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  • richardmitnick 11:42 am on January 5, 2019 Permalink | Reply
    Tags: Ask Ethan: How Close Could Two Alien Civilizations Get To One Another?, , , , , Ethan Siegel, There are lots of steps that have to happen to make life but the ingredients for it are literally everywhere.   

    From Ethan Siegel: “Ask Ethan: How Close Could Two Alien Civilizations Get To One Another?” 

    From Ethan Siegel
    May 12, 2018

    9
    Here on Earth, the closest world to us is our barren, uninhabited moon. But in many imaginable cases, there could be another inhabited world close by our own, maybe even within our Solar System. How close could one be? (flickr user Kevin Gill)

    Here on Earth, all the right conditions occurred for intelligent life to come about, but the nearest aliens, if they’re on another world, are light years away. But it doesn’t have to be that way at all!

    Here on planet Earth, in orbit around the Sun, we’re the only intelligent-life game in town. There might be possibilities for either past life or microbial life elsewhere in the Solar System, but as far as intelligent, complex, differentiated and multicellular life goes, what’s on our world is far more advanced than anything else we could hope to find. Intelligent aliens, if they’re out there inhabiting another world, are at least four light years away. But must that be the case for aliens anywhere in the galaxy? That’s what our Patreon supporter Jason McCampbell wants to know:

    What’s [the] closest two, independent intelligent civilizations could be, ignoring interstellar travel and assuming they develop in different star systems and follow roughly what we know as ‘life’? Globular clusters can have a high density of stars, but does too high a density rule out habitability? An astrophysicist in a dense cluster would have a much different view of the universe and the search for exoplanets.

    There are lots of steps that have to happen to make life, but the ingredients for it are literally everywhere. Even if you’re restricting yourself to looking for life that looks (chemically) like us, the Universe is full of possibilities.

    1
    Atoms can link up to form molecules, including organic molecules and biological processes, in interstellar space as well as on planets. Is it possible that life began not only prior to Earth, but not on a planet at all? (Jenny Mottar)

    You need to form enough heavy elements so that you can have rocky planets, organic molecules, and the building blocks of life. The Universe isn’t born with these! In the aftermath of the Big Bang, the Universe is 99.999999% hydrogen and helium, with no carbon, no oxygen, no nitrogen, phosphorous, calcium, iron, or any of the other complex elements necessary for life. In order to get there, we have to have multiple generations of stars live, burn through their fuel, die in a supernova explosion, and recycle those newly-created heavy elements into the next generation of stars. We need neutron star-neutron star mergers to build up the heaviest elements, many of which are necessary for life processes here on Earth and in our bodies, in copious amounts. This requires a lot of astrophysics to make it so.

    2
    The Omega nebula, known also as Messier 17, is an intense and active region of star formation, viewed edge-on, which explains its dusty and beam-like appearance. Stars that form at different times in the Universe’s history have different abundances of heavy elements. (ESO / VST survey)

    ESO VST interior


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

    Even though Earth formed over 9 billion years after the Big Bang, the Universe didn’t have to wait so long. We classify stars into three populations:

    Population I: stars like the Sun, with 1–2% of the elements making them up being heavier than hydrogen and helium. This material is very processed and leads to solar systems with a mix of gas giants and rocky planets capable of housing life.
    Population II: these are mostly older, more pristine stars. They may only have 0.001–0.1% of the heavy elements the Sun has, and most of their worlds are diffuse, gassy worlds. These may be too primitive and too low in heavy elements for life.
    Population III: the first stars in the Universe, that must be entirely unpolluted by heavy elements. These haven’t yet been discovered, but are theoretically the first stars of all.

    When we look at the earliest galaxies, they’re full of pretty much all Population II stars. But nearby, we have a mix of young-and-old, metal-rich and metal-poor stars.

    3
    The distances between the Sun and many of the nearest stars shown here are accurate, but each star — even the largest ones here — would be less than one-one millionth of a pixel in diameter if this were to scale. Image credit: Andrew Z. Colvin, under a c.c.a.-s.a.-3.0.(Andrew Z. Colvin / Wikimedia Commons)

    One of the most important lessons came from the Kepler mission, and specifically the system Kepler-444. This is a Population I star (with planets around it), but it’s much, much older than Earth. While our world is about 4.5 billion years old, Kepler-444 is 11.2 billion years old, meaning that the Universe could’ve formed a world like Earth very early on, at least ~7 billion years earlier than Earth formed. Given that possibility, and the fact that areas like the center of our galaxy got even more metal-rich than our region did very, very quickly, it’s possible that there are locations in the Universe (and perhaps even in the Milky Way) that are even more conducive to bringing about intelligent life than the Sun-Earth system is.

    4
    Sugar molecules in the gas surrounding a young, Sun-like star. The raw ingredients for life may exist everywhere, but not every planet that contains them will develop life. (ALMA (ESO/NAOJ/NRAO)/L. Calçada (ESO) & NASA/JPL-Caltech/WISE Team)

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

    NASA Wise Telescope

    So given all that we know about where the stars that are good candidates for life can be, what’s the closest two alien civilizations could be to one another? Where would be the places to look? And what would the answers be under different circumstances? Let’s look at five major possibilities.

    5
    This artist’s impression displays TRAPPIST-1 and its planets reflected in a surface. The potential for water on each of the worlds is also represented by the frost, water pools, and steam surrounding the scene. However, it is unknown whether any of these worlds actually still possess atmospheres, or if they’ve been blown away by their parent star. One thing is certain, however: the potentially habitable worlds are close to each other: separated by only ~1 million km each. (NASA/R. Hurt/T. Pyle)

    1.) The same solar system. This is the real dream. In the early days of our Solar System, it’s plausible that Venus, Earth, and Mars (and potentially even Theia, the hypothetical planet that collided with Earth to create the Moon) all had the same life-friendly conditions. They likely had a crust and atmosphere full of the ingredients for life, along with a past history of liquid water on their surface. Venus and Mars each, at closest approach to Earth, come within a few tens of millions of kilometers: 38 million for Venus and 54 million for Mars. But around an M-class (red dwarf) star, planetary separation distances are much smaller: separation distances are approximately only 1 million km between potentially habitable worlds in the TRAPPIST-1 system. Twin moons around a giant world, or a binary planet, could be even closer. If life succeeds once given certain conditions, why not twice in almost exactly the same place?

    6
    The globular cluster Terzan 5 as seen by the ESO’s Very Large Telescope, with other data as well. The densities in the center of a globular cluster are higher, while still being stable, than anyplace else. (ESO-VLT, F.R. Ferraro et al., HST-NICMOS, ESA/Hubble & NASA)

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo

    NASA/ESA Hubble Telescope

    2.) Within a globular cluster. Globular clusters are massive collections of somewhere around hundreds of thousands of star contained within a sphere of perhaps a few dozen light years in radius. In the outer regions, stars are typically separated by a light year, but in the innermost regions of the densest clusters, star separations may be as small as the distance from the Sun to the Kuiper belt. The orbits of planets within those star systems should be stable even in these dense environments, and given that we know of globular clusters far younger than the 11.2 billion years that Kepler-444 is, there should be good candidates for life and habitability among them. A few hundred astronomical units, although this distance will change over time as stars move, could be a fascinatingly close encounter between two civilizations.

    6
    High resolution near-infrared imaging has led to the discovery of three stellar superclusters at the Galactic Center. Since near-infrared wavelengths cut through the dense dust between Earth and the Galactic Center, we are able to see these superclusters. They include the Central Parsec, Quintuplet, and Arches clusters. But all the stars found there, and in the galactic center in general, are quite young. (Gemini Observatory)

    3.) Near the galactic center. The closer you get to the center of the galaxy, the denser the stars get. Within the central few light years, we have extremely high densities of stars, rivaling what we see in the cores of globular clusters. In some ways, the galactic center is an even denser environment, with large black holes, extremely massive stars, and new star-forming clusters, all things that globular clusters don’t have. But the problem with the stars that we see in the Milky Way’s core is that they’re all relatively young. Perhaps due to the volatility of the environment there, stars rarely make it to even a billion years of age. Despite the increased density, these stars are unlikely to have advanced civilizations. They just don’t live long enough.

    7
    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)

    4.) In a dense star cluster or spiral arm. Okay, so what about the star clusters that form in the galactic plane? Spiral arms are denser than typical regions of a galaxy, and that’s where new stars are likely to form. The star clusters that remain from those epochs often contain thousands of stars located in a region just a few light years wide. But again, stars don’t remain in these environments for very long. The typical open star cluster dissociates after a few hundred million years, with only a small fraction lasting billions of years. Stars move in-and-out of spiral arms all the time, including the Sun. Overall, even though stars inside may have typical distances between them of between 0.1 and 1 light year, they’re unlikely to be good candidates for life.

    8
    A logarithmic chart of distances, showing the Voyager spacecraft, our Solar System and our nearest star, for comparison. (NASA / JPL-Caltech)

    5.) Distributed throughout interstellar space. Otherwise, we come back to what we see in our own neighborhood: distances that are typically a few light years. As you get closer to the center of a galaxy, you can decrease that to the same distance you see in an open cluster: between 0.1–1 light years. But if you try to get closer than that, you run into the problem we’ve seen too close to the galactic center: mergers, interactions, and other catastrophes are likely to ruin your stable environment. You can get closer, but typical interstellar space isn’t the way to go. If you insist on it, your best bet is to wait for another star to pass close by, something that happens about once every million years for a typical star.

    9
    A plot of how frequently stars within the Milky Way is likely to pass within a certain distance of our Sun. This is a log-log plot, with distance on the y-axis and how long you typically need to wait for such an event to happen on the x-axis. (E. Siegel)

    While we don’t expect intelligent alien life to be ubiquitous and plentiful throughout the Universe in the same way that planets and stars are, every such world that meets the right conditions is a chance. And every time you get a chance, that’s an opportunity, with finite odds, for success. Each one of these possibilities could be real! They may not be likely, but until we go out and find what is (and isn’t) out there, it’s vital to keep an open mind about what the Universe could bring to us as far as alien intelligence is concerned. The truth is no doubt out there, but it’s important to recognize that if we had gotten a lot luckier, it could be closer than we dare to imagine today.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

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  • richardmitnick 10:59 am on December 26, 2018 Permalink | Reply
    Tags: Aliens? Or Alien Impostors? Finding Oxygen Might Not Mean Life After All, , , , , , Ethan Siegel, ,   

    From Ethan Siegel: “Aliens? Or Alien Impostors? Finding Oxygen Might Not Mean Life, After All” 

    From Ethan Siegel
    Dec 25, 2018

    1
    Both reflected sunlight on a planet and absorbed sunlight filtered through an atmosphere are two techniques humanity is presently developing to measure the atmospheric content and surface properties of distant worlds. In the future, this could include the search for organic signatures as well. (MELMAK / PIXABAY)

    The most surefire, easily-seen signature of life on Earth might be a cosmic red herring around other worlds.

    In our quest for life beyond the Solar System, it makes sense to look for a world like our own. We’ve long hoped to find an Earth-sized world around a Sun-like star at the right distance for liquid water as our first step, and with thousands of planets in our coffers already, we’re extremely close. But not every world with the right physical properties is going to have life; we need additional information to know whether a potentially habitable world is actually inhabited.

    The follow-up would be to analyze the planet’s atmosphere for Earth-like signatures: potential signs of life. Earth’s combination of atmospheric gases — nitrogen, oxygen, water vapor, carbon dioxide and more — has been assumed to be a dead giveaway for a planet with life on it. But a new study by planetary scientist Dr. Sarah Hörst’s team throws that into doubt [see paper below]. Even worlds rich in oxygen might not harbor aliens, but an impostor process that could fool us all.

    2
    Most of the planets we know of that are comparable to Earth in size have been found around cooler, smaller stars than the Sun. This makes sense with the limits of our instruments; these systems have larger planet-to-star size ratios than our Earth does with respect to the Sun. (NASA / AMES / JPL-CALTECH)

    The scientific story of how to even reach that point is fascinating, and closer to becoming a reality than ever before. We can understand how this happens by imagining we were aliens, looking at our Sun from a large distance away, trying to determine if it possessed an inhabited world.

    By measuring the slight variations in the frequency of the Sun’s light over long periods of time, we’d be able to deduce the gravitational influence of the planets on them. This detection method is known either the radial velocity or the stellar wobble method, and can tell us information about a planet’s mass and orbital period. Most of the early (pre-Kepler) exoplanets were discovered with this technique, and it’s still the best method we have for both determining planetary masses and confirming the existence of candidate exoplanets.

