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  • richardmitnick 1:53 pm on January 8, 2019 Permalink | Reply
    Tags: , , , , Dark Energy Survey, DES remains one of the most sensitive and comprehensive surveys of distant galaxies ever performed, DES scientists also spotted the first visible counterpart of gravitational waves ever detected, , , Now the job of analyzing that data takes center stage, Recently DES issued its first cosmology results based on supernovae, Scientists on DES took data on 758 nights over six years, They recorded data from more than 300 million distant galaxies   

    From Fermi National Accelerator Lab: “Dark Energy Survey completes six-year mission” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

    January 8, 2019

    Scientists’ effort to map a portion of the sky in unprecedented detail is coming to an end, but their work to learn more about the expansion of the universe has just begun.

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    After scanning in depth about a quarter of the southern skies for six years and cataloguing hundreds of millions of distant galaxies, the Dark Energy Survey (DES) will finish taking data tomorrow, on Jan. 9.

    The survey is an international collaboration that began mapping a 5,000-square-degree area of the sky on Aug. 31, 2013, in a quest to understand the nature of dark energy, the mysterious force that is accelerating the expansion of the universe. Using the Dark Energy Camera, a 520-megapixel digital camera funded by the U.S. Department of Energy Office of Science and mounted on the Blanco 4-meter telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory in Chile, scientists on DES took data on 758 nights over six years.

    Over those nights, they recorded data from more than 300 million distant galaxies. More than 400 scientists from over 25 institutions around the world have been involved in the project, which is hosted by the U.S. Department of Energy’s Fermi National Accelerator Laboratory. The collaboration has already produced about 200 academic papers, with more to come.

    According to DES Director Rich Kron, a Fermilab and University of Chicago scientist, those results and the scientists who made them possible are where much of the real accomplishment of DES lies.

    “First generations of students and postdoctoral researchers on DES are now becoming faculty at research institutions and are involved in upcoming sky surveys,” Kron said. “The number of publications and people involved are a true testament to this experiment. Helping to launch so many careers has always been part of the plan, and it’s been very successful.”

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    DES remains one of the most sensitive and comprehensive surveys of distant galaxies ever performed. The Dark Energy Camera is capable of seeing light from galaxies billions of light-years away and capturing it in unprecedented quality.

    According to Alistair Walker of the National Optical Astronomy Observatory, a DES team member and the DECam instrument scientist, equipping the telescope with the Dark Energy Camera transformed it into a state-of-the-art survey machine.

    “DECam was needed to carry out DES, but it also created a new tool for discovery, from the solar system to the distant universe,” Walker said. “For example, 12 new moons of Jupiter were recently discovered with DECam, and the detection of distant star-forming galaxies in the early universe, when the universe was only a few percent of its present age, has yielded new insights into the end of the cosmic dark ages.”

    The survey generated 50 terabytes (that’s 50 million megabytes) of data over its six observation seasons. That data is stored and analyzed at the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign.

    “Even after observations are ended, NCSA will continue to support the scientific productivity of the collaboration by making refined data releases and serving the data well into the 2020s,” said Don Petravick, senior project manager for the Dark Energy Survey at NCSA.

    Now the job of analyzing that data takes center stage. DES has already released a full range of papers based on its first year of data, and scientists are now diving into the rich seam of catalogued images from the first several years of data, looking for clues to the nature of dark energy.

    The first step in that process, according to Fermilab and University of Chicago scientist Josh Frieman, former director of DES, is to find the signal in all the noise.

    “We’re trying to tease out the signal of dark energy against a background of all sorts of noncosmological stuff that gets imprinted on the data,” Frieman said. “It’s a massive ongoing effort from many different people around the world.”

    The DES collaboration continues to release scientific results from their storehouse of data, and scientists will discuss recent results at a special session at the American Astronomical Society winter meeting in Seattle today, Jan. 8. Highlights from the previous years include:

    the most precise measurement of dark matter structure in the universe, which, when compared with cosmic microwave background results, allows scientists to trace the evolution of the cosmos.
    the discovery of many more dwarf satellite galaxies orbiting our Milky Way, which provide tests of theories of dark matter.
    the creation of the most accurate dark matter map of the universe.
    the spotting of the most distant supernova ever detected.
    the public release of the survey’s first three years of data, enabling astronomers around the world to make additional discoveries.

    DES scientists also spotted the first visible counterpart of gravitational waves ever detected, a collision of two neutron stars that occurred 130 million years ago. DES was one of several sky surveys that detected this gravitational wave source, opening the door to a new kind of astronomy.

    Recently DES issued its first cosmology results based on supernovae (207 of them taken from the first three years of DES data) using a method that provided the first evidence for cosmic acceleration 20 years ago. More comprehensive results on dark energy are expected within the next few years.

