces General Relativity as your theory of gravity to explain the entire Universe?” As gravitational wave astronomy has further confirmed Einstein’s greatest theory even more spectacularly, even many of the fringe alternatives to General Relativity have fallen away. The way it stands now, there are no theories that exist that successfully do away with dark matter and dark energy and still explain everything that we see. Until there are, there are no real alternatives to the modern picture that deserve to be taken seriously.

    13
    A detailed look at the Universe reveals that it’s made of matter and not antimatter, that dark matter and dark energy are required, and that we don’t know the origin of any of these mysteries. However, the fluctuations in the CMB, the formation and correlations between large-scale structure, and modern observations of gravitational lensing, among many others, all point towards the same picture.(Chris Blake and Sam Moorfield)

    It might not feel right to you, in your gut, that 95% of the Universe would be dark. It might not seem like it’s a reasonable possibility when all you’d need to do, in principle, is to replace your underlying laws with new ones. But until those laws are found, and it hasn’t even been shown that they could mathematically exist, you absolutely have to go with the description of the Universe that all the evidence points to. Anything else is simply an unscientific conclusion.

    And, here we are:

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 11:50 am on April 16, 2018 Permalink | Reply
    Tags: , , , , Ethan Siegel, This Is What It Looks Like When Solar Systems Form   

    From Ethan Siegel: “This Is What It Looks Like When Solar Systems Form” 

    From Ethan Siegel
    Apr 16, 2018

    1
    The star TW Hydrae. an analogue of the Sun and other sun-like stars, in its very early stages already shows evidence of new planets forming at various radii in its protoplanetary disk. S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO)

    CfA Submillimeter Array Mauna Kea, Hawaii, USA,4,207 m (13,802 ft) above sea level

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    After generations of speculations, we’ve finally got the images that tell us the full story.

    Some 4.5 billion years ago, our Sun and Solar System were born from a collapsing cloud of gas, likely alongside many other stars.

    2
    Artist’s impression of a young star surrounded by a protoplanetary disk. There are many unknown properties about protoplanetary disks around Sun-like stars, but observations are catching up. (ESO/L. Calçada)

    Over time, a protoplanetary disk forms, where imperfections will lead to young planets that eventually create full fledged solar systems.

    3
    A large number of protoplanetary systems have been imaged, but the state-of-the-art infrared imager designed for exoplanet disk pictures is SPHERE, which routinely obtains resolutions of ~10″, or less than 0.003 degrees per pixel. (SHINE (SpHere INfrared survey for Exoplanets) collaboration / Arthur Vigan)

    The details of how that work, however, have varied wildly depending on which stars we look at.

    4
    The young F-class star, HD 135344, exhibits a transitional structure showing both rings and a spiral shape to it. This star is more massive than our Sun, and right on the border of being or not being a T Tauri star. (T. Stolker et al., A&A, 595 (2016) A113)

    Some stars, more massive than ours, show spiral shapes in their disks.

    5
    The observational structure of the young star MWC 758, at right, compared with a simulation involving a large outer planet, at left. This Herbig star is much more massive than our Sun ever was. (NASA, ESA, ESO, M. Benisty et al. (University of Grenoble), R. Dong (Lawrence Berkeley National Laboratory), and Z. Zhu (Princeton University))

    NASA/ESA Hubble Telescope

    ESO VLT Platform at Cerro Paranal elevation 2,635 m (8,645 ft)

    The more massive they are, the more likely they are to show this structure, consistent with a large, outer, structure-driving planet.

    6
    The protoplanetary disk around the star HL Tauri in a young star cluster may well be the best analogue of a Sun-like star forming, with planets around it, that we’ve ever seen. (ALMA (ESO/NAOJ/NRAO)/NASA/ESA)

    Others, lower in mass, show clear, symmetric rings.

    7
    Some stars, like HD 141569, show evidence of both ring-like structures and a disrupted, discontinuous presence. Most protoplanetary disks, like this one, are around closer, higher-mass stars. (C. Perrot et al., A&A, 590 (2016) L7)

    Still others show a hybrid structure, where the rings exhibit some circularly-symmetric and some non-symmetric features.

