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  • richardmitnick 12:18 pm on July 16, 2017 Permalink | Reply
    Tags: Ask Ethan: How close are we to a Theory of Everything?, , , , , Electromagnetic and weak and strong and gravitational forces are the four fundamental forces known to exist in this Universe, Ethan Siegel, Formulation of the Standard Model in 1968, , It’s not even a certainty that there even is a theory of everything, , , The Standard Model can be written as a single equation but all the forces within are not unified   

    From Ethan Siegel: “Ask Ethan: How close are we to a Theory of Everything?” 

    Ethan Siegel
    July 15, 2017

    1
    The idea that the forces, particles and interactions that we see today are all manifestations of a single, overarching theory is an attractive one, requiring extra dimensions and lots of new particles and interactions. Image credit: Wikimedia Commons user Rogilbert.

    “Those who begin coercive elimination of dissent soon find themselves exterminating dissenters. Compulsory unification of opinion achieves only the unanimity of the graveyard.” -Robert Jackson

    Since well before Einstein, it was the dream of those who study the Universe to find a single equation to govern as many phenomena as possible. Rather than have a separate law for each and every physical property the Universe has, we could unify these laws into a single, overarching framework. All the laws of electric charge, magnetism, electric currents, induction and more were unified into a single framework by James Clerk Maxwell in the mid-1800s. Ever since, physicists have dreamed of a Theory of Everything: a single equation governing all the laws of the Universe. What progress have we made? That’s the question of Paul Harding, who wants to know:

    “Has science made any progress with regards to the Grand Unified Theory and the Theory of Everything? And could you elaborate on what it would mean if we did find a unified equation?”

    Yes, we’ve made progress, but we’re not there yet. Not only that, but it’s not even a certainty that there even is a theory of everything.

    2
    The electromagnetic, weak, strong and gravitational forces are the four fundamental forces known to exist in this Universe. Image credit: Maharishi University of Management.

    The laws of nature, as we’ve discovered them so far, can be broken down into four fundamental forces: the force of gravity, governed by General Relativity, and the three quantum forces that govern particles and their interactions, the strong nuclear force, the weak nuclear force, and the electromagnetic force. The earliest attempts at a unified theory of everything came shortly after the publication of General Relativity, before we understood that there were fundamental laws to govern nuclear forces. These ideas, known as Kaluza-Klein theories, sought to unify gravitation with electromagnetism.

    3
    The idea of unifying gravitation with electromagnetism goes all the way back to the early 1920s, and the work of Theodr Kaluza and Oskar Klein. Image credit: SLAC National Accelerator Laboratory.

    SLAC Campus

    By adding an extra spatial dimension to Einstein’s General Relativity, a fifth dimension overall (in addition to the standard three space and one time) gave rise to Einstein’s gravity, Maxwell’s electromagnetism, and a new, extra scalar field. The extra dimension would need to be small enough to avoid interfering with the laws of gravity, and the details were such that the extra scalar field needed to have no discernible effects on the Universe. Since there was no way to formulate a quantum theory of gravity with this, the discovery of quantum physics and the nuclear forces — which this attempt at unification couldn’t account for — caused this to fall out of favor.

    4
    The quarks, antiquarks, and gluons of the standard model have a color charge, in addition to all the other properties like mass and electric charge. The Standard Model can be written as a single equation, but all the forces within are not unified. Image credit: E. Siegel.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    However, the strong and weak nuclear forces led to the formulation of the Standard Model in 1968, which brought the strong, weak, and electromagnetic forces under the same overarching umbrella. Particles and their interactions were all accounted for, and a slew of new predictions were made, including a big one about unification. At high energies of around 100 GeV (the energy required to accelerate a single electron to a potential of 100 billion volts), a symmetry unifying the electromagnetic and the weak forces would be restored. New, massive bosons were predicted to exist, and with the discovery of the W and Z bosons in 1983, this prediction was confirmed. The four fundamental forces were reduced down to three.

    5
    The idea of unification holds that all three of the Standard Model forces, and perhaps even gravity at higher energies, are unified together in a single framework. Image credit: © ABCC Australia 2015 http://www.new-physics.com.

    Unification was already an interesting idea, but models took off. People assumed that at higher energies still, the strong force would unify with the electroweak; that was where the idea of Grand Unification Theories (GUTs) came from. Some assumed that at even higher energies, perhaps around the Planck scale, the gravitational force would unify as well; this is one of the main motivations for string theory. What’s very interesting about these ideas, however, is that if you want to have unification, you need to restore symmetries at higher energies. And if the Universe has symmetries at high energies that are broken today, that translates into something observable: new particles and new interactions.

    6
    The Standard Model particles and their supersymmetric counterparts. This spectrum of particles is an inevitable consequence of unifying the four fundamental forces in the context of String Theory. Image credit: Claire David.

    So what new particles and interactions are predicted? This depends on which variant of unification theories you go for, but include:

    Heavy, neutral, dark-matter-like particles,
    supersymmetric partner particles,
    magnetic monopoles,
    heavy, charged, scalar bosons,
    multiple Higgs-like particles,
    and particles that mediate proton decay.

    Although we can be certain, from indirect observations, that there is some origin to our Universe’s dark matter, none of these particles or predicted decays have been observed to exist.

    7
    In 1982, an experiment running under the leadership of Blas Cabrera, one with eight turns of wire, detected a flux change of eight magnetons: indications of a magnetic monopole. Unfortunately, no one was present at the time of detection, and no one has ever reproduced this result or found a second monopole. Image credit: Cabrera B. (1982). First Results from a Superconductive Detector for Moving Magnetic Monopoles, Physical Review Letters, 48 (20) 1378–1381.

    This is a pity, in many regards, because we’ve searched, and hard. In 1982, one of the experiments searching for magnetic monopoles registered a single positive result, spawning many copycats which attempted to discover large numbers of others. Unfortunately, that one positive result was anomalous, and no one has ever replicated it. Also in the 1980s, people began building giant tanks of water and other atomic nuclei, searching for evidence of proton decay. While those tanks eventually wound up being repurposed as neutrino detectors, not a single proton has ever been observed to decay. The proton lifetime is now constrained to be greater than 1035 years: some 25 orders of magnitude greater than the age of the Universe.

    8
    The water-filled tank at Super Kamiokande, which has set the most stringent limits on the lifetime of the proton. In later years, detectors set up in this fashion have made outstanding neutrino observatories, but have yet to detect a single proton decay. Image credit: Kamioka Observatory, ICRR, University of Tokyo.

    This is also too bad, because Grand Unification offers a clean and elegant path to generating the matter/antimatter asymmetry in the Universe. At very early times, the Universe is hot enough to produce matter-and-antimatter pairs of all the particles that can possibly exist. In most GUTs, two of those particles that exist are superheavy X-and-Y bosons, which are charged, and contain both quark and lepton couplings. There’s expected to be an asymmetry in the way the matter versions and the antimatter versions decay, and they can give rise to a leftover presence of matter over antimatter, even if there was none initially. Unfortunately, again, we have yet to find any positive evidence for such particles and/or interactions.

    9
    An equally-symmetric collection of matter and antimatter (of X and Y, and anti-X and anti-Y) bosons could, with the right GUT properties, give rise to the matter/antimatter asymmetry we find in our Universe today. Image credit: E. Siegel / Beyond The Galaxy.

    Ethan Siegel Beyond the Galaxy

    Some physicists contend that the Universe must have these symmetries, and the evidence must simply lie at energies too high for even the LHC to probe.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    But others are coming around to a more uncomfortable possibility: perhaps nature doesn’t unify. Perhaps there is no Grand Unified Theory that describes our physical reality; perhaps a quantum theory of gravity doesn’t unify with the other forces; perhaps the problems of baryogenesis and dark matter have other solutions that aren’t rooted in these ideas. After all, the ultimate arbiter of what the Universe is like isn’t our ideas about it, but rather the results of experiment and observations. We can only ask the Universe what it’s like; it’s up to us to listen to what it tells us and go from there.

    6
    The Standard Model Lagrangian is a single equation encapsulating the particles and interactions of the Standard Model. It has five independent parts: the gluons (1), the weak bosons (2), how matter interacts with the weak force and the Higgs field (3), the ghost particles that subtract the Higgs-field redundancies (4), and the Fadeev-Popov ghosts, which affect the weak interaction redundancies (5). Neutrino masses are not included. Image credit: Thomas Gutierrez, who insists there is one ‘sign error’ in this equation.

    Although we can write the Standard Model as a single equation, it isn’t really a unified entity in the sense that there are multiple, separate, independent terms to govern different components of the Universe. The various parts of the Standard Model don’t interact with each other, as color charge doesn’t affect the electromagnetic or weak forces, and there are unanswered questions about why interactions that should occur, like CP-violation in the strong force, don’t.

    7
    When symmetries are restored (at the top of the potential), unification occurs. However, the breaking of symmetries, at the bottom of the hill, corresponds to the Universe we have today, complete with new species of massive particles. Image credit: Luis Álvarez-Gaumé & John Ellis, Nature Physics 7, 2–3 (2011).

    It’s the hope of many that unification holds the answer to these questions, and will solve many of the open problems and puzzles in physics today. However, any sort of additional symmetries — symmetries which are restored at high energies but are broken today — lead to new particles, new interactions, and new physical rules that the Universe plays by. We’ve tried to reverse-engineer some predictions using what rules we’d need for things to work out, yet the particles and unifications we were hoping to find never materialized. Unification won’t help you derive emergent properties like chemistry, biology, geology, or consciousness, but will help us better understand the origin of where everything came from, and how.

    8
    The cosmic history of the entire known Universe shows that we owe the origin of all the matter within it, and all the light, ultimately, to the end of inflation and the beginning of the Hot Big Bang. Image credit: E. Siegel / ESA and the Planck Collaboration.