    The task of amassing such a comprehensive survey was no small feat. Over the course of the survey, hundreds of scientists were called on to work the camera in nightly shifts supported by the staff of the observatory. To organize that effort, DES adopted some of the principles of high-energy physics experiments, in which everyone working on the experiment is involved in its operation in some way.

    “This mode of operation also afforded DES an educational opportunity,” said Fermilab scientist Tom Diehl, who managed the DES operations. “Senior DES scientists were paired with inexperienced ones for training and, in time, would pass that knowledge on to more junior observers.”

    The organizational structure of DES was also designed to give early-career scientists valuable opportunities for advancement, from workshops on writing research proposals to mentors who helped review and edit grant and job applications.

    Antonella Palmese, a postdoctoral researcher associate at Fermilab, arrived at Cerro Tololo as a graduate student from University College London in 2015. She quickly came up to speed and returned in 2017 and 2018 as an experienced observer. She also served as a representative for early-career scientists, helping to assist those first making their mark with DES.

    “Working with DES has put me in contact with many remarkable scientists from all over the world,” Palmese said. “It’s a special collaboration because you always feel like you are a necessary part of the experiment. There is always something useful you can do for the collaboration and for your own research.”

    The Dark Energy Camera will remain mounted on the Blanco telescope at Cerro Tololo for another five to 10 years and will continue to be a useful instrument for scientific collaborations around the world. Cerro Tololo Inter-American Observatory Director Steve Heathcote foresees a bright future for DECam.

    “Although the data-taking for DES is coming to an end, DECam will continue its exploration of the universe from the Blanco telescope and is expected remain a front-line ‘engine of discovery’ for many years,” Heathcote said.

    The DES collaboration will now focus on generating new results from its six years of data, including new insights into dark energy. With one era at an end, the next era of the Dark Energy Survey is just beginning.

    Follow the Dark Energy Survey online at http://www.darkenergysurvey.org and connect with the survey on Facebook at http://www.facebook.com/darkenergysurvey, on Twitter at http://www.twitter.com/theDESurvey and on Instagram at http://www.instagram.com/darkenergysurvey.

    The Dark Energy Survey is a collaboration of more than 400 scientists from 26 institutions in seven countries. Funding for the DES Projects has been provided by the U.S. Department of Energy Office of Science, U.S. National Science Foundation, Ministry of Science, Innovation and Universities of Spain, Science and Technology Facilities Council of the United Kingdom, Higher Education Funding Council for England, ETH Zurich for Switzerland, National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, Kavli Institute of Cosmological Physics at the University of Chicago, Center for Cosmology and AstroParticle Physics at Ohio State University, Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and Ministério da Ciência e Tecnologia, Deutsche Forschungsgemeinschaft, and the collaborating institutions in the Dark Energy Survey, the list of which can be found at http://www.darkenergysurvey.org/collaboration.

    Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. NSF is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future.

    NCSA at the University of Illinois at Urbana-Champaign provides supercomputing and advanced digital resources for the nation’s science enterprise. At NCSA, University of Illinois faculty, staff, students and collaborators from around the globe use advanced digital resources to address research grand challenges for the benefit of science and society. NCSA has been advancing one third of the Fortune 50® for more than 30 years by bringing industry, researchers and students together to solve grand challenges at rapid speed and scale. For more information, please visit http://www.ncsa.illinois.edu.

    See the full article here .


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    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.


    FNAL/MINERvA

    FNAL DAMIC

    FNAL Muon g-2 studio

    FNAL Short-Baseline Near Detector under construction

    FNAL Mu2e solenoid

    Dark Energy Camera [DECam], built at FNAL

    FNAL DUNE Argon tank at SURF

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    FNAL Don Lincoln

    FNAL/MINOS

    FNAL Cryomodule Testing Facility

    FNAL Minos Far Detector

    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

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    FNAL Holometer

     
  • richardmitnick 11:09 am on September 7, 2018 Permalink | Reply
    Tags: , , , , , Dark Energy Survey, Fierce Winds Quench Wildfire-like Starbirth in Far-flung Galaxy, Galaxy SPT2319-55, ,   

    From ALMA: “Fierce Winds Quench Wildfire-like Starbirth in Far-flung Galaxy” 

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

    From ALMA

    6 September, 2018

    Nicolás Lira
    Education and Public Outreach Coordinator
    Joint ALMA Observatory, Santiago – Chile
    Phone: +56 2 2467 6519
    Cell phone: +56 9 9445 7726
    Email: nicolas.lira@alma.cl

    Charles E. Blue
    Public Information Officer
    National Radio Astronomy Observatory Charlottesville, Virginia – USA
    Phone: +1 434 296 0314
    Cell phone: +1 202 236 6324
    Email: cblue@nrao.edu

    Calum Turner
    ESO Assistant Public Information Officer
    Garching bei München, Germany
    Phone: +49 89 3200 6670
    Email: calum.turner@eso.org

