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  • richardmitnick 7:52 pm on July 13, 2015 Permalink | Reply
    Tags: , , Cosmic microwave background,   

    From U Hawaii IFA: “A Cold Cosmic Mystery Solved: “ 

    U Hawaii

    University of Hawaii

    Institute for Astronomy

    U Hawaii Institute for Astonomy Mauna Kea
    IFA at Manua Kea

    April 20, 2015
    Contacts:

    Dr. István Szapudi
    +1 808 956-6196
    szapudi@ifa.hawaii.edu

    Dr. András Kovács
    +34 93 176 3966
    akovacs@ifae.es

    Dr. Roy Gal
    +1 808-956-6235
    cell: +1 301-728-8637
    rgal@ifa.hawaii.edu

    Ms. Louise Good
    Media Contact
    +1 808-381-2939

    Astronomers discover what might be the largest known structure in the universe that leaves its imprint on cosmic microwave background radiation.
    Synopsis: A very large cold spot that has been a mystery for over a decade can now be explained.

    In 2004, astronomers examining a map of the radiation leftover from the Big Bang (the cosmic microwave background, or CMB) discovered the Cold Spot, a larger-than-expected unusually cold area of the sky.

    Cosmic Background Radiation Planck
    CMB per ESA/Planck

    The physics surrounding the Big Bang theory predicts warmer and cooler spots of various sizes in the infant universe, but a spot this large and this cold was unexpected.

    Now, a team of astronomers led by Dr. István Szapudi of the Institute for Astronomy at the University of Hawaii at Manoa may have found an explanation for the existence of the Cold Spot, which Szapudi says may be “the largest individual structure ever identified by humanity.”

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    The Cold Spot area resides in the constellation Eridanus in the southern galactic hemisphere. The insets show the environment of this anomalous patch of the sky as mapped by Szapudi’s team using PS1 and WISE data and as observed in the cosmic microwave background temperature data taken by the Planck satellite. The angular diameter of the vast supervoid aligned with the Cold Spot, which exceeds 30 degrees, is marked by the white circles. Graphics by Gergő Kránicz. Image credit: ESA Planck Collaboration.

    If the Cold Spot originated from the Big Bang itself, it could be a rare sign of exotic physics that the standard cosmology (basically, the Big Bang theory and related physics) does not explain. If, however, it is caused by a foreground structure between us and the CMB, it would be a sign that there is an extremely rare large-scale structure in the mass distribution of the universe.

    Using data from Hawaii’s Pan-STARRS1 (PS1) telescope located on Haleakala, Maui, and NASA’s Wide Field Survey Explorer (WISE) satellite, Szapudi’s team discovered a large supervoid, a vast region 1.8 billion light-years across, in which the density of galaxies is much lower than usual in the known universe.

    Pann-STARSR1 Telescope
    Pann-STARSR1 Telescope

    NASA Wise Telescope
    NASA/WISE

    This void was found by combining observations taken by PS1 at optical wavelengths with observations taken by WISE at infrared wavelengths to estimate the distance to and position of each galaxy in that part of the sky.

    Earlier studies, also done in Hawaii, observed a much smaller area in the direction of the Cold Spot, but they could establish only that no very distant structure is in that part of the sky. Paradoxically, identifying nearby large structures is harder than finding distant ones, since we must map larger portions of the sky to see the closer structures. The large three-dimensional sky maps created from PS1 and WISE by Dr. András Kovács (Eötvös Loránd University, Budapest, Hungary) were thus essential for this study. The supervoid is only about 3 billion light-years away from us, a relatively short distance in the cosmic scheme of things.

    Imagine there is a huge void with very little matter between you (the observer) and the CMB. Now think of the void as a hill. As the light enters the void, it must climb this hill. If the universe were not undergoing accelerating expansion, then the void would not evolve significantly, and light would descend the hill and regain the energy it lost as it exits the void. But with the accelerating expansion, the hill is measurably stretched as the light is traveling over it. By the time the light descends the hill, the hill has gotten flatter than when the light entered, so the light cannot pick up all the energy it lost upon entering the void. The light exits the void with less energy, and therefore at a longer wavelength, which corresponds to a colder temperature.

    Getting through a supervoid can take millions of years, even at the speed of light, so this measurable effect, known as the Integrated Sachs-Wolfe (ISW) effect, might provide the first explanation one of the most significant anomalies found to date in the CMB, first by a NASA satellite called the Wilkinson Microwave Anisotropy Probe (WMAP), and more recently, by Planck, a satellite launched by the European Space Agency.

