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  • richardmitnick 6:16 am on January 28, 2014 Permalink | Reply
    Tags: , , , , Hubble CANDLES   

    From CANDELS: “A New Type Ia Supernova in M82″ 

    Hubble Candles

    January 27, 2014
    David Jones

    Just a couple of days ago, a dim, but quickly brightening, supernova was discovered in M82, the beautiful “cigar galaxy.” At only 12 million light years away, this is the nearest supernova to Earth since 1987 and the nearest Type Ia supernova since 1972. With the enormous changes in our imaging technology since then (including the launch and subsequent improvements to the Hubble Space Telescope), this is a fantastic opportunity for precision measurements of one of the brightest and most mysterious explosions in the universe.

    m82
    The new supernova in M82, discovered by students at the University College London
    Observatory. Photo by Adam Block/Mount Lemmon SkyCenter/University of Arizona

    Discovering more about the nature of Type Ia supernovae has been one of the primary goals of the CANDELS project. These supernovae begin as stars like our sun, which have shed their outer layers at the end of their lives and become white dwarfs. White dwarfs are the extremely dense cores of a burned-out star, and although they’re only the size of our earth, they have the mass of our entire sun. The detonation happens when a nearby star adds even more mass onto this dwarf — when the weight becomes too much, nuclear fusion ignites it and a supernova occurs.

    In CANDELS, we study the most distant Type Ia supernovae that we can find, the farthest of which stands at over 10 billion light years away. Our supernovae tell us about the early expansion of the universe (and its Dark Energy), the chemical evolution of the universe, and how quickly supernovae form and explode around 8-10 billion years ago — at the peak of star formation in the universe.

    This nearby galaxy offers a completely different, and rarer, perspective. In 1972, when the last Type Ia supernova this close to Earth exploded, it was still a year before anyone proposed the idea that these supernovae were formed in binary star systems. It was 12 years before someone realized that both stars could be white dwarfs, and 18 years before supernovae could be studied from space with the Hubble Space Telescope. It was over 25 years before such supernovae were used to discover that Dark Energy was accelerating the expansion of our universe.

    NASA Hubble Telescope
    Hubble

    Motivated by the knowledge and technology gained since the last close Type Ia supernova went off, scientists will be asking an entirely different set of questions this time around. First, we’ll be looking for a giant companion star that could have fed mass onto the white dwarf. If a companion star is visible, this would be the first direct evidence that a system with one white dwarf can lead to a supernova; if a companion star is not found, the theory that two white dwarfs can make a Type Ia supernova will gain credibility.

    concept
    Artist’s conception of the single-degenerate (one white dwarf)
    theory of Type Ia supernova explosions, wherein
    a white dwarf accretes mass from its companion
    star. (original) © ESA and Justyn Maund (Queens Univ. Belfast)

    double
    Artist’s conception of the double-degenerate theory
    of Type Ia supernova explosions, in which two white dwarfs merge
    together as they emit gravitational waves. (original) © NASA,
    Tod Strohmayer (GSFC), and Dana Berry (Chandra X-ray Observatory)

    Second, scientists will be studying the geometry of the supernova from the fraction of polarized light emitted. Polarization, the orientation of a light ray’s electric field, is entirely random when it originates from a spherically symmetric star. However, if one side becomes longer than the other, the light’s polarization will have a preferential direction that can be measured on Earth. As the outer layers of the M82 supernova expand, they will become transparent and expose the inner material. Over the next month, scientists will be able to measure the shape of different layers and examine the three-dimensional explosion. With this structural information, we’ll learn more about how supernova detonation occurs; specifically, how nuclear fusion begins and spreads through the layers of the white dwarf.

    m82
    The location of M82 on the night sky from Sky and Telescope.
    A more detailed chart is available here

    Lastly, Type Ia supernovae are nearly uniform in brightness, serving as excellent distance indicators for most of the visible universe. CANDELS supernova principal investigator Adam Riess — among others — will be measuring the distance and doppler shift velocity (the reddening of its light) of this supernova to determine how fast the local universe is expanding — and infer the amount of the mysterious Dark Energy that surrounds us.

    This supernova is particularly rare in that it offers opportunities not only to scientists, but for anyone with access to a dark night sky. It will brighten for approximately a week and a half, and at its peak it will be visible near Ursa Major (the Big Dipper) to anyone with a set of binoculars. Although it’s impossible to predict when the next close supernova will be, I’m looking forward to seeing an exploding star with my own eyes – it may be 40 years before there’s another opportunity.

    See the full article here.

    About the CANDELS blog

    In late 2009, the Hubble Space Telescope began an ambitious program to map five carefully selected areas of the sky with its sensitive near-infrared camera, the Wide-Field Camera 3. The observations are important for addressing a wide variety of questions, from testing theories for the birth and evolution of galaxies, to refining our understanding of the geometry of the universe.

    This is a research blog written by people involved in the project. We aim to share some of the excitement of working at the scientific frontier, using one of the greatest telescopes ever built. We will also share some of the trials and tribulations of making the project work, from the complications of planning and scheduling the observations to the challenges of trying to understand the data. Along the way, we may comment on trends in astronomy or other such topics.

    CANDELS stands for the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. It builds on the legacy of the Hubble Deep Field, as well as the wider-area surveys called GOODS, AEGIS, COSMOS, and UKIDSS UDS. The CANDELS observations are designed to search for galaxies within about a billion years of the big bang, study galaxies at cosmic high-noon about 3 billion years after the big bang – when star-formation and black hole growth were at their peak intensity – and discover distant supernovae for refining our understanding of cosmic acceleration. You can find more details, and download the CANDELS data, from the CANDELS website.

    You can also use the Hubble Legacy Archive to view the CANDELS images.


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  • richardmitnick 1:46 pm on August 15, 2013 Permalink | Reply
    Tags: , , , , Hubble CANDLES,   

    From CANDLES: “What Did Galaxies Look Like at Cosmic High Noon?” 

    Hubble Candles

    Thursday, August 15, 2013
    Joel Primack

    “The rate of star formation was highest about 10 billion years ago, a period that CANDELS astronomers call ‘Cosmic High Noon.’ The redshift then was about 2, which means that the universe has expanded by a factor of three since then in each of the three spatial dimensions, so it was 3x3x3 = 27 times denser back then. The universe was also much brighter, with so many galaxies so much closer together forming lots of short-lived massive stars, which shine much more brightly than lower-mass long-lived stars like our sun.

    What did those early galaxies look like, and how did they evolve into the galaxies we see around us today? Answering that question is one of the most important goals of the CANDELS survey. The infrared capability of the Wide Field Camera 3 (WFC3), installed in the last astronaut visit to Hubble Space Telescope in 2009, gives us the ability to see galaxies at redshift 2 in the wavelengths of visible light. Visible light, with wavelengths ranging from blue at 0.4 to red at 0.7 microns (a micron is a millionth of a meter), gives us crucial information about the long-lived stars in galaxies. The wavelengths of light emitted at redshift 2 expand by a factor of 3, just as space does, so visible wavelengths expand to 1.2 to 2.1 microns. WFC3 allows us to make images at wavelengths as long as 1.7 microns, while WFC3 and other HST cameras make images at shorter wavelengths that allow us to trace recent star formation because such ultraviolet light is emitted by short-lived massive stars.

    images
    Simulated galaxy at redshift 2.1 from a high-resolution cosmological simulation. Top: rest-frame optical
    image from the Sunrise computer code, taking in account stellar evolution and the scattering and absorption
    of light by dust and subsequent dust re-radiation. Bottom: The same simulated galaxy, as seen by Hubble
    Space Telescope in V (visual light) and H (1.5-1.7 micron infrared wavelengths) bands. Because of the
    redshift of the radiation from this galaxy, what HST sees as V-band light was emitted as ulraviolet in the
    galaxy rest frame, which mainly traces new star formation, while what HST sees as H-band light was emitted
    as red light, which traces the older stellar population in the high-redshift galaxy. Note that the V-band image
    is clumpy, which is also often the case for real galaxies at these redshifts. Image Credit: Joel Primack

    One of the things that we have found is that star-forming galaxies at redshift 2 were often rather clumpy, unlike the rather smooth Milky Way and other nearby galaxies. My colleagues and I have been simulating the formation and evolution of galaxies, and our simulations often also look rather clumpy, with giant star-forming regions in their disks. The clumps occur partly because the galaxies have so much gas in their disks that the disks become gravitationally unstable and break up into clumps of gas that rapidly form stars. We have been comparing the observed and simulated galaxies systematically, and we have been gratified to find that they appear fairly similar in their sizes and shapes, as well as their clumpiness.”

    See the full article here.

    About the CANDELS blog

    In late 2009, the Hubble Space Telescope began an ambitious program to map five carefully selected areas of the sky with its sensitive near-infrared camera, the Wide-Field Camera 3. The observations are important for addressing a wide variety of questions, from testing theories for the birth and evolution of galaxies, to refining our understanding of the geometry of the universe.

    This is a research blog written by people involved in the project. We aim to share some of the excitement of working at the scientific frontier, using one of the greatest telescopes ever built. We will also share some of the trials and tribulations of making the project work, from the complications of planning and scheduling the observations to the challenges of trying to understand the data. Along the way, we may comment on trends in astronomy or other such topics.

    CANDELS stands for the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. It builds on the legacy of the Hubble Deep Field, as well as the wider-area surveys called GOODS, AEGIS, COSMOS, and UKIDSS UDS. The CANDELS observations are designed to search for galaxies within about a billion years of the big bang, study galaxies at cosmic high-noon about 3 billion years after the big bang – when star-formation and black hole growth were at their peak intensity – and discover distant supernovae for refining our understanding of cosmic acceleration. You can find more details, and download the CANDELS data, from the CANDELS website.

    You can also use the Hubble Legacy Archive to view the CANDELS images.


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