    ESA/Planck

    Of course, there is the other possibility: that the Universe simply doesn’t unify. That the multiple different laws and rules we have are there for a reason: these symmetries that we’ve invented are simply our own mathematical inventions, and not descriptive of the physical Universe. For every elegant, beautiful, compelling physical theory that’s out there, there’s an equally elegant, beautiful, and compelling physical theory that is wrong. In these matters, as in all scientific matters, it’s up to humanity to ask the right questions. But it’s up to the Universe to tell us the answers. Whatever they are, that’s the Universe we have. It’s up to us to figure out what those answers mean.

    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 12:30 pm on July 14, 2017 Permalink | Reply
    Tags: , , , , Ethan Siegel, That extra ingredient is a heavy isotope of hydrogen: deuterium, The Universe was born almost exclusively with mere hydrogen and helium, This One Imperfection In Nuclear Physics Allowed Earth To Exist   

    From Ethan Siegel: “This One Imperfection In Nuclear Physics Allowed Earth To Exist” 

    Ethan Siegel
    Jul 13, 2017

    1
    The Bubble Nebula is on the outskirts of a supernova remnant occurring thousands of years ago. Nebulae like this showcase where massive stars are born, and also where heavy elements get added back into the Universe, giving rise to rocky planets and organic materials like what we find here on Earth. T.A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF.

    NOAO WIYN Telescope, Kitt Peak National Observatory, Kitt Peak of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O’odham Nation, 88 kilometers (55 mi) west-southwest of Tucson, Arizona

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

    In order to create a rocky planet that’s teeming with life, the Universe needed to create large amounts of the heavy elements required for life’s processes. To make many of those elements, such as Tin, Iodine, Selenium, Molybdenum, Zinc, and Copper, you need supernovae to have occurred many times in our galaxy’s past. To get many more, such as Iron, Calcium, Cobalt, Sulfur, and Potassium, you need stars massive enough to create them. Yet the Universe was born, almost exclusively, with mere hydrogen and helium. If all you had was hydrogen and helium, it would be impossible to make a star more massive than about three times the Sun’s mass; these heavy elements would never be created and spread throughout the Universe. The only reason we can exist, today, is because one tiny imperfection in the early Universe allows the stars to grow hundreds of times as massive.

    2
    The ultra-massive star Wolf-Rayet 124, shown with its surrounding nebula, is one of thousands of Milky Way stars that could be our galaxy’s next supernova. It’s also much, much larger and more massive than you’d be able to form in a Universe containing only hydrogen and helium. Hubble Legacy Archive / A. Moffat / Judy Schmidy.

    NASA/ESA Hubble Telescope

    In order for the Universe to exist as we know it, we need these massive stars. In a star like our Sun, the central region reaches high enough temperatures to fuse hydrogen into helium, which we’ll do until the core run out of fuel. When that happens, the inner parts of the Sun contract down, heating up to temperatures large enough to fuse helium into carbon, along with trace amounts of other elements. But when we’re out of helium fuel, that’s the end-of-the-line for the Sun; we don’t have it in us to fuse carbon or any heavier elements. It takes a star at least eight times as massive as the Sun to do that. It’s those very same massive stars that end their lives in supernovae, creating and recycling large amounts of heavy elements back into the Universe.

    3
    Supernova remnants provide all the evidence we need to know that supernovae are responsible for providing the vast majority of heavy elements found in the Universe today. NASA/JPL-Caltech.

    In most Milky Way-sized galaxies, we see multiple supernovae every century, indicating that these massive stars are common. In fact, there’s strong evidence that wherever in the Universe you form large bursts of stars, even for the first time, you’ll make many stars massive enough to create these heavy elements. But if all you had were hydrogen and helium, this would create a huge problem: hydrogen fusion begins at temperatures of approximately 4,000,000 K, which requires at least 1.6 × 1029 kg of mass to collapse down into a star. Once hydrogen fusion ignites, however, the outward flux becomes so energetic, very quickly, that no new mass can be added to that star. Once you become a star, you push those gaseous elements that would otherwise gravitate towards you away, preventing your star from growing further.

    4
    A combination of instruments on the ESO’s very large telescope reveals wide-field and narrow-angle views of the Tarantula Nebula. The cluster shown at the center contains some of the most massive stars in the known Universe, including many over 100 solar masses.
    ESO/P. Crowther/C.J. Evans.

    ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    If all you had were conventional hydrogen and helium, where hydrogen is made of one proton and helium is made of two protons and two neutrons, your proto-star would contract down rapidly, heating up to fusion temperatures in short order and emitting large amounts of high-intensity light. This radiation pushes against the nearby material that helped form the star in the first place, blowing it away from the star and overcoming gravity. You might form stars up to about three times the mass of the Sun, but the more massive ones — the ones we need to create an Earth-like world — would never come to exist.

    5
    Stars form in a wide variety of sizes, colors and masses, including many bright, blue ones that are tens or even hundreds of times as massive as the Sun. This is demonstrated here in the open star cluster NGC 3766, in the constellation of Centaurus. ESO.

    Thankfully, the Universe has, even from birth, an extra ingredient that makes much more massive stars possible. That extra ingredient is a heavy isotope of hydrogen: deuterium, which contains a proton and a neutron together. When you have deuterium and normal hydrogen nuclei together, it takes only a temperature of 1,000,000 K to fuse them together into helium-3, producing radiation that’s much less violent and forceful. This deuterium-burning is the first nuclear reaction to happen in a proto-star, and it pushes the core outwards enough to cause the temperature to rise far more slowly than if there were only hydrogen. Even a small amount of deuterium, less than 0.01% of the initial star’s mass, can delay the temperature increase up to hydrogen fusion by tens of millions of years, buying gravitation the time it needs to grow stars up to tens or even hundreds of times the mass of the Sun.

    6
    From beginning with just protons and neutrons, the Universe builds up helium-4 rapidly, with small but calculable amounts of deuterium and helium-3 left over as well. E. Siegel / Beyond The Galaxy.

    8

    So where did this deuterium come from? During the first few seconds after the Big Bang, the Universe was made of protons and neutrons, which attempt to fuse in a chain reaction to form heavier elements. But that first step involves making deuterium, which is easily destroyed by the high-energy radiation permeating the young Universe. It isn’t until minutes have passed that you can make deuterium without it being blasted apart. While this leads to a Universe that’s about 75% hydrogen and 25% helium, there are tiny, trace amounts of deuterium and helium-3 that get formed, along with even smaller amounts of lithium-7.

    9
    The abundances of helium, deuterium, helium-3 and lithium-7 are highly dependent on only one parameter, the baryon-to-photon ratio, if the Big Bang theory is correct. The fact that we have 0.0025% deuterium is needed to allow stars to form as massive as they do. NASA, WMAP Science Team and Gary Steigman.

    NASA/WMAP

    Even though only about 0.0025% of the Universe, by mass, becomes deuterium (about 1/40,000th) in this process, that’s enough to give even the first stars up to 50 million years to grow in size before hydrogen fusion takes over. Once you make stars that massive, the standard story of hydrogen-helium-carbon fusion takes place, generating large quantities of heavier elements that will get returned to the Universe for future generations of stars.

    10
    The nebula from supernova remnant W49B, still visible in X-rays, radio and infrared wavelengths. It takes a star at least 8-10 times as massive as the Sun to go supernova, and create the necessary heavy elements the Universe requires to have a planet like Earth. X-ray: NASA/CXC/MIT/L.Lopez et al.; Infrared: Palomar; Radio: NSF/NRAO/VLA.

    NASA/Chandra Telescope

    Caltech Palomar Intermediate Palomar Transient Factory telescope at the Samuel Oschin Telescope at Palomar Observatory,located in San Diego County, California, United States

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

    Rocky planets become possible; the essential elements for life get spread throughout the Universe. By time many billions of years have passed, planets like Earth can form, and organic materials like sugars, amino acids, and aromatic hydrocarbons will simply bind together naturally. The raw ingredients for everything we know life requires automatically pop into place.

    11
    A multiwavelength view of the galactic center, showing stars, gas, radiation and black holes, among other sources. Heavy elements and complex molecules also abound, and much of this material will be useful in forming future generations of stars. NASA/ESA/SSC/CXC/STScI.

    But without that tiny bit of inefficiency — without that easily-destroyed deuterium left over from the Big Bang to delay the fusion reactions in the cores of stars — it would all be impossible. Our Universe is an imperfect place. But that’s an absolute necessity. Without those imperfections, we’d never be able to exist.

    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 4:15 pm on July 8, 2017 Permalink | Reply
    Tags: , , , , , E=MC2 wins, Ethan Siegel, , , Sir Arthur Eddington, Sir Isaac Newton   

    Brought Foward by Larry Zamick, Rutgers Physics: From Ethan Siegel: “The Last 100 Years: 1919, Einstein and Eddington” 

    Ethan Siegel
    June 11, 2009 [Lary has been at this longer than I.]

    100 years ago, the way we viewed our Universe was vastly different than the way we view it now. The night sky, with stars, planets, comets, asteroids, nebulae, and the Milky Way, was viewed to make up the entire contents of the Universe.

    1
    The Universe was static, governed by two laws only: Newton’s Gravity and Maxwell’s Electromagnetism. There were the first hints that the Universe was made up of quantum particles, such as the photoelectric effect, Rutherford’s first hints at the existence of the nucleus, and Planck’s view that energy was quantized. But other than that — and Einstein’s new Theory of Special Relativity, there were very few mysteries about the Universe in 1909. But one of them would change our view of the Universe forever.

    2
    You see, there was a tiny, tiny problem with the planet Mercury. Its orbit just wasn’t quite right. Kepler’s Laws (which can be derived from Newton’s Gravity) said that all the planets should move in ellipses around the Sun. But Mercury (above) doesn’t quite do that. Mercury makes an ellipse that precesses — or rotates — ever so slightly. Specifically, it precessed at a rate of 1.555 degrees per century. A greatly exaggerated example of precession is shown below:

    3
    Now, physicists and astronomers have always been very detail-oriented people. So they calculated what the effects of the Earth’s equinoxes precessing were, and were able to account for 1.396 of those degrees. They realized that there were seven other major planets (and the asteroids) acting on Mercury, and that was able to account for another 0.148 degrees. That left them with only 0.011 degrees per century that was different between their theoretical predictions and their observations. But this minuscule difference was significant enough that it led some to consider that Newton’s Law of Universal Gravitation might be wrong.