    NASA WMAP satellite
    NASA/WMAP

    ESA Planck
    ESA/Planck

    While the existence of the supervoid and its expected effect on the CMB do not fully explain the Cold Spot, it is very unlikely that the supervoid and the Cold Spot at the same location are a coincidence. The team will continue its work using improved data from PS1 and from the Dark Energy Survey being conducted with a telescope in Chile to study the Cold Spot and supervoid, as well as another large void located near the constellation Draco.

    Dark Energy Icon
    Dark Energy Camera
    Dark Energy Survey and it DECam camera, built at FNAL and housed in the CTIO Victor M Blanco 4 meter telescope

    The study is being published online on April 20 in Monthly Notices of the Royal Astronomical Society by the Oxford University Press. In addition to Szapudi and Kovács, researchers who contributed to this study include UH Manoa alumnus Benjamin Granett (now at the National Institute for Astrophysics, Italy), Zsolt Frei (Eötvös Loránd), and Joseph Silk (Johns Hopkins).

    U Hawaii IFA just put up a bunch of older articles into RSS. This is one of the best.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    System Overview

    The University of Hawai‘i System includes 10 campuses and dozens of educational, training and research centers across the Hawaiian Islands. As the public system of higher education in Hawai‘i, UH offers opportunities as unique and diverse as our Island home.

    The 10 UH campuses and educational centers on six Hawaiian Islands provide unique opportunities for both learning and recreation.

    UH is the State’s leading engine for economic growth and diversification, stimulating the local economy with jobs, research and skilled workers.

     
  • richardmitnick 11:53 am on February 14, 2015 Permalink | Reply
    Tags: , , , Cosmic microwave background,   

    From Ethan Siegel: “How can we still see the Big Bang?” 

    Starts with a bang
    Starts with a Bang

    Feb 14, 2015
    Ethan Siegel

    If it happened billions of years ago, what’s it still doing here?

    “We like to admit to only that which already glows, although it is nobler to support brightness before it glows, not afterwards.” –Dejan Stojanovic

    Sometimes, the simplest questions make for the most profound answers, and give us the opportunity to really dig deep into how we view the fabric of the Universe itself. This week, after sifting through your questions and suggestions for our Ask Ethan column, I couldn’t pass up the spectacular but straightforward question of Joseph McFarland, who wants to know:

    Why do we continue to detect the cosmic background radiation?
    Is the fact that we continue to eternally see the cosmic background radiation billions of years after it was generated proof of either inflation, or that the universe must be curved back upon itself (i.e. that it is finite but unbounded)?
    Or if neither of these are requirements, then what are other explanations?

    I want you to think about the history of the Universe.

    1
    Image credit: NASA / CXC / M.Weiss.

    In particular, I want you to think of why it’s such a remarkable thing that we do detect the Cosmic Microwave Background at all. The story starts at the moment of the Big Bang, or more specifically, at the hot Big Bang.

    2
    Image credit: RHIC collaboration, Brookhaven, via http://www.bnl.gov/newsroom/news.php?a=11403.

    The hot Big Bang refers to a time some 13.8 billion years ago, when the Universe first emerged from an inflationary state — one where all the energy in it was inherent to space itself — and got converted into matter, antimatter and radiation. We can think of this as inflation being a field that’s in an unstable state, like a ball at the top of a hill, that then rolls down that hill and into a valley.

    While the ball is at the top of the hill, space itself expands at an exponential rate. When the ball rolls into the valley, and starts oscillating back-and-forth, that energy-of-space gets converted into matter, antimatter and radiation: a process known as reheating.

    3
    Image credit: E. Siegel. Inflation ends when the ball rolls into the valley.

    The Universe still continues to expand, but because it’s filled with matter, antimatter and radiation, it no longer maintains a very large expansion rate for long. The expansion rate is tied — in General Relativity — to the energy density of the Universe, or how much energy there is per-unit-volume.

    When all you had was energy inherent to space itself, as the Universe expanded, you simply made more empty space, and the energy density stayed the same. But now that you’ve got stuff in the Universe instead, it dilutes (and gets less dense) as the Universe expands. In the case of radiation, the wavelength of light also stretches, which is why the Universe not only gets less dense, it also cools as time goes on.

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    Images credit: TAKE 27 LTD / Science Photo Library, via Nature {above], Chris Palma of Penn State / Chaisson and McMillan, Astronomy [below].

    As the Universe expands and cools, from an incredibly hot, dense, uniform, rapidly expanding state down to a cool, sparse, clumpy, slowly expanding state, a huge number of important events happen:

    The fundamental symmetries of nature that are restored at the highest energies become broken, giving rise to things like particle rest masses.
    The Universe gets cool enough so that photons stop spontaneously forming matter/antimatter pairs. The excess antimatter annihilates away, leaving only 1 matter particle per ~1,400,000,000 photons.
    The interaction strength and rate drops significantly enough that neutrinos stop interacting with everything else in the Universe.
    The photon temperature drops enough so that the first stable, atomic nuclei can form without immediately being blasted apart.
    The temperature drops even further — by about another factor of a million — so that neutral atoms can stably form.

    And after that, the overdense regions grow into stars, galaxies and clusters of galaxies, giving rise to the Universe we see today, all while the photon energy continues to drop thanks to the ongoing expansion.

    8
    Image credit: NASA / GSFC, via http://cosmictimes.gsfc.nasa.gov/universemashup/archive/pages/expanding_universe.html

    That next-to-last step — the one about the atoms becoming neutral — is where the Cosmic Microwave Background (CMB) originates. Prior to that time, the atoms were all ionized, meaning that they were simply positively charged nuclei and free electrons, bathed in a sea of photons. But photons have an extremely large scattering cross-section with electrons, meaning that they bounced around a tremendous amount.

    It’s only when the Universe cooled enough to become neutral that photons stopped seeing free electrons and started seeing only neutral, stable atoms. Because neutral atoms only absorb photons at very particular frequencies, and most of the photons that exist are not at those frequencies, these atoms are effectively transparent to all the photons that exist in the Universe!

    7
    9
    Images credit: Amanda Yoho, of the ionized plasma [upper] before the CMB is emitted, followed by the transition to a neutral Universe [lower] that’s transparent to photons.

    But because the Universe has been expanding and cooling for so long, you can take our location in space and fix it, and recognize one disconcerting fact: all the light from the Big Bang in the regions surrounding our own has been passing us by, continuously, for 13.8 billion years.

    All the stars, galaxies, large-scale structure, gas clouds and cosmic voids located thousands, millions, billions or even tens of billions of light-years away saw their CMB light pass us by ages and ages ago.

    9
    Image credit: Wikimedia Commons user Unmismoobjetivo; of a logarithmic view of the Universe as centered on the Earth.

    Yet — to the point of Joseph’s original question — we still see the CMB, which corresponds (today) to a surface that’s some 45.3 billion light-years away.

    The fact that we still see the CMB at all tells us something very important: the Big Bang happened everywhere at once in a region of space that’s at least 45.3 billion light-years in radius, as seen from our perspective.

    1
    Image credit: NASA/WMAP SCIENCE TEAM.

    And the fact that the CMB is not only visible in all directions, but is of a uniform temperature in all directions tells us — in the context of an inflationary Universe — that the amount that the (observable) Universe inflated must have taken it from an initial size that was, at maximum, 10^-29 meters (or less than a trillionth of 1% the size of a proton) and grew it by at least a factor of 10,000,000,000,000,000,000,000.

    The part of the Universe that we see, today, as our observable Universe could have been even smaller than that scale of 10^-29 meters, initially, and the amount that inflation grew that initial patch of space could have been arbitrarily larger than the factor of 10^22; there is no upper limit on that.

    2
    Image credit: ESA and the Planck collaboration.

    So when we look at the Cosmic Microwave Background, at its uniformity and its small-scale, low-magnitude fluctuations, and the fact that there are no regions of it that are identifiable with one another (i.e., that the Universe does not exhibit a closed topology), we can conclude from this alone that the Big Bang must have occurred everywhere at once in a large region as viewed from our perspective.

    In the context of inflation — something we know an awful lot about — this gives us a lower bound as to the duration and scope of inflation, and ties it in to our observable Universe. The reason the CMB is still around is because the Big Bang, which itself came about at the end of inflation, happened over an incredibly large region of space, a region that’s at least as large as where we observe the CMB to still be. In all probability, that true region is much larger, and that not only will observers anywhere in the Universe see roughly the same CMB, but that we’ll continue to see it (albeit, redshifted a little farther) arbitrarily far into the future.

    3
    Images credit: Wikimedia Commons users Theresa Knott and chris 論, modified by me (L); NASA / COBE science team (R), DMR (top) and FIRAS (bottom).

    Thanks for a great question, Joseph, and thanks to all of you for sending in a great selection of questions and suggestions for Ask Ethan! The truths of the Universe are written on the face of the Universe itself, and we’re doing everything we can to uncover them!

    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.

     
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