    Masaaki Hiramatsu
    Education and Public Outreach Officer, NAOJ Chile
    Observatory
, Tokyo – Japan
    Phone: +81 422 34 3630
    Email: hiramatsu.masaaki@nao.ac.jp

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    ALMA, aided by a gravitational lens, imaged the outflow, or “wind”, from a galaxy seen when the universe was only one billion years old. The ALMA image (circle call out) shows the hydroxyl (OH) molecules. These molecules trace the location of star-forming gas as it is fleeing the galaxy, driven by a supernova or black-hole powered “wind.” The background star field (Blanco Telescope Dark Energy Survey) shows the location of the galaxy. The circular, double-lobe shape of the distant galaxy is due to the distortion caused by cosmic magnifying effect of an intervening galaxy. Credit: ALMA (ESO/NAOJ/NRAO), Spilker; NRAO/AUI/NSF, S. Dagnello; AURA/NSF

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    Astronomers using ALMA, with the aid of a gravitational lens, have detected the most-distant galactic “wind” of molecules ever observed, seen when the universe was only one billion years old. By tracing the outflow of hydroxyl (OH) molecules, which herald the presence of star-forming gas in galaxies, the researchers show how some galaxies in the early universe quenched an ongoing wildfire of starbirth.

    Some galaxies, like the Milky Way and Andromeda, have relatively slow and measured rates of starbirth, with about one new star igniting each year. Other galaxies, known as starburst galaxies, forge 100s or even 1000s of stars each year. This furious pace, however, cannot be maintained indefinitely.

    Milky Way NASA/JPL-Caltech /ESO R. Hurt

    Andromeda Galaxy Adam Evans

    To avoid burning out in a short-lived blaze of glory, some galaxies throttle back their runaway starbirth by ejecting, at least temporarily, vast stores of gas into their expansive halos, where the gas either escapes entirely or slowly rains back in on the galaxy, triggering future bursts of star formation.

    Up to now, however, astronomers have been unable to directly observe these powerful outflows in the very early universe, where such mechanisms are essential to prevent galaxies from growing too big, too fast.

    New observations with the Atacama Large Millimeter/submillimeter Array (ALMA), show, for the first time,a powerfulgalactic “wind” of molecules in a galaxy seen when the universe was only one billion years old. This result provides insights into how certain galaxies in the early universe were able to self-regulate their growth,so they could continue forming stars across cosmic time.

    “Galaxies are complicated, messy beasts, and we think outflows and winds are critical pieces to how they form and evolve, regulating their ability to grow,” said Justin Spilker, an astronomer at the University of Texas at Austin and lead author on a paper appearing in the journal Science.

    Astronomers have observed winds with the same size, speed, and mass in nearby starbursting galaxies, but the new ALMA observation is the most distant unambiguous outflow ever seen in the early universe.

    The galaxy, known as SPT2319-55, is more than 12 billion light-years away. It was discovered by the National Science Foundation’s South Pole Telescope.

    South Pole Telescope SPTPOL. The SPT collaboration is made up of over a dozen (mostly North American) institutions, including the University of Chicago, the University of California, Berkeley, Case Western Reserve University, Harvard/Smithsonian Astrophysical Observatory, the University of Colorado Boulder, McGill University, The University of Illinois at Urbana-Champaign, University of California, Davis, Ludwig Maximilian University of Munich, Argonne National Laboratory, and the National Institute for Standards and Technology. It is funded by the National Science Foundation.

    ALMA was able to observe this object at such tremendous distance with the aid of a gravitational lens provided by a different galaxy that sits almost exactlyalong the line of sight between Earth and SPT2319-55. Gravitational lensing – the bending of light due to gravity — magnifies the background galaxy to make it appear brighter, which allows the astronomers to observe it in more detail than they would otherwise be able to.

    Radio galaxies gravitationally lensed by a very large foreground galaxy cluster Hubble

    Astronomers use specialized computer programs to “unscramble” the effects of gravitational lensing to reconstruct an accurate image of the more-distant object.

    This lens-aided view revealed a powerful“wind” of star-forming gas exiting the galaxy at nearly 800 kilometers per second. Rather than a constant, gentle breeze, the wind is hurtling away in discrete clumps, removing the star-forming gas just as quickly as the galaxy can turn that gas into new stars.

    The outflow was detected by the millimeter-wavelength signature of a molecule called hydroxyl (OH), which appeared as an absorption line: essentially, the shadow of an OH fingerprint in the galaxy’s bright infrared light.

    As new, dust-enshrouded stars form, that dust heats up and glows brightly in infrared light. However, the galaxy is also launching a wind, and some of it is blowing in our direction. As the infrared light passes through the wind on its journey toward Earth, the OH molecules in the wind absorb some of the infrared light at a very particular wavelength that ALMA can observe.