    Radial Velocity Method-Las Cumbres Observatory


    Radial velocity Image via SuperWasp http:// http://www.superwasp.org/exoplanets.htm

    Veloce Rosso, Australia’s next premier astronomical instrument. On the the Anglo-Australian Telescope (AAT). a precision radial velocity spectrograph, capable of detecting Earth-like planets


    AAO Anglo Australian Telescope near Siding Spring, New South Wales, Australia, Altitude 1,100 m (3,600 ft)

    4
    Today, we know of over 3,500 confirmed exoplanets, with more than 2,500 of those found in the Kepler data. These planets range in size from larger than Jupiter to smaller than Earth. Yet because of the limitations on the size of Kepler and the duration of the mission, there have been zero Earth-sized planets found around Sun-like stars that fall into Earth-like orbits. (NASA/AMES RESEARCH CENTER/JESSIE DOTSON AND WENDY STENZEL; MISSING EARTH-LIKE WORLDS BY E. SIEGEL)

    We also need to know the size of the planet. With the stellar wobble alone, we’ll only know what the mass of the world is relative to the angle-of-inclination of its orbit. A world that’s the mass of Earth could be well-suited to life if it’s got an Earth-like atmosphere, but it could be disastrous for life if it’s an iron-like world with no atmosphere at all, or a low-density, puffy world with a large gaseous envelope.

    The transit method, where a planet passes in front of its parent star, is our most prolific method for measuring a planet’s radius.

    Planet transit. NASA/Ames

    By calculating how much of the parent star’s light it blocks when it crosses our line-of-sight, we can determine its size. For an alien civilization whose line-of-sight was properly aligned with Earth orbiting the Sun, we’d be able to detect it with technology only about 20% more sensitive than Kepler was.

    5
    Kepler was designed to look for planetary transits, where a large planet orbiting a star could block a tiny fraction of its light, reducing its brightness by ‘up to’ 1%. The smaller a world is relative to its parent star, the more transits you need to build up a robust signal, and the longer its orbital period, the longer you need to observe to get a detection signal that rises above the noise. (MATT OF THE ZOONIVERSE/PLANET HUNTERS TEAM)

    This is roughly where we are today. We’ve found hundreds of worlds that we suspect are rocky orbiting their stars, many of them right around Earth-sized. For a large fraction of them, we’ve measured their mass, radius, and orbital period, with a small percentage being at the right orbital distance to have Earth-like temperatures.

    Most of them orbit red dwarf stars — the most common class of star in the Universe — which means the forces should tidally lock them: the same side should always face the star. These stars flare often, posing a danger to any potential atmospheres on these worlds.

    But a significant fraction will orbit K, G, or F-class stars, where they can rotate on their axes, maintain an atmosphere, and have the potential for Earth-like life. That’s where we want to look.

    6
    When a planet transits in front of its parent star, some of the light is not only blocked, but if an atmosphere is present, filters through it, creating absorption or emission lines that a sophisticated-enough observatory could detect. If there are organic molecules or large amounts of molecular oxygen, we might be able to find that, too. (ESA / DAVID SING)

    And that’s where future technology is hoping to take us. If a larger Kepler-like telescope were equipped with the right instruments, we could break up the light passing through an exoplanet’s atmosphere during a transit, and determine its atomic and molecular contents. If we were looking at Earth, we could determine that it was composed of nitrogen, oxygen, argon, water vapor, and carbon dioxide, along with other trace signatures.

    Even without an ideal alignment, direct imaging will still be possible.

    Direct imaging-This false-color composite image traces the motion of the planet Fomalhaut b, a world captured by direct imaging. Credit: NASA, ESA, and P. Kalas (University of California, Berkeley and SETI Institute

    Potential NASA flagship missions, such as HabEx or LUVOIR (with either a starshade or a coronagraph), could block the light of the parent star and detect the light from an orbiting planet directly. This light could again be broken up into its individual wavelengths, determining its molecular content.

    NASA Habitable Exoplanet Imaging Mission (HabEx) The Planet Hunter

    NASA Large UV Optical Infrared Surveyor (LUVOIR)

    Whether from absorption (transit) or emission (direct imaging), we could learn what a potential Earth-twin’s atmosphere is composed of.

    7
    The Starshade concept could enable direct exoplanet imaging as early as the 2020s. This concept drawing illustrates a telescope using a star shade, enabling us to image the planets that orbit a star while blocking the star’s light to better than one part in 10 billion. (NASA AND NORTHROP GRUMMAN)

    So what if we find an oxygen-rich world? No other planets, dwarf planets, moons, or other objects contain even 1% oxygen that we know of. Earth’s atmosphere transformed over nearly 2 billion years before it had an oxygen content comparable to what it does today, and it was anaerobic life processes that created our modern atmosphere that’s rich in molecular oxygen. Because of how easily oxygen is destroyed by ultraviolet light and how difficult it is to produce in large quantities via inorganic, chemical processes, oxygen has long been taken as the one biosignature we could rely on to indicate a living world.

    If organic molecules were found there as well, it would seem like a surefire indicator that life, indeed, must have taken hold on such a planet.

    And that’s where the Hörst lab’s new findings come into play. In a paper just published in ACS Earth and Space Chemistry, a specially-designed chamber to mimic the environment of a hazy exoplanet atmosphere showed that molecular oxygen (O2) could be created in a number of environmental conditions likely to occur naturally, with no life necessary to create it.

    The ingenious method was to create a gas mixture that would be consistent with what we expect an Earth-like or super-Earth-like environment might hold. That mixture was then inserted into a specially-designed chamber and subjected to a variety of temperature, pressure, and energy-injection conditions that would likely mimic the activity that could occur on actual exoplanets.

    7
    Chao He explaining how the study’s PHAZER setup works, where PHAZER is the specially-designed Planetary HAZE chamber found in the Hörst lab at Johns Hopkins University. (CHANAPA TANTIBANCHACHAI / JOHNS HOPKINS UNIVERSITY)

    A total of nine different gas mixtures were used at temperatures ranging from 27 °C (80 °F) up to approximately 370 °C (700 °F), representing the temperature range expected to naturally occur. The energy injection came in two different forms: from ultraviolet light and from plasma discharges, which represent natural conditions likely to be caused by sunlight or lightning-like activity.

    The results? There were multiple scenarios that resulted in the production of both organic molecules (like sugar and amino acid precursors) and oxygen, yet didn’t require any life at all to get them. According to first author Chao He,

    People used to suggest that oxygen and organics being present together indicates life, but we produced them abiotically in multiple simulations. This suggests that even the co-presence of commonly accepted biosignatures could be a false positive for life.

    8
    By heating atmospheric gases thought to mimic exoplanet atmospheres to various temperatures and subjecting them to ultraviolet and plasma-based energy injections, organic molecules and oxygen can be produced. We must be careful that we don’t mistake an abiotic signature of coincidence oxygen and organics for life. (C. HE ET AL., ‘GAS PHASE CHEMISTRY OF COOL EXOPLANET ATMOSPHERES: INSIGHT FROM LABORATORY SIMULATIONS,’ ACS EARTH SPACE CHEM. (2018))

    The experiment wasn’t some cherry-picked design to attempt to produce this false-positive result, either. The gases inside the chamber were designed to mimic the contents of known exoplanetary atmospheres, with the ultraviolet energy injection designed to simulate sunlight. The experiments simulated a variety of atmospheric (hydrogen-rich, water-rich, and carbon dioxide-rich) environments, and all of them created haze particles and yielded organic molecules such as hydrogen cyanide, acetylene, and methanimine.

    Multiple environments generated organic molecules, prebiotic precursor molecules, and oxygen all at once, at Earth-like temperatures and much hotter temperatures as well. The paper itself states the main conclusion very succinctly:

    Our laboratory results indicate that complex atmospheric photochemistry can happen in diverse exoplanet atmospheres and lead to the formation of new gas products and haze particles, including compounds (O2 and organics) that could be falsely identified as biosignatures.

    The amount of molecular oxygen produced in these experiments was relatively small by some metrics; Hörst herself wouldn’t call the atmospheres created in the lab “oxygen-rich.” But it’s nevertheless possible that these processes would translate into an oxygen-rich atmosphere on an exoplanet, given the right conditions and enough time. At this point, it appears possible that finding the presence of both organics and molecular oxygen could be due to abiotic, non-life processes exclusively.

    9
    Signatures of organic, life-giving molecules are found all over the cosmos, including in the largest, nearby star-forming region: the Orion Nebula. Someday soon, we may be able to look for biosignatures in the atmospheres of Earth-sized worlds around other stars, or we may detect simple life directly on another world in our Solar System. (ESA, HEXOS AND THE HIFI CONSORTIUM; E. BERGIN)

    This doesn’t mean that finding an Earth-like world with an oxygen-rich atmosphere won’t be incredibly interesting; it absolutely will be. It doesn’t mean that finding organic molecules coincident with the oxygen won’t be compelling; it will be a finding worth getting excited over. It doesn’t even mean that it won’t be indicative of life; a world with oxygen and organic molecules may well be overflowing with living organisms. But it does mean that we have to be careful.

    Historically, when we’ve looked to the skies for evidence of life beyond Earth, we’ve been biased by hope and what we know on Earth. Theories of dinosaurs on Venus or canals on Mars still linger in our memories, and we must be careful that extraterrestial oxygen signatures don’t lead us to falsely optimistic conclusions. We now know that both abiotic processes and life-dependent ones can create an oxygen-rich atmosphere.

    The hard problem, then, will be disentangling the potential causes when we actually find our first oxygen-rich, Earth-like exoplanet. Our reward, if we’re successful, will be the knowledge of whether or not we’ve actually found life around another star.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

     
  • richardmitnick 12:27 pm on December 24, 2018 Permalink | Reply
    Tags: 20 Incredible New Images Show How Planets First Form Around Stars, , , , , Ethan Siegel   

    From Ethan Siegel: “20 Incredible New Images Show How Planets First Form Around Stars” 

    From Ethan Siegel
    Dec 24, 2018

    1
    20 new protoplanetary disks, as imaged by the Disk Substructures at High Angular Resolution Project (DSHARP) collaboration, showcasing what newly-forming planetary systems look like. (S. M. ANDREWS ET AL. AND THE DSHARP COLLABORATION, ARXIV:1812.04040)

    For generations, planet formation was only a theory. As 2018 comes to an end, here’s the evidence of what’s going on.

    The theory of planet formation has been around for a long time, but lacked validation.

    2
    Artist’s impression of a young star surrounded by a protoplanetary disk. There are many unknown properties about protoplanetary disks around Sun-like stars, but they all exhibit infrared radiation. Tabby’s star has none. (ESO/L. CALÇADA)

    3
    The very young protostar M17-SO1, as imaged way back in 2005 with the ground-based Subaru telescope, shows features of a protoplanetary disk around a newly-forming star, but internal features were unable to be resolved with instrumentation of that time. (SUBARU / NAOJ)


    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level

    As protostars grow, they heat up, while their disks race to form planets before the volatile material evaporates.

    4
    30 protoplanetary disks, or proplyds, as imaged by Hubble in the Orion Nebula. Hubble is a brilliant resource for identifying these disk signatures in the optical, but has little power to probe the internal features of these disks, even from its location in space. (NASA/ESA AND L. RICCI (ESO))

    With observatories like Hubble, we’ve found and identified many disks, but couldn’t measure their internal properties.

    In theory, those disks ought to display gaps where massive, early planets have begun their formation.

    At the Very Large Telescope, the SPHERE instrument successfully imaged a number of protoplanetary disks directly.

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo

    ESO SPHERE extreme adaptive optics system and coronagraphic facility on the extreme adaptive optics system and coronagraphic facility on the VLT MELIPAL UT3, Cerro Paranal, Chile, with an elevation of 2,635 metres (8,645 ft) above sea level

    5
    The observational structure of the young star MWC 758, at right, compared with a simulation involving a large outer planet, at left. This Herbig star is much more massive than our Sun ever was, but also is not a true star. (NASA, ESA, ESO, M. BENISTY ET AL. (UNIVERSITY OF GRENOBLE), R. DONG (LAWRENCE BERKELEY NATIONAL LABORATORY), AND Z. ZHU (PRINCETON UNIVERSITY))

    Some displayed spirals due to massive outer planets, while others possessed symmetric rings caused by lower-mass worlds.