    8
    The ESO’s Very Large Telescope (VLT) contains a new imaging instrument on it, SPHERE, which allows us to image exoplanets and protoplanetary disks around smaller, lower-mass stars at high resolution than ever before, and to do so rapidly as well. (ESO / Serge Brunier)

    ESO/SPHERE extreme adaptive optics system and coronagraphic facility on the VLT


    ESO SPHERE extreme adaptive optics system and coronagraphic facility on the extreme adaptive optics system and coronagraphic facility on the VLT, Cerro Paranal, Chile, with an elevation of 2,635 metres (8,645 ft) above sea level

    Owing to a new instrument on a remarkable telescope, the ESO’s Very Large Telescope, we can now image protoplanetary disks directly.

    9
    The SPHERE Common Path Infrastructure includes the main optical bench, connects the other sub-systems to the light path, and guarantees a static alignment of SPHERE to the VLT focus. The IRDIS instrument, in particular (at lower-left), is what enables these new, spectacular images. (ESO / SPHERE collaboration)

    The SPHERE instrument, optimized for infrared exoplanet research, includes the IRDIS imager, designed for high-resolution viewing.

    10
    Eight young T Tauri stars, as imaged by SPHERE, show disks, rings, and symmetric, unperturbed structures. These 8 disks range in age from 1 to 15 million years, and are all around stars of 2 solar masses or less.(H. Avenhaus et al. (2018), https://arxiv.org/abs/1803.10882)

    When it looked at T Tauri stars, very young stars of 2 solar masses or less, here’s what it saw.

    11
    The best ring-like fits around these stars, done automatically where the fits are good and manually where they are not.(H. Avenhaus et al. (2018), https://arxiv.org/abs/1803.10882)

    Regardless of age or mass, symmetric and well-defined rings, disks, and gaps exist around every one.

    12
    All eight of these systems, imaged and processed and fitted to better understand what’s going on around these pre-main-sequence stars. The infant stages of planet formation are all in play here.(H. Avenhaus et al. (2018), https://arxiv.org/abs/1803.10882)

    This should be exactly what our youthful Sun looked like.

    13
    The evolving protoplanetary disk, with large gaps, around the young star HL Tauri. ALMA image on the left, VLA image on the right. With the upcoming 30-meter class telescopes like GMT and ELT, new views of a protoplanetary disk like this, including in the optical, will become possible at last. (Carrasco-Gonzalez, et al.; Bill Saxton, NRAO/AUI/NSF)

    Giant Magellan Telescope, to be at the Carnegie Institution for Science’s Las Campanas Observatory, to be built some 115 km (71 mi) north-northeast of La Serena, Chile, over 2,500 m (8,200 ft) high

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile, at an altitude 3,046 m (9,993 ft)

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 10:30 am on April 15, 2018 Permalink | Reply
    Tags: , , , , Ethan Siegel, How Fast Could Life Have Arisen In The Universe?   

    From Ethan Siegel: “How Fast Could Life Have Arisen In The Universe?” 

    Ethan Siegel
    Apr 14, 2018

    1
    Organic molecules are found in star forming regions, stellar remnants and interstellar gas, all throughout the Milky Way. In principle, the ingredients for rocky planets and life on them could have come about quite quickly in our Universe, long before Earth ever existed. (NASA / ESA and R. Humphreys (University of Minnesota))

    NASA/ESA Hubble Telescope

    It took the Universe 9.2 billion years to create the Earth, and another 4 billion for complex life. Could we have gotten there faster?

    The story of how the Universe came to be the way it is today, from the Big Bang to the vast void of space littered with clusters, galaxies, stars, planets, and life, is the one story we all have in common. From our perspective here on Earth, it took about 2/3rds of our shared cosmic history before the Sun and Earth were even created. Yet life appeared on our world as far back as we’re able to measure: perhaps as much as 4.4 billion years ago. It makes one wonder if life in the Universe predated our planet, and, for that matter, how far back life could possibly go? That’s what Matt Wedel wants to know, as he asks:

    How soon after the Big Bang would there have been enough heavy elements to form planets and possibly life?

    Even restricting ourselves to the type of life that we would recognize as being “like us,” the answer to this question goes back farther than you might ever imagine.