    “That’s the absorption signature that we detected, and from that, we can also tell how fast the wind is moving and get a rough idea of how much material is contained in the outflow,” said Spilker. ALMA can detect this infrared light because it has been stretched to millimeter wavelengths on its journey to Earth by the ongoing expansion of the Universe.

    Molecular winds are an efficient way for galaxies to self-regulate their growth, the researchers note. These winds are likely triggered by either the combined effectof all the supernova explosions that go along with rapid, massive star formation or by a powerful release of energy as some of the gas in the galaxy falls down onto the supermassive black hole at its center.

    “So far, we have only observed one galaxy at such a remarkable cosmic distance, but we’d like to know if winds like these are also present in other galaxies to see just how common they are,” concluded Spilker. “If they occur in basically every galaxy, we know that molecular winds are both ubiquitous and also a prevalent way for galaxies to self-regulate their growth.”

    “This ALMA observation demonstrates how nature coupled with exquisite technology can give us insights into distant astronomical objects,” said Joe Pesce, NSF Program Director for NRAO/ALMA, “and the frequency range accessible to ALMA meant it was able to the detect the redshifted spectral feature from this important molecule.”

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    Artist impression of an outflow of molecular gas from an active star-forming galaxy. Credit: NRAO/AUI/NSF, D. Berry

    NRAO/Karl V Jansky Expanded Very Large Array, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    This research is presented in a paper titled Fast Molecular Outflow from a Dusty Star-Forming Galaxy in the Early Universe, by J.S. Spilker et al. in the journal Science and Science

    The research team was composed by J. S. Spilker [1,2,∗],M. Aravena [3], M. Béthermin [4], S. C. Chapman [5], C.-C. Chen [6], D. J. M. Cunningham [5,7], C. De Breuck [6], C. Dong [8], A. H. Gonzalez [8], C. C. Hayward [9,10], Y. D. Hezaveh [11], K. C. Litke [2], J. Ma [12], M. Malkan [13], D. P. Marrone [2], T. B. Miller [5,14], W. R. Morningstar [11], D. Narayanan [8], K. A. Phadke [15], J. Sreevani [15], A. A. Stark [10], J. D. Vieira [15], A. Weiß [16].

    [1] Department of Astronomy, University of Texas at Austin, 2515 Speedway Stop C1400, Austin, TX 78712, USA.

    [2] Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA.

    [3] Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile.

    [4] Aix-Marseille Univ., Centre National de la Recherche Scientifique, Laboratoire d’Astrophysique de Marseille, Marseille, France.

    [5] Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada.

    [6] European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany.

    [7] Department of Astronomy and Physics, Saint Mary’s University, Halifax, Nova Scotia, Canada.

    [8] Department of Astronomy, University of Florida, Bryant Space Sciences Center, Gainesville, FL 32611, USA.

    [9] Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA.

    [10] Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.

    [11] Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305, USA.

    [12] Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA

    [13] Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA.

    [14] Department of Astronomy, Yale University, 52 Hillhouse Avenue, New Haven, CT 06511, USA.

    [15] Department of Astronomy, University of Illinois, 1002 West Green St., Urbana, IL 61801, USA.

    [16] Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69 D-53121 Bonn, Germany.

    ∗Corresponding author. E-mail: spilkerj@gmail.com.

    See the full article here .

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    Please help promote STEM in your local schools.

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    The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

    ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

    NRAO Small
    ESO 50 Large
    NAOJ

     
  • richardmitnick 12:52 pm on August 27, 2018 Permalink | Reply
    Tags: , Dark Energy Survey, , ,   

    From Physics: “Viewpoint: Weak Lensing Becomes a High-Precision Survey Science” 

    Physics LogoAbout Physics

    Physics Logo 2

    From Physics

    August 27, 2018
    Anže Slosar, Physics Department
    Brookhaven National Laboratory

    Analyzing its first year of data, the Dark Energy Survey has demonstrated that weak lensing can probe cosmological parameters with a precision comparable to cosmic microwave background observations.

    Weak gravitational lensing NASA/ESA Hubble

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    Over the last decades, scientists have built a paradigm cosmological model, based on the premises of general relativity, known as the ΛCDM model. This model has successfully explained many aspects of the Universe’s evolution from a homogeneous primeval soup to the inhomogeneous Universe of planets, stars, and galaxies that we see today. The ΛCDM model is, however, at odds with the minimal standard model of particle physics, which cannot explain the two main ingredients of ΛCDM cosmology: the cold dark matter (CDM) that represents approximately 85% of all matter in the Universe and the cosmological constant ( Λ), or dark energy, that drives the Universe’s accelerated expansion.