    6
    Eight young T Tauri stars, as imaged by SPHERE, show disks, rings, and symmetric, unperturbed structures. These 8 disks range in age from 1 to 15 million years, and are all around stars of 2 solar masses or less. (H. AVENHAUS ET AL. (2018), ARXIV.ORG/ABS/1803.10882)

    The best portraits of protoplanetary disks, however, arise from ALMA.

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

    ALMA’s crisp images are striking.

    7
    The distance from the young, central star determines the type of material that’s present. Heat and energy flux changes everything in these systems. The gaps in the rings and disk indicate the likely presence of planets, which are details that ALMA can reveal. (K. ZHANG IN G. A. BLAKE’S RESEARCH GROUP, FROM GEOFFREY A. BLAKE & EDWIN A. BERGIN, NATURE 520, 161–162 (09 APRIL 2015))

    Its Disk Substructures at High Angular Resolution Project (DSHARP) has just released their first results, revealing 20 nearby protoplanetary disks.

    8
    These 20 protoplanetary disks, as they appear in the most recent ApJ letters paper (in press), showcase the diversity and intricate details found in both face-on and tilted protoplanetary disks imaged by the DSHARP team. (S. M. ANDREWS ET AL. AND THE DSHARP COLLABORATION, ARXIV:1812.04040)

    Most have gaps, rings, and easily-identifiable locations where candidate planets may lie.

    9
    HD 163296 is representative of a typical protoplanetary disk viewed by the DSHARP collaboration. It has a central protoplanetary disk, outer emission rings, and gaps between them. There ought to be multiple planets in this system, and one can identify an odd artifact interior to the 2nd-from-the-outermost ring that may be a telltale sign of a perturbing planet. The scale bar at lower right is 10 AU, and appears in all DSHARP images shown here. (S. M. ANDREWS ET AL. AND THE DSHARP COLLABORATION, ARXIV:1812.04040)

    The most common features are the concentric emission rings and dust-depleted gaps.

    Understanding planetary evolution, from nebulae to protoplanets to full-blown solar systems, is finally within reach.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

     
  • richardmitnick 3:34 pm on December 11, 2018 Permalink | Reply
    Tags: , , , , Ethan Siegel, Five Surprising Truths About Black Holes From LIGO, ,   

    From Ethan Siegel: “Five Surprising Truths About Black Holes From LIGO” 

    From Ethan Siegel
    Dec 11, 2018

    1
    A still image of a visualization of the merging black holes that LIGO and Virgo have observed so far. As the horizons of the black holes spiral together and merge, the emitted gravitational waves become louder (larger amplitude) and higher pitched (higher in frequency). The black holes that merge range from 7.6 solar masses up to 50.6 solar masses, with about 5% of the total mass lost during each merger. (TERESITA RAMIREZ/GEOFFREY LOVELACE/SXS COLLABORATION/LIGO-VIRGO COLLABORATION)

    With a total of 10 black holes detected, what we’ve learned about the Universe is truly amazing.

    On September 14th, 2015, just days after LIGO first turned on at its new-and-improved sensitivity, a gravitational wave passed through Earth. Like the billions of similar waves that had passed through Earth over the course of its history, this one was generated by an inspiral, merger, and collision of two massive, ultra-distant objects from far beyond our own galaxy. From over a billion light years away, two massive black holes had coalesced, and the signal — moving at the speed of light — finally reached Earth.

    But this time, we were ready. The twin LIGO detectors saw their arms expand-and-contract by a subatomic amount, but that was enough for the laser light to shift and produce a telltale change in an interference pattern. For the first time, we had detected a gravitational wave. Three years later, we’ve detected 11 of them, with 10 coming from black holes. Here’s what we’ve learned.

    2
    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 whether black hole mergers emit electromagnetic emission is not yet settled. (LIGO, NSF, A. SIMONNET (SSU))

    There have been two “runs” of LIGO data: a first one from September 12, 2015 to January 19, 2016 and then a second one, at somewhat improved sensitivity, from November 30, 2016 to August 25, 2017. That latter run was, partway through, joined by the VIRGO detector in Italy, which added not only a third detector, but significantly improved our ability to pinpoint the location of where these gravitational waves occurred. LIGO is currently shut down right now, as it’s undergoing upgrades that will make it even more sensitive, as it prepares to begin a new data-taking observing run in the spring of 2019.

    On November 30th, the LIGO scientific collaboration released the results of their improved analysis, which is sensitive to the final stages of mergers between objects between about 1 and 100 solar masses.

    3
    The 11 gravitational wave events detected by LIGO and Virgo, with their names, mass parameters, and other essential information encoded in Table form. Note how many events came in the last month of the second run: when LIGO and Virgo were operating simultaneously. (THE LIGO SCIENTIFIC COLLABORATION, THE VIRGO COLLABORATION; ARXIV:1811.12907)

    The 11 detections that have been made so far are shown above, with 10 of them representing black hole-black hole mergers, and only GW170817 representing a neutron star-neutron star merger. Those merging neutron stars was the closest event at a mere 130–140 million light years away. The most massive merger seen — GW170729 — comes to us from a location that, with the expansion of the Universe, is now 9 billion light years away.

    These two detections are also the lightest and heaviest gravitational wave mergers ever detected, with GW170817 colliding a 1.46 and a 1.27 solar mass neutron star, and GW170729 colliding a 50.6 and a 34.3 solar mass black hole together.

    Here are the five surprising truths that we’ve learned from all of these detections combined.

    4
    LIGO, as designed, should be sensitive to black holes of a particular mass range that inspiral and merge: from 1 up to a few hundred solar masses. The fact that what we observe appears to be capped at 50 solar masses places severe constraints on black hole merger rates above that figure. (NASA / DANA BERRY (SKYWORKS DIGITAL))

    1.) The largest merging black holes are the easiest to see, and they don’t appear to get larger than about 50 solar masses. One of the best things about looking for gravitational waves is that it’s easier to see them from farther away than it is for a light source. Stars appear dimmer in proportion to their distance squared: a star 10 times the distance is just one-hundredth as bright. But gravitational waves are dimmer in direct proportion to distance: merging black holes 10 times as far away produce 10% the signal.

    As a result, we can see very massive objects to very great distances, and yet we don’t see black holes merging with 75, 100, 150, or 200+ solar masses. 20-to-50 solar masses are common, but we haven’t seen anything above that yet. Perhaps the black holes arising from ultra-massive stars truly are rare.

    6
    Aerial view of the Virgo gravitational-wave detector, situated at Cascina, near Pisa (Italy). Virgo is a giant Michelson laser interferometer with arms that are 3 km long, and complements the twin 4 km LIGO detectors. (NICOLA BALDOCCHI / VIRGO COLLABORATION)

    2.) Adding in a third detector both improves our ability to pinpoint their positions and increases the detection rate significantly. LIGO ran for about 4 months during its first run and 9 months during its second. Yet, fully half of their detections came in the final month: when VIRGO was running alongside it, too. In 2017, gravitational wave events were detected on:

    July 29th (50.6 and 34.3 solar mass black holes),
    August 9th (35.2 and 23.8 solar mass black holes),
    August 14th (30.7 and 25.3 solar mass black holes),
    August 17th (1.46 and 1.27 solar mass neutron stars),
    August 18th (35.5 and 26.8 solar mass black holes), and
    August 23rd (39.6 and 29.4 solar mass black holes).

    During this final month of observing, we were detecting more than one event per week. It’s possible that, as we becomes sensitive to greater distances and smaller-amplitude, lower-mass signals, we may begin seeing as many as one event per day in 2019.

    4
    Cataclysmic events occur throughout the galaxy and across the Universe, from supernovae to active black holes to merging neutron stars and more. When two black holes merge, their peak brightness is enough, for a few short milliseconds, to outshine all the stars in the observable Universe combined. (J. WISE/GEORGIA INSTITUTE OF TECHNOLOGY AND J. REGAN/DUBLIN CITY UNIVERSITY)

    3.) When the black holes we’ve detected collide, they release more energy at their peak than all the stars in the Universe combined. Our Sun is the standard by which we came to understand all other stars. It shines so brightly that its total energy energy output — 4 × 10²⁶ W — is equivalent to converting four million tons of matter into pure energy with every second that goes by.

    With an estimated ~10²³ stars in the observable Universe, the total power output of all the stars shining throughout the sky is greater than 10⁴⁹ W at any given time: a tremendous amount of energy spread out over all of space. But for a brief few milliseconds during the peak of a binary black hole merger, every one of the observed 10 events outshone, in terms of energy, all the stars in the Universe combined. (Although it’s by a relatively small amount.) Unsurprisingly, the most massive merger tops the charts.

    5
    Even though black holes should have accretion disks, there aren’t any significant electromagnetic signals expected to be generated by a black hole-black hole merger. Their energy instead gets converted into gravitational radiation: ripples in the fabric of space itself. We see this radiation, and it’s the most energetic event to occur in the Universe when it happens. (AEI POTSDAM-GOLM)

    4.) About 5% of the total mass of both black holes gets converted into pure energy, via Einstein’s E = mc², during these mergers. The ripples in space that these black hole mergers produce need to get their energy from somewhere, and realistically, that has to come out of the mass of the merging black holes themselves. On average, based on the magnitude of the gravitational wave signals we’ve seen and the reconstructed distances to them, black holes lose about 5% of their total mass — having it converted into gravitational wave energy — when they merge.

    GW170608, the lowest mass black hole merger (of 10.9 and 7.6 solar masses), converted 0.9 solar masses into energy.
    GW150914, the first black hole merger (of 35.6 and 30.6 solar masses), converted 3.1 solar masses into energy.
    And GW170729, the most massive black hole merger (at 50.6 and 34.3 solar masses), converted 4.8 solar masses into energy.

    These events, creating ripples in spacetime, are the most energetic events we know of since the Big Bang. They produce more energy than any neutron star merger, gamma-ray burst, or supernova ever created.

    6
    Illustrated here is the range of Advanced LIGO and its capability of detecting merging black holes. Merging neutron stars may have only one-tenth the range and 0.1% the volume, but we caught one, last year, just 130 million light years away. Additional black holes are likely present and merging, and perhaps run III of LIGO will find them.(LIGO COLLABORATION / AMBER STUVER / RICHARD POWELL / ATLAS OF THE UNIVERSE)

    5.) With everything we’ve seen so far, we fully expect there are lower-mass, more frequent black hole mergers just waiting to be seen. The most massive black hole mergers produce the largest-amplitude signals, and so are the easiest to spot. But with the way volume and distance are related, going twice as distant means encompassing eight times the volume. As LIGO gets more sensitive, it’s easier to spot massive objects at greater distances than low-mass objects that are close by.

    We know there are black holes of 7, 10, 15, and 20 solar masses out there, but it’s easier for LIGO to spot a more massive one farther away. We expect there are black hole binaries with mismatched masses: where one is much more massive than the other. As our sensitivities improve, we expect there are more of these out there to find, but the most massive ones are easier to find. We expect the most massive ones to dominate the early searches, just as “hot Jupiters” dominated early exoplanet searches. As we get better at finding them, expect there to be greater numbers of lower-mass black holes out there.

    7
    LIGO and Virgo have discovered a new population of black holes with masses that are larger than what had been seen before with X-ray studies alone (purple). This plot shows the masses of all ten confident binary black hole mergers detected by LIGO/Virgo (blue). Also shown are neutron stars with known masses (yellow), and the component masses of the binary neutron star merger GW170817 (orange).(LIGO/VIRGO/NORTHWESTERN UNIV./FRANK ELAVSKY)

    When the first gravitational wave detection was announced, it was heralded as the birth of gravitational wave astronomy. People likened it to when Galileo first pointed his telescope at the skies, but it was so much more than that. It was as though our view of the gravitational wave sky had always been shrouded in clouds, and for the first time, we had developed a device to see through them if we got a bright enough gravitational source: merging black holes or neutron stars. The future of gravitational wave astronomy promises to revolutionize our Universe by letting us see it in a whole new way. And that future has already arrived; we are seeing the first fruits of our labor.

    8
    This visualization shows the coalescence of two orbiting neutron stars. The right panel contains a visualization of the matter of the neutron stars. The left panel shows how space-time is distorted near the collisions. For black holes, there is no matter-generated signal expected, but thanks to LIGO and Virgo, we can still see the gravitational waves. (KARAN JANI/GEORGIA TECH)

    As our technology improves, we gain an ever-improved ability to see through those clouds: to see fainter, lower-mass, and more distant gravitational sources. When LIGO starts taking data again in 2019, we fully expect greater rates of ~30 solar mass black holes merging, but we hope to finally know what the lower-mass black holes are doing. We hope to see neutron star-black hole mergers. And we hope to go even farther out into the distant reaches of the Universe.

    Now that we’ve made it into the double digits for the number of detected events, it’s time to go even farther. With LIGO and VIRGO fully operational, and at better sensitivities than ever, we’re ready to go one step deeper in our exploration of the gravitational wave Universe. These merging, massive stellar remnants were just the start. It’s time to visit the stellar graveyard, and find out what the skeletons are truly like.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

     
  • richardmitnick 2:59 pm on December 1, 2018 Permalink | Reply
    Tags: Ask Ethan: Are The Smallest Particles Of All Truly Fundamental?, , , , , Ethan Siegel   

    From Ethan Siegel: “Ask Ethan: Are The Smallest Particles Of All Truly Fundamental?” 

    From Ethan Siegel
    Dec 1, 2018

    1
    Going to smaller and smaller distance scales reveals more fundamental views of nature, which means if we can understand and describe the smallest scales, we can build our way to an understanding of the largest ones. (PERIMETER INSTITUTE)

    We can go to deeper and deeper levels, finding more fundamental quantities as we do. But is there a truly fundamental quantity?

    What is the Universe, at a fundamental level, truly made out of? Is there a smallest possible building block, or set of building blocks, that we can both construct everything in our entire Universe out of and also that can never be divided into something smaller? It’s a question that science can say a lot about, but it doesn’t necessarily give us the final, ultimate answer. It’s also the question that Paul Riggs wants us to look at for this edition of Ask Ethan:

    Is there theoretical or experimental evidence which unambiguously establishes the existence of fundamental particles?

    There is always room for uncertainty in physics, especially when it comes to speculating what we’ll find in the future. But whether that ambiguity is reasonable or not is up for us to decide.

    If you wanted to know what the Universe was made of, how would you approach the problem? Thousands of years ago, imaginative ideation and the application of logic were the best tools we had. We knew about matter, but we had no way of knowing what composed it. It was hypothesized that there were a few fundamental ingredients that could be combined together — in various ways and under different conditions — to create everything that exists today.

    We could experimentally demonstrate that matter, whether solid, liquid, or gas, occupied space. We could show that it possessed mass. We could combine it into larger quantities or break it down into smaller ones. It’s only this last idea, however, of breaking the matter we can access down into smaller components, that lead to the idea of what “fundamental” truly might be.

    2
    From macroscopic scales down to subatomic ones, the sizes of the fundamental particles play only a small role in determining the sizes of composite structures. Whether the building blocks are truly fundamental and/or point-like particles is still not known.(MAGDALENA KOWALSKA / CERN / ISOLDE TEAM)

    Some thought matter might be made of different elements, such as fire, earth, air, and water. Others, such as the monists, thought that there was just one fundamental component of reality from which all others could be derived and assembled from. Still others, such as the Pythagoreans, opined that there must be a geometric mathematical structure that set out the rules for reality to obey, and the assembly of these structures led to the Universe we perceive today.

    3
    The five Platonic solids are the only five polygonal shapes in three dimensions that are made of regular, 2D polygons. Many early scientists equated these five solids to the five fundamental elements. It’s a nice idea, but doesn’t come close to the standards of modern science. (ENGLISH WIKIPEDIA PAGE FOR PLATONIC SOLIDS)

    The idea that there was a truly fundamental particle, though, goes back to Democritus of Abdera, some 2400 years ago. Although it was merely an idea, Democritus held that all of matter was made of indivisible particles that he referred to as atoms (ἄτομος), meaning “uncuttable,” that combined together amidst a backdrop of otherwise empty space. Although his ideas contained many other irrelevant and bizarre details, the notion of fundamental particles persisted.

    4
    Individual protons and neutrons may be colorless entities, but there is still a residual strong force between them. All the known matter in the Universe can be divided into atoms, which can be divided into nuclei and electrons, where nuclei can be divided even farther. We may not have even yet reached the limit of division, or the ability to cut a particle into multiple components. (WIKIMEDIA COMMONS USER MANISHEARTH)

    Take whatever piece of matter you want and try cutting it. Try breaking it up into a smaller and smaller component. Every time you succeed, try cutting it again, until you have to go beyond even the idea of cutting to arrive at the next layer. Macroscopic objects become microscopic ones; complex compounds become simple molecules; molecules become atoms; atoms become electrons and atomic nuclei; atomic nuclei become protons and neutrons, which themselves divide into quarks and gluons.

    At the smallest level imaginable, we can reduce everything we know of into fundamental, indivisible, particle-like entities: the quarks, leptons, and bosons of the Standard Model.

    5
    The particles and antiparticles of the Standard Model have now all been directly detected, with the last holdout, the Higgs Boson, falling at the LHC earlier this decade. All of these particles can be created at LHC energies, and the masses of the particles lead to fundamental constants that are absolutely necessary to describe them fully. These particles can be well-described by the physics of the quantum field theories underlying the Standard Model, but whether they are fundamental is not yet known. (E. SIEGEL / BEYOND THE GALAXY)

    As far as physical sizes go, we have the rules of quantum physics to guide us. Every quantum in the Universe — a structure with a non-zero energy to it — can be described as containing a certain amount of energy. Because everything that exists can be described as both particle-like and wave-like in nature, you can place limits and constraints on a physical size for any such quanta.

    While molecules might be good descriptors of reality at the nanometer-level (10^-9 meters) scale, and atoms are good at Angstrom (10^-10 meter) scales, atomic nuclei are even smaller, with individual protons and neutrons getting down to femtometer (10^-15 meter) scales. But for the Standard Model particles, they go even smaller. At the energies we’ve probed, we can safely say that all the known particles are point-like and structure-free down to 10^-19 meter scales.

    6
    A candidate Higgs event in the ATLAS detector. Note how even with the clear signatures and transverse tracks, there is a shower of other particles; this is due to the fact that protons are composite particles. This is only the case because the Higgs gives mass to the fundamental constituents that compose these particles. At high enough energies, the currently most-fundamental particles known may yet split apart themselves. (THE ATLAS COLLABORATION / CERN)

    To the best of our experimental knowledge, these are what we equate to being truly fundamental in nature. The particles and antiparticles and bosons of the Standard Model appear to be fundamental, from both an experimental and theoretical perspective. As we go to higher and higher particle energies, we can probe the structure of reality to even greater levels.

    The Large Hadron Collider offers the best constraints to date, but future colliders or extremely sensitive cosmic ray experiments could take us many orders of magnitude farther: to scales of 10^-21 meters for the most energetic terrestrial colliders and potentially all the way down to 10^-26 meters for the most extreme-energy cosmic rays.

    7
    The objects we’ve interacted with in the Universe range from very large, cosmic scales down to about 10^-19 meters, with the newest record set by the LHC. There’s a long, long way down (in size) and up (in energy) to the scales that the hot Big Bang achieves, which is only about a factor of ~1000 lower than the Planck energy. If the Standard Model particles are composite in nature, higher energy probes may reveal that. (UNIVERSITY OF NEW SOUTH WALES / SCHOOL OF PHYSICS)

    Even at that, though, these ideas only impose limits on what we know and can say. They tell us that if we collide a particle (or antiparticle, or photon) with a certain amount of energy to it with another particle at rest, the particle that gets struck will behave in a fundamentally point-like fashion to within the limits of our experiments, detectors, and attainable energies. These experiments set an empirical limit on how large a presently thought-to-be fundamental particle can be, and are collectively known as deep inelastic scattering experiments.

    8
    When you collide any two particles together, you probe the internal structure of the particles colliding. If one of them isn’t fundamental, but is rather a composite particle, these experiments can reveal its internal structure. Here, an experiment is designed to measure the dark matter/nucleon scattering signal. However, there are many mundane, background contributions that could give a similar result. This particular signal will show up in Germanium, liquid XENON and liquid ARGON detectors. (DARK MATTER OVERVIEW: COLLIDER, DIRECT AND INDIRECT DETECTION SEARCHES — QUEIROZ, FARINALDO S. ARXIV:1605.08788)

    But does this mean that these particles are truly fundamental? Not at all. They could be:

    further divisible, meaning that they could be broken up into smaller sub-components,
    or they could be resonances of one another, where the heavier “cousins” of the lightest particles are either excited states or composite versions of the lighter ones,
    or these particles could all be not “particles” at all, but rather apparent particles with a deeper, underlying structure.

    These ideas abound in scenarios like technicolor (which is constrained since the discovery of the Higgs boson, but not ruled out), but are most prominently represented by String Theory.

    9
    Feynman diagrams (top) are based off of point particles and their interactions. Converting them into their string theory analogues (bottom) gives rise to surfaces which can have non-trivial curvature. In string theory, all particles are simply different vibrating modes of an underlying, more fundamental structure: strings. (PHYS. TODAY 68, 11, 38 (2015))

    There is no immutable law requiring that everything be made out of particles at all. Particle-based reality is a theoretical idea that is supported by and is consistent with experiments, but our experiments are limited in energy and the kind of information they can tell us about fundamental reality. In a scenario like String Theory, everything that we call a “fundamental particle” today might be nothing more than a string, vibrating or rotating at a certain frequency, with either an open nature (where the two ends are unattached) or a closed nature (where the two ends are attached to one another). Strings can snap, creating two quanta where one existed previously, or combine, creating a single quantum from two pre-existing ones.

    At a fundamental level, there is no requirement that the components of our Universe be zero-dimensional, point-like particles.

    8
    Quantum gravity tries to combine Einstein’s general theory of relativity with quantum mechanics. Quantum corrections to classical gravity are visualized as loop diagrams, as the one shown here in white. Whether space (or time) itself is discrete or continuous is not yet decided, as is the question of whether gravity is quantized at all, or particles, as we know them today, are fundamental or not. (SLAC NATIONAL ACCELERATOR LAB)

    There are many scenarios where the undiscovered mysteries of our Universe, such as dark matter and dark energy, aren’t made of particles at all, but rather are either some type of fluid or property of space. The nature of space and time themselves is not yet known; they could be fundamentally quantum or non-quantum in nature; they could be discrete (capable of being broken-up into chunks) or continuous.

    The particles we know of today, that we assume are fundamental today, could either have a finite, non-zero size in one or more dimensions, or they could be truly point-like, potentially all the way down to the Planck length or even, conceivably, smaller.

    10
    Instead of an empty, blank, 3D grid, putting a mass down causes what would have been ‘straight’ lines to instead become curved by a specific amount. In General Relativity, we treat space and time as continuous, and masses/particles as discrete and fundamental. Neither one of these is necessarily the case. (CHRISTOPHER VITALE OF NETWORKOLOGIES AND THE PRATT INSTITUTE)

    The most important thing you should take away from this question — of whether truly fundamental particles exist or not — is that everything we know in science is only provisional. There is nothing that we know so well or so solidly that it is immutable. All of our scientific knowledge is merely the best approximation of reality that we’ve been able to construct at present. The theories that best describe our Universe might explain all the phenomena we can observe, they might make new, powerful, testable predictions, and they might even be unchallenged by any alternatives we know of at present.

    But that does not mean they are correct in any absolute sense. Science is always seeking to collect more data, explore new territory and scenarios, and to revise itself if ever a conflict arises. The particles we know of look fundamental today, but that’s no guarantee that nature will continue to indicate the existence of fundamental particles the deeper we learn to look.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

     
  • richardmitnick 12:47 pm on November 8, 2018 Permalink | Reply
    Tags: , , , , Ethan Siegel, This Is Why There Are No Alternatives To The Big Bang   

    From Ethan Siegel: “This Is Why There Are No Alternatives To The Big Bang” 

    From Ethan Siegel
    Sep 11, 2018

    1
    A visual history of the expanding Universe includes the hot, dense state known as the Big Bang and the growth and formation of structure subsequently. The full suite of data, including the observations of the light elements and the Cosmic Microwave Background, leaves only the Big Bang as a valid explanation for all we see. (NASA / CXC / M. WEISS)

    Not everyone is satisfied with the Big Bang. But every alternative is a disastrous failure.

    It’s treated as though it’s an unassailable scientific truth: 13.8 billion years ago, the Universe as we know it emerged from a hot, dense state known as the Big Bang. While there were a number of serious alternatives considered for decades, throughout the 20th century, a scientific consensus emerged more than 50 years ago with the discovery of the Cosmic Microwave Background [CMB].