    2
    Graphite deposits found in Zircon, some of the oldest pieces of evidence for carbon-based life on Earth. These deposits, and the carbon-12 ratios they show in the inclusions, date life on Earth to more than 4 billion years ago. (E A Bell et al, Proc. Natl. Acad. Sci. USA, 2015)

    We can’t go back to the very beginning of the Universe, of course. In the aftermath of the Big Bang, there were not only no stars or galaxies to start with, but there weren’t even atoms. Everything takes time to form, and the Universe, born containing a sea of matter, antimatter, and radiation, began as a mostly uniform place. The densest regions were only a tiny fraction of a percent — perhaps 0.003% — denser than average. This means it will take a tremendous amount of gravitational collapse to create something like a planet, which is around 1030 times denser than the mean density of the Universe. And yet, the Universe is free to take exactly as much time as it needs to make it all happen.

    3
    A standard cosmic timeline of our Universe’s history. While Earth didn’t come to exist until 9.2 billion years after the Big Bang, many steps that are required to create our world took place at extremely early times. (NASA/CXC/M.Weiss)

    After the first second-or-so, the antimatter has all annihilated away with most of the matter, leaving just a tiny bit of leftover protons, neutrons, and electrons amidst a sea of neutrinos and photons. After 3–4 minutes, the protons and neutrons have formed stable atomic nuclei, but it’s almost all isotopes of hydrogen and helium. And it’s only when the Universe sufficiently cools below a particular threshold, which takes approximately 380,000 years, that we can bind electrons to these nuclei, forming neutral atoms for the first time. Even with these fundamental ingredients in place, life — and even rocky planets — are not yet possible. Hydrogen and helium atoms alone simply will not do.

    4
    As the Universe cools, atomic nuclei form, followed by neutral atoms as it cools further. However, all of these atoms (practically) are hydrogen or helium, and it isn’t until many millions of years later, when stars form, that you can have the heavier elements needed for rocky planets and life. (E. Siegel)

    But gravitational collapse is a real thing, and given enough time, it will change the Universe. Even though it happens slowly at first, it’s relentless and it builds upon itself. The denser a region of space gets, the better it becomes at attracting more and more matter to it. The regions that begin with the greatest overdensities grow the fastest, with simulations indicating that the very first stars of all should form somewhere around 50–100 million years after the Big Bang. These stars should be made of hydrogen and helium exclusively, and ought to be capable of growing to very large masses: hundreds or perhaps even a thousand times the mass of our Sun. And when a star this massive forms, it’s a matter of only perhaps one or two million years before those stars die.

    But what goes on when those stars die is tremendous, because of how those stars lived. All stars fuse hydrogen into helium in their cores, but the most massive ones not only fuse helium into carbon, but then carbon into oxygen, oxygen into neon/magnesium/silicon/sulfur, and then on and on up the periodic table until you get to iron, nickel and cobalt. After that, there’s nowhere else to go, and the core collapses, triggering a supernova explosion. These explosions recycle huge amounts of now-heavy elements into the Universe, triggering new generations of stars and enriching the interstellar medium. All of a sudden, heavy elements, including the ingredients we need for rocky planets and organic molecules, now fill these proto-galaxies.

    5
    Atoms can link up to form molecules, including organic molecules and biological processes, in interstellar space as well as on planets. Once the proper types of heavy elements are available in the Universe, the formation of these ‘seeds of life’ is inevitable. (Jenny Mottar)

    The more stars live, burn, and die, the more enriched the next generation of stars will be. Many supernovae create neutron stars, and it’s neutron star-neutron star mergers that create the largest amounts of the heaviest elements in the periodic table.

    Periodic table Sept 2017. Wikipedia

    Greater fractions of heavy elements mean more rocky planets of greater density, greater amounts of the elements essential to life-as-we-know it, and greater probabilities for complex organic molecules to take place. We don’t need the average place in the Universe to look like our Solar System; we simply need for a few generations of stars to live and die in the densest regions of space in order to produce the conditions for rocky planets and organic molecules.

    6
    There is a very slowly-rotating neutron star at the core of the supernova remnant RCW 103, which was a massive star that reached the end of its life. While supernovae can send heavy elements that were fused in a star’s core back into the Universe, it’s the subsequent neutron star-neutron star mergers that create the majority of the heaviest elements of all. (X-ray: NASA/CXC/University of Amsterdam/N.Rea et al; Optical: DSS)

    NASA/Chandra Telescope

    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    By time the Universe is just one billion years old, the most distant objects we can measure the heavy element abundance for have huge amounts of carbon: as much as our own Solar System contains. The other heavy elements become more abundant even more quickly; carbon perhaps takes more time to reach a high abundance because it’s primarily produced in stars that don’t go supernova, rather than the ultra-massive ones which do. Rocky planets don’t need carbon; other heavy elements will do just fine. (And many supernovae will create phosphorous; don’t worry about recent reports falsely exaggerating its absence.) It’s quite likely that only a few hundred million years after the first stars turned on — by time the Universe is 300 to 500 million years old — we had rocky planets forming around the most enriched stars at the time.