    Standard Model of Particle Physics from Symmetry Magazine

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

    1
    Figure 1: The CCD imager of the Dark Energy Camera (DECam) used by the Dark Energy Survey. DECam is mounted on the Victor M. Blanco 4-m-aperture telescope in the Chilean Andes.
    R. Hahn/Fermilab

    One potential way to sort out the nature of dark matter and dark energy exploits an effect called weak gravitational lensing—a subtle bending of light induced by the presence of matter. Measurements of this effect, however, have proven challenging and so far have delivered less information than many physicists had hoped for. In a series of articles [1], the Dark Energy Survey (DES) now reports remarkable progress in the field. Analyzing data from its first year of operation, the DES has combined weak lensing and galaxy clustering observations to derive new constraints on cosmological parameters. The results suggest that we have reached an era in which weak gravitational lensing has become a systematic, high-precision technique for probing the Universe, on par with other well-established techniques, such as those based on observations of the cosmic microwave background (CMB) and on measurements of baryonic acoustic oscillations (BAO).

    2
    Figure 2: Constraints on cosmological parameters as determined by the DES (blue), Planck (green), and by the combination of DES and Planck (red). Within the measurements’ accuracy, the Planck and DES constraints are consistent with each other (Ωm is the matter density divided by the total energy density, and S8 is a parameter related to the amplitude of density fluctuations). For each color, the contour plots represent 68% and 95% confidence levels.

    Gravitational lensing is a consequence of the curvature of spacetime induced by mass.

    Gravitational Lensing NASA/ESA

    As light travels toward Earth from distant galaxies, it passes through clumps of matter that distort the light’s path. If lensing is strong, this distortion can dramatically stretch the images of the galaxies into long arcs. But in most situations, lensing is weak and causes subtler deformations—think of the distortions of images printed on a T-shirt that’s slightly stretched. Galaxies in the same part of the sky, whose light travels a similar path to us, are subjected to similar stretching, making them appear “aligned”—an effect known as cosmic shear. By quantifying the alignment of “background” galaxies, weak-lensing measurements derive information on the “foreground” mass that causes the distortions. Since dark matter constitutes the majority of matter, weak gravitational lensing largely probes dark matter.

    The potential of the technique has been known for decades [2]. Initially, however, researchers didn’t realize how difficult it would be to measure the tiny signal due to weak lensing and to isolate it from myriad other effects that cause similar distortions. Most importantly, for ground-based observations, the light reaching the telescope goes through Earth’s atmosphere. Atmospheric conditions, optical imperfections of the telescope, or simply inadequate data reduction techniques can blur or distort the images of individual objects. If such effects are coherent across the telescope’s field of view, they can lead to subtle alignments that can be misinterpreted as consequences of weak lensing. Moreover, most galaxies are elliptical to start with, and these ellipticities can be aligned for astrophysical reasons unrelated to weak lensing.

    Despite these difficulties, several pioneering efforts established the feasibility of weak gravitational lensing. In 2000, several groups reported the first detections of cosmic shear [3]. These were followed by 15 years of important advances, such as those obtained using data from the Sloan Digital Sky Survey [4], the Kilo-Degree Survey [5], and the Hyper Suprime-Cam Subaru Strategic Survey [6].

    However, the new DES results mark an important milestone in terms of accuracy and breadth of analysis. Two main factors enabled these results. The first was the use of the Dark Energy Camera (DECam), a sensitive detector, custom-designed for weak-lensing measurements (Fig. 1), which was mounted on the 4-m-aperture Victor M. Blanco telescope in Chile, where DES has a generous allocation of observing time. The second factor was the size of the collaboration—more on the scale of a particle-physics collaboration than an astrophysics one. This resource allowed DES to dedicate unprecedented attention to data analysis. For example, two independent weak-lensing “pipelines” performed an important cross check of the results. [7]

    As reported in the latest crop of DES papers, the collaboration mapped out the dark matter in a patch of sky spanning 1321 deg2

    , or about 3% of the full sky. They performed this mapping using two independent approaches. The first provided a direct probe of dark matter by measuring the cosmic shear caused by foreground dark matter on 26 million background galaxies. The second approach entailed measuring the correlation between galaxy positions and cosmic shear and the cross correlation between galaxy positions. Comparing these correlations allowed the underlying dark matter distribution to be inferred. The two approaches led to the same results, providing a compelling consistency check on the weak-lensing dark matter map.

    The collaboration used the weak-lensing result to derive constraints on a number of cosmological parameters. In particular, they combined their data with data from other cosmological probes (such as CMB, BAO, and Type 1a supernovae) to derive the tightest constraints to date on the dark energy equation-of-state parameter (w), defined as the ratio of the pressure of the dark energy to its density. This parameter is related to the rate at which the density of dark energy evolves. The data indicate that w is equal to −1

    , within an experimental accuracy of a few percentage points. Such a value supports a picture in which dark energy is unchanging and equal to the inert energy of the vacuum—Einstein’s cosmological constant—rather than a more dynamical component, which many theorists had hoped for.

    One of the most important aspects of the DES reports is the comparison with the most recent CMB measurements from the Planck satellite mission [8]. The CMB is the radiation that was left over when light decoupled from matter around 380,000 years after the big bang, so Planck probes the Universe at high redshift ( z∼1100
    ). The DES data, on the other hand, concern much more recent times, at redshifts between 0.2 and 1.3. To check whether Planck and DES are consistent, the CMB-constrained parameters need to be extrapolated across cosmic history (from z∼1100 to z∼1) using the standard cosmological model. Within the experimental uncertainties, this extrapolation shows good agreement (Fig. 2), thus confirming the standard cosmological model’s predictive power across cosmic ages. While this success has to be cherished, everyone also silently hopes that experimenters will eventually find some breaches in the Λ

    CDM model, which could provide fresh hints as to what dark matter and dark energy are.

    The next few years will certainly be exciting for the field. DES already has five years of data in the bag and will soon release the analysis of their three-year results. Ultimately, DES will map 5000 deg2 , or one eighth of the full sky. The DES results are also very encouraging in view of the Large Synoptic Survey Telescope (LSST)—a telescope derived from the early concept of a “dark matter telescope” proposed in 1996. LSST should become operational in 2022, and it will survey almost the entire southern sky. Within this context, we can be hopeful that weak-lensing measurements will provide important insights into the most pressing open questions of cosmology.

    This research is published in Physical Review D.
    References

    T. M. C. Abbot et al., “Dark Energy Survey year 1 results: Cosmological constraints from galaxy clustering and weak lensing,” Phys. Rev. D 98, 043526 (2018); J. Elvin-Poole et al., “Dark Energy Survey year 1 results: Galaxy clustering for combined probes,” 98, 042006 (2018); J. Prat et al., “Dark Energy Survey year 1 results: Galaxy-galaxy lensing,” 98, 042005 (2018); M. A. Troxel et al., “Dark Energy Survey Year 1 results: Cosmological constraints from cosmic shear,” 98, 043528 (2018).
    A. Albrecht et al., “Report of the Dark Energy Task Force,” arXiv:0609591.
    D. M. Wittman et al., “Detection of weak gravitational lensing distortions of distant galaxies by cosmic dark matter at large scales,” Nature 405, 143 (2000); D. J. Bacon et al., “Detection of weak gravitational lensing by large-scale structure,” Mon. Not. R. Astron. Soc. 318, 625 (2000); N. Kaiser, G. Wilson, and G. A. Luppino, “Large-Scale Cosmic Shear Measurements,” arXiv:0003338; L. Van Waerbeke et al., “Detection of correlated galaxy ellipticities from CFHT data: First evidence for gravitational lensing by large-scale structures,” Astron. Astrophys. 358, No. 30, 2000.
    H. Lin et al., “The SDSS Co-add: Cosmic shear measurement,” Astrophys. J. 761, 15 (2012).
    F. Köhlinger et al., “KiDS-450: the tomographic weak lensing power spectrum and constraints on cosmological parameters,” Mon. Not. R. Astron. Soc. 471, 4412 (2017).
    R. Mandelbaum et al., “The first-year shear catalog of the Subaru Hyper Suprime-Cam Subaru Strategic Program Survey,” Publ. Astron. Soc. Jpn. 70, S25 (2017).
    It’s worth mentioning that the data analysis used “blinding,” a protocol in which the people carrying out the analysis cannot see the final results, so as to eliminate possible biases towards specific results..
    N. Aghanim et al. (Planck Collaboration), “Planck 2018 results. VI. Cosmological parameters,” arXiv:1807.06209.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments (physics@aps.org).

     
  • richardmitnick 2:39 pm on January 18, 2018 Permalink | Reply
    Tags: , , , , Dark Energy Survey, Journey of a Photon – from Camera to Catalog   

    From Dark Energy Survey: “Journey of a Photon – from Camera to Catalog” 

    Dark Energy Icon
    The Dark Energy Survey

    January 17, 2018
    Rutuparna Das

    This DArchive describes some of the process in making the Dark Energy Survey data set described in Dark Energy Survey Year 1 Results: Photometric data set for cosmology

    Raw astronomical images are beautiful. Little pinpricks of white scattered on a dark background compose a medley of stars, galaxies, and myriad other sources of light. To the casual observer, this is an archetypical piece of astronomical data. To a cosmologist, in this form, the image is pretty useless.

    From the moment a photon lands on a CCD – one of the imaging chips that makes up the Dark Energy Camera (DECam) – it must pass through an obstacle course of calibrations, transformations, and calculations before finding its way into a catalog of objects. This catalog is a cohesive listing of all relevant sources of light observed by DECam, and is the springboard for DES’s many explorations into the composition of the universe. Let us follow the progress of a photon as it passes through the DES data processing pipeline.

    1
    Achernar, aka Alpha Eri, the 10th brightest star in the sky, reflects off the structures that hold up DECam – right onto our image.

    Images that are deemed worthy continue on their journey through the pipeline. The first set of calibrations make the images usable for everyone, without any prior knowledge about the telescope or instrumentation necessary. Among other fixes, they:

    Remove background noise produced by DECam.
    Make flatfield corrections – the camera does not always detect light uniformly across the field of view. Every afternoon before a night of observations, we take images of a large piece of aluminum painted with a special white material that gives it a near-perfect matte finish. Ideally, these images should be perfectly uniformly white – any variations in brightness point out which areas need to be corrected in images taken the following night, and tell us how much to correct by.

    2
    Satellites passing through a DECam image.

    Adjust coordinates of each image to make sure we know where we are pointing – when the telescope moves from one area of the sky to the next, it ends up very close to its destination, but due to mechanical limitations is usually off by a very small amount. To make sure we measure object positions accurately, we find previously-discovered stars in each image, and align the image so the coordinates of these stars match their known positions.

    Remove “artifacts” – objects that intrude upon our images. Stars that are not bright enough to mess up an entire image can still sometimes “spill over” into camera pixels they should not occupy. Cosmic rays give off energy as they pass by, producing little worm-like structures in our images. Satellites and meteorites passing by – objects we eagerly try to spot with our eyes – are only nuisances when they show up in our data.

    3
    A bright star “spills over” into the row of nearby pixels.

    4
    Lots of cosmic rays! (Odd-looking wiggly or straight lines.)

    After these fixes, we create a catalog – a list of all sources of light in the resulting image. This catalog contains information on the position of each object, how bright it is, and how bright the background sky is.

    However, these brightnesses do not quite mean anything yet. External factors, such as atmospheric conditions or dust on the telescope optics, can make the brightness of an object vary from night to night. There is a long string of corrections – known as photometric calibrations – to undo these effects. In the first step, we take a few images each night of dense star fields, where we already know the properties of the stars from previous astronomical surveys. By comparing the known brightnesses of these stars to how bright they look each night in our data, we can measure the external effects and remove them from images taken that night. Further steps correct for this effect on nights where we could not observe the star fields, and run tests to double- and triple-check the quality of these corrections. Following these, we are finally done with calibrations for individual images.

    But the journey does not end there.

    The point of DES is to overlay many images of the same parts of sky. This helps us measure object properties with far greater precision, and lets us detect objects that are too faint to find in any one image. The area of sky DES looks at – its “footprint” – is divided into about ten thousand sections called “tiles.” Each tile is observed multiple times, using five different optical filters. Each filter lets in a certain range of light. Comparing the brightnesses of an object through different filters gives us information on that object’s true color.

    5
    Seen here are three images of the same galaxy, taken with the r, i, and z filters. The original images are all black-and-white (above). The brightness of each image gives us information about how much of each type of light we detect from the galaxy – i.e., how “red” an object is, etc. Putting this information together, we can generate a colored image of the galaxy. As some of our filters provide information about non-visible light (i.e. infrared), this image does not show us exactly what the galaxy would look like to our eyes, but gives us a sense of its color relative to the other objects we see.

    Multiple images of each tile, grouped by filter type, are stacked on top of each other. Each tile ends up with five stacked images, each one containing information from several images using the same filter. We then use these stacked images – also called coadded images – to create a new object catalog with one entry per object in the footprint, combining information from all images and filters. This catalog contains more precise information on object positions, their brightnesses through each filter, and a whole host of other data for each source of light.

    This catalog must now undergo quality cuts. Objects are removed for several reasons, including:

    They are only visible through some filters, but not all.
    They are too close to bright stars, which affect the light that reaches us from these objects.
    Their positions vary from filter to filter.
    The relative observed brightnesses through different filters are clearly off – i.e., the objects are “too blue” or “too red” compared to what actual cosmic objects look like.
    They are too close to us. Large objects in the foreground are some of the most beautiful parts of our images – sprawling spiral galaxies, magnificent globular clusters, the nearby Large Magellanic Cloud. When it comes to making actual cosmological measurements though, they are only nuisances, getting in the way of data from our precious background galaxies.

    6
    Spiral galaxies in the foreground. Image credit: Erin Sheldon

    7
    A globular cluster (center) getting in the way of observations of a possible galaxy cluster (lower right).

    The remaining set of objects live up to our gold standards for data, and are thus collectively known as the “GOLD” catalog.

    After passing through innumerable cuts, calibrations, image combinations, and cataloging, the photons that had landed on our camera have finally made their way into a usable form. There are still many more measurements to be made – object shapes, redshifts, classifications – but for now, we finally have a gold-standard catalog of the hundreds of millions of sources of light in the sky that we can use to do science.