    4
    Newton said that mass and separation distance was what determined gravity. There was a force that he called “action at a distance” that made everything attract. But during the time from 1909-1916, a new theory came about.

    5
    The same guy who discovered the photoelectric effect, special relativity, and E=mc^2 came up with a new theory of gravity. Instead of an “action at a distance” due to mass, this new theory said that space gets bent by energy, and causes everything — even massless things — to bend beneath what we see as gravity.

    6
    Now this new theory was very interesting for a few reasons. First off, it accounted for those 0.011 degrees that Newton’s Gravity did not. Second, it predicted — as a simple solution — the existence of black holes. And third, it predicted that something very exciting and testable would happen: that light would be bent by gravity.

    7
    Big deal, said Newton’s advocates. If I take E=mc^2, and I know that light has energy, I can just substitute E/c^2 for mass in Newton’s equations, and get a prediction that Newton’s gravity would bend light, too. It just so happened that Einstein’s bending was predicted to be twice as much as Newton’s bending, and that there was a total Solar Eclipse coming up in 1919. The stage was set for the most dramatic test of gravity ever.

    8
    The director of Cambridge Observatory, Sir Arthur Eddington, led an expedition to observe the total solar eclipse of May 29, 1919. During an eclipse, the sky gets dark enough that you can see stars, even close to the Sun. So Eddington set out to map the position of the stars when they were close to the Sun, and see how the Sun bent the light. Would it match up with Einstein’s prediction, Newton’s prediction, or would it not bend at all?

    9
    Image credit: American Institute of Physics.

    Lo and behold, Einstein’s prediction was spot on. Just like that, Newton’s theory of Universal Gravitation, the most solid foundation in all of physics — unchallenged for over 200 years — was obsolete. All of this was done in the years 1909-1919, and it was just the start of changing how we view the Universe.

    And (FYI) so far, in the 90 years since, every single prediction of Einstein’s gravity that’s ever been tested — from gravitational lensing to binary pulsar decay to time dilation in a gravitational field — have confirmed General Relativity as the most successful physical theory of all-time.

    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

    Rutgers, The State University of New Jersey, Larry’s school as a Professor of Physics and mine as a student is a leading national research university and the state’s preeminent, comprehensive public institution of higher education. Rutgers is dedicated to teaching that meets the highest standards of excellence; to conducting research that breaks new ground; and to providing services, solutions, and clinical care that help individuals and the local, national, and global communities where they live.

    Founded in 1766, Rutgers teaches across the full educational spectrum: preschool to precollege; undergraduate to graduate; postdoctoral fellowships to residencies; and continuing education for professional and personal advancement.

    Rutgers smaller
    Please give us back our original beautiful seal which the University stole away from us.
    As a ’67 graduate of University college, second in my class, I am proud to be a member of

    Alpha Sigma Lamda, National Honor Society of non-tradional students.

     
  • richardmitnick 9:28 am on July 2, 2017 Permalink | Reply
    Tags: Ask Ethan: Could We Save The Earth By Migrating It Away From The Sun?, Ethan Siegel, Physically possible? Absolutely. With current technology? Not a chance.   

    From Ethan Siegel: “Ask Ethan: Could We Save The Earth By Migrating It Away From The Sun?” 

    Ethan Siegel
    Jul 1, 2017

    1
    The NEXIS Ion Thruster, at Jet Propulsion Laboratories, is a prototype for a long-term thruster that could move large-mass objects over very long timescales. NASA / JPL.

    Someday, in the distant future, the Earth’s oceans will boil, destroying all life on the planet’s surface and potentially rendering Earth completely inhospitable. It’s the type of global warming that no human can avert: the gradual warming that the Sun experiences by burning its core fuel over its lifetime. But there may be a way to keep the Earth inhabited if we plan a very long-term solution: migrating the entire Earth. Is this really plausible, though? That’s what Mathieu Nisen wants to know:

    “I want to dream a bit: do you think it could be physically feasible to migrate the earth’s orbit with our current knowledge in science?”

    To find out, we need to figure out how hot it’s going to get, and how fast, in order to move the Earth quickly enough to save it.

    2
    This cutaway showcases the various regions of the surface and interior of the Sun, including the core, which is where nuclear fusion occurs. Wikimedia Commons user Kelvinsong.

    The way any star gets its energy is by fusing lighter elements into heavier ones in its core. Our Sun, in particular, fuses hydrogen into helium in regions where the core temperature exceeds 4,000,000 K. The hotter things get, the faster the rate of fusion; the very center of the core may be as hot as 15,000,000 K. This rate is almost perfectly constant, but not quite. Over very long periods of time, the percentage of hydrogen-to-helium in the core changes, causing the interior to heat up a little bit more over billions of years. When it heats up, three things happen:

    It gets more luminous, meaning it outputs more total energy over time,
    It swells slightly in size, increasing appreciably in radius by a few percent every billion years,
    And its temperature remains almost perfectly constant, changing by less than 1%-per-billion years.

    3
    The Sun has increased in size, brightness, and temperature according to the curves above, and those three quantities will continue to evolve as shown by their respective lines into the future. Wikimedia Commons user RJHall, based on Ribas, Ignasi (2010).

    All of this adds up to one uncomfortable fact: the amount of energy that reaches the Earth is very slowly increasing over time. For every 110 million years that pass, the solar luminosity increases by about 1%, which means that the energy reaching the Earth also rises by 1% over that exact same time. Back when the Earth was four billion years younger, our planet received barely 70% of the energy we do today. And after another one-to-two billion years, if we do nothing else to mitigate it, eventually this increase will cause a severe problem for Earth. At that point, we will hit a mean surface temperature of 373 kelvin (100 °C / 212 °F). In other words, at some point, the Sun will become so hot that the Earth’s oceans will boil.

    4
    If the surface temperature becomes too high, our planet will be unable to support the existence of liquid water on the surface. NASA Goddard Space Flight Center.

    So how can we mitigate it? There are a few potential solutions:

    We can set up a series of large reflectors at the L1 Lagrange point, preventing some of the incident light from reaching the Earth.
    We can geoengineer the atmosphere/albedo of our planet to reflect more light and absorb less.
    We can de-greenhouse our planet, removing molecules like methane and carbon dioxide from the atmosphere.
    We can abandon Earth and focus on terraforming outer worlds, such as Mars.

    5
    A possible pathway for the eventual terraforming of Mars to be more Earth-like. English Wikipedia user Ittiz.

    Any of these would work, in theory, but would also require a tremendous amount of effort and ongoing maintenance.

    However, the solution of migrating the Earth to a more distant orbit would be permanent! And although we’d have to push our orbit out quite considerably to keep temperatures constant, timescales of hundreds of millions of years give us plenty of time, if we need it. To cancel out an effect of a 1% increase in the luminosity of the Sun, we’d need to push Earth an additional 0.5% away from the Sun; to cancel out an increase of 20% (what we expect over the next 2 billion years, total), we need the Earth an extra 9.5% more distant than we are now. Instead of the Earth being a mean distance of 149,600,000 km from the Sun, we’d be looking at more like 164,000,000 km.

    6
    The Earth-Sun distance has not changed by much over the past 4.5 billion years. But if the Sun is going to heat up and we don’t want Earth to heat up commensurately, we should seriously consider migrating our planet outward. ISS Expedition 7 Crew, EOL, NASA.

    This is going to take a lot of energy! To move the Earth — all six septillion (6 × 1024) kilograms of it — that extra distance away from the Sun is going to change our orbital parameters by quite a bit. If we were to push Earth’s mean distance from the Sun out to 164,000,000 km (102 million miles), there would be some significant changes we’d notice:

    It would take an extra 14.6% longer for the Earth to complete a single revolution around the Sun.
    To maintain a stable orbit, our orbital speed would have to slow down, from 30 km/s to 28.5 km/s.
    If the period of Earth’s rotation stayed the same (24 hours), we’d have 418 days in a year, instead of 365.
    The Sun would appear slightly smaller in the sky — by about 10% — and the Sun’s effects on the tides would weaken by a few centimeters.

    7
    If the Sun swelled in size but Earth migrated outward, the two effects would not quite cancel; the Sun would appear slightly smaller from Earth overall. Public domain.

    But in order to get the Earth out that far, we’d need to make a very big energetic change: we’d need to alter the gravitational potential energy of the Sun-Earth system. Even accounting for all the other factors, including the slower-moving Earth around the Sun, we’d have to change the Earth’s orbital energy by 4.7^1035 Joules, which is the equivalent of 1.3^1020 Terawatt-hours: about 1015 times humanity’s total annual energy supply. You might think that given two billion years would help, and it does, but only a little. We would need about 500,000 times the amount of energy that humanity presently generates today, globally, all pumped into migrating the planet outward in order to migrate the Earth to a safe, consistent distance.

    8
    The speed at which planets revolve around the Sun is dependent on their distance from the Sun. Migrating Earth outwards, slowly, by 9.5% ought not perturb the orbits of the other planets. NASA / JPL.

    The conversion technology is the least of our worries; the biggest concern is more fundamental: how do we get all that energy? Realistically, there’s only one place that has enough for those needs, and that is the Sun itself. At present, the Earth receives about 1,500 Watts of power per square meter from the Sun. In order to obtain enough power to migrate the Earth in the right amount of time, we’d need to build an array (in space) that collected that entire 4.7^1035 Joules of energy, evenly, over a time period of two billion years. That means an array that’s 5^1015 square meters in size (and 100% efficient), or the equivalent of the entire surface area of ten Earths.

    9
    The concept of space-based solar power has been around for a long time, but no one has ever conceived of an array that’s 5 billion square kilometers in size. NASA.

    So to migrate the Earth to a higher, safe orbit, that’s what it takes: five billion square kilometers of a 100%-efficient solar array, whose energy goes entirely into pushing the Earth into a more distant orbit around the Sun for two billion years. Physically possible? Absolutely. With current technology? Not a chance. And is it practically possible? Almost definitely not, at least not with what we currently know. The reason that migrating the entire planet is so difficult is twofold: because of how strong the Sun’s gravitational pull is and how massive the Earth is. But this is the planet we have and the Sun we have, and the Sun is going to heat up, regardless of what we do. Until we find a way to gather and utilize that massive amount of energy, we’re going to need other strategies if we want to survive the ultimate global warming apocalypse!

    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 8:37 pm on June 24, 2017 Permalink | Reply
    Tags: Ask Ethan: Can Failed Stars Eventually Succeed?, , , , , Ethan Siegel   

    From Ethan Siegel: “Ask Ethan: Can Failed Stars Eventually Succeed?” 

    Ethan Siegel
    Jun 24, 2017


    The closest brown dwarf system to Earth, Luhman 16, contains enough total mass to form a red dwarf star if everything within it were combined. The question of whether this will ever happen in our Universe is an interesting one. Janella Williams, Penn State University.

    In the night sky, the most apparent thing of all are the stars, found in every direction we dare to look. But for every star that gathers enough mass to ignite nuclear fusion in its core, burning hydrogen into helium and turning matter into energy via E = mc2, there are many other objects that didn’t make it that far. Most collections of mass that start to form in a nebula never get big enough to become a star, and instead become fragmented gas clouds, asteroids, rocky worlds, gas giants, or brown dwarfs. The brown dwarfs are the “failed stars” of the Universe, having gathered enough mass to ignite some rare-isotope fusion reactions, but not enough to become true stars. But many brown dwarfs come in binary pairs, leading Ibnul Hussaini to wonder if they might, someday, merge:

    “Will the orbit of these [brown dwarfs] over a long period of time, eventually become smaller and smaller from the loss of energy through gravitational waves? Will they then eventually end up merging? If so, what happens in a [brown dwarf] merger? Will they merge to become an actual star that goes through fusion? Or is it something else entirely?”

    In astronomy, as in life, just because you didn’t make it on the first try doesn’t mean you’ll never get there. Let’s start by looking at the ones that make it.

    2
    An illustration of a giant planet around a red dwarf star. The difference between a planet, a failed star, and a true star comes down to one thing only: mass. ESO.

    In order to ignite nuclear fusion in the core of a star — to get hydrogen nuclei to fuse — you need to reach a temperature of around 4,000,000 K. The gas that stars form from in interstellar space begins at relatively cold temperatures: just a few tens of degrees above absolute zero. But once gravitation kicks in, it causes this cloud of gas to collapse. When collapse occurs, the atoms inside gain speed, collide with each other, and heat up. If there were only a small number of atoms present, they’d emit that heat out into the interstellar medium, sending light streaming throughout the galaxy. But when you get large numbers of atoms together, they trap that heat, causing the interior of the gas cloud to heat up.

    3
    The constellation of Orion, along with the great molecular cloud complex and including its brightest stars. Many new stars are presently forming here due to the collapse of gas, which traps the heat from stellar formation. Rogelio Bernal Andreo.

    If you form something very small, like of the mass of an asteroid, Earth, or even Jupiter, you might heat up to thousands or even tens of thousands of degrees in your core, but you’ll still be very far away from that fusion temperature. But if you hit a certain critical mass — about thirteen times the mass of Jupiter — you’ll achieve a temperature of about 1,000,000 K. That’s not enough to begin fusing hydrogen into helium, but is a critical temperature for a very specific reaction: deuterium fusion. About 0.002% of the hydrogen in the Universe doesn’t just have a single proton as its nucleus, but rather a proton and a neutron bound together, known as a deuteron. At temperatures of a million degrees, a deuteron and a proton can fuse together into helium-3 (an uncommon isotope of helium), a reaction which releases energy.

    4
    The proton-proton chain responsible for producing the vast majority of the Sun’s power is an example of nuclear fusion. In deuterium fusion, only the deuterium (H-2) + proton (H-1) going to helium-3 (He-3) reaction can occur. Borb / Wikimedia Commons.

    This is important! This release of energy, particularly during the protostar (i.e., star-formation) phase, generates high-energy radiation that pushes back against internal gravitational collapse, preventing the very center from getting too hot and hitting that 4,000,000 K threshold. This buys you extra time — tens of thousands of years or more — allowing you to gather more and more mass. Once you start fusing pure hydrogen (i.e., protons) in your core, the energy release is so intense that stars don’t grow any larger, so those early, first stages are critical. If it weren’t for deuterium fusion, the most massive stars would cap out at only about three times the mass of our Sun, instead of the hundreds of solar masses they reach in our backyard.

    5
    A composite image of the first exoplanet ever directly imaged (red) and its brown dwarf parent star, as seen in the infrared. A true star would be much physically larger and higher in mass than the brown dwarf shown here. European Southern Observatory (ESO).

    In order to ever reach that 4,000,000 K temperature in your core, and thereby become a true star, you need a minimum of about 7.5% the mass of our Sun: around 1.5 × 1029 kg of mass. To become a deuterium-fusing brown dwarf, also known as a failed star, you need somewhere between 2.5 × 1028 kg and 1.5 × 1029 kg of mass. And just as there are binary stars out there in great numbers, so, too, are there binary brown dwarfs.

    6
    These are the two brown dwarfs that make up Luhman 16, and they may eventually merge together to create a star. NASA/JPL/Gemini Observatory/AURA/NSF.

    Gemini/North telescope at Mauna Kea, Hawaii, USA

    Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile

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

    In fact, the closest brown dwarf to us, the system Luhman 16, is a binary system, while other brown dwarfs have been known to have giant planets orbiting them. In the specific case of Luhman 16, the masses of the two brown dwarfs are determined to be:

    Between 8.0 × 1028 kg and 1.0 × 1029 kg, for the primary, and
    between 6.0 × 1028 kg and 1.0 × 1029 kg, for the secondary.

    In other words, there’s an excellent chance that if these two failed stars, orbiting at about three times the Earth-Sun distance from one another, were to merge, they would form an actual star. In fact, any addition of mass that takes a failed star over that mass threshold to begin burning hydrogen in its core ought to do it.

    7
    The two brown dwarfs that make up Luhman 16 have been imaged twelve separate times by the Hubble Space Telescope, indicating their motion and relative orbits over a multi-year time period. Image credit: Hubble / ESA, L. Bedin / INAF.

    Ibnul’s hunch is on the right track: yes, it’s true that orbiting masses do emit gravitational waves, and that the emission of these waves will cause orbits to decay. But for these masses and distances, we’re talking about decay times of somewhere in the neighborhood of 10200 years, which is much, much longer than the lifetime of the Universe. In fact, it’s much longer than the lifetime of any star at all, of the galaxy, or even of the galaxy’s central black hole. If you wait around for gravitational waves to turn this binary pair of brown dwarfs into a star, you’re going to be waiting a disappointingly long time.

    8
    The inspiral and merger scenario for brown dwarfs as well-separated as these two are would take a very long time due to gravitational waves. But collisions are quite likely. Just as red stars colliding produce blue straggler stars, brown dwarf collisions can make red dwarf stars. Melvyn B. Davies, Nature 462, 991-992 (2009).

    Every once in a while, you get random collisions between objects in space. Just the fact that stars, failed stars, rogue planets and more move through the galaxy, primarily influenced by gravitation, means that there’s a finite chance that you’ll just randomly get a collision between two objects. This is a much better strategy than waiting for gravitational waves to take your orbits down, except in the most extreme cases. On timescales of about 1018 years, “only” about 100 million times older than the Universe presently is, brown dwarfs will randomly collide with either other brown dwarfs or stellar corpses, giving new life to a failed star. About 1% of brown dwarfs, according to current estimates, will meet that fate.

    9
    The Sun’s atmosphere is not confined to the photosphere or even the corona, but rather extends out for millions of miles in space, even under non-flare or ejection conditions. NASA’s Solar Terrestrial Relations Observatory.

    NASA/STEREO spacecraft

    But even if you can’t wait for gravitational radiation, and even if you don’t get lucky enough to collide with another brown dwarf in interstellar space, you still have a chance to merge. We normally think of stars as having a certain extent in space: that they take up a certain volume. For that matter, that’s how we think of Earth’s atmosphere, too: as a hard edge, with a boundary between what we consider the atmosphere and outer space. How foolish is that! In reality, atoms and particles extend outward for millions of miles (or kilometers), with flares from stars reaching well beyond the orbit of Earth. It was recently discovered that brown dwarfs emit flares, too, so just as a satellite in low-Earth orbit will fall back down to our planet, the friction from a brown dwarf in orbit around another will eventually draw them in. It won’t quite work for Luhman 16, but if the distance between the two failed stars were more like the Sun-Mercury distance, rather than the Sun-Ceres distance, this effect would have a shot.

    10
    Luigi Bedin’s multi-year study observing the motions of the failed stars in Luhman 16 has shown us how their positions and motions have changed over time, with the cycloid nature resulting from Earth’s motion during the year. Hubble / ESA, L. Bedin / INAF.

    NASA/ESA Hubble Telescope

    So what happens if you do get a merger or a collision? These events are rare and will, for the most part, take much longer than the present age of the Universe to occur. By that point, even a brown dwarf will have burned up all of its deuterium, while the corpse will have cooled off to just a few degrees above absolute zero at the surface. But the energy of a collision or merger ought to create enough heat and pressure in the core that we should — so long as we cross that critical mass threshold — still ignite nuclear fusion in the core. The star will be low-mass, red in color, and extremely long-lived, burning for more than 10 trillion years. When a failed star at last ignites, it will most likely be the only star shining in the galaxy for its entire life; these events will be that rare and spaced out in time. Yet the type of star you become is interesting in its own right.

    11
    When two brown dwarfs, far into the future, finally do merge together, they will likely be the only light shining in the night sky, as all other stars have gone out. The red dwarf that results will be the only primary light source left in the Universe at that time. user Toma/Space Engine; E. Siegel.

    It will burn its fuel so slowly that the helium-4 which gets made — the product of the core’s hydrogen fusion — will eventually convect out of the core, enabling more hydrogen to fuse in the core. The convection is efficient enough that 100% of the star’s hydrogen should burn to completion, leaving a solid mass of helium atoms. There won’t be enough mass to burn that helium any further, so the stellar remnant will contract down to a type of star that doesn’t yet exist in the Universe today: a helium white dwarf. It will take roughly a quadrillion years for this white dwarf to cool down and stop emitting light, during which time other brown dwarfs in the galaxy will collide and ignite. By time a failed star finally succeeds and goes through its entire life cycle, becoming a black dwarf, another failed star will gets its opportunity.

    12
    An accurate size/color comparison of a white dwarf (L), Earth reflecting our Sun’s light (middle), and a black dwarf (R). When white dwarfs finally radiate the last of their energy away, they will all eventually become black dwarfs. BBC / GCSE (L) / SunflowerCosmos (R).

    If you managed to achieve some type of immortality, you could, in theory, travel from failed star to failed star, continuing on by drawing your energy from the Universe’s final, rare successes. Most failed stars will remain failures forever, but the few that succeed will be burning long after all other lights have gone out. As Winston Churchill famous said, “Success is not final, failure is not fatal: it is the courage to continue that counts.” Perhaps that applies to even the stars, even moreso than to ourselves.

    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 2:49 pm on June 22, 2017 Permalink | Reply
    Tags: Ethan Siegel, , What Ethan left out   

    From Ethan Siegel: “The future of astronomy: thousands of radio telescopes that can see beyond the stars” 

    Ethan Siegel
    June 21, 2017

    [SO, DID ETHAN FINALLY DISCOVER SKA? IT LOOKS LIKE THAT IS TRUE. I DID A SEARCH, “ETHAN SIEGEL AND SKA” AND CAME UP WITH NOTHING BUT THIS POST. ETHAN, WHAT ROCK HAVE YOU BEEN LIVING UNDER? COME BACK TO ME AND ENLIGHTEN ME.]

    The future of astronomy: thousands of radio telescopes that can see beyond the stars.

    1
    The Square Kilometer Array will, when completed, be comprised of an array of thousands of radio telescopes, capable of seeing farther back into the Universe than any observatory that has measured any type of star or galaxy. Image credit: SKA Project Development Office and Swinburne Astronomy Productions.

    Never heard of SKA, the square kilometer Array? Once it starts taking data, you’ll never forget it.

    SKA Square Kilometer Array

    SKA South Africa

    “Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in beer.” -Dave Barry

    By building bigger telescopes, going to space, and looking from ultraviolet to visible to infrared wavelengths, we can view stars and galaxies as far back as stars and galaxies go. But for millions of years in the Universe, there were no stars, no galaxies, nor anything that emitted visible light. Prior to that, the only light that existed was the leftover glow from the Big Bang, along with the neutral atoms created during the first few hundred thousand years.

    CMB per ESA/Planck

    ESA/Planck

    For those millions of years, there’s simply never been a way to gather information from the electromagnetic part of the spectrum. But a combination of advances in computing and the new construction of an array of thousands of large-scale radio telescopes across twelve countries opens up an incredible possibility like never before: the ability to map the neutral atoms themselves.

    2
    Distant sources of light — even from the cosmic microwave background [CMB, above] — must pass through clouds of gas. If there’s neutral hydrogen present, it can absorb that light, or, if it’s excited in some way, it can emit light of its own. Image credit: Ed Janssen, ESO [Includes inage of ESO’s VLT at Cerro Paranel, Chile].

    How can you see neutral atoms? After all, unless you’re dealing in either reflected light or with atoms that are themselves in an excited state, neutral atoms are some of the most optically boring materials that there are. Atoms are made of negatively charged electrons surrounding a positively charged nucleus, capable of occupying a variety of quantum states. But early on, for millions of years after the Big Bang, 92% of the atoms are the most boring type that exists: hydrogen, with a single proton and electron. While many different energy states exist, without any external source to excite it, hydrogen atoms are doomed to live in the lowest-energy (ground) state.

    3
    The energy levels and electron wavefunctions that correspond to different states within a hydrogen atom. The energy levels are quantized in multiples of Planck’s constant, but even the lowest energy, ground state has two possible configurations depended on the relative electron/proton spin. Image credit: PoorLeno of Wikimedia Commons.

    But when you first make neutral hydrogen, not all the atoms are perfectly in the ground state. You see, in addition to energy levels, the particles in atoms also have a property called spin: their intrinsic angular momentum. A particle like a proton or an electron can either be spin up (+½) or spin down (-½), and so a hydrogen atom can either have the spins aligned (both up or both down) or anti-aligned (one up and the other down). The anti-aligned combination is slightly lower in energy, but not by much. The transition from an aligned state to an anti-aligned one takes millions of years to occur, and when it does, the atom emits a photon of a very particular wavelength: 21 centimeters.

    4
    The 21-centimeter hydrogen line comes about when a hydrogen atom containing a proton/electron combination with aligned spins (top) flips to have anti-aligned spins (bottom), emitting one particular photon of a very characteristic wavelength. Image credit: Tiltec of Wikimedia Commons.

    Every time you undergo a burst of star formation, you ionize hydrogen atoms, meaning that electrons will fall back onto protons eventually, forming a large number of aligned atoms. By looking for this 21-cm signal, we can:

    construct a map of nearby, recent star formation,
    detect absorbing, neutral sources of anti-aligned gas,
    build a 3D map of neutral gas throughout the Universe,
    detect how star clusters and galaxies formed and evolved over time,
    and possibly detect the absorption and emission features of hydrogen gas immediately after, during, and possibly even before the formation of the first stars.

    5
    Before the formation of the first stars, there’s still neutral hydrogen gas to observe, if we look for it in the right way. Image credit: European Southern Observatory.

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation


    Somehow, this image seems fitting at this point.

    Next year, in 2018, just as the James Webb Space Telescope prepares for launch,

    NASA/ESA/CSA Webb Telescope annotated

    construction will begin on the Square Kilometer Array (SKA) [This is not correct. much has already been done. If Ethan skips over it, I will not let it pass uncovered.] SKA will wind up, at completion, being an array of some 4,000 radio telescopes, each approximately 12 meters in diameter, and capable of detecting this 21-cm line back farther than any galaxy we’ve ever seen. While the current galactic record-holder comes from when the Universe was just 400 million years old — 3% of its current age — SKA should be able to get the first 1% of the Universe that even James Webb might not see.

    6
    Only because this distant galaxy, GN-z11, is located in a region where the intergalactic medium is mostly reionized, can Hubble reveal it to us at the present time. James Webb will go much farther, but SKA will image the hydrogen that’s invisible to all other optical and infrared observatories. Image credit: NASA, ESA, and A. Feild (STScI).

    To go beyond the first stars, or to arrive at a cosmic destination where no ultraviolet or visible light can pass through the opaque, intergalactic medium, you need to probe what’s actually there. And in this Universe, the overwhelming majority of what’s there, at least that we can detect, is hydrogen. That’s what we know is out there, and that’s what we’re building SKA with the intention of seeing. It will collect more than ten times the data per second than any array today; it will have more than ten times the data collecting power; and it is expected to map the entire Universe from here all the way back to before the first galaxies. We will learn, in the most powerful way ever, how stars, galaxies, and the gas in the Universe grew up and evolved over time.

    7
    A single dish that’s currently part of the MeerKAT array will be incorporated into the Square Kilometer Array, along with around 4,000 other equivalent dishes. Image credit: SKA Africa Technical Newsletter, 1 (2016).

    A better image, and this is just South Africa:

    SKA Meerkat telescope, 90 km outside the small Northern Cape town of Carnarvon, SA

    According to Simon Ratcliffe, SKA scientist, we know some of what we’re going to find with SKA, but it’s the unknowns that are the most exciting.

    “Every time we’ve set out to measure something, we’ve discovered something entirely surprising.”

    Radio astronomy has brought us pulsars, quasars, microquasars, and mysterious sources like Cygnus X-1, which turned out to be black holes. The entire Universe is out there, waiting for us to discover it. When SKA is completed, it will shed a light on the Universe beyond stars, galaxies, and even gravitational waves. It will show us the invisible Universe as it truly is. As with anything in astronomy, all we need to do is look with the right tools.

    O.K., not O.K., here is some of what Ethan did not include:

    SKA/ASKAP radio telescope at the Murchison Radio-astronomy Observatory (MRO) in Mid West region of Western
    Australia

    Murchison Widefield Array,SKA Murchison Widefield Array, Boolardy station in outback Western Australia, at the Murchison Radio-astronomy Observatory (MRO)

    Artist’s impression of the Mid-Frequency Aperture Array telescope when deployed on the African site (C) SKA Organisation

    SKA LOFAR core (“superterp”) near Exloo, Netherlands

    6
    EMBRACE is the Electronic MultiBeam Radio Astronomy ConcEpt which is the Pathfinder instrument for the SKA at frequencies between 500MHz and 1500MHz.

    Seriously, Ethan, come back to me and tell me why you did not include these assets. After that, do a serious piece on Radio Astronomy that includes the Jansky VLA, the EHT, the European VLBI, The Global mm-VLBI Array, the NRAO VLBA. GBO, Parkes, The Goldstone Deep Space Communications Complex, NASA’s DEEP SPACE NETWORK, and whatever else is slipping my mind. I could put in all of the images because I have them. But, you are fantastic with images, so I will leave it to you to do it right.

    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 4:24 pm on June 17, 2017 Permalink | Reply
    Tags: , , , Can The Universe Ever Expand Faster Than The Speed Of Light?, , Ethan Siegel   

    From Ethan Siegel: “Can The Universe Ever Expand Faster Than The Speed Of Light?” 

    Ethan Siegel
    Jun 17, 2017

    1
    This image represents the evolution of the Universe, starting with the Big Bang. NASA / GSFC

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation

    It’s the most fundamental law of special relativity, and the realization that led Einstein to some of the greatest physics breakthroughs of all time: the idea that nothing can travel faster than light. That holds true even today, as all massless particles in a vacuum move exactly at the speed of light, while anything else — a massive particle anywhere or a massless one in a medium — are doomed to move slower than the speed of light. But when it comes to the expanding Universe, this seems like it might not still hold. Kevin Forward wants to know, as he asks:

    In the first millionths of a second of the Big Bang did the universe not expand faster than the speed of light?

    As a spoiler: no, it didn’t expand faster than light then, nor at any other time, nor will it ever do so. But there’s a good reason why one might think it once did.

    2
    Our Universe, from the hot Big Bang until the present day, underwent a huge amount of growth and evolution, and continues to do so.
    NASA / CXC / M.Weiss

    Our Universe, as we see it today, has been around for 13.8 billion years since the hot Big Bang. But if you’re asking how far we can see in any direction, the answer isn’t 13.8 billion light years; it’s much farther than that. You might, if you think very hard, imagine that twice that distance is possible: if a light-emitting object were 13.8 billion light years away 13.8 billion years ago, perhaps it emitted light while it was speeding away from us, maybe even at a speed approaching the speed of light. If a bright object existed back then and was constantly moving away from us at 299,792 km/s, its light would be just arriving now, while the object itself would be 27.6 billion light years distant. All of that is solid reasoning, but it makes an assumption that isn’t necessarily good: that space itself is static.

    3
    The Hercules galaxy cluster showcases a great concentration of galaxies many hundreds of millions of light years away. The farther away we look, the less reliable the assumption that we can treat an observed object as being in the same location in space and time that we are.
    ESO/INAF-VST/OmegaCAM. Acknowledgement: OmegaCen/Astro-WISE/Kapteyn Institute

    ESO Omegacam on VST at ESO’s Cerro Paranal observatory

    ESO VST telescope, at ESO’s Cerro Paranal Observatory, with an elevation of 2,635 metres (8,645 ft) above sea level

    The space we inhabit isn’t static; it’s expanding. In fact, we can measure what the expansion rate is today, what it was like in the distant past, and at every epoch in between. As it turns out, an object that was merely 168 meters away at the Big Bang (okay, at 10^33 seconds after the Big Bang) would only have its light reach us today, 13.8 billion years later, after an incredible journey, and an incredible amount of stretching, and would presently be 46.1 billion light years away.

    4
    The observable Universe might be 46 billion light years in all directions from our point of view, but there’s certainly more, unobservable Universe, perhaps even an infinite amount, just like ours beyond that. This is just the limit of what’s observable to us today. Frédéric MICHEL and Andrew Z. Colvin, annotated by E. Siegel

    “A-ha,” you proclaim, “that means space expanded faster than light!”

    Did it though? Because for something to go faster-than-light, it needs to have a speed inherent to it: something you can measure in, for example, kilometers per second. But that’s not how the Universe expands at all.

    5
    At greater distances and earlier times in the Universe, it was expanding more rapidly. But this does not mean it expanded at a faster speed, but rather at a faster rate, which is a speed-per-unit-distance. NASA, ESA, and A. Feild (STScI)

    Instead, the Universe expands as a speed per unit distance: we normally measure it in kilometers per second per megaparsec, where one megaparsec is about 3.26 million light years. If the expansion rate is 70 km/s/Mpc, that means, on average, an object that’s 10 Mpc away should expand away at 700 km/s; one that’s 200 Mpc away should recede at 14,000 km/s; and one that’s 5,000 Mpc away should appear to be moving away at 350,000 km/s.

    6
    The farther a galaxy is, the faster it expands away from us, and the more its light gets redshifted, necessitating that we look at longer and longer wavelengths. Beyond a certain distance, galaxies become unreachable by anything we emit today, even at the speed of light. Larry McNish of RASC Calgary Center

    Does that mean anything is moving faster than light, though? Let’s go all the way back to Einstein’s special theory of relativity, and ask what it means when we say that nothing can move faster than light. It means that, if you have two objects at the same spacetime event — occupying the same space at the same time — then they can’t move relative to one another at a speed faster than the speed of light. Even if one is moving north at 99% the speed of light and the other moves south at 99% the speed of light, they won’t be moving at 198% the speed of light relative to each other, but 99.995% the speed of light. No matter how fast each one moves, they will never exceed the speed of light relative to one another.

    7
    Particles might move very quickly, either in the same direction, opposite directions, or at an angle relative to one another. But when you measure the speed between two particles, it only makes sense, in the context of relativity, if you measure their speeds at the same location in space and time. NASA/Sonoma State University/Aurore Simonnet

    That’s why it’s called relativity in the first place, because it measures relative motion between two objects at the same location in space and time. But that type of relativity — special relativity — only sets the rules in your local, non-expanding space. General relativity adds another layer on top of that: the fact that space itself expands. By measuring the amount of normal matter, dark matter, dark energy, neutrinos, radiation and more present in the Universe today, and how light reaching us from all different distances in the Universe redshifts with that expansion, we can reconstruct exactly how big the Universe was at any point in the past.

    8
    The timeline of our observable Universe’s history, where the observable portion expands to larger and larger sizes as we move forward in time away from the Big Bang. NASA / WMAP science team

    NASA WMAP

    When it was approximately 10,000 years old, the observable Universe was already 10 million light years in size. When it was just one year old, the observable Universe was nearly 100,000 light years in size. When it was one second old, it was already more than 10 light years in size. That sure does sound like expanding faster than light, doesn’t it? But at no point did any particle move faster than light relative to any other particle that it interacted with.

    9
    A graph of the size/scale of the observable Universe vs. the passage of cosmic time. This is displayed on a log-log scale, with a few major size/time milestones identified. E. Siegel

    Instead, all that happened was that the space between particles expanded, and as it did, it increased the distance between them and stretched the wavelength of radiation present within that space. This has continued for the billions of years of cosmic history that took place since, and continues to take place today. While we may never reach any objects farther away than 15.6 billion light years today, even if we went at the speed of light, that’s not because they’re receding faster than light, but because the space between different locations continues to expand.

    The key takeaway is that space doesn’t expand at a particular speed, but rather at a particular rate: a speed-per-unit-distance. As a result, the farther away you look, the more the expansion of space affects the distance between you and that object you’re viewing. As long as it’s expanding, you can calculate a distance that, if you exceed it, everything appears to be receding away from you faster than 299,792 m/s. The farther away an object is, you can be sure that its light will be redder, its distance will be greater, and it will appear to be moving away from you more and more quickly. But faster than the speed of light? You need to be in the same location in order to measure that. Relative to our location, nothing moves faster than light, and that’s true in every location in the Universe at all times. Space expands, but not only does it not expand faster than light, it doesn’t expand at a speed at all!

    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 3:32 pm on June 15, 2017 Permalink | Reply
    Tags: , , , Black Hole Mergers, , , , Ethan Siegel   

    From Ethan Siegel: “Newest LIGO signal raises a huge question: do merging black holes emit light?” 

    Ethan Siegel
    June 15, 2017

    1
    There are many cases in the Universe, such as imploding stars or neutron star collisions, that are strongly suspected of creating high-energy bursts of electromagnetic energy. Black hole mergers aren’t supposed to be one of them, but the observational data may yet surprise us. Image credit: NASA / Skyworks Digital.

    Gravitational waves and electromagnetic ones don’t need to go together. But physics says it’s possible; what do the observations say?

    “The black holes collide in complete darkness. None of the energy exploding from the collision comes out as light. No telescope will ever see the event.”
    -Janna Levin

    Billions of years ago, two black holes much more massive than the Sun — 31 and 19 solar masses each — merged together in a distant galaxy far across the Universe. On January 4th of this year, those gravitational waves, traveling through the Universe at the speed of light, finally reached Earth, where they compressed and stretched our planet by the width of no more than a few atoms. Yet that was enough for the twin LIGO detectors in Washington and Louisiana to pick up the signal and reconstruct exactly what happened. For the third time ever, we had directly detected gravitational waves. Meanwhile, telescopes and observatories all over the world, including in orbit around Earth, were looking for an entirely different signal: for some type of light, or electromagnetic radiation, that these merging black holes might have produced.

    2
    Illustration of two black holes merging, of comparable mass to what LIGO has seen. The expectation is that there ought to be very little in the way of an electromagnetic signal emitted from such a merger, but the presence of strongly heated matter surrounding these objects could change that. Image credit:Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project (http://www.black-holes.org).

    According to our best models of physics, merging black holes aren’t supposed to emit any light at all. A massive singularity surrounded by an event horizon might emit gravitational waves, due to the changing curvature of space time as it orbits an inspirals with another giant mass, in line with General Relativity’s predictions. Because that gravitational energy, emitted as radiation, needs to come from somewhere, the final black hole post-merger is about two solar masses lighter than the sum of the originals that created it. This is completely in line with the other two mergers LIGO observed: where around 5% of the original masses were converted into pure energy, in the form of gravitational radiation.


    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

    3
    The masses of known binary black hole systems, including the three verified mergers and one merger candidate coming from LIGO. Image credit: LIGO/Caltech/Sonoma State (Aurore Simonnet).

    But if there’s anything outside of those black holes, such as an accretion disk, a firewall, a hard shell, a diffuse cloud, or any other possibility, the acceleration and heating of that material could conceivably create electromagnetic radiation traveling right alongside those gravitational waves. In the aftermath of the first LIGO detection, the Fermi Gamma-ray Burst Monitor made headlines as they claimed to detect a high energy burst of radiation coincident within a second of the gravitational wave signal.

    NASA/Fermi Telescope


    NASA/Fermi LAT

    Unfortunately, ESA’s Integral satellite not only failed to confirm Fermi’s results, but scientists working there uncovered a flaw in Fermi’s analysis of their data, completely discrediting their results.

    ESA/Integral

    4
    Artist’s impression of two merging black holes, with accretion disks. The density and energy of the matter here should be insufficient to create gamma ray or X-ray bursts, but you never know what nature holds. Image credit: NASA / Dana Berry (Skyworks Digital).

    The second merger held no such hints of electromagnetic signals, but that was less surprising: the black holes were of significantly lower mass, so any signal arising from them would be expected to be correspondingly lower in magnitude. But the third merger was large in mass again, more comparable to the first than the second. While Fermi has made no announcement, and Integral again reports a non-detection, there are two pieces of evidence that suggest there may have been an electromagnetic counterpart after all. The AGILE satellite from the Italian Space Agency detected a weak, short-lived event that occurred just half a second before the LIGO merger, while X-ray, radio and optical observations combined to identify a strange afterglow less than 24 hours after the merger.

    Italian Space Agency AGILE Spacecraft

    5
    Our galaxy’s supermassive black hole has witnessed some incredibly bright flares, but none as bright or long-lasting as XJ1500+0134. These transient events and afterglows do occur for quite some time, but if they’re associated with a gravitational merger, you’d expect the arrival time of the electromagnetic and gravitational wave signals to be concurrent. Image credit: NASA/CXC/Stanford/I. Zhuravleva et al.

    If either of these were connected to the black hole merger, it would be absolutely revolutionary. There is so little we presently know about black holes in general, much less merging black holes. We’ve never directly imaged one before, although the Event Horizon Telescope hopes to grab the first later this year.

    Event Horizon Telescope Array

    Event Horizon Telescope map

    The locations of the radio dishes that will be part of the Event Horizon Telescope array. Image credit: Event Horizon Telescope sites, via University of Arizona at https://www.as.arizona.edu/event-horizon-telescope.

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

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

    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

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    We’ve only just this year determined that black holes don’t have hard shells encircling the event horizon, and even that evidence is only statistical. So when it comes to the possibility that black holes might have an electromagnetic counterpart, it’s important to keep an open mind, to look, and to go wherever the data takes us.

    6
    Distant, massive quasars show ultramassive black holes in their cores, and their electromagnetic counterparts are easy to detect. But it remains to be seen whether merging black holes, particularly of these lower-mass (under 100 Suns) mergers, emit anything detectable. Image credit: J. Wise/Georgia Institute of Technology and J. Regan/Dublin City University.

    Unfortunately, neither one of these observations provide the necessary data to take us to a place where we’d conclude that merging black holes really do have a light-emitting counterpart. It’s very difficult to get compelling evidence in the first place, since even the twin LIGO detectors, operating with their incredible precision, can’t pinpoint the location of a gravitational wave signal to better accuracy than a constellation or three. Since gravitational waves and electromagnetic waves both travel at the speed of light, it’s extraordinarily unlikely that there would be nearly a 24 hour delay between a gravitational wave signal and an electromagnetic signal; in addition, that transient event appears to occur at a distance far too great to be associated with the gravitational wave event.

    7
    The observational field-of-view of the AGILE observatory during the moment of the LIGO observations (in color), with the possible location of the gravitational wave source shown in the magenta outlines.

    But the AGILE observations may potentially provide a hint that something interesting is going on. At the moment that the gravitational wave event occurred, AGILE was pointed at a region of space that contains 36% of the candidate LIGO region. And they do claim an “excess of detected X-ray photons” coming from somewhere on the sky over the standard, average background. But when you look at the data yourself, you have to ask yourself: how compelling is this?

    7
    Three critical figures, showing the raw data of the alleged ‘signal’ along with the background of X-ray emissions observed by the AGILE satellite, from the recently submitted publication, AGILE Observations of the Gravitational Wave Source GW170104.

    Over a few seconds before-and-after the LIGO merger, they pulled out an interesting event that they identify as “E2” in the three charts above. After doing a full analysis, where they account for what they saw and what sort of random fluctuations and backgrounds just naturally occur, they can conclude that there’s about a 99.9% chance that something interesting happened. In other words, that they saw an actual signal of something, rather than a random fluctuation. After all, the Universe is full of objects that emit gamma rays and X-rays, and that’s what the background is made of. But was it related to the gravitational merger of these two black holes?

    7
    Computer simulation of two merging black holes producing gravitational waves. The big, unanswered question is whether there will be any sort of electromagnetic, light counterpart to this signal? Image credit: Werner Benger, cc by-sa 4.0.

    If it were, you’d expect other satellites to see it. The best we can conclude, so far, is that if black holes do have an electromagnetic counterpart, it’s one that’s:

    incredibly weak,
    that occurs mostly at lower energies,
    that doesn’t have a bright optical or radio or gamma-ray component,
    and that occurs with an offset to the actual emission of gravitational waves.

    8
    The 30-ish solar mass binary black holes first observed by LIGO are very difficult to form without direct collapse. Now that it’s been observed twice, these black hole pairs are thought to be quite common. But the question of electromagnetic emission from these mergers is not yet settled. Image credit: LIGO, NSF, A. Simonnet (SSU).

    Also, everything we see is perfectly consistent — and arguably, more consistent — with the notion that merging black holes don’t have any electromagnetic counterparts at all. But the truth about it all is that we don’t have sufficient data to decide just yet. With more gravitational wave detectors, more black hole mergers of high masses, better pinpointing of the location, and better all-sky coverage of transient events, we just might find out the answer to this. If the missions and observatories proposed to collect this data are successfully built, operated, and (where necessary) launched, then 15 years from now, we can expect to actually know the scientific answer for certain.

    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 5:36 pm on June 12, 2017 Permalink | Reply
    Tags: , , , , , Ethan Siegel, , The scientific story of how each element was made   

    From Ethan Siegel: “The scientific story of how each element was made” 

    Ethan Siegel
    June 12, 2017

    1
    The visible light spectrum of the Sun, which helps us understand not only its temperature and ionization, but the abundances of the elements present. Image credit: Nigel A. Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF.

    U Arizona Steward Observatory at Kitt Peak, AZ, USA

    Think the periodic table is complicated? Now learn how each element in it was created.

    “It is the function of science to discover the existence of a general reign of order in nature and to find the causes governing this order. And this refers in equal measure to the relations of man — social and political — and to the entire universe as a whole.” -Dmitri Mendeleev

    There are over 100 elements in the periodic table, of which 91 are naturally found on Earth.

    2
    The primary source of the abundances of each of the elements found in the Universe today. A ‘small star’ is any star that isn’t massive enough to become a supergiant and go supernova; many elements attributed to supernovae may be better-created by neutron star mergers. Image credit: Periodic Table of Nucleosynthesis / Mark R. Leach / FigShare.

    But at the moment of the Big Bang, none of them existed at all.

    3
    The early Universe was full of matter and radiation, and was so hot and dense that the quarks and gluons present didn’t form into individual protons and neutrons, but remained in a quark-gluon plasma. Image credit: RHIC collaboration, Brookhaven.

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL RHIC PHENIX

    After the first second, quarks and gluons cooled to form bound states: protons and neutrons.

    4
    As matter and antimatter annihilate away in the early Universe, the leftover quarks and gluons cool to form stable protons and neutrons. Image credit: Ethan Siegel / Beyond The Galaxy.

    5
    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. Image credit: NASA / WMAP Science Team.

    NASA WMAP

    After tens of millions of years, we finally formed the first stars, making additional helium.

    6
    An artist’s impression of the environment in the early Universe after the first few trillion stars have formed, lived and died. Lithium is no longer the third most abundant element at this point. Image credit: NASA/ESA/ESO/Wolfram Freudling et al. (STECF).

    Massive enough stars become giants, fusing helium into carbon, also producing nitrogen, oxygen, neon, and magnesium.

    6
    The color-magnitude diagram of notable stars. The brightest red supergiant, Betelgeuse, is shown at the upper right. Image credit: European Southern Observatory.

    The most massive stars become supergiants, fusing carbon, oxygen, silicon, and sulphur, reaching the transition metals.

    8
    Fusing elements in onion-like layers, ultra-massive stars can build up carbon, oxygen, silicon, sulphur, iron and more in short order. Image credit: Nicole Rager Fuller of the NSF.

    Giant and supergiant stars create free neutrons, which can build up nuclei all the way to lead/bismuth.

    9
    The creation of free neutrons during high-energy phases in the core of a star’s life allow elements to be built up the periodic table, one at a time, by neutron absorption and radioactive decay. Supergiant stars and giant stars entering the planetary nebula phase are both shown to do this via the s-process. Image credit: Chuck Magee / http://lablemminglounge.blogspot.com.

    Most supergiants go supernova, where fast neutrons get absorbed, reaching uranium and beyond.

    10
    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. Image credit: ESO / Very Large Telescope / FORS instrument & team (L); NASA, ESA, C.R. O’Dell (Vanderbilt), and D. Thompson (Large Binocular Telescope) (R).

    ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level


    ESO/FORS1

    U Arizona Large Binocular Telescope, Mount Graham, Arizona, USA

    Neutron star mergers create the greatest heavy element abundances of all, including gold, mercury, and platinum.

    11
    Two neutron stars colliding, which is the primary source of many of the heaviest periodic table elements in the Universe. About 3–5% of the mass gets expelled in such a collision; the rest becomes a single black hole. Image credit: Dana Berry, SkyWorks Digital, Inc.

    Meanwhile, cosmic rays blast nuclei apart, creating the Universe’s lithium, beryllium, and boron.

    12
    Cosmic rays produced by high-energy astrophysics sources can reach Earth’s surface. When a cosmic ray collides with a heavy nucleus, spallation — producing lighter elements — occurs. Three elements are made by this process more than any other in the Universe. Image credit: ASPERA collaboration / AStroParticle ERAnet.

    Finally, the heaviest, unstable elements are made in terrestrial laboratories.

    13
    Updating the periodic table, Albert Ghiorso inscribes “Lw” (lawrencium) in space 103; codiscoverers (l. to r.) Robert Latimer, Dr. Torbjorn Sikkeland, and Almon Larsh look on approvingly. It was the first element to be created using entirely nuclear means in terrestrial conditions. Image credit: Public Domain / US Government.

    The result is the rich, diverse Universe we inhabit today.

    14
    The abundances of the elements in the Universe today, as measured for our Solar System. Image credit: Wikimedia Commons user 28bytes.

    At last, each element’s primary origin is known.

    15
    The most current, up-to-date image showing the primary origin of each of the elements that occur naturally in the periodic table. Neutron star mergers and supernovae may allow us to climb even higher than this table shows. Image credit: Jennifer Johnson; ESA/NASA/AASNova.

    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 1:24 pm on June 10, 2017 Permalink | Reply
    Tags: Ask Ethan: Why Do Stars Come In Different Sizes?, , , , Ethan Siegel   

    From Ethan Siegel: “Ask Ethan: Why Do Stars Come In Different Sizes?” 

    From Ethan Siegel
    June 10, 2017

    1
    Even a single star, like the Sun, will vary wildly in size throughout its lifetime. What is it, then, that explains the huge variety of stellar sizes we see today? ESO/M. Kornmesser

    If you were to compare planet Earth to the Sun, you’d find that you’d have to stack 109 Earths atop one another just to go from one end of the Sun to the other. Yet there are stars out there that are much smaller than the Earth… and much, much larger than even Earth’s orbit around the Sun! How is this possible, and what determines a star’s size? That’s what Roman Stangl wants to know:

    “Why can suns grow to… many different sizes? That is, ranging from somewhat larger [than] Jupiter up to suns exceeding Jupiter’s orbit?”

    It’s a tougher question than you think, because for the most part, we can’t see the size of a star.

    2
    A deep, telescopic image of the stars in the night sky clearly reveals stars of different colors and brightnesses, but all the stars shown here appear only as points. Differences in size are optical illusions, owing to saturation of the observing cameras. ESO

    Even through a telescope, most stars appear as simple points of light due to their incredible distances from us. Their differences in color and brightness are easy to see, but size is a different matter entirely. An object of a certain size a specific distance away will have what’s known as an angular diameter: the apparent size it appears to take up on the sky. The closest Sun-like star, Alpha Centauri A, is just 4.3 light years away, and is actually 22% larger than the Sun in radius.

    3
    The two sun-like stars, Alpha Centauri A and B, are located just 4.37 light years away from us and orbit one another at between the distances of Saturn and Neptune in our own solar system. Even in this Hubble image, however, they are simply oversaturated point sources; no disk can be resolved. NASA/ESA Hubble

    NASA/ESA Hubble Telescope

    Yet it appears to us to have an angular diameter of just 0.007″, or arc-seconds, where it takes 60 arc-seconds to make one arc-minute, 60 arc-minutes to make 1 degree, and 360 degrees to make a full circle. Even a telescope like Hubble can only resolve down to about 0.05″; there are very few stars in the Universe that a telescope can actually resolve. These tend to be giant stars that are close by, like Betelgeuse or R Doradus, which are among the largest stars in angular diameter in the entire sky.

    4
    A radio image of the very, very large star, Betelgeuse, with the extent of the optical disk overlayed. This is one of the very few stars resolvable as more than a point source as seen from Earth. NRAO/AUI and J. Lim, C. Carilli, S.M. White, A.J. Beasley, and R.G. Marson

    Fortunately, there are indirect measurements that allow us to calculate the physical size of a star, and those are incredibly reliable. If you have a spherical object that gets so hot it emits radiation, the total amount of radiation emitted by the star is determined by only two things: the temperature of the object and its physical size. The reason for this is that the only place that emits light out into the Universe is the star’s surface, and the surface area of a sphere always follows the same formula: 4πr2, where r is the radius of your sphere. If you can measure the distance to that star, its temperature, and how bright it appears, you can know its radius (and hence, its size) just by applying the laws of physics.

    5
    A zoomed-in picture of the red giant star UY Scuti, picture processed through the Rutherford Observatory’s telescope. This bright star may still only appear like a ‘point’ through most telescopes, but is the largest star presently known to humanity. Haktarfone / Wikimedia Commons

    6
    Columbia University Rutherford Observatory’s telescope

    When we make our observations, we see that some stars are as small as only a few tens of kilometers in size, while others go all the way up to more than 1,500 times the size of our Sun. Of the supergiant stars, the largest one known is UY Scuti at around 2.4 billion kilometers in diameter, which is larger than Jupiter’s orbit around the Sun. The thing is, these extreme examples of stars aren’t for stars like our Sun at all. Sure, the most common type of star is a main-sequence star like our Sun: a star made out of mostly hydrogen that gets its energy by fusing hydrogen into helium in its core. And these do come in a very large variety of sizes, determined by the mass of the star itself.

    7
    A young, star-forming region found within our own Milky Way. As gas clouds collapse down gravitationally, the proto-stars heat up and become denser, eventually igniting fusion in the core. NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration; Acknowledgment: R. O’Connell (University of Virginia) and the WFC3 Scientific Oversight Committee

    NASA/ESA Hubble WFC3

    When you form a star, gravitational contraction results in the conversion of potential energy (gravitational potential energy) into kinetic energy (the heat/motion) of particles in the star’s core. If there’s enough mass, the temperature can get high enough to ignite nuclear fusion in the innermost regions, as hydrogen nuclei undergo a chain reaction to convert into helium. In a low-mass star, only a tiny portion of the very center will hit that threshold of 4,000,000 K and undergo fusion, and that will be at a very slow rate. On the other hand, the largest stars can be hundreds of times as massive as the Sun, and achieve core temperatures of many tens of millions of degrees, fusing hydrogen into helium at rate that are millions of times as large as our Sun’s.

    8
    The (modern) Morgan–Keenan spectral classification system, with the temperature range of each star class shown above it, in kelvin. The overwhelming majority (75%) of stars today are M-class stars, with only 1-in-800 being massive enough for a supernova. Wikimedia Commons user LucasVB, additions by E. Siegel

    The smallest stars, in this sense, have the smallest outward fluxes and radiation pressures, while the most massive stars have the largest ones. This outward radiation and energy is what holds the star up against gravitational collapse, but it might surprise you to learn the range is relatively narrow. The lowest-mass red dwarf stars, like Proxima Centauri and VB 10 are only 10% the size of the Sun; a little larger than Jupiter.

    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

    On the other hand, the largest blue giant, R136a1, is over 250 times the Sun’s mass… but only about 30 times the Sun’s diameter. If you’re fusing hydrogen into helium, your star isn’t going to vary in size by all that much.

    9
    The cluster RMC 136 (R136) in the Tarantula Nebula in the Large Magellanic Cloud, is home to the most massive stars known. R136a1, the greatest of them all, is over 250 times the mass of the Sun. European Southern Observatory/P. Crowther/C.J. Evans

    But not every star is fusing hydrogen into helium! The smallest stars aren’t fusing anything at all, while the largest ones are onto a far more energetic phase of their lives. We can break down the types of stars we have by size range, and what we find are five generic classes:

    Neutron stars: these supernova remnants contain the mass of one-to-three suns, but are basically compressed into one giant atomic nucleus. They still emit radiation, but only in tiny amounts due to their minuscule size. A typical neutron star is around 20-100 km in size.

    White dwarf stars: formed when a sun-like star runs out of the last of its helium fuel in its core, and the outer layers get blown off while the inner layers contract down. Typically, a white dwarf star has between 0.5 and 1.4 times the mass of the Sun, but is only the physical volume of Earth: around 10,000 km across, and is made out of highly compressed atoms.

    Main sequence stars: these include the red dwarfs, the sun-like stars, and the blue behemoths we talked about earlier. Ranging from about 100,000 km to 30,000,000 km, they cover a fairly wide set of sizes, but even the largest one, if it replaced the Sun, wouldn’t engulf Mercury.

    Red giant stars: so what happens when you run out of hydrogen in your core? If you’re not a red dwarf (in which case, you’ll just turn into a white dwarf), gravitational contraction will heat your core up so much that you’ll begin fusing helium into carbon. Oh, and fusing helium into carbon releases way more energy than plain old hydrogen fusion, causing your star to expand tremendously. The simple physics is that the outward force (radiation) at the edge of the star has to balance the inward force (gravitation) in order to keep your star stable, and with a much greater outward force, your star simply has to be much larger. Red giants are typically around 100-150,000,000 km in diameter: large enough to engulf Mercury, Venus, and possibly Earth.

    Supergiant stars: the most massive stars will go beyond helium fusion and begin fusing even heavier elements in their cores, like carbon, oxygen, and even silicon and sulfur. These stars are destined for supernova and/or black hole fates, but before they get there, they swell to tremendous sizes that can extend for a billion (1,000,000,000) kilometers or more. These are the largest stars of all, like Betelgeuse, and would engulf all of the rocky planets, the asteroid belt, and the biggest ones would even swallow up Jupiter if they were to replace our Sun.

    10
    The Sun, today, is very small compared to giants, but will grow to the size of Arcturus in its red giant phase. A monstrous supergiant like Antares will be forever beyond our Sun’s reach. English Wikipedia author Sakurambo

    For the tiniest stars of all, the remnants like neutron stars and white dwarfs, it’s the fact that their trapped energy can only escape through a tiny surface area that keeps them so bright for so long. But for all other stars, their sizes are determined by that simple balance: the force from the outward radiation, at the surface, has to equal the inward pull of gravitation. Larger radiation forces means the star swells to larger sizes, with the largest stars of all swelling to billions of kilometers.

    11
    The Earth, if calculations are correct, should not be engulfed by the Sun when it swells into a red giant. It should, however, become very, very hot. Wikimedia Commons user Fsgregs

    In fact, as the Sun ages, its core heats up, and it both expands and grows hotter over time. In a billion or two years, it will be hot enough that it should boil Earth’s oceans, unless we do something to migrate our planet’s orbit outward to safety. Give it enough time, and we’ll swell to a red giant ourselves. For a few hundred million years, we’ll be larger and brighter than some of the most massive stars of all. As impressive as that may be, don’t be fooled: size matters in astronomy, but it isn’t the only thing. Both the smallest neutron stars and the largest supergiants, as well as many white dwarfs and main sequence stars, will still be more massive that we will as a red giant!

    See the full article here .

    Please help promote STEM in your local schools.

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    “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

     
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