    CMB per ESA/Planck

    Despite many attempts to revive a variety of the discredited ideas, as well as attempts to formulate new possibilities, all have fallen away under the burden of the full suite of astronomical data. The Big Bang reigns supreme as the only valid theory of our cosmic origins.

    Here’s how we discovered our Universe started with a bang.

    2
    he expanding Universe, full of galaxies and the complex structure we observe today, arose from a smaller, hotter, denser, more uniform state. It took thousands of scientists working for hundreds of years for us to arrive at this picture, and yet the lack of viable alternatives isn’t a flaw, but a feature of how successful the Big Bang truly is. (C. FAUCHER-GIGUÈRE, A. LIDZ, AND L. HERNQUIST, SCIENCE 319, 5859 (47))

    A suite of new discoveries in the early 20th century revolutionized our view of the Universe. In 1923, Edwin Hubble measured individual stars in spiral nebulae, measuring their variable periods and their observed brightness.

    Edwin Hubble at Caltech Palomar Samuel Oschin 48 inch Telescope, (credit: Emilio Segre Visual Archives/AIP/SPL)

    Thanks to the work of Henrietta Leavitt in formulating Leavitt’s law, which related such a star’s variable period to its intrinsic brightness, we obtained distance measurements to the galaxies that housed them. These galaxies were well outside our own Milky Way, with most residing millions of light years away.

    Henrietta Swan Leavitt discovered a relationship between the period of a star’s brightness cycle to its absolute magnitude. The discovery made it possible to calculate their distance from Earth

    3
    Hubble’s discovery of a Cepheid variable in Andromeda galaxy, M31, opened up the Universe to us, giving us the observational evidence we needed for galaxies beyond the Milky Way and leading to the expanding Universe. (E. HUBBLE, NASA, ESA, R. GENDLER, Z. LEVAY AND THE HUBBLE HERITAGE TEAM)

    Combined with redshift measurements, we were able to discover an important relationship: the farther away a galaxy appeared to be from us, the greater its redshift was measured to be. A number of possible explanations were advanced, such as the light from these objects lost energy as they traveled through space, or the more distant galaxies were moving away faster than the nearer ones, as though they all originated from an explosion.

    However, one explanation emerged as the most compelling: the Universe was expanding. This explanation was consistent with the predictions of General Relativity, as well as the observed large-scale smoothness observed in all directions and locations. As more galaxies at greater distances were discovered, this picture was validated further. The Universe was expanding.

    4
    The farther a galaxy is, the faster it expands away from us, and the more its light appears redshifted. A galaxy moving with the expanding Universe will be even a greater number of light years away, today, than the number of years (multiplied by the speed of light) that it took the light emitted from it to reach us. (LARRY MCNISH OF RASC CALGARY CENTER)

    Again, multiple valid explanations, even in the context of General Relativity, emerged. Sure, if the Universe were expanding in all directions, then we’d see distant objects moving away from us, with the more distant objects appearing to recede more rapidly. But this could be:

    because the objects also had large, unmeasurable transverse motions, as though the Universe were rotating as well,
    or because the Universe was oscillating, and if we looked far enough, we would see the expansion reverse,
    or because the expansion caused the slow creation of new matter, resulting in a Universe that appeared unchanging in time,
    or because the Universe originated from a hot, dense state.

    Only this last option represents the hot Big Bang.

    5
    As far back as humanity has ever seen in the Universe, just a few hundred million years after the Big Bang, we still know that the very first stars and galaxies should have existed before even that. Our picture of the Big Bang, General Relativity, the seeds of structure formation, and much more, all forms a consistent picture that tells us we are not quite yet at the beginning. (NASA, ESA, AND A. FEILD (STSCI))

    But if the idea of the Big Bang were correct, there would be a slew of new predictions that should arise. The expanding Universe, in the context of General Relativity, was the first, but there were three other, major ones that would lead to different observable consequences from the alternatives.

    6
    Galaxies comparable to the present-day Milky Way are numerous, but younger galaxies that are Milky Way-like are inherently smaller, bluer, more chaotic, and richer in gas in general than the galaxies we see today. For the first galaxies of all, this ought to be taken to the extreme. (NASA AND ESA)

    The first is that if the Universe originated from an arbitrarily hot, dense, and more uniform state to expand-and-cool to what we see today, then as we look farther away, we’re looking back in time, and we should see the Universe as it was when it was younger. We should see, therefore, galaxies that were smaller, less massive, and made up of younger, bluer stars at great distances, before arriving at a time where there were no stars or galaxies at all.

    7
    A Universe where electrons and protons are free and collide with photons transitions to a neutral one that’s transparent to photons as the Universe expands and cools. Shown here is the ionized plasma (L) before the CMB is emitted, followed by the transition to a neutral Universe (R) that’s transparent to photons. It’s the spectacular two-photon transition in a hydrogen atom which enables the Universe to become neutral exactly as we observe it. (AMANDA YOHO)

    The second, extrapolating even farther back, would be that there should be a time when the Universe was so hot and energetic that not even neutral atoms could form. At some very early stage, therefore, the Universe transitioned from an ionized plasma to one filled with neutral atoms. Any radiation that was around at that early stage should simply stream to our eyes, affected only by the expansion of the Universe.

    Arno Penzias and Robert Wilson, AT&T, Holmdel, NJ USA, with the Holmdel horn antenna, first caught the faint echo of the Big Bang

    Based on the temperature at which atoms become neutral vs. ionized, we expect this radiation to be just a few degrees above absolute zero, shifting it into the microwave portion of the spectrum today. This is where the term Cosmic Microwave Background comes from. Furthermore, because it had a thermal origin but redshifted with the expanding Universe, we also expect it to exhibit a particular shape to its spectrum: a blackbody spectrum. The radiation background was initially detected at right around 3 K, and has since had measurements refined so that we not only know it to be 2.7255 K, but that its spectrum is definitively blackbody and not consistent with an explanation of reflected starlight. (Which could be accommodated by one of the alternative explanations.)

    8
    Long before the data from BOOMERanG came back, the measurement of the spectrum of the CMB, from COBE, demonstrated that the leftover glow from the Big Bang was a perfect blackbody in a way that reflected starlight, as the quasi-steady-state model predicted, could not explain what we saw. (E. SIEGEL / BEYOND THE GALAXY)

    COBE/CMB


    NASA/COBE 1989 to 1993.

    Finally, there’s a third prediction: that based on the early history of the Universe, elements should have been forged by nuclear fusion in particular ratios. Today, this should mean that before any stars were formed, the Universe should have been about:

    75% hydrogen (by mass),
    25% helium-4,
    0.01% deuterium,
    0.01% helium-3, and
    1-part-in-a-billion lithium-7.

    That’s it; there should have been no elements heavier than that. Hydrogen, helium, a little bit of isotopes of each, and a tiny bit of lithium.

    9
    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. The Universe is 75–76% hydrogen, 24–25% helium, a little bit of deuterium and helium-3, and a trace amount of lithium by mass. After tritium and beryllium decay away, this is what we’re left with, and this remains unchanged until stars form. (NASA / WMAP SCIENCE TEAM)

    CMB per NASA/WMAP


    NASA/WMAP 2001 to 2010

    Observationally, this has been confirmed as well. Distant light, either from early galaxies or distant quasars, gets absorbed by intervening clouds of gas, allowing us to probe the contents of that gas. In 2011, we discovered two pristine clouds of gas, detecting hydrogen and helium in the exact, predicted ratios, and discovering (for the first time) a population of gas that had no oxygen or carbon: the first products of newly-formed stars.

    10
    The absorption spectra of different populations of gas (L) allow us to derive the relative abundances of elements and isotopes (center). In 2011, two distant gas clouds containing no heavy elements and a pristine deuterium-to-hydrogen ratio (R) were discovered for the first time. (MICHELE FUMAGALLI, JOHN M. O’MEARA, AND J. XAVIER PROCHASKA, VIA ARXIV.ORG/ABS/1111.2334)

    The only way to arrive at the Cosmic Microwave Background with the uniformity, spectrum, and temperature it possesses is to posit a hot, thermal origin for it in the context of the expanding Universe. This was conjectured back in the 1940s by George Gamow and his collaborators, first observed in the 1960s by Arno Penzias and Bob Wilson, and had its spectrum definitively proven to be blackbody in the 1990s with the COBE satellite.

    The large-scale structure of the Universe has been determined through all-sky surveys and deep field measurements with ground-and-space-based observatories, and has revealed a Universe consistent with the Big Bang and not with the alternatives. And the evolution of the elemental abundances, from metal-free early stages to metal-poor intermediate stages to the late-time, metal-rich stages that we observe today, all demonstrate the validity of the Big Bang.

    11
    There are now many independent observations of pristine gas from shortly after the Big Bang, showcasing the sensitive deuterium quantities relative to hydrogen. The agreement between observation and the theoretical predictions of the Big Bang is another victory for our best model of the Universe’s origin. (S. RIEMER-SØRENSEN AND E. S. JENSSEN, UNIVERSE 2017, 3(2), 44)

    If you can come up with an alternative explanation for these four observations, you will have the start of a viable alternative to the Big Bang. Explain the observed expansion of the Universe, the large-scale structure and the evolution of galaxies, the Cosmic Microwave Background along with its temperature and spectral properties, and the relative abundances and evolution of the elements in the Universe, and you’ll challenge the theory of our cosmic beginnings.

    12
    After the Big Bang, the Universe was almost perfectly uniform, and full of matter, energy and radiation in a rapidly expanding state. As time goes on, the Universe not only forms elements, atoms, and clumps and clusters together that lead to stars and galaxies, but expands and cools the entire time. No alternative can match it. (NASA / GSFC)

    For more than 50 years, no alternative has been able to deliver on all four counts. No alternative can even deliver the Cosmic Microwave Background as we see it today. It isn’t for lack of trying or a lack of good ideas; it’s because this is what the data indicates. Scientists don’t believe in the Big Bang; they conclude it based on the full suite of observations. The last adherents to the ancient, discredited alternatives are at last dying away. The Big Bang is no longer a revolutionary endpoint of the scientific enterprise; it’s the solid foundation we build upon. It’s predictive successes have been overwhelming, and no alternative has yet stepped up to the challenge of matching its scientific accuracy in describing the Universe.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

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

     
  • richardmitnick 1:33 pm on November 4, 2018 Permalink | Reply
    Tags: , , , , Ethan Siegel, What Is Energy?   

    From Ethan Siegel: “What Is Energy?” 

    From Ethan Siegel
    Nov 3, 2018

    1
    The preamplifiers of the National Ignition Facility are the first step in increasing the energy of laser beams as they make their way toward the target chamber. NIF recently achieved a 500 terawatt shot — 1,000 times more power than the United States uses at any instant in time. Despite our uses and applications for energy, it remains notoriously difficult to define. (DAMIEN JEMISON/LLNL)


    National Ignition Facility at LLNL

    We speak about it, argue over it, and even fight wars for it. We know it when we see it. But just what is energy, anyway?

    When it comes to being a human on planet Earth, energy affects practically every aspect of our lives. The energy content of a room determines its temperature; the ability to use it in a directed fashion is how we transport ourselves; we harness it to cook our food; the energy we burn in our bodies is necessary to keep us alive. From the energy of motion to stored energy to distributing or conserving it, energy affects all aspects of our lives. But even defining what energy is can be an awfully big challenge. That’s why Raza Usman asked, for this edition of our Ask Ethan column:

    We talk about energy and we know that there are various forms of energy (PE, KE …) and you can do work with it, and it has to be conserved, and energy and matter are interchangeable, etc. But what is energy?

    Physics can say a lot about energy, but even the top theoretical physicists have trouble concocting a definition that everyone can be happy with.

    2
    During an inspiral and merger of two neutron stars, a tremendous amount of energy should be released, along with heavy elements, gravitational waves, and an electromagnetic signal, as illustrated here. There are a variety of energy types that come into play in an event like this, and yet we still lack an unambiguous, universally applicable definition of energy itself. (NASA/JPL)

    The first definition of energy that the physical definition is built off of was this: energy is the ability to do work. But work, in physics, isn’t haphazardly defined as it is in the colloquial sense. Instead, work means something very specific: a force applied to an object that moves a certain distance, in the same direction the object moves.

    If you push on a box with a force of 10 N in the same direction that the box moves a distance of 1 meter, you do 10 J of work.

    If you push on a box with a force of 10 N in the opposite direction that the box moves a distance of 1 meter, you do -10 J of work.

    And if you push on a box, with a force of 10 N, perpendicular to the direction it moves 1 meter, you do no work at all.

    3
    The DEEP laser-sail concept relies on a large laser array striking and accelerating a relatively large-area, low-mass spacecraft. This has the potential to accelerate non-living objects to speeds approaching the speed of light, making an interstellar journey possible within a single human lifetime. The work done by the laser, applying a force as an object moves a certain distance, is an example of energy transfer from one form into another. (© 2016 UCSB EXPERIMENTAL COSMOLOGY GROUP)

    Traditionally, all other definitions of energy rely on the ability to transform into this: the ability to do work. Energy is defined by your ability to do work, but work is (circularly) defined as the transfer of energy from one source to another. Despite our ignorance, however, there are plenty of things we can confidently say about energy that are non-controversial, including:

    all mass and matter contains it,
    it can be quantified,
    we can store it electrically, chemically, thermally, sonically, etc.,
    we can convert it from one form to another,
    we can use it to accomplish things (i.e., to do work),
    we neither create nor destroy it,
    and we can generate, calculate, and measure its various forms.

    4
    By ‘pumping’ electrons into an excited state and stimulating them with a photon of the desired wavelength, you can cause the emission of another photon of exactly the same energy and wavelength. This action is how the light for a laser is first created: by the stimulated emission of radiation. Note that the radiation out plus the heat generated equals the energy inputted: it is conserved. (WIKIMEDIA COMMONS USER V1ADIS1AV)

    As far as the various forms of energy go, there is really no limit. If you have any configuration from which energy can be extracted, transferred, or from which work can be done, you’ve got a new form of energy. This can be mechanical, electrical, or chemical; it can be in a kinetic (moving) or potential (unreleased) form; it can be in the form of heat or light; it can be particle-based or wave-based; it can be classical or quantum in nature.

    But energy can’t always be extracted. Along with all of these different forms, physics also gives you this idea of a ground state, or a lowest-energy state that any quantum system can achieve. This zero-point energy is not necessarily equal to the classical value of a zero-energy state, but can often be a finite, non-zero value. For example, the energy of a hydrogen atom in the lowest (ground) state isn’t zero, but a larger value.

    5
    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. The opposite-spin configuration in the n=1 energy level represents the ground state of hydrogen, but its zero-point-energy is a finite, non-zero value. (TILTEC OF WIKIMEDIA COMMONS)

    That difference, between the ground state and the classical value of zero, defines what we know of as zero-point energy. In perhaps the most stunning discovery in the history of physics, studies of the expanding Universe have, for the past 20 years, led scientists to the conclusion that the zero-point energy of space itself is not zero, but some larger, finite value.

    Remember the original definition of energy: that it’s the ability to do work (exert a force along the direction of motion). If space itself is filled with some sort of energy, known today as dark energy, then it exerts a negative pressure, which is a force over an area. And if the Universe is expanding, that means the surface area of the observable Universe’s boundary is changing by a certain distance. Therefore, dark energy does work on the expanding Universe itself.

    6
    The effects of increasing the temperature of a gas inside a container. The outward pressure can result in an increase in volume, where the interior molecules do work on the container walls. (BEN BORLAND’S (BENNY B’S) SCIENCE BLOG)

    But how is this okay? It seems like a Universe filled with dark energy doesn’t conserve energy. If the energy density — energy-per-unit-volume — remains constant, but the volume of the Universe is increasing, doesn’t that mean the total amount of energy in the Universe is increasing? And doesn’t that violate the conservation of energy?

    Here’s where we start encountering problems. You see, I lied to you a little bit, when I talked about dark energy exerting a force that works against the Universe as it expands. The truth is more complex and counterintuitive, but boils down to this: in an expanding Universe, energy is not conserved. In fact, in an expanding spacetime under the laws of General Relativity, energy isn’t even, at a global level, defined at all.

    7
    If you had a static spacetime that weren’t changing, energy conservation would be guaranteed. But if the fabric of space changes as the objects you’re interested in move through them, there is no longer an energy conservation law under the laws of General Relativity. (DAVID CHAMPION, MAX PLANCK INSTITUTE FOR RADIO ASTRONOMY)

    The two major takeaways are as follows:

    When particles interact in an unchanging spacetime, energy must be conserved. When the spacetime they’re in changes, that conservation law no longer holds.
    If you redefine energy to include the work done, both positive and negative, by a patch of space on its surroundings, you can save the conservation of energy in an expanding Universe. This is true for both positive-pressure quantities (like photons) and negative pressure ones (like dark energy).

    But this redefinition is not robust; it’s simply a mathematical redefinition we can use to force energy to be conserved. The truth of the matter is that energy is not conserved in an expanding Universe.

    So, this brings us back full circle to the original question. What is energy? As best as we know it, energy cannot exist independently of particles or systems of particles. (Even gravitational waves are made of theoretical particles known as gravitons, just as electromagnetic waves are made of photons.) Energy comes in a variety of forms: some fundamental and some derived.

    8
    An artist’s impression of the three LISA spacecraft shows that the ripples in space generated by longer-period gravitational wave sources should provide an interesting new window on the Universe. These waves can be viewed as ripples in the fabric of spacetime itself, but they are still energy-carrying entities that, in theory, are made up of particles. (EADS ASTRIUM)

    A particle’s rest mass energy, for example, is inherent to every particle in the Universe itself. But all other forms of energy that exist are relative. Kinetic energy is relative; electric energy is stored relative to other charges; chemical energy relies on breaking and forming bonds. An atom in an excited state has more energy than an atom in a ground state, but that energy can only be released through the emission of a photon.

    You cannot make that transition from one energy state to another without conserving energy, and that energy needs to be carried by a particle.

    9
    In the absence of a magnetic field, the energy levels of various states within an atomic orbital are identical (L). If a magnetic field is applied, however (R), the states split according to the Zeeman effect. Here we see the Zeeman splitting of a P-S doublet transition. In all cases, energy can only be released through the emission of a particle, such as a transition as illustrated here. (EVGENY AT ENGLISH WIKIPEDIA)

    As far as we can tell, energy is not something we can isolate in a laboratory, but only one of many properties that matter, antimatter and radiation all possess. Energy can only be defined relative to another, somewhat arbitrary state. and is entirely dependent on the full suite of particles that make up your system. It has been over 300 years since physics introduced the work-related definition of energy, and while we still use it for everything that transitions, it doesn’t apply universally.

    A little over a century ago, the esteemed physicist Henri Poincaré noted the following, “science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house.” We speak all the time of what energy can do, how it’s used, where it appears and in what quantities, and how to accomplish a myriad of tasks with it. But a fundamental, universal definition? That’s an accomplishment that’s still beyond our reach.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

     
  • richardmitnick 8:27 pm on October 24, 2018 Permalink | Reply
    Tags: , , , , Ethan Siegel, What Was It Like When Starlight First Broke Through The Universe’s Neutral Atoms?   

    From Ethan Siegel: “What Was It Like When Starlight First Broke Through The Universe’s Neutral Atoms?” 

    From Ethan Siegel
    Oct 24, 2018

    1
    Neutral atoms were formed just a few hundred thousand years after the Big Bang. The very first stars began ionizing those atoms once again, but it took hundreds of millions of years of forming stars and galaxies until this process, known as reionization, was completed.(THE HYDROGEN EPOCH OF REIONIZATION ARRAY (HERA))

    For hundreds of millions of years, most of the starlight never made it through space. Here’s how that changed.

    Forming stars sounds like the easiest thing in the Universe to do. Get some mass together, give it enough time to gravitate, and watch it collapse down into small, dense clumps. If you get enough of it together under the right conditions, stars will no doubt ensue. This is how you form stars today, and it’s how we’ve formed stars all throughout our cosmic history, going back to the very first ones some 50–100 million years after the Big Bang.

    But even with the first stars burning, fusing hydrogen into heavier elements and emitting tremendous amounts of light, the Universe is too good at absorbing and blocking that light. The reason? All of the atoms in the Universe are neutral, and there are simply too many of them for the starlight to penetrate. It took hundreds of millions of years for the Universe to allow the light through. It’s a vital part of the cosmic story of us that almost no one realizes.

    2
    Schematic diagram of the Universe’s history, highlighting reionization. Before stars or galaxies formed, the Universe was full of light-blocking, neutral atoms. While most of the Universe doesn’t become reionized until 550 million years afterwards, with the first major waves happening at around 250 million years, a few fortunate stars may form just 50-to-100 million years after the Big Bang, and with the right tools, we may reveal the earliest galaxies. (S. G. DJORGOVSKI ET AL., CALTECH DIGITAL MEDIA CENTER)

    The Universe is always illuminated by the cosmic microwave background [CMB]: the leftover radiation from the Big Bang itself.

    CMB per ESA/Planck

    Less than half-a-million years after the Big Bang, neutral atoms formed and this radiation simply streamed, freely, amidst the sea of atoms. But this is only due to the fact that the cosmic radiation was much lower in energy than neutral (mostly hydrogen) atoms are capable of absorbing.

    If the radiation were higher in energy, atoms would not only absorb it, they would re-scatter it in all directions, where it would be further absorbed by additional atoms. It’s only because the radiation is so low in energy — it’s primarily infrared light — that it can freely pass through space.

    3
    This four-panel view shows the Milky Way’s central region in four different wavelengths of light, with the longer (submillimeter) wavelengths at top, going through the far-and-near infrared (2nd and 3rd) and ending in a visible-light view of the Milky Way. Note that the dust lanes and foreground stars obscure the center in visible light, but not so much in the infrared. (ESO/ATLASGAL CONSORTIUM/NASA/GLIMPSE CONSORTIUM/VVV SURVEY/ESA/PLANCK/D. MINNITI/S. GUISARD ACKNOWLEDGEMENT: IGNACIO TOLEDO, MARTIN KORNMESSER)

    We see this even in our own galaxy: the galactic center cannot be seen in visible light. The dust and gas blocks it, but infrared light goes clear through. This explains why the cosmic microwave background doesn’t get absorbed, but starlight does.

    Thankfully, the stars that we form can be massive and hot, where the most massive ones are much more luminous and hotter than even our Sun. Early stars can be tens, hundreds, or even a thousand times as massive as our own Sun, meaning they can reach surface temperatures of tens of thousands of degrees and brightnesses that are millions of times as luminous as our Sun. These behemoths are the biggest threat to the neutral atoms spread throughout the Universe.

    4
    An artist’s conception of what the Universe might look like as it forms stars for the first time. As they shine and merge, radiation will be emitted, both electromagnetic and gravitational. The neutral atoms surrounding it get ionized, but as long as there are more neutral atoms around them, the light won’t penetrate through an arbitrary distance.(NASA/ESA/ESO/WOLFRAM FREUDLING ET AL. (STECF))

    The key is that, for stars above a certain temperature, they’ll emit some fraction of their light in the ultraviolet portion of the spectrum: energetic enough to ionize a neutral atom. For a hydrogen atom in its lowest-energy state, it takes a photon of 13.6 eV (or more) to ionize it, which very few photons emitted from most stars possess. But the hotter and more massive your star is, the more ionizing photons they produce. Because these are the shortest-lived stars, it’s only within a few million years of forming a new burst of stars that you get an excessive amount of ionizing photons.

    5
    The first stars and galaxies in the Universe will be surrounded by neutral atoms of (mostly) hydrogen gas, which absorbs the starlight. The large masses and high temperatures of these early stars helps ionize the Universe, but more than these first generation of star can provide is required. (NICOLE RAGER FULLER / NATIONAL SCIENCE FOUNDATION)

    If all the atoms in the Universe were ionized, the depths of star-free space would be clear for light to travel through, meaning we could see the distant Universe without a problem. But even so long as a small percentage of the atoms remained neutral, that starlight would be effectively absorbed, making it extraordinarily challenging to detect anything from the era of the first stars and galaxies.

    What we need to happen, therefore, is for enough star formation to occur that it floods the Universe with a sufficient number of ultraviolet photons to ionize enough of the neutral matter that starlight can travel unimpeded. This requires a large amount of star formation, and requires it to occur quickly enough that the ionized protons and electrons don’t find one another and recombine again.

    6
    An enormous star-forming region in the dwarf galaxy UGCA 281, as imaged by Hubble in the visible and the ultraviolet, as part of the LEGUS survey. The blue light is starlight from hot, young stars reflected off of the background, neutral gas, while the brightest patches indicate the greatest emission of UV light. The red portions, however, are evidence of ionized hydrogen gas, which emits a characteristic red glow as electrons combine with the free protons.(NASA, ESA AND THE LEGUS TEAM)

    NASA/ESA Hubble Telescope

    The first stars make a small dent in this, but the earliest star clusters are small and short lived. The Universe will remain largely neutral with them alone. The second generation of stars, formed in the aftermath of the first generation’s death, fare little better.

    The problem is that these newly formed stars form in clumps and clusters of perhaps a few million solar masses at most. While a modern galaxy like our Milky Way might have a mass of around a trillion solar masses, filled with hundreds of billions of stars, the early star clusters only have about 0.001% of those numbers. For the first few hundred million years of our Universe, they’re barely enough to make a dent in the neutral matter throughout space.

    7
    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. Star clusters can form much more quickly than galaxies in the early Universe, but as they merge together, they can build their way up to becoming galaxies. (ESO [?])

    ESO/Cerro LaSilla, 600 km north of Santiago de Chile at an altitude of 2400 metres.


    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo

    But that begins to change when star clusters merge together, forming the first galaxies. As large clumps of gas, stars, and other matter merge together, they trigger a tremendous burst of star formation, lighting up the Universe as never before. As time goes on, a slew of phenomena take place all at once:

    the regions with the largest collections of matter attract even more early stars and star clusters towards them,
    the regions that haven’t yet formed stars can begin to,
    and the regions where the first galaxies are made attract other young galaxies,

    all of which serves to increase the overall star formation rate.

    If we were to map out the Universe at this time, what we’d see is that the star formation rate increases at a relatively constant rate for the first few billion years of the Universe’s existence. In some favorable regions, enough of the matter gets ionized early enough that we can see through the Universe before most regions are reionized; in others, it may take as long as two or three billion years for the last neutral matter to be blown away.

    If you were to map out the Universe’s neutral matter from the start of the Big Bang, you would find that it starts to transition to ionized matter in clumps, but you’d also find that it took hundreds of millions of years to mostly disappear. It does so unevenly, and preferentially along the locations of the densest parts of the cosmic web.

    8
    Past a certain distance, or a redshift (z) of 6, the Universe still has neutral gas in it, which blocks-and-absorbs light. These galactic spectra show the effect as a drop-to-zero in flux to the left of the big (Lyman-series) bump for all the galaxies past a certain redshift, but not for any of the ones at lower redshift. This physical effect is known as the Gunn-Peterson trough, and will block the brightest light produced by the earliest stars and galaxies. (X. FAN ET AL, ASTRON.J.132:117–136, (2006))

    On average, it takes 550 million years from the inception of the Big Bang for the Universe to become reionized and transparent to starlight. We see this from observing ultra-distant quasars, which continue to display the absorption features that only neutral, intervening matter causes. By the same token, though, there are a few directions where the matter is reionized much earlier, indicating to us that structure formation is uneven, and giving us hopes of finding early galaxies even before that 550 million year limit.

    In fact, the earliest galaxy that Hubble has uncovered, GN-z11, already comes from an earlier time than that: just 407 million years after the Big Bang.

    9
    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. To see further, we require a better observatory, optimized for these kinds of detection, than Hubble. (NASA, ESA, AND A. FEILD (STSCI))

    There are not yet galaxy clusters in the Universe, and the first galaxies, which largely formed between 200 and 250 million years after the Big Bang, will not be revealed in visible light. But through the eyes of an infrared observatory, where the light is long-enough in wavelength to not be absorbed by these neutral atoms, this starlight might shine through after all.

    It’s no coincidence, then, that the James Webb Space Telescope was designed to look in the near-and-mid-infrared portion of the spectrum, all the way out to wavelengths of 30 microns: some 50 times as long as the longest-wavelength light that human eyes can see.

    10
    As we’re exploring more and more of the Universe, we’re able to look farther away in space, which equates to farther back in time. The James Webb Space Telescope will take us to depths, directly, that our present-day observing facilities cannot match, with Webb’s infrared eyes revealing the ultra-distant starlight that Hubble cannot hope to see. (NASA / JWST AND HST TEAMS)

    he light created in the earliest era of stars and galaxies all plays a role. The ultraviolet light works to ionize the matter around it, enabling visible light to progressively farther and farther as the ionization fraction increases. The visible light gets scattered in all directions until reionization has gotten far enough to enable our best telescopes today to see it. But the infrared light, also created by the stars, passes through even the neutral matter, giving our 2020s-era telescopes a chance to find them.

    When starlight breaks through the sea of neutral atoms, even before reionization completes, it gives us a chance to detect the earliest objects we’ll ever have seen. When the James Webb Space Telescope launches, that will be the first thing we look for. The most distant reaches of the Universe are within our view. We just have to look and find out what’s truly out there.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

     
  • richardmitnick 8:37 am on October 19, 2018 Permalink | Reply
    Tags: , , , , Ethan Siegel, What Was It Like When The Universe Made The Very First Galaxies?   

    From Ethan Siegel: “What Was It Like When The Universe Made The Very First Galaxies?” 

    From Ethan Siegel
    Oct 17, 2018

    1
    The large-scale structure of the Universe changes over time, as tiny imperfections grow to form the first stars and galaxies, then merge together to form the large, modern galaxies we see today. Looking to great distances reveals a younger Universe, similar to how our local region was in the past. (CHRIS BLAKE AND SAM MOORFIELD)

    They may have arisen less than 200 million years after the Big Bang, but the Universe was a very different place back then.

    When you look out beyond the Milky Way today, as far as we’ve ever been able to see, there are galaxies absolutely everywhere. Even if you take a dark patch of sky without stars, galaxies, or any known matter at all, if you look deep enough, thousands upon thousands of galaxies will be your reward. All told, there are an estimated two trillion galaxies within the observable Universe, stretching for tens of billions of light years in all directions.

    Yet despite all the galaxies we’ve seen, never have we gone far enough back to encounter the very first ones ever made in the Universe. The current record-holder, despite its light arriving from when the Universe was only 400 million years old — 3% of its present age — is already evolved and full of old stars. The first galaxies come from a time before we’ve ever probed. But if we get lucky, we’ll get there soon. Here’s what those galaxies should be like.

    2
    The galaxy NGC 7331 and smaller, more distant galaxies beyond it. The farther away we look, the farther back in time we see. We will eventually reach a point where no galaxies at all have formed if we go back far enough. (ADAM BLOCK/MOUNT LEMMON SKYCENTER/UNIVERSITY OF ARIZONA)

    U Arizona Mount Lemmon Observatory on Mount Lemmon in the Santa Catalina Mountains 17 mi northeast of Tucson, Arizona ,US. Altitude 2,791 meters (9,157 ft)

    The galaxies we see today are old. They’re massive, they’re huge, and they’re full of a variety of stars. For the most part, there are lots of heavy elements [?] in there: approximately 1–2% of all the atoms present in galaxies (by weight) are something other than hydrogen or helium. That’s a big deal, considering that the Universe was born without carbon, nitrogen, oxygen, silicon, sulfur, iron, or practically any of the elements we find in stars and galaxies today.

    But it took billions of years and innumerable generations of stars to bring them about today. If we look back to the distant Universe, we also look back in time, and find that galaxies were vastly different back then from how they appear today. They were smaller, bluer, more numerous, and poorer in these heavy elements than the galaxies we have today. Over the history of the Universe, galaxies have evolved substantially.

    3
    Galaxies comparable to the present-day Milky Way are numerous, but younger galaxies that are Milky Way-like are inherently smaller, bluer, more chaotic, and richer in gas in general than the galaxies we see today. For the first galaxies of all, this ought to be taken to the extreme, and remains valid as far back as we’ve ever seen. (NASA/ESA Hubble)

    NASA/ESA Hubble Telescope

    But how did the very first ones form? And what was the Universe like when they did?

    The cosmic story that brought them to us saw a number of important steps happen first. Matter won out over antimatter; atomic nuclei and then neutral atoms formed; the first generation of stars were born, died, and gave rise to the second generation of stars. But even after all these steps, there were still no galaxies around.

    The simple reason? The smallest-volume cosmic scales gravitationally collapse first, while the larger scales take longer.

    Think about two important factors at play here: gravity and the speed of light. Gravity is the only mechanism that can bring ever larger and larger clumps of matter together. It’s limited, however, by the speed at which things can gravitationally grow.

    Imagine you start with a small mass, over and above whatever the average density is. If you have some additional mass for it to attract that’s a light-year away, it will take that matter an entire year to feel the force from the mass, since the gravitational force only travels at the speed of light. But if there’s an additional mass a hundred, or a million, or a billion light-years away, you have to wait for all that additional time to pass. Gravity isn’t instantaneous; it only travels at the speed of light.

    4
    Any distant gravitational source can emit gravitational waves and send out a signal that deforms the fabric of space, which manifests as gravitational attraction. But this deformation only travels at the speed of light; distant objects must wait a long time before feeling that force. (EUROPEAN GRAVITATIONAL OBSERVATORY, LIONEL BRET/EUROLIOS)


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    So what happens, then, when you finally get a large amount of mass together in one place, from gravitational collapse of your first stars and star clusters? They attract one another, and can finally do so effectively.

    But the timescale for one massive star cluster attracting another is going to be much longer than the timescale for individual star clusters to form. Instead of looking at volumes of space that might be a few thousand light years on a side — the scale of what might collapse to form a star cluster — you need to look on scales tens or hundreds of times as large to bring together enough matter to start to make the first galaxies.

    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. Star clusters form more quickly than galaxies in the early Universe. (ESO)

    ESO/Cerro LaSilla, 600 km north of Santiago de Chile at an altitude of 2400 metres.


    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo

    But remember, also, that the original overdensities that lead to both star clusters and galaxies are only one-part-in-about-30,000, meaning that these overdensities need to grow over large amounts of time. If it takes gravity tens or hundreds of times as long to reach between star clusters than it does for an individual cluster, you might worry that it takes tens or hundreds of times as much time to make galaxies than stars.

    Luckily, this isn’t true! It takes longer, but not by nearly that amount. The power of an attractive gravitational force is cumulative, so it’s basically like starting a clock on a delay. The “star cluster” clock starts a few million years after the Big Bang; the “galaxy” clock begins perhaps ten million years after that, and starts with a handicap: it has farther to go to collapse.

    6
    Streams of dark matter drive the clustering of galaxies and the formation of large-scale structure, as shown in this KIPAC/Stanford simulation. (O. HAHN AND T. ABEL (SIMULATION); RALF KAEHLER (VISUALIZATION))

    But this is okay! This is how large-scale structure formation works. We have density imperfections on all scales, and they grow as soon as enough time has passed for gravity to attract matter a certain distance away.

    We form the first star clusters quickly, after perhaps 50-to-100 million years. We form the second generation of stars almost immediately after, because the first generation of stars lives-and-dies so fast, triggering a new generation shortly thereafter.

    Then we have to wait tens of millions of years for the first galaxies to form, since that requires star clusters to attract one another across the abyss of empty space, where they finally merge. And it will take even longer timescales for large galaxies and then galaxy groups and galaxy clusters to arise.

    7
    Large scale projection through the Illustris volume at z=0, centered on the most massive cluster, 15 Mpc/h deep. Shows dark matter density (left) transitioning to gas density (right). The large-scale structure of the Universe cannot be explained without dark matter. The full suite of what’s present in the Universe dictates that structure forms on small scales first, eventually leading to progressively larger and larger ones. (ILLUSTRIS COLLABORATION / ILLUSTRIS SIMULATION)

    The hardest challenge for finding these first galaxies is that there haven’t yet been enough stars formed throughout the Universe to ionize all the neutral atoms in intergalactic space. Protons and electrons are still bound to one another, and will remain so until the Universe is flooded with enough sustained ultraviolet light to permanently kick those electrons off of their atoms.

    This means that the light from the first stars (and first galaxies) gets absorbed by those atoms; the Universe is still opaque. The earliest galaxies we’ve ever seen date back to 400 million years after the Big Bang, and were only discovered because they are located along a serendipitously more-ionized-than-average line of sight.

    8
    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. To see further, we require a better observatory, optimized for these kinds of detection, than Hubble. (NASA, ESA, AND A. FEILD (STSCI))

    However, we can do a little better than that. We’ve observed a slew of galaxies from a little bit later on than that, and we’ve been able to determine how old the stars in them are!

    The galaxy MACS1149-JD1 is the second-most-distant galaxy ever found, whose light arrives from 530 million years after the Big Bang. Yet, when we observe it, we find that the stars inside of it are approximately 280 million years old, meaning that they formed in a massive burst just 250 million years after the Big Bang.

    9
    The distant galaxy MACS1149-JD1 is gravitationally lensed by a foreground cluster, allowing it to be imaged at high resolution and in multiple instruments, even without next-generation technology.(ALMA (ESO/NAOJ/NRAO), NASA/ESA HUBBLE SPACE TELESCOPE, W. ZHENG (JHU), M. POSTMAN (STSCI), THE CLASH TEAM, HASHIMOTO ET AL.)

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

    These massive bursts of star formation don’t simply occur because you had a star cluster; they occur when large mergers happen, giving rise to what astronomers call a starburst. Colliding gas causes material to collapse, which can trigger massive amounts of new star formation. Much larger and more powerful than a mere collapsing star cluster, these should signify the true first galaxies.

    They will be larger, contain more stars, be more massive, more luminous, and will leave an unmistakable signature. They will imprint themselves on the Universe. And that imprint will be observable.

    10
    Our entire cosmic history is theoretically well-understood, but only qualitatively. It’s by observationally confirming and revealing various stages in our Universe’s past that must have occurred, like when the first stars and galaxies formed, that we can truly come to understand our cosmos. (NICOLE RAGER FULLER / NATIONAL SCIENCE FOUNDATION)

    Not only will they begin contributing to the reionization of the Universe, but wherever they form stars, we will find electrons recombining with their ionized nuclei. That act, when it occurs for hydrogen atoms, has a 50% chance of forming a configuration where the spins are aligned (up-up or down-down) and a 50% chance where the spins will be anti-aligned (up-down or down-up).

    The up-down or down-up configurations are more stable, by a tiny amount. If you form the aligned configuration, it will transition down to the anti-aligned configuration on timescales of around 10 million years. And when it transitions, it emits a photon of a very specific wavelength: 21 centimeters.

    11
    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. (TILTEC OF WIKIMEDIA COMMONS)

    That photon then travels throughout the Universe, arriving at our eyes, redshifted by the expansion of the Universe. Earlier in 2018, there was a paper that came out, albeit very controversially, that claimed to detect this signature for the first time. Impressively, the timescale for when these first galaxies ought to have formed coincides very nicely with these observations.

    Whenever “cosmic dawn” occurred, whenever these first galaxies arrive, every piece of evidence points to a timetable of 200–250 million years as the main origin of the first galaxies.

    12
    The enormous ‘dip’ that you see in the graph here, a direct result of a recent study from Bowman et al. (2018), shows the unmistakable signal of 21-cm emission from when the Universe was between 180 and 260 million years in age. This corresponds, we believe, to the turn-on of the first wave of stars and galaxies in the Universe. Based on this evidence, the beginning of ‘cosmic dawn’ starts at a redshift of 22 or so. (J.D. BOWMAN ET AL., NATURE, 555, L67 (2018))

    The first galaxies required a large number of steps to happen first: they needed stars and star clusters to form, and they needed for gravity to bring these star clusters together into larger clumps. But once you make them, they are now the largest structures, and can continue to grow, attracting not only star clusters and gas, but additional small galaxies. The cosmic web has taken its first major step up, and will continue to grow further, and more complex, over the hundreds of millions and billions of years to follow.

    Meanwhile, the regions with smaller initial overdensities will continue to grow, forming stars for the first (or second) time in places where they didn’t form earlier. The great cosmic story of forming structures doesn’t happen all at once, but in bits-and-pieces throughout the cosmos. But with the first galaxies, the race to form galaxies like our own has officially begun.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

     
  • richardmitnick 8:23 am on October 17, 2018 Permalink | Reply
    Tags: , , , , , Ethan Siegel, Speed of Light, The CMB: the cosmic microwave background, The CNB: the cosmic neutrino background, The Universe Has A Speed Limit And It Isn’t The Speed Of Light, The WHIM: the warm-hot intergalactic medium   

    From Ethan Siegel: “The Universe Has A Speed Limit, And It Isn’t The Speed Of Light” 

    From Ethan Siegel

    Oct 16, 2018

    1
    All massless particles travel at the speed of light, including the photon, gluon and gravitational waves, which carry the electromagnetic, strong nuclear and gravitational interactions, respectively. Particles with mass must always travel at speeds below the speed of light, and there’s an even more restrictive cutoff in our Universe. (NASA/Sonoma State University/Aurore Simonnet)

    Nothing can go faster than the speed of light in a vacuum. But particles in our Universe can’t even go that fast.

    When it comes to speed limits, the ultimate one set by the laws of physics themselves is the speed of light. As Albert Einstein first realized, everyone looking at a light ray sees that it appears to move at the same speed, regardless of whether it’s moving towards you or away from you. No matter how fast you travel or in what direction, all light always moves at the same speed, and this is true for all observers at all times. Moreover, anything that’s made of matter can only approach, but never reach, the speed of light. If you don’t have mass, you must move at the speed of light; if you do have mass, you can never reach it.

    But practically, in our Universe, there’s an even more restrictive speed limit for matter, and it’s lower than the speed of light. Here’s the scientific story of the real cosmic speed limit.

    When scientists talk about the speed of light — 299,792,458 m/s — we implicitly mean “the speed of light in a vacuum.” Only in the absence of particles, fields, or a medium to travel through can we achieve this ultimate cosmic speed. Even at that, it’s only the truly massless particles and waves that can achieve this speed. This includes photons, gluons, and gravitational waves, but not anything else we know of.

    Quarks, leptons, neutrinos, and even the hypothesized dark matter all have masses as a property inherent to them. Objects made out of these particles, like protons, atoms, and human beings all have mass, too. As a result, they can approach, but never reach, the speed of light in a vacuum. No matter how much energy you put into them, the speed of light, even in a vacuum, will forever be unattainable.

    But there’s no such thing, practically, as a perfect vacuum. Even in the deepest abyss of intergalactic space, there are three things you absolutely cannot get rid of.

    The WHIM: the warm-hot intergalactic medium. This tenuous, sparse plasma are the leftovers from the cosmic web. While matter clumps into stars, galaxies, and larger groupings, a fraction of that matter remains in the great voids of the Universe. Starlight ionizes it, creating a plasma that may make up about 50% of the total normal matter in the Universe.

    WHIM-Warm-Hot Intergalactic Medium Trevor Ponman U Birmingham


    The CMB: the cosmic microwave background. This leftover bath of photons originates from the Big Bang, where it was at extremely high energies. Even today, at temperatures just 2.7 degrees above absolute zero, there are over 400 CMB photons per cubic centimeter of space.

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    The CNB: the cosmic neutrino background. The Big Bang, in addition to photons, creates a bath of neutrinos. Outnumbering protons by perhaps a billion to one, many of these now-slow-moving particles fall into galaxies and clusters, but many remain in intergalactic space as well.

    CNB- the cosmic neutrino background-Amand Faessler U Tuebingen

    3
    A multiwavelength view of the galactic center shows stars, gas, radiation and black holes, among other sources. But the light coming from all of these sources, from gamma rays to visible to radio light, can only indicate what our instruments are sensitive enough to detect from 25,000+ light years away. (NASA/ESA/SSC/CXC/STScI)

    Any particle traveling through the Universe will encounter particles from the WHIM, neutrinos from the CNB, and photons from the CMB. Even though they’re the lowest-energy things, the CMB photons are the most numerous and evenly-distributed particles of all. No matter how you’re generated or how much energy you have, it’s not really possible to avoid interacting with this 13.8 billion year old radiation.

    When we think about the highest-energy particles in the Universe — i.e., the ones that will be moving the fastest — we fully expect they’ll be generated under the most extreme conditions the Universe has to offer. That means we think we’ll find them where energies are highest and fields are strongest: in the vicinity of collapsed objects like neutron stars and black holes.

    4
    In this artistic rendering, a blazar is accelerating protons that produce pions, which produce neutrinos and gamma rays. (IceCube/NASA)

    U Wisconsin IceCube experiment at the South Pole



    Neutron stars and black hole are where you can not only find the strongest gravitational fields in the Universe, but — in theory — the strongest electromagnetic fields, too. The extremely strong fields are generated by charged particles, either on the surface of a neutron star or in the accretion disk around a black hole, that move close to the speed of light. Moving charged particles generate magnetic fields, and as particles move through these fields, they accelerate.

    This acceleration causes not only the emission of light of a myriad of wavelengths, from X-rays down to radio waves, but also the fastest, highest-energy particles ever seen: cosmic rays.

    Cosmic rays produced by high-energy astrophysics sources (ASPERA collaboration – AStroParticle ERAnet)

    Artist’s impression of the active galactic nucleus (DESY, Science Communication Lab)

    Whereas the Large Hadron Collider accelerates particles here on Earth up to a maximum velocity of 299,792,455 m/s, or 99.999999% the speed of light, cosmic rays can smash that barrier. The highest-energy cosmic rays have approximately 36 million times the energy of the fastest protons ever created at the Large Hadron Collider. Assuming that these cosmic rays are also made of protons gives a speed of 299,792,457.99999999999992 m/s, which is extremely close to, but still below, the speed of light in a vacuum.

    There’s a very good reason that, by time we receive them, these cosmic rays aren’t more energetic than this.

    The problem is that space isn’t a vacuum. In particular, the CMB will have its photons collide and interact with these particles as they travel through the Universe. No matter how high the energy is of the particle you made, it has to pass through the radiation bath that’s left over from the Big Bang in order to reach you.

    Even though this radiation is incredibly cold, at an average temperature of some 2.725 Kelvin, the mean energy of each photon in there isn’t negligible; it’s around 0.00023 electron-Volts. Even though that’s a tiny number, the cosmic rays hitting it can be incredibly energetic. Every time a high-energy charged particle interacts with a photon, it has the same possibility that all interacting particles have: if it’s energetically allowed, by E=mc², then there’s a chance it can create a new particle!

    5
    Whenever two particles collide at high enough energies, they have the opportunity to produce additional particle-antiparticle pairs, or new particles as the laws of quantum physics allow. Einstein’s E = mc² is indiscriminate this way. (E. Siegel / Beyond The Galaxy)

    If you ever create a particle with energies in excess of 5 × 10¹⁹ eV, they can only travel a few million light years — max — before one of these photons, left over from the Big Bang, interacts with it. When that interaction occurs, there will be enough energy to produce a neutral pion, which steals energy away from the original cosmic ray.

    The more energetic your particle is, the more likely you are to produce pions, which you’ll continue to do until you fall below this theoretical cosmic energy limit, known as the GZK cutoff. (Named for three physicists: Greisen, Zatsepin, and Kuzmin.) There’s even more braking (Bremsstrahlung) radiation that arises from interactions with any particles in the interstellar/intergalactic medium. Even lower-energy particles are subject to it, and radiate energy away in droves as electron/positron pairs (and other particles) are produced.

    We believe that every charged particle in the cosmos — every cosmic ray, every proton, every atomic nucleus — should limited by this speed. Not just the speed of light, but a little bit lower, thanks to the leftover glow from the Big Bang and the particles in the intergalactic medium. If we see anything that’s at a higher energy, then it either means:

    1.particles at high energies might be playing by different rules than the ones we presently think they do,
    2.they are being produced much closer than we think they are: within our own Local Group or Milky Way, rather than these distant, extragalactic black holes,
    3.or they’re not protons at all, but composite nuclei.

    The few particles we’ve seen that break the GZK barrier are indeed in excess of 5 × 10¹⁹ eV, in terms of energy, but do not exceed 3 × 10²¹ eV, which would be the corresponding energy value for an iron nucleus. Since many of the highest-energy cosmic rays have been confirmed to be heavy nuclei, rather than individual protons, this reigns as the most likely explanation for the extreme ultra-high-energy cosmic rays.

    6
    The spectrum of cosmic rays. As we go to higher and higher energies, we find fewer and fewer cosmic rays. We expected a complete cutoff at 5 x 10¹⁹ eV, but see particles coming in with up to 10 times that energy. (Hillas 2006 / University of Hamburg)

    There is a speed limit to the particles that travel through the Universe, and it isn’t the speed of light. Instead, it’s a value that’s very slightly lower, dictated by the amount of energy in the leftover glow from the Big Bang. As the Universe continues to expand and cool, that speed limit will slowly rise over cosmic timescales, getting ever-closer to the speed of light. But remember, as you travel through the Universe, if you go too fast, even the radiation left over from the Big Bang can fry you. So long as you’re made of matter, there’s a cosmic speed limit that you simply cannot overcome.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

     
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