    7
    The protoplanetary disk around the young star, HL Tauri, as photographed by ALMA. The gaps in the disk indicate the presence of new planets. Once enough heavy elements are present, some of these planets can be rocky. (ALMA (ESO/NAOJ/NRAO))

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    If it weren’t for the necessity of carbon for life, there would likely be regions of space that could have begun life processes at that time as well. But we need carbon for life like ours, and that means we have to wait a little longer for a good possibility to have life. Although carbon atoms will be present, a large enough abundance will probably require waiting between 1–1.5 billion years: until the Universe is about 10% of its present age, rather than the 3–4% it requires for rocky planets. It’s interesting to think that the Universe formed planets and had all the ingredients in the right abundances to create life except for carbon, and that it takes the life-and-death of the most massive Sun-like stars to give us enough of the most important life-giving ingredient of all.

    8
    Supernova remnants (L) and planetary nebulae (R) are both ways for stars to recycle their burned, heavy elements back into the interstellar medium and the next generation of stars and planets. The Sun-like stars that die in planetary nebulae, however, are the major source of carbon in the Universe. This takes longer to produce, since stars that die in planetary nebulae live longer than the ones that die in supernovae. (ESO / Very Large Telescope / FORS instrument & team (L); NASA, ESA, C.R. O’Dell (Vanderbilt), and D. Thompson (Large Binocular Telescope) (R))

    ESO/FORS1

    ESO VLT Platform at Cerro Paranal elevation 2,635 m (8,645 ft)

    U Arizona Large Binocular Telescope, Mount Graham, Arizona, USA, Altitude 3,221 m (10,568 ft)

    It’s an interesting exercise that if you extrapolate back the most advanced forms of life we find on Earth at various epochs in our planet’s history, you’ll find that the genomes have a complexity that increases with a particular trend. If you go all the way back to single base pairs, however, you get a figure that’s closer to 9–10 billion years ago than 12–13 billion years ago. Is this an indication that the life we have on Earth began well before Earth did? And furthermore, is it an indication that life could have began billions of years earlier, but where we are it took an extra few billion years to get started?

    9
    On this semilog plot, the complexity of organisms, as measured by the length of functional non-redundant DNA per genome counted by nucleotide base pairs (bp), increases linearly with time. Time is counted backwards in billions of years before the present (time 0).(Shirov & Gordon (2013), via https://arxiv.org/abs/1304.3381)

    At this point, we don’t know. But at the same time, we also don’t know where that line is between life and non-life. We also don’t know if terrestrial life got its start here, on an earlier planet, or if it began in the depths of interstellar space, without a planet at all.

    10
    Scores of amino acids not found in nature are found in the Murchison Meteorite, which fell to Earth in Australia in the 20th century. The fact that 80+ unique types of amino acids exist in just a plain old space rock might indicate that the ingredients for life, or even life itself, began not on a planet at all. (Wikimedia Commons user Basilicofresco)

    What’s incredibly interesting, though, is that the raw elemental ingredients necessary for life began existing back shortly after the first stars formed, and the most important ingredient — carbon, the fourth most common element in the Universe — is actually the very last ingredient to come about in the abundance we need. Rocky planets, at least in some locations, come about much earlier than life can: just half a billion years after the Big Bang, or perhaps even sooner. Once we have carbon, however, 1-to-1.5 billion years after the Big Bang, all the steps we need to take to produce organic molecules and the first steps towards life are inevitable. Whatever life processes took place to lead to humanity’s existence, as best as we understand them, could have begun when the Universe was just one-tenth the age it is now.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
    • stewarthoughblog 12:03 am on April 16, 2018 Permalink | Reply

      “Atoms can link up to form molecules, including organic molecules and biological processes…” There are no biological processes that form from atom combinations in abiotic organic molecules. Chemical evolution is a myth, like Darwin’s “warm little ponds” and Oparin-Haldane prebiotic soup. There is some interesting science here, but an contention that naturalistic processes caused the origin of life are intellectually insulting, as is any speculation that The ” formation of the ‘seeds of life’ being inevitable.”

      Like

c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: