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  • richardmitnick 10:54 am on March 22, 2017 Permalink | Reply
    Tags: , , , , , Ethan Siegel,   

    From Ethan Siegel: “What Will Happen When Betelgeuse Explodes?” 

    Ethan Siegel
    Mar 22, 2017

    1
    The constellation of Orion, along with the great molecular cloud complex and including its brightest stars. Betelgeuse, the nearby, bright red supergiant (and supernova candidate), is at the lower left. Rogelio Bernal Andreo

    Every star will someday run out of fuel in its core, bringing an end to its run as natural source of nuclear fusion in the Universe. While stars like our Sun will fuse hydrogen into helium and then — swelling into a red giant — helium into carbon, there are other, more massive stars which can achieve hot enough temperatures to further fuse carbon into even heavier elements. Under those intense conditions, the star will swell into a red supergiant, destined for an eventual supernova after around 100,000 years or so. And the brightest red supergiant in our entire night sky? That’s Betelgeuse, which could go supernova at any time.

    2
    The color-magnitude diagram of notable stars. The brightest red supergiant, Betelgeuse, is shown at the upper right. European Southern Observatory.

    Honestly, at its distance of 640 light years from us, it could have gone supernova at any time from the 14th century onwards, and we still wouldn’t know. Betelgeuse is one of the ten brightest stars in the sky in visible light, but only 13% of its energy output is detectable to human eyes. If we could see the entire electromagnetic spectrum — including into the infrared — Betelgeuse would, from our perspective, outshine every other star in the Universe except our Sun.

    3
    Three of the major stars in Orion — Betelgeuse, Meissa and Bellatrix — as revealed in the infrared. In IR light, Betelgeuse (lower left) is the brightest star in the night sky. NASA / WISE.

    It was the first star ever to be resolved as more than a point source. At 900 times the size of our Sun, it would engulf Mercury, Venus, Earth, Mars and even the asteroid belt if it were to replace our parent star. It’s a pulsating star, so its diameter changes with time.

    In addition, it’s constantly losing mass, as the intense fusion reactions begin to expel the outermost, tenuously-held layers. Direct radio observations can actually detect this blown-off matter, and have found that it extends to beyond the equivalent of Neptune’s orbit.

    4
    The nebula of expelled matter created around Betelgeuse, which, for scale, is shown in the interior red circle. This structure, resembling flames emanating from the star, forms because the behemoth is shedding its material into space. ESO/P. Kervella

    But when we study the night sky, we’re studying the past. We know that Betelgeuse, with an uncertain mass between about 12 and 20 times that of our Sun, was never destined to live very long: maybe around 10 million years only. The more massive a star is, the faster it burns through its fuel, and Betelgeuse is burning so very, very brightly: at around 100,000 times the luminosity of our Sun. It’s currently in the final stages of its life — as a red supergiant — meaning that when the innermost core begins fusing silicon and sulphur into iron, nickel and cobalt, the star itself will only have minutes left.

    5
    The anatomy of a very massive star throughout its life, culminating in a Type II Supernova. Nicole Rager Fuller for the NSF.

    At those final moments, the core will be incredibly hot, yet iron, nickel and cobalt will be unable to fuse into anything heavier. It’s energetically unfavorable to do so, and so no new radiation will be produced in the innermost regions. Yet gravitation is still at play, trying to pull the star’s core in on itself. Without nuclear fusion to hold it up, the core has no other options, and begins to implode. The contraction causes it to heat up, become denser, and achieve pressures like it’s never seen before. And once a critical junction has passed, it happens: the atomic nuclei in the star’s core begin a runaway fusion reaction all at once.

    This is what creates a Type II supernova: the core-collapse of an ultra-massive star. After a brief, initial flash, Betelgeuse will brighten tremendously over a period of weeks, rising to a maximum brightness that, intrinsically, will be billions of times as bright as the Sun. It will remain at maximum brightness for months, as radioactive cobalt and expanding gases cause a continuous bright emission of light.

    6
    At peak brightness, a supernova can shine nearly as brightly as the rest of the stars in a galaxy combined. This 1994 image shows a typical example of a core-collapse supernova relative to its host galaxy. NASA/ESA, The Hubble Key Project Team and The High-Z Supernova Search Team

    Supernovae have occurred in our Milky Way in the past: in 1604, 1572, 1054 and 1006, among others, with a number of them being so bright that they were visible during the day. But none of them were as close at Betelgeuse.

    At only 600-or-so light years distant, Betelgeuse will be far closer than any supernova ever recorded by humanity. It’s fortunately still far away enough that it poses no danger to us. Our planet’s magnetic field will easily deflect any energetic particles that happen to come our way, and it’s distant enough that the high-energy radiation reaching us will be so low-density that it will have less of an impact on you than the banana you had at breakfast. But oh, will it ever appear bright.

    Not only will Betelgeuse be visible during the day, but it will rival the Moon for the second-brightest object in the sky. Some models “only” have Betelgeuse getting as bright as a thick crescent moon, while others will see it rival the entire full moon. It will conceivably be the brightest object in the night sky for more than a year, until it finally fades away to a dimmer state.

    7
    The ultra-massive star Wolf-Rayet 124, shown with its surrounding nebula, is one of thousands of Milky Way stars that could be our galaxy’s next supernova. Betelgeuse is merely the closest known potential candidate. Hubble Legacy Archive / A. Moffat / Judy Schmidy

    Unfortunately, the key question of “when” is not one we have an answer to; thousands of other stars in the Milky Way may go supernova before Betelgeuse does. Until we develop an ultra-powerful neutrino telescope to measure the energy spectrum of neutrinos being generated by (and hence, which elements are being fused inside) a star like Betelgeuse, hundreds of light years away, we won’t know how close it is to going supernova. It could have exploded already, with the light from the cataclysm already on its way towards us… or it could remain no different than it appears today for another hundred thousand years.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 10:37 am on March 9, 2017 Permalink | Reply
    Tags: After All, , , , , Ethan Siegel, Proxima b And The Worlds Around TRAPPIST-1 Might Be Habitable   

    From Ethan Siegel: “Proxima b And The Worlds Around TRAPPIST-1 Might Be Habitable, After All” 

    From Ethan Siegel
    Mar 9, 2017

    When it comes to life in the Universe, we only have one confirmed example of success: Earth. The raw ingredients for life, however, are everywhere. This includes both the necessary building blocks for life (the raw elements and organic molecules) and also the necessary conditions for it, too. We normally look to our own planet for those conditions, which include a rocky world that’s rich in water, a thin atmosphere, an active magnetic field, and the right temperatures for liquid oceans on its surface. We measure other planets against Earth for their chances of success, and use words like “super-Earth” and “habitable zone” to describe and classify them. But this approach, as common as it is, may lead to us overlooking life where it’s most abundant if it’s not found on worlds like our own.

    1
    An artist’s impression of the Tau Ceti system, a star slightly cooler than the Sun with numerous ‘super-Earths’ orbiting it.

    Those conditions I mentioned aren’t the only ones that give Earth the properties we observe it to have. Some scientists, when enumerating the conditions for life on Earth, also include a large moon, a solar system with a gas giant just beyond the asteroid belt, our parent star’s ultraviolet radiation, Earth’s rapid night-and-day rotation, and our location far from the galactic center. But how many of these conditions are truly necessary for life to arise? In fact, how many of the earlier ones are necessary? With insufficient evidence, we don’t know. In fact, given that the Sun is larger, hotter and more massive than 95% of stars in the galaxy, it may be that life on Earth-like worlds is the rarity.

    2
    Different colors, masses and sizes of main-sequence stars. The most massive ones produce the greatest amounts of heavy elements the fastest.

    Three out of every four stars in the Universe are red dwarfs, or M-class stars. These are stars ranging from 8-40% the mass of the Sun, giving off as little as 0.05% of our Sun’s energy and living for hundreds of billions or even trillions of years. Our nearest star, Proxima Centauri, is a red dwarf like this, and so is TRAPPIST-1, at just 40 light years away.


    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

    Proxima Centauri has an Earth-sized world at the right distance from its star that — if its atmosphere is Earth-like — it should have liquid water on its surface. TRAPPIST-1 has seven Earth-sized worlds around it; three of them meet those conditions.

    3
    NASA/R. Hurt/T. Pyle
    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.

    Yet many in the scientific community claim that life on these worlds is a very improbable proposition. Why? Because they’re comparing these worlds to Earth.

    But this isn’t fair. Calling a world a “super-Earth” implies that it’s Earth-like, but most aren’t. Once you rise to a size that’s only about 20% larger than Earth, or double our planet’s mass, you become more Neptune-like than Earth-like. With the right atmosphere, Venus could be habitable, and so could Mars or even Ceres, yet all are often excluded from the “habitable zone.”

    4
    The 21 Kepler planets discovered in the habitable zones of their stars, no larger than twice the Earth’s diameter. Most of these worlds orbit red dwarfs, closer to the “bottom” of the graph, and are likely not Earth-like.

    We aren’t interested in habitable zones, however; we are interested in habitable planets. And if the diversity of the planets we’ve discovered and/or explored has taught us nothing else, let it be this: Earth is not the only way.

    5
    ESO/M. Kornmesser/spaceengine.org
    This artist’s impression shows the view just above the surface of one of the planets in the TRAPPIST-1 system, which may contain liquid water on the surface if the atmospheric conditions are right.

    If you want to exchange interior material with surface material on a planet, you could do it with plate tectonics, like Earth does. Plate tectonics are often taken — among the general public and among scientists, too — as a necessity this type of exchange, and therefore, for life. But a world with sufficient volcanic activity could accomplish exactly the same thing.

    5
    NASA / JPL / Galileo mission
    The ‘Prometheus plume’ on Jupiter’s moon Io is an example of extreme volcanic activity within our Solar System.

    Worlds around M-class stars need to orbit much closer than even Mercury orbits the Sun in order to receive an appreciable amount of energy, and so their properties will be very different than Earth. These worlds will likely exhibit:

    more volcanoes,
    tidal locking (where one side always faces the Sun),
    more intense susceptibility to flaring from their star,
    less steady ultraviolet and visible light radiation,
    and faster attempts to strip their atmospheres.

    With all of these obstacles, you might think life on these worlds is impossible. After all, many do think exactly that.

    6
    TRAPPIST-1 system compared to the solar system; all seven planets of TRAPPIST-1 could fit inside the orbit of Mercury. Note that at least the inner six worlds of TRAPPIST-1 are all locked to the star.

    But the volcanoes may be beneficial, not detrimental. The tidal locking may mean that the permanent “day” side (or the permanent “sunset” ring) is even more hospitable to life than Earth is. The flaring from the star may pose no danger at all to a world with a strong magnetic field. A separate day/night rotation may not be necessary to sustain a magnetic field on a tidally locked world; the ultra-close orbit to a red dwarf gives it nearly as much rotational energy as Earth. The UV and visible light may not be so important to the origin of life; many molecules operate on red or infrared energy frequencies. And atmospheres need not be made of light molecules like nitrogen, but could be heavier (like carbon dioxide) and resistant to stripping.

    7
    A world like Mars, without a protective magnetic field, is stripped of its atmosphere relatively quickly. But a strong enough magnetic field protects Earth, and could protect worlds around M-class stars as well.

    The major point we should all take home is that yes, life arose on Earth, but it’s foolish to demand that a planet or its conditions be “Earth-like” in the search for habitability. (Although, see Bruce Dorminey, here, for a counterpoint.) So long as there exists energy, liquid water and long-term stable conditions, life may well be possible. The most common type of star in the Universe isn’t a Sun-like star, but rather are low-mass stars that emit only a tiny fraction of the Sun’s energy. Their worlds will be vastly different than our own, yet may house life all the same. It’s up to us to look in the right way, and to keep our minds open to potential surprises. We’re only at the beginning of this journey.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 2:43 pm on March 3, 2017 Permalink | Reply
    Tags: , , , Ethan Siegel, How depressing, , There are none.   

    From Ethan Siegel: “Cosmic superclusters, the Universe’s largest structures, don’t actually exist” [How depressing] 

    Ethan Siegel
    Mar 3, 2017

    1
    The Laniakea supercluster, containing the Milky Way (red dot), on the outskirts of the Virgo Cluster (large white collection near the Milky Way). Image credit: Tully, R. B., Courtois, H., Hoffman, Y & Pomarède, D. Nature 513, 71–73 (2014).

    You may have heard of Laniakea, but don’t count on it being real.

    “It’s the gravity that shapes the large scale structure of the universe, even though it is the weakest of four categories of forces.” -Stephen Hawking

    On the largest scales, the Universe looks like a vast cosmic web. Stars link up into galaxies, which are clustered together in galactic groups. Many groups bound together lead to galaxy clusters, and occasionally clusters merge together, creating even larger clusters. Many clusters together, spanning hundreds of millions or even billions of light years across, appear to make the largest structures of all: superclusters. Our own supercluster, Laniakea, consists of approximately 100,000 galaxies, more than 10 times richer than the largest known clusters. Yet these superclusters only appear to be structures. As the Universe ages, the individual components of superclusters are being pushed apart, showing that they’re not true structures after all.

    There’s a simple recipe for building the Universe as we know it today: take a sea of matter and radiation that starts off hot, dense and expanding, and give it time to cool. Over long enough timescales, atomic nuclei, neutral atoms, and eventually stars, galaxies, and clusters of galaxies will form. The irresistible force of gravity makes this inevitable, thanks to its effects on both the normal (atomic) matter we know and the dark matter filling our Universe, whose nature is still unknown.

    2
    Over time, gravitational interactions will turn a mostly uniform, equal-density Universe into one with large concentrations of matter and huge voids separating them. Image credit: Volker Springel.

    When we look out into the Universe — beyond our galaxy to the largest known structures beyond — this picture has tremendous supper. At least it appears to, at first glance. While many galaxies exist in isolation, or grouped together in collections of only a few, there are also huge gravitational “wells” in the Universe, that have pulled in hundreds or even thousands of galaxies, creating enormous clusters. Quite often, there are supermassive elliptical galaxies at the center, with the most massive yet discovered shown below: IC 1101, which is more than a thousand times as massive as our own Milky Way.

    4
    The giant galaxy cluster Abell 2029, and its central galaxy, IC 1101. Image credit: Digitized Sky Survey / NASA.

    So what’s larger than a galaxy cluster? A supercluster, of course. Superclusters are collections of clusters connected by great cosmic filaments of dark-and-normal matter, whose gravitation mutually attracts them towards their common center-of-mass. You wouldn’t be alone if you thought it was only a matter of time — time and gravity, that is — until the clusters comprising a supercluster all merged together. When that happens, the thought goes, you’ll wind up creating a single bound, cosmic structure of unparalleled mass.

    5
    A large collection of many thousands of galaxies makes up our nearby neighborhood within 100,000,000 light years. It’s dominated by the Virgo Cluster, but many other mass collections abound. Image credit: Wikimedia Commons user Andrew Z. Colvin.

    In our own neighborhood, the local group, made up of Andromeda, the Milky Way, Triangulum and maybe 50 smaller, dwarf galaxies, lies on the outskirts of the Laniakea supercluster. Our location places us some 50,000,000 light years away from the main source of mass in our nearby Universe: the massive Virgo Cluster, which contains over a thousand Milky Way-sized galaxies. Along the way, many other galaxies, groups of galaxies and smaller clusters can be found.

    On even larger scales, the Virgo cluster is only one of many in the portion of the Universe we’ve mapped, along with the two next-nearest ones: the Centaurus cluster and the Perseus-Pisces cluster. Where the galaxies are most concentrated represent the largest clusterings of mass; where the lines connect them, along filaments, we find “strings” of galaxies, like pearls strung too thin on a necklace; and in the great bubbles between the filaments, we find huge underdensities of matter, as those regions have given up their mass to the denser ones.

    6
    The greatest overdensities (in red) and underdensities (in black) came about as small gravitational differences in the early Universe evolved over billions of years. Image credit: Helene M. Courtois, Daniel Pomarede, R. Brent Tully, Yehuda Hoffman, Denis Courtois, from “Cosmography of the Local Universe” (2013).

    If we take a look at our own neighborhood, we find that there’s a large collection of more than 3,000 galaxies that makes up the large-scale structure that includes ourselves, Virgo, Leo and many other surrounding groups. The dense Virgo cluster is the largest part of it, making up a little more than a third of the total mass, but there are many other concentrations of mass within it, including our own local group (shown in blue, below), connected together by the invisible force of gravity and the unseen filaments of dark matter.

    We call this supercluster “Laniakea,” the Hawaiian word for immense heaven. It links up our own massive cluster, Centaurus, the Great Attractor and many others, and contains over 100,000 galaxies total. Additionally, it’s a beautiful name, a beautiful idea, and a beautiful collection of galaxies that includes us. But there’s a problem with not only Laniakea, but with the idea of a supercluster in general: it isn’t real.

    8
    Outlined in light blue, giant collections of galaxies can be divided up into superclusters. But this classification doesn’t make superclusters real. Image credit: The Laniakea supercluster of galaxies R. Brent Tully, Hélène Courtois, Yehuda Hoffman & Daniel Pomarède, Nature 513, 71–73 (04 September 2014).

    Our Universe isn’t just the combined effects of an initial expansion along with the counteracting, attractive force of gravitation. In addition, there’s also dark energy, or the energy intrinsic to space itself, which causes the recession of distant galaxies to accelerate, or speed up, as time goes on. The struggle between gravitational attraction (which pulls distant masses together) and the expansion of the Universe (dominated by dark energy) actually had its end determined some six billion years ago, when dark energy became the dominant factor in our Universe. At that point, any objects that weren’t already gravitationally bound to one another — where gravitation hadn’t overcome the expansion of the Universe — never would become so.

    9
    What we used to identify as superclusters were superseded by even larger structures like Laniakea. But contrary to what we thought, they aren’t structures at all, as they’re gravitationally unbound. Image credit: Richard Powell of http://www.atlasoftheuniverse.com/nearsc.html, under C.C.-by-S.A.-2.5.

    It means that all the identified superclusters are unbound from one another, but even worse, it means that the individual groups and clusters that we know within a supercluster like our own are, for the most part, unbound from one another as well. It means we’ll never merge with the Virgo cluster; it means we’ll never merge with the Leo group, the N96 group, or pretty much anything outside of our local group. It means that except for the few groups or clusters which were already gravitationally bound to one another billions of years ago, no new ones ever will become so. What’s bound today is all that will ever be bound together in the future.

    9
    Galaxy clusters, like Abell 1689, are the largest bound structures in the Universe. Other, larger collections aren’t actual structures, but merely temporary alignments that will disappear over time. Image credit: NASA, ESA, E. Jullo (Jet Propulsion Laboratory), P. Natarajan (Yale University), and J.-P. Kneib (Laboratoire d’Astrophysique de Marseille, CNRS, France).

    Clusters? Yes.

    Groups, galaxies and smaller structures? Absolutely.

    But superclusters? They’re only visual figments of our imagination.

    They’re not real structures. They’re not bound together, and they’ll never become so. The idea of a supercluster and the name for ours, “Laniakea,” will persist for a long time. But just because we named it doesn’t make it real. Billions of years from now, all the different components will simply be strewn farther and farther apart from one another, and in the farthest futures of our imaginings, they’ll disappear from our view and reach entirely. It’s all because of the simple fact that superclusters, despite their names, aren’t structures at all, but merely temporary configurations destined to be torn apart by the expansion of the Universe.

    [HOW DEPRESSING]

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 7:35 am on February 21, 2017 Permalink | Reply
    Tags: , , , , Ethan Siegel, Faintest galaxies ever seen explain the ‘Missing Link’ in the Universe   

    From Ethan Siegel: “Faintest galaxies ever seen explain the ‘Missing Link’ in the Universe” 

    From Ethan Siegel
    2.20.17

    How gravitational magnification allows us to see what we’ve never seen before.

    “The problem is, you’re trying to find these really faint things, but you’re looking behind these really bright things. The brightest galaxies in the universe are in clusters, and those cluster galaxies are blocking the background galaxies we’re trying to observe.” -Rachael Livermore

    To see farther than ever, we point our most powerful space telescopes at a single region and collect light for days.

    1
    One of the most massive, distant galaxy clusters of all, MACS J0717.5+3745, was revealed by the Hubble Frontier Fields program. Image credit: NASA / STScI / Hubble Frontier Fields.

    The Hubble Frontier Fields program focused on massive galaxy clusters, using their gravity to enhance our sight even further.

    2
    Ultra-distant, colliding galaxy clusters have been revealed by the Hubble Frontier Fields program, looking fainter, wider-field and deeper than any other survey before it. Image credit: NASA, ESA, D. Harvey (École Polytechnique Fédérale de Lausanne, Switzerland), R. Massey (Durham University, UK), the Hubble SM4 ERO Team, ST-ECF, ESO, D. Coe (STScI), J. Merten (Heidelberg/Bologna), HST Frontier Fields, Harald Ebeling(University of Hawaii at Manoa), Jean-Paul Kneib (LAM)and Johan Richard (Caltech, USA).

    By warping space, the light from background objects gets magnified, revealing extraordinarily faint galaxies.

    3
    Gravitational lenses, magnifying and distorting a background source, allow us to see fainter, more distant objects than ever before. Image credit: ALMA (ESO/NRAO/NAOJ), L. Calçada (ESO), Y. Hezaveh et al.

    The only problem? The cluster itself is closer and overwhelmingly luminous, making it impossible to tease out the distant signals.

    4
    The overwhelmingly large brightness of the galaxies within a foreground cluster, like Abell S1063, shown here, make it a challenge to use gravitational lensing to identify ultra-faint, ultra-distant background galaxies. Image credit: NASA, ESA, and J. Lotz (STScI).

    Until now. Thanks to a superior new technique devised by Rachael Livermore, light from the foreground cluster galaxies can be modeled and subtracted, revealing faint, distant galaxies never seen before.

    5
    The ultra-distant, lensed galaxy candidate, MACS0647-JD, appears magnified and in three disparate locations thanks to the incredible gravity of the gravitational lens of the foreground cluster, MACS J0647. Image credit: NASA, ESA, M. Postman and D. Coe (STScI), and the CLASH Team.

    With Steven Finkelstein and Jennifer Lotz, Livermore has applied this technique to two Frontier Fields clusters already: Abell 2744 and MACS 0416.

    6
    The galaxy cluster MACS 0416 from the Hubble Frontier Fields, with the mass shown in cyan and the magnification from lensing shown in magenta. Image credit: STScI/NASA/CATS Team/R. Livermore (UT Austin).

    The galaxies that came out were up to 100 times fainter than the dimmest galaxies in the Hubble eXtreme Deep Field, setting a new record.

    7
    The smallest, faintest, most distant galaxies identified in the deepest Hubble image ever taken. This new study has them beat, thanks to stronger gravitational lenses. Image credit: NASA, ESA, R. Bouwens and G. Illingworth (UC, Santa Cruz).

    From when the Universe was less than 10% of its current age, the light from these faint, young galaxies made the Universe transparent.

    8
    The reionization and star-formation history of our Universe, where reionization was driven by these faint, early but theoretically numerous galaxies. At last, thanks to Livermore’s work, we’re discovering them. Image credit: NASA / S.G. Djorgovski & Digital Media Center / Caltech.

    Four more Frontier Fields clusters await, while James Webb, launching next year, will extend this technique even further.

    NASA/ESA/CSA Webb Telescope annotated
    NASA/ESA/CSA Webb Telescope annotated

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 2:48 pm on February 16, 2017 Permalink | Reply
    Tags: , , , , Ethan Siegel, The first galaxies: what we know and what we still need to learn   

    From Ethan Siegel: “The first galaxies: what we know and what we still need to learn” 

    From Ethan Siegel
    2.16.17

    1
    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. Image credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona.

    We haven’t found the truly “first” ones yet, but we’re not just on our way; we’re almost there.

    “For the first time we can learn about individual stars from near the beginning of time. There are surely many more out there.” -Neil Gehrels

    When you think of a galaxy today, you think of something like the Milky Way: hundreds of billions of stars, grand spiral arms, loaded with gas and dust, and ready to form the next generation of stars. Such a behemoth exerts a tremendous gravitational pull acting on everything else nearby. And you will know this galaxy from afar by the starlight streaming out of it, which travels unimpeded through the transparent Universe. But because what we know as our Universe began with the Big Bang some 13.8 billion years ago, we know that galaxies weren’t always this way. In fact, if we look back far enough, we can see the differences start to appear.

    2
    Galaxies similar to the Milky Way as they were at earlier times in the Universe. Image credit: NASA, ESA, P. van Dokkum (Yale University), S. Patel (Leiden University), and the 3D-HST Team.

    Galaxies in the past were different than the galaxies we see today. In detail, the farther back we look in time, we see galaxies that are:

    Younger, as evidenced by an increase in young stars,
    Bluer, since the bluest stars die the fastest,
    Smaller, because galaxies merge together and attract more matter over time, and
    Less spiral-like, because we are only seeing the brightest parts of the most active, star-forming galaxies.

    While the galaxies are intrinsically bluer, if we look at them through our optical telescopes, they actually appear redder, and this is a real effect.

    3
    The smallest, faintest, most distant galaxies appear red. Not because they are red, but because of the expansion of the Universe. Image credit: NASA, ESA, R. Bouwens and G. Illingworth (UC, Santa Cruz).

    Because the Universe is expanding, the light from distant galaxies — though very blue (and even ultraviolet) when created — gets stretched by the fabric of spacetime. As the wavelength of light stretches, it becomes redder, less energetic and more difficult to see. Yet as we build telescopes, particularly in space, capable of seeing into the infrared portion of the spectrum, more information about these galaxies gets revealed. The best data comes from combinations of the Hubble and Spitzer Space Telescopes, and can tell us what happens throughout the Universe’s history.

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    NASA/Spitzer Telescope
    NASA/Spitzer Telescope

    4
    The farthest galaxy known to date, which was confirmed by Hubble, spectroscopically, dating back from when the Universe was only 407 million years old. Image credits: NASA, ESA, and A. Feild (STScI).

    As we look farther back in time, we find that younger galaxies formed stars at faster rates than galaxies do today. We can measure the star-formation rate, and find that at earlier and earlier times, it was more intense. But then we find it hits a peak when the Universe is about two billion years old. Go younger than that, and the rate goes down again.

    5
    An illustration of CR7, the first galaxy detected that’s thought to house Population III stars: the first stars ever formed in the Universe. This is from before peak star formation. Image credit: ESO/M. Kornmesser.

    We know the Universe must have been born with no stars or galaxies, and there must have been a “first star” and a “first galaxy” somewhere back in time. We can’t see it yet; Hubble and Spitzer aren’t powerful enough to do so. But if we look as far back as we can see, here’s what we find, going backwards:

    Earlier than 2 billion years of age, the star formation rate falls at a steady rate.
    Prior to 600 million years (0.6 billion years), the star formation rate fell off even faster; there was a very rapid growth during those critical few hundreds-of-millions of years.

    The youngest galaxy we’ve ever seen so far, Gz-11, comes from when the Universe was 400 million years old. There were stars and galaxies before that.
    And all the way back when the Universe was 380,000 years of age, there were definitely no stars or galaxies, and that was the milestone where stable, neutral atoms formed for the first time.

    6
    A diagram for reionization in the early Universe: when the first stars and galaxies formed. Image credit: NASA / WMAP science team.

    But there’s an interesting conundrum when the Universe is first filled with neutral atoms: those atoms absorb visible light. This means that the Universe wasn’t transparent, like it is today, but is opaque. When the first stars form, we can’t see their starlight the same way we see starlight today. Instead, we need to do two things:

    We need to look for signals of reionization, which is where the ultraviolet radiation from the first stars and galaxies kick electrons off of those atoms, making the Universe transparent to starlight.
    And we need to look in the longer-wavelength portion of the electromagnetic spectrum, as neutral atoms have a harder time absorbing light of longer wavelengths.

    If we can make those observations, we’ll know not only how the first stars and galaxies formed, but how they led the Universe to assemble into the giant galactic structures and superstructures we see today.

    The star formation data we’ve collected very closely mirrors the reionization measurements we’ve made, which is remarkable. Reionization appears to start when the Universe is about 400–450 million years old, has a big acceleration when the Universe is about 600–650 million years old and is complete by time the Universe is about 900–950 million years old. The intergalactic medium behaves consistently with what we see for galaxies.

    8
    This deep-field region of the GOODS-South field contains 18 galaxies forming stars so quickly that the number of stars inside will double in just 10 million years: just 0.1% the lifetime of the Universe. Image credit: NASA, ESA, A. van der Wel (Max Planck Institute for Astronomy), H. Ferguson and A. Koekemoer (Space Telescope Science Institute), and the CANDELS team.

    The biggest lesson from all of it is that the galaxies — and in particular the newly star-forming galaxies — are the components of the Universe responsible for reionization. There will be two incredible advances over the next decade that will enable us to understand these earliest stages of starlight in the Universe once and for all: the James Webb Space Telescope and WFIRST.

    9
    The sizes of Hubble and James Webb’s mirrors, along with James Webb’s sensitivities (inset) versus other great observatories. Image credit: NASA / JWST team, via http://jwst.nasa.gov/comparison.html (main); NASA / JWST science team (inset).

    By looking farther and deeper in the infrared than any telescope before it, James Webb will be able to see galaxies back to when the Universe was only 250 million years old. This will likely include the first direct observations of pristine stars and tiny galaxies, collections which may be no more than a few star-forming regions merging together. It should be able to prove that it’s galaxies, not isolated star formation, are responsible for reionizing the Universe.

    10
    A conceptual image of NASA’s WFIRST satellite, set to launch in 2024 and give us our most precise measurements ever of dark energy, among other incredible cosmic finds. Image credit: NASA/GSFC/Conceptual Image Lab.

    But if the first galaxies form even earlier than that, James Webb will run into limitations, and all we’ll be able to do is make inferences for the truly first sources of stellar light. Another huge advance will come from WFIRST, NASA’s true successor to Hubble, launching in 2024. WFIRST will have the same capability of seeing deep into the visible and near-infrared portion of the spectrum, but with one hundred times the field-of-view of Hubble. With WFIRST, we should be able to measure star formation and reionization over the entire Universe. At last’ we’re finally learning how the Universe went from no stars or galaxies to the very first ones and evolved into the rich, beautiful but ultra-distant Universe we inhabit today!

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 7:42 pm on February 11, 2017 Permalink | Reply
    Tags: , , , , Ethan Siegel, Is There A Center Of The Universe   

    From Ethan Siegel: “Is There A Center Of The Universe” 

    From Ethan Siegel
    Feb 11, 2017

    1
    The Universe looks roughly the same in all directions, but distant galaxies appear younger and less evolved than nearer ones. Image credit: NASA, ESA, R. Windhorst, S. Cohen, M. Mechtley, and M. Rutkowski (Arizona State University, Tempe), R. O’Connell (University of Virginia), P. McCarthy (Carnegie Observatories), N. Hathi (University of California, Riverside), R. Ryan (University of California, Davis), H. Yan (Ohio State University), and A. Koekemoer (Space Telescope Science Institute).

    Our Universe began from a Big Bang, but that doesn’t mean we picture it correctly. Most of us think of it as an explosion: where everything started out hot and dense all at once, then expanded and cooled as the different fragments sped away from one another. But as tempting as that picture is, it isn’t correct at all. This led Jasper Evers to ask a very good question:

    I am wondering how there isn’t a centre of the universe and how the cosmic background radiation is [equally] far away everywhere we look. It seems to me that when the universe expands … there should be a place where it started expanding.

    Let’s think about the physics of an explosion for a moment, and what our Universe would be like if it began from one.

    2
    The first stages of the explosion of the Trinity nuclear test, just 16 milliseconds after detonation. The top of the fireball is 200 meters high. Image credit: Berlyn Brixner, from July 16, 1945.

    An explosion begins at a point, and expands outwards rapidly. The fastest-moving material moves outwards the most rapidly, and hence spreads out the fastest. The farther away you are from the center of the explosion, the less material will reach you. The energy density goes down as time goes on everywhere, but it goes down faster farther away from the explosion, because the energetic material is more sparse at the outskirts. No matter where you are, you’ll always be able — assuming you’re not destroyed — to reconstruct the center of the explosion.

    3
    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. https://www.pinterest.com/CosmosUp/galaxies/

    But this isn’t the Universe we see. The Universe looks the same at large and short distances: the same densities, the same energies, the same galaxy counts, etc. The objects far away, moving away from us at greater speeds, don’t appear to be the same age as the objects closer to us which move at slower speeds; they appear younger. There aren’t fewer objects at great distances, but more of them. And if we take a look at how everything is moving in the Universe, we find that despite the fact that we can see out for tens of billions of light years, the reconstructed center lands right on us.

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

    Does that mean we, out of all the trillions of galaxies in the Universe, happened to be at the center of the Big Bang? And that the initial ‘bang’ was configured in just such a way — with irregular, inhomogeneous densities, energies, ‘start times’ and a mysterious 2.7 K glow — to conspire so that we’re at the center? What an ungenerous Universe it would be if that were the case: to configure itself in this incredibly unrealistic way at the start.

    5
    An explosion in space would have the outermost material move away the fastest, which means it would get less dense, would lose energy the fastest, and would display different properties the farther away you went from the center. It would also need to expand into something, rather than stretching space itself. Our Universe doesn’t support this. Image credit: ESO.

    Instead, what General Relativity predicts is not an explosion, but an expansion. A Universe that begins from a hot, dense state has its very fabric expand. There’s a misconception that this would have started from a single point; it isn’t so! Instead, there’s a region that has these properties — filled with matter, energy, etc. — and then the Universe evolves under the laws of gravity.

    It has similar properties everywhere, including density, temperature, number of galaxies, etc. If we were to look out, though, what we’d see would be evidence of an evolving Universe. Because the Big Bang happened everywhere at once a finite amount of time ago in a region of space, and that region is all that’s observable to us, when we look out from our vantage point, we’re seeing a region of space that’s not so different from our own position in the past.

    7
    Looking back to great cosmic distances is akin to looking back in time. We are 13.8 billion years since the Big Bang where we are, but the Big Bang also occurred everywhere else we can see. The light-travel-time to those galaxies means we’re seeing those distant regions as they were in the past. Image credit: NASA, ESA, and A. Feild (STScI), via http://www.spacetelescope.org/images/heic0805c/.

    Galaxies whose light took a billion years to get here appear as they were a billion years ago; galaxies whose light took ten billion years to get here appear as they were ten billion years ago! 13.8 billion years ago, the Universe was dominated by radiation, not matter, and when the Universe first formed neutral atoms, that radiation still persists, having been cooled and redshifted due to the expanding Universe. What we perceive as the Cosmic Microwave Background is not only the leftover glow from the Big Bang, but this radiation is observable from any location in the Universe.

    8
    Only a few hundred µK — a few parts in 100,000 — separate the hottest regions from the coldest when we look back at the Cosmic Microwave Background. Image credit: ESA and the Planck Collaboration, via http://crd-legacy.lbl.gov/~borrill/cmb/planck/217poster.html.

    There isn’t necessarily a center to the Universe; what we call a “region” of space where the Big Bang occurred could be infinite. If there is a center, it could literally be anywhere and we wouldn’t know; the part of the Universe we can observe is insufficient to reveal that information. We’d need to see an edge, a fundamental anisotropy (where different directions appear different) in temperatures and galaxy counts, and our Universe, on the largest scales, really does look the same everywhere and in all directions.

    9
    Artist’s logarithmic scale conception of the observable universe. Image credit: Wikipedia user Pablo Carlos Budassi.

    There isn’t a place where the Universe started expanding because of the Big Bang; there’s a time when the Universe began expanding. That’s what the Big Bang is: a condition affecting the entire observable Universe at a specific moment. It’s why looking to greater distances in all directions means looking back in time. It’s why all directions appear to have roughly uniform properties. And it’s why our story of cosmic evolution can be traced back as far as our observatories can see.

    10
    Galaxies similar to the Milky Way as they were at earlier times — and greater distances — in the Universe. Image credit: NASA, ESA, P. van Dokkum (Yale University), S. Patel (Leiden University), and the 3D-HST Team.

    Perhaps the Universe has a finite shape and a finite size, but if it does, that information is inaccessible to us. The portion of the Universe observable to us is finite, and that information isn’t contained within it. If you think of the Universe as a balloon, a loaf of bread or any other analogy you like, remember that you’re only able to access a tiny part of the actual Universe; what’s observable to us is only a lower limit on what’s out there. It could be finite, it could be infinite, but what we’re sure of is that it’s expanding, it’s getting less dense, and the farther away we look, the farther back in time we’re able to see. As astrophysicist Katie Mack says:

    “The Universe is expanding the way your mind is expanding. It’s not expanding into anything; you’re just getting less dense.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 3:06 pm on February 1, 2017 Permalink | Reply
    Tags: , , , , Ethan Siegel, UH Pan-STARRS   

    From Ethan Siegel: “Pan-STARRS Solves The Biggest Problem Facing Every Astronomer” 

    Ethan Siegel
    Feb 1, 2017

    1
    A small selection of the galaxy as seen by UH Pan-STARRS provides the most comprehensive 3D data ever taken. Image credit: Danny Farrow, UH Pan-STARRS1 Science Consortium and Max Planck Institute for Extraterrestial Physics.

    When you look out at any object in the Universe, the easiest thing to measure is how bright it is. But what you’re seeing might not accurately measure what the object is actually doing. Gas, dust, and the atmosphere all contribute to blocking some of the light, preventing it from reaching your eyes. As atmospheric conditions change over time, what you see might change as well. Observations you make in the bluer part of the spectrum might be affected differently than observations in the redder part, as dust grains of different sizes have different sensitivities to a variety of wavelengths. If you’re looking at something hundreds, thousands or millions of light years away, you’ll need an entirely different calibration, all dependent on what’s between you and the object you’re trying to observe. It’s astronomy’s hardest problem: understanding how light is affected from when its emitted until it reaches your eye.

    2
    UH Pan-STARRS1 Observatory atop Haleakala Maui at sunset. Image credit: Rob Ratkowski.

    The UH Pan-STARRS1 observatory, after three years of observing all of the sky it’s capable of seeing from its perch in Hawaii, has just made public the results from the largest digital sky survey in history. UH Pan-STARRS sports the world’s largest camera, taking a 1.4 gigapixel image every 45 seconds. In a single night, it collects almost a Terabyte of astronomical data; over three years of observations, that adds up to almost two Petabytes: two quadrillion bytes of data. Every region of the sky accessible to it — spanning 75% of the entire Universe — has been imaged at least 60 times total: 12 times apiece in each of five different wavelength bands. The data is publicly available today, but what it means for science is unprecedented.


    Access mp4 video here .

    Every time a professional astronomer makes an observation, they have to calibrate their data. They need to know what they’re looking at in some standardized way. According to Ken Chambers, the director of UH Pan-STARRS observatory, every ground-based observatory will use these images and catalogues for their day-to-day observations. The previous large survey used for calibrations — the Digitized Sky Survey 2 — was good to about 13 milli-magnitudes, or an absolute brightness of about 1.2%. Thanks to UH Pan-STARRS, that’s been lowered to only 3 or 4 milli-magnitudes, or an absolute brightness of around 0.3%. Unlike previous surveys that surveyed the sky once or twice, UH Pan-STARRS surveyed it over and over again, enabling this unprecedented catalogue.

    4
    The near-Earth objects discovered on a year-by-year basis. Since UH Pan-STARRS began operations, it’s discovered about a third of the total NEO population known to humanity. Image credit: NASA / JPL, via http://neo.jpl.nasa.gov/stats/.

    The science that came out of it alone is staggering. Nobody has had as much astronomical data in all of history as what UH Pan-STARRS has produced. They’ve discovered about 3,000 new near-Earth objects; tens of thousands of asteroids in the main belt, approximately 300 Kuiper belt objects (about a third of all the Kuiper belt objects ever discovered), and imaged a total of more than three billion verified objects. For those of you wondering, there’s no evidence for or against Planet Nine in the data, but the UH Pan-STARRS data does support that our Solar System ejected a fifth gas giant in its distant past.

    Because the vast majority of these objects are stars within our own galaxy, and they’ve imaged them at different wavelengths so many time, they’ve been able to create the first 3D map of dust spanning the entire Milky Way. They’ve catalogued and categorized more stars than ever before, more deep-sky objects than ever before, and have given us a better understanding of what’s present in our galactic plane than we’ve ever known previously.

    5
    The Milky way’s central region in visible light, with the location of the galactic center marked by E. Siegel. Billions of stars can be found there, and UH Pan-STARRS has collected data on more of them than ever before. Image credit: Jaime Fernández, via http://www.castillosdesoria.com/astropics/imagen.asp?id=1&seccion=1&id_prod=246.

    Stars can be classified by their color and magnitude to a better accuracy than ever before thanks to UH Pan-STARRS. From that, we can learn what type of star they are, where they are in their evolutionary sequence and what’s a dwarf, giant, or other exotic type of star. We’ve also learned their distances and how much dust (and of what type) is present in the space between us and each star observed. All of the calibrated data is now freely available, and it empowers every astronomer to have a better starting point for every observation they make than was ever possible before. The European Space Agency’s GAIA mission — in space — will only be about half as good as UH Pan-STARRS at this.

    6
    Observatories like Hubble and SDSS will have better calibration information thanks to UH Pan-STARRS even for observations of distant galaxies and quasars. Image credit: ESA, NASA, K. Sharon (Tel Aviv University) and E. Ofek (Caltech).

    Although the greatest leap forward will be for measurements within our own galaxy, the most distant observations go all the way out to galaxies and quasars at a redshift of z ~ 7, at a time when the Universe was only 6% of its current age. From new transients like asteroids and comets to ultra-distant supernovae, the UH Pan-STARRS database will be the new gold standard for identifying previously unseen objects in the Universe. Every observation, moving forward, has a new gold standard of calibrations to rely on. Every observatory will do their observatory work better, making UH Pan-STARRS the unsung hero of all astronomical observations to come. And because the data is publicly available, there’s a treasure trove of new discoveries just waiting to be found. It won’t be superseded until the 2030s, when the LSST has been operational for a decade. It isn’t even scheduled to come online until 2022.

    LSST
    LSST/Camera, built at SLAC
    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.
    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    8
    This compressed view of the entire sky visible from Hawai’i by the UH Pan-STARRS1 Observatory is the result of half a million exposures, each about 45 seconds in length. Image credit: Danny Farrow, UH Pan-STARRS1 Science Consortium and Max Planck Institute for Extraterrestrial Physics.

    If you were to print out the UH Pan-STARRS map of the Universe that it sees at full resolution, it would stretch for more than two kilometers in length. But it’s more than just a pretty picture. The data is something that every astronomer in the world should be using — and the UH Pan-STARRS collaboration is one they should be thanking (and citing) — every time they look at the sky.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 12:35 pm on January 29, 2017 Permalink | Reply
    Tags: Einstein's theory of general relativity and the Metric Sensor or Reiman Metric, Einstein's theory of special relativity, Ethan Siegel, Minkowski space, Minowski developed the formalism of spacetime, Quanta, What Is Spacetime?   

    From Ethan Siegel: “What Is Spacetime?” 

    Ethan Siegel
    Jan 28, 2017

    1
    The fabric of the Universe, spacetime, is a tricky concept to understand. But we’re up to the challenge. Image credit: Pixabay user JohnsonMartin.

    When it comes to understanding the Universe, there are a few things everyone’s heard of: Schrödinger’s cat, the Twin Paradox and E = mc^2. But despite being around for over 100 years now, General Relativity — Einstein’s greatest achievement — is largely mysterious to everyone from the general public to undergraduate and graduate students in physics. For this week’s Ask Ethan, Katia Moskovitch wants that cleared up:

    Could you one day write a story explaining to a lay person what the metric is in GR?

    Before we get to “the metric,” let’s start at the beginning, and talk about how we conceptualize the Universe in the first place.

    2
    Quanta, whether waves, particles or anything in between, have properties that define what they are. But they require a stage on which to interact and play out the Universe’s story. Image credit: Wikimedia Commons user Maschen.

    At a fundamental level, the Universe is made up of quanta — entities with physical properties like mass, charge, momentum, etc. — that can interact with each other. A quantum can be a particle, a wave, or anything in some weird in-between state, depending on how you look at it. Two or more quanta can bind together, building up complex structures like protons, atoms, molecules or human beings, and all of that is fine. Quantum physics might be relatively new, having been founded in mostly the 20th century, but the idea that the Universe was made of indivisible entities that interacted with each other goes back more than 2000 years, to at least Democritus of Abdera.

    But no matter what the Universe is made of, the things it’s composed of need a stage to move on if they’re going to interact.

    3
    Newton’s law of Universal Gravitation has been superseded by Einstein’s general relativity, but relied on the concept of an instantaneous action (force) at a distance. Image credit: Wikimedia commons user Dennis Nilsson.

    In Newton’s Universe, that stage was flat, empty, absolute space. Space itself was a fixed entity, sort of like a Cartesian grid: a 3D structure with an x, y and z axis. Time always passed at the same rate, and was absolute as well. To any observer, particle, wave or quantum anywhere, they should experience space and time exactly the same as one another. But by the end of the 19th century, it was clear that Newton’s conception was flawed. Particles that moved close to the speed of light experienced time differently (it dilates) and space differently (it contracts) compared to a particle that was either slow-moving or at rest. A particle’s energy or momentum was suddenly frame-dependent, meaning that space and time weren’t absolute quantities; the way you experienced the Universe was dependent on your motion through it.

    4
    A “light clock” will appear to run different for observers moving at different relative speeds, but this is due to the constancy of the speed of light. Einstein’s law of special relativity governs how these time and distance transformations take place. Image credit: John D. Norton, via http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/Special_relativity_clocks_rods/.

    That was where the notion of Einstein’s theory of special relativity came from: some things were invariant, like a particle’s rest mass or the speed of light, but others transformed depending on how you moved through space and time. In 1907, Einstein’s former professor, Hermann Minkowski, made a brilliant breakthrough: he showed that you could conceive of space and time in a single formulation. In one fell swoop, he had developed the formalism of spacetime. This provided a stage for particles to move through the Universe (relative to one another) and interact with one another, but it didn’t include gravity. The spacetime he had developed — still today known as Minkowski space — describes all of special relativity, and also provides the backdrop for the vast majority of the quantum field theory calculations we do.

    5
    Quantum field theory calculations are normally done in flat space, but general relativity goes beyond that to include curved space. QFT calculations are far more complex there. Image credit: SLAC National Accelerator Laboratory.

    If there were no such thing as the gravitational force, Minkowski spacetime would do everything we needed. Spacetime would be simple, uncurved, and would simply provide a stage for matter to move through and interact. The only way you’d ever accelerate would be through an interaction with another particle. But in our Universe, we do have the gravitational force, and it was Einstein’s principle of equivalence that told us that so long as you can’t see what’s accelerating you, gravitation treats you the same as any other acceleration.

    6
    The identical behavior of a ball falling to the floor in an accelerated rocket (left) and on Earth (right) is a demonstration of Einstein’s equivalence principle. Image credit: Wikimedia Commons user Markus Poessel, retouched by Pbroks13.

    It was this revelation, and the development to link this, mathematically, to the Minkowski-an concept of spacetime, that led to general relativity. The major difference between special relativity’s Minkowski space and the curved space that appears in general relativity is the mathematical formalism known as the Metric Tensor, sometimes called Einstein’s Metric Tensor or the Riemann Metric. Riemann was a pure mathematician in the 19th century (and a former student of Gauss, perhaps the greatest mathematician of them all), and he gave a formalism for how any fields, lines, arcs, distances, etc., can exist and be well-defined in an arbitrarily curved space of any number of dimensions. It took Einstein (and a number of collaborators) nearly a decade to cope with the complexities of the math, but all was said and done, we had general relativity: a theory that described our three-space-and-one-time dimensional Universe, where gravitation existed.

    7
    The warping of spacetime by gravitational masses, as illustrated to represent General Relativity. Image credit: LIGO/T. Pyle.

    Conceptually, the metric tensor defines how spacetime itself is curved. Its curvature is dependent on the matter, energy and stresses present within it; the contents of your Universe define its spacetime curvature. By the same token, how your Universe is curved tells you how the matter and energy is going to move through it. We like to think that an object in motion will continue in motion: Newton’s first law. We conceptualize that as a straight line, but what curved space tells us is that instead an object in motion continuing in motion follows a geodesic, which is a particularly-curved line that corresponds to unaccelerated motion. Ironically, it’s a geodesic, not necessarily a straight line, that is the shortest distance between two points. This shows up even on cosmic scales, where the curved spacetime due to the presence of extraordinary masses can curve the background light from behind it, sometimes into multiple images.

    8
    An example/illustration of gravitational lensing, and the bending of starlight due to mass. Image credit: NASA / STScI, via http://hubblesite.org/newscenter/archive/releases/2000/07/image/c/.

    Physically, there are a number of different pieces that contribute to the Metric Tensor in general relativity. We think of gravity as due to masses: the locations and magnitudes of different masses determine the gravitational force. In general relativity, this corresponds to the mass density and does contribute, but it’s one of only 16 components of the Metric Tensor! There are also pressure components (such as radiation pressure, vacuum pressure or pressures created by fast-moving particles) that contribute, which are three additional contributors (one for each of the three spatial directions) to the Metric Tensor. And finally, there are six other components that tell us how volumes change and deform in the presence of masses and tidal forces, along with how the shape of a moving body is distorted by those forces. This applies to everything from a planet like Earth to a neutron star to a massless wave moving through space: gravitational radiation.

    9
    As masses move through spacetime relative to one another, they cause the emission of gravitational waves: ripples through the fabric of space itself. These ripples are mathematically encoded in the Metric Tensor. Image credit: ESO/L. Calçada.

    You might have noticed that 1 + 3 + 6 ≠ 16, but 10, and if you did, good eye! The Metric Tensor may be a 4 × 4 entity, but it’s symmetric, meaning that there are four “diagonal” components (the density and the pressure components), and six off-diagonal components (the volume/deformation components) that are independent; the other six off-diagonal components are then uniquely determined by symmetry. The metric tells us the relationship between all the matter/energy in the Universe and the curvature of spacetime itself. In fact, the unique power of general relativity tells us that if you knew where all the matter/energy in the Universe was and what it was doing at any instant, you could determine the entire evolutionary history of the Universe — past, present and future — for all eternity.

    10
    The four possible fates of the Universe, with the bottom example fitting the data best: a Universe with dark energy. Image credit: E. Siegel.

    This is how my sub-field of theoretical physics, cosmology, got its start! The discovery of the expanding Universe, its emergence from the Big Bang and the dark energy-domination that will lead to a cold, empty fate are all only understandable in the context of general relativity, and that means understanding this key relationship: between matter/energy and spacetime. The Universe is a play, unfolding every time a particle interacts with another, and spacetime is the stage on which it all takes place. The one key counterintuitive thing you’ve got to keep in mind? The stage isn’t a constant backdrop for everyone, but it, too, evolves along with the Universe itself.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 12:11 pm on January 25, 2017 Permalink | Reply
    Tags: , , , , Ethan Siegel, , World's Largest Telescope Will Revolutionize The Future Of Astronomy   

    From Ethan Siegel: “World’s Largest Telescope Will Revolutionize The Future Of Astronomy” – the GMT 

    Ethan Siegel
    Jan 25, 2017

    1
    The Giant Magellan Telescope, Las Campanas Observatory, to be built some 115 km (71 mi) north-northeast of La Serena, Chile ,as it will appear upon completion. Image credit: Giant Magellan Telescope / GMTO Corporation.

    Want to see deeper into the Universe than ever before. Build a bigger telescope. No matter what other tricks you use, there’s no substitute for size. The bigger your primary mirror is:

    1. the more light you gather,
    2. the better your resolution is,
    3. and more details can be seen, more distant and faster than under any other circumstances.

    The problem is, there’s a size limit to how big you can build a single mirror and still have it be shaped correctly. Until we start manufacturing mirrors in zero-gravity, we’ve had two options: cast a single mirror up to the maximum size you can manufacture it — around 8 meters — or build a large number of smaller segments and stitch them together.

    2
    The interior and the primary mirror of the GTC, the largest single optical telescope in the world today. Image credit: Miguel Briganti (SMM/IAC).

    The current record-holder takes the latter approach, and is the Gran Telescopio Canarias in Spain, made of 36 hexagonal segments that total a diameter of 10.4 meters. As of 2015, it’s the world’s largest optical telescope, but it won’t remain that way for long. In the Chilean Andes, another project that’s been in the works since 2003 is poised to break every optical telescope records: the Giant Magellan Telescope (GMT). By fusing both approaches — building seven of the largest, single-cast optical mirrors we can manufacture on Earth and stitching them together on a single, giant mount — it’s prepared to come in at a whopping 25 meters in diameter.

    3
    A side-view of the completed GMT as it will look in the telescope enclosure. The laser guide system will be online whenever so chosen, illuminating the sodium layer 60 km up in the atmosphere. Image credit: Giant Magellan Telescope – GMTO Corporation.

    The GMT will be the largest optical telescope ever designed and built, and construction has not only already begun, it’s expected to see first light in 2023 and to reach completion in 2025. It will gather more than 100 times the light of the space-based Hubble, and more than five times as much as any currently existing ground-based telescopes. While many plans for the next generation of ground-based telescopes existed, the three other famous ones — the Thirty Meter Telescope (TMT), the European Extremely Large Telescope (EELT) and Overwhelmingly Large Telescope (OWL) — have either suffered major setbacks or been cancelled entirely. But not only is GMT coming in on schedule, it’s already overcome its biggest scientific challenges.

    TMT-Thirty Meter Telescope, proposed for Mauna Kea, Hawaii, USA
    TMT-Thirty Meter Telescope, proposed for Mauna Kea, Hawaii, USA

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile
    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile

    3
    OWL – a future milestone for Astronomy? A 100-M CLASS OPTICAL AND NEAR-INFRARED TELESCOPE [cancelled?]

    4
    A comparison of the mirror sizes of various existing and proposed telescopes. When GMT comes online, it will be the world’s largest, and will be the first 25 meter+ class optical telescope in history. Image credit: Wikimedia Commons user Cmglee, under c.c.a.-s.a.-3.0.

    The first big challenge was the mirrors themselves. Go larger than about 8 meters, and the mirrors themselves will deform at those necessary weights. Add a large number of segments, and you start producing large numbers of image artifacts: wherever sharp lines meet, you have a difficult-to-remove bit of noise added to each image. By designing their telescope to have just 7 large, nearly-spherical mirrors on a single mount, GMT avoided most of these problems. However, it introduced a new challenge: the first manufacture of an off-axis, asymmetrical section of an ellipsoid that needed to be differentially polished. The central mirror (of the 7) can be a nice, symmetric shape, but each of the six off-axis ones required a revolution in mirror technology. But the University of Arizona’s mirror lab has succeeded at this task, polishing their mirror to better than 20 nanometers in smoothness.

    4
    The third GMT mirror on the Large Polishing Machine (LPM), shown during the fine grinding phase on the rear surface. Image credit: Richard F. Caris Mirror Lab, University of Arizona.

    There will be a technical challenge in stitching together mirrors this large, both in terms of focal length (less than a millimeter of accuracy over all 25 meters) and in terms of alignment. Fortunately, once you calibrate and align the mirrors once, using interferometry, it’s good to go for the rest of your observing run. This was demonstrated as a proof-of-concept by the Large Binocular Telescope, which used this technique to observe one of Jupiter’s moons, Europa, occulting another one, Io.

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

    You can even watch the volcanoes on Io — visible in the infrared — erupting in the process!

    5
    The occultation of Jupiter’s moon, Io, with its erupting volcanoes Loki and Pele, as occulted by Europa, which is invisible in this infrared image. GMT will provide significantly enhanced resolution and imaging. Image credit: LBTO.

    One remarkable facet of this telescope will be the adaptive optics. The Earth’s atmosphere tends to get in the way of viewing any space-based targets from the ground, which is why you build your observatories at high altitudes where the air is still. But even with that, there’s still deformation. While having a guide star is helpful, the key to adaptive optics is to have a secondary mirror that deforms in real-time to turn that distorted light back into the known configuration it must be in. So far, we’ve only ever successfully done that for a single mirror.


    Access mp4 video here.

    GMT is so large that we’d actually get substantial differences from how the atmosphere affects the light impinging on the mirrors on opposite sides of the telescope. But adaptive optics systems have been used with tremendous success for 8 meter telescopes previously, so what they’re doing is nothing short of genius: building seven separate adaptive optics systems and synchronizing them all together!

    6
    The adaptive optics systems — on the attached secondary mirrors (top) — will enable the reconstruction of an unprecedentedly accurate image. Image credit: Giant Magellan Telescope – GMTO Corporation.

    You wind up with a single, clean image that’s atmospherically corrected, that doesn’t have the image artifacts of other segmented mirrors, and that can get resolutions of between 6-10 milli-arc-seconds, depending on what wavelength you look at. Remember, an arc second is 1/3600th of a degree, and the full Moon is about half a degree wide on a side. This is 10 times the resolution of Hubble, and it will see first light just six years from now. The science we’re going to learn is incredible.

    7
    A selection of some of the most distant galaxies in the observable Universe, from the Hubble Ultra Deep Field. GMT will be capable of imaging all of these galaxies with ten times the resolution of Hubble. Image credit: NASA, ESA, and N. Pirzkal (European Space Agency/STScI).

    Distant galaxies will be imaged out to ten billion light years. We’ll be able to measure their rotation curves, look for signatures of mergers, measure galactic outflows, look for star formation regions and ionization signatures.

    8
    An artist’s rendition of Proxima b orbiting Proxima Centauri. With GMT, we’ll be able to directly image it, as well as any outer, yet-undetected worlds. Image credit: ESO/M. Kornmesser.

    We’ll be able to directly image Earth-like exoplanets, including Proxima b, out to somewhere between 15-30 light years distant. Jupiter-like planets will be visible out to more like 300 light years.

    9
    Because of its equipped spectrograph, GMT will be able to measure interstellar and intergalactic gas clouds to greater sensitivity than ever before. Image credit: Ed Janssen, ESO.

    We’ll be able to directly image the closest spatial objects at highest resolutions. This includes individual stars in crowded clusters and environments, the substructure of nearby galaxies, as well as close-in binary, trinary and multi-star systems. This largest-ever telescope will be equipped with a state-of-the-art spectrograph, and will do wider-field imaging than Hubble or even James Webb will be capable of. In addition to luminous objects, we’ll be able to measure molecular clouds, interstellar matter, intergalactic plasma, as well as the most pristine, metal-poor stars in the galaxy. And as far as speed goes, it will be tremendous: all the light that Hubble can gather, GMT can gather, only 100 times faster.

    10
    The core of the globular cluster Omega Centauri is one of the most crowded regions of old stars. GMT will be able to resolve more of them than ever before. Image credit: NASA/ESA and The Hubble Heritage Team (STScI/AURA), via http://www.spacetelescope.org/images/opo0133a/.

    But that’s only what we know we’re going to see. Perhaps most exciting will be the advances that we don’t know are coming. No one could’ve predicted that Edwin Hubble would discover the expanding Universe when the 100-inch Hooker telescope was first commissioned; no one could’ve predicted how the Hubble Deep Field would open up the Universe when that image was first taken; no one could’ve predicted that measuring distant supernovae would lead to the discovery of dark energy. What will GMT find when it starts viewing the Universe? The future of any scientific endeavor — and perhaps astronomy in particular — requires you to be ambitious, and to invest in looking for the unknown. Thanks to the Giant Magellan Telescope, we’re on track to see the Universe in ways and in locations where no one has gone before.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 2:34 pm on January 16, 2017 Permalink | Reply
    Tags: , , , brightest galaxies shine a ghostly green in surprising new find, , Earliest, Ethan Siegel   

    From Ethan Siegel: “Earliest, brightest galaxies shine a ghostly green in surprising new find” 

    From Ethan Siegel
    1.16.17

    Only a few galaxies exhibit this green glow in the nearby Universe. At early times, it’s practically all of the brightest ones.

    1
    Some rare galaxies exhibit a green glow thanks to the presence of doubly ionized oxygen. This requires UV light from stellar temperatures of 50,000 K and above. Image credit: NASA, ESA, and W. Keel (University of Alabama, Tuscaloosa), of NGC 5972.

    “The discovery that young galaxies are so unexpectedly bright–if you look for this distinctive green light–will dramatically change and improve the way that we study Galaxy formation throughout the history of the Universe.”
    -Matthew Malkan

    Here in the nearby Universe, 13.8 billion years since the Big Bang, galaxies come in great varieties.

    2
    A great variety of galaxies in color, morphology, age and inherent stellar populations can be seen in this deep-field image. Image credit: NASA, ESA, R. Windhorst, S. Cohen, M. Mechtley, and M. Rutkowski (Arizona State University, Tempe), R. O’Connell (University of Virginia), P. McCarthy (Carnegie Observatories), N. Hathi (University of California, Riverside), R. Ryan (University of California, Davis), H. Yan (Ohio State University), and A. Koekemoer (Space Telescope Science Institute).

    Spirals, ellipticals, rings and irregulars, they glow blue, white or red, depending on their stellar populations.

    3
    Galaxies undergoing massive bursts of star formation expel large quantities of matter at great speeds. They also glow red covering the whole galaxy, thanks to hydrogen emissions. Image credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA), of the Cigar Galaxy, Messier 82.

    The most violent star-forming galaxies and nebulae are so hot they turn red, as ultraviolet radiation ionizes neutral hydrogen.

    4
    The great Orion Nebula is a fantastic example of an emission nebula, as evidenced by its red hues and its characteristic emission at 656.3 nanometers. Image credit: NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team.

    5
    This image from ESO’s Very Large Telescope shows the glowing green planetary nebula IC 1295 surrounding a dim and dying star located about 3300 light-years away. Image credit: ESO / FORS instrument.

    But there’s another, green line that happens only when oxygen gets doubly ionized at the hottest temperatures of all: 50,000 K and above.

    6
    Modern ‘green pea’ galaxies have their doubly-ionized oxygen emission offset from the main galaxy; in the Subaru Deep Field, the galaxies themselves exhibit the strong emission. Image credit: NASA, ESA, and Z. Levay (STScI), with science by NASA, ESA, and W. Keel (University of Alabama, Tuscaloosa).

    Only planetary nebulae, with super-hot young white dwarfs, and the ultra-rare “green pea” galaxies exhibit these features.

    7
    The Subaru Deep Field, containing thousands of distant galaxies exhibiting these oxygen lines. Image credit: Subaru telescope, National Astronomical Observatory of Japan (NAOJ); Image processing: R. Jay GaBany.

    But by looking at the most active star-forming galaxies in the Subaru Deep Field (above), Matthew Malkan and Daniel Cohen found, that all galaxies from 11 billion years ago or more emit this green signature.

    8
    The strong green emission line (highest point) as shown in a sample of over 1,000 galaxies, spectrally stacked from the Subaru Deep Field. The other point “above” the curves is from hydrogen; the strong green oxygen line indicates incredibly intense radiation. Image credit: Malkan and Cohen (2017).

    The unexpected brightness and hotness of these galaxies hints that the stars in the ultra-distant Universe are somehow hotter than the hottest stars today.

    9
    The merging star clusters at the heart of the Tarantula Nebula, which contains the hottest stars in the local group, are still below 50,000 K. Perhaps lower metallicities, higher masses, or even a top-heavy initial mass function among stars in the early Universe are responsible for the increased, high temperatures. Image credit: NASA, ESA, and E. Sabbi (ESA/STScI); Acknowledgment: R. O’Connell (University of Virginia) and the Wide Field Camera 3 Science Oversight Committee.

    10
    The reionization and star-formation history of our Universe. The study hints that green, oxygen-rich galaxies may have been responsible for reionization. Image credit: NASA / S.G. Djorgovski & Digital Media Center / Caltech.

    JWST, launching 2018, will find out for sure.

    NASA/ESA/CSA Webb Telescope annotated
    NASA/ESA/CSA Webb Telescope annotated

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
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