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    See the full article here .

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    DECam, built at FNAL
    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile
    DECam, built at FNAL; NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile
    The Dark Energy Survey (DES) is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 120 scientists from 23 institutions in the United States, Spain, the United Kingdom, Brazil, and Germany are working on the project. This collaboration [has built] an extremely sensitive 570-Megapixel digital camera, DECam, and [has mounted] it on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory high in the Chilean Andes. Started in Sept. 2012 and continuing for five years, DES will survey a large swath of the southern sky out to vast distances in order to provide new clues to this most fundamental of questions.

     
  • richardmitnick 2:02 pm on November 1, 2017 Permalink | Reply
    Tags: , Dark Energy Survey, Jennifer Marshall, Texas A&M Astronomer Jennifer Marshall Witnesses Cosmic History in Chile, ,   

    From Texas A&M: Women in STEM – “Texas A&M Astronomer Jennifer Marshall Witnesses Cosmic History in Chile” 

    Texas A&M logo

    Texas A&M

    1

    Marshall (above and below), operating the Dark Energy Camera on the Blanco Telescope at the Cerro Tololo Inter-American Observatory in August 2017. The image displayed on the monitor is the gravitational wave event GW170817, the source just to the top left of the larger galaxy NGC 4993 in the center of the screen. (Credit: Erika Cook, Texas A&M University.)

    2

    “It was truly amazing. I felt so fortunate to be in the right place at the right time to help make perhaps one of the most significant observations of my career.”
    Dr. Jennifer Marshall, Texas A&M astronomer

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    August 17 dawned as the first day in an otherwise ordinary observing run for Texas A&M University astronomer Jennifer Marshall. She had arrived in Chile a few days earlier as part of another routine visit to the National Optical Astronomy Observatory’s (CTIO), distinguished solely by the fact that it happened to kick off the fifth and final year of the Dark Energy Survey (DES), a five-year international project led by the U.S. Department of Energy’s Fermi National Accelerator Laboratory to map one-eighth of the sky in unprecedented detail.

    CTIO Cerro Tololo Inter-American Observatory, CTIO Cerro Tololo Inter-American Observatory,approximately 80 km to the East of La Serena, Chile, at an altitude of 2200 meters

    However, just as swiftly as day turned to night and darkness descended over the Andes Mountains, Marshall found herself at the fateful crossroads of proximity and cosmic history, courtesy of one universally significant target of opportunity observation.

    By virtue of being in the right place at the right time, Marshall got to witness firsthand the fiery aftermath of a recently detected burst of gravitational waves, personally recording some of the initial images of the first confirmed explosion from two colliding neutron stars ever seen by astronomers.

    The discovery, historic because it marks the first cosmic event observed in both gravitational waves and light, was made using the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO); the Europe-based Virgo detector in Italy; and more than 60 ground- and space-based telescopes.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    During the course of seven days in Chile, Marshall watched the extraordinary event play out in real time through two telescopes — the 4-meter Victor M. Blanco Telescope at CTIO, then moving on to the 6.5-meter Magellan Telescope at nearby Las Campanas Observatory. She was the only astronomer present and observing for DES at Blanco during the unprecedented occurrence.

    3
    The Twin Magellan telescope domes on Cerro Manqui at 8370 feet (2450 m) above sea level. Each dome houses a 6.5-meter class telescope, with the Landon Clay telescope in the left dome and
    Walter Baade telescope in the right dome. The building connecting the two domes serves as a storage area for various instruments and a maintenance facility for realuminizing the mirrors.
    Note the tall, slender silo next to the domes. This is a differential image motion monitor (DIMM) telescope used to measure atmospheric seeing.

    “It is my observation that every telescope in Chile, including the two I was using, was pointed at this thing for the entire week,” Marshall said. “It was definitely the most important science I have ever had the opportunity to be involved in.”

    Images taken by Marshall using the 570-megapixel Dark Energy Camera (DECam) captured the flaring up and fading over time of a kilonova — an explosion similar to a supernova but on a smaller scale — that occurs when collapsed stars, called neutron stars, crash into each other, theoretically creating heavy radioactive elements.

    This particular violent merger, which occurred 130 million years ago in a galaxy (NGC 4993) relatively near our own Milky Way galaxy, is the source of the gravitational waves detected by the LIGO and the Virgo collaborations on Aug. 17. Although this is the fifth source of gravitational waves to be detected, it is unique because it is the first one with a visible electromagnetic counterpart observable by optical telescopes — the glowing aftermath of the collision of two neutron stars — as opposed to binary black holes, which are not expected to produce a remnant that can be seen through telescopes.

    Capitalizing on a Target of Opportunity

    When DES officials at Fermilab learned along with dozens of LIGO-affiliated collaborations and observatories around the world that a strong gravitational signal, named GW170817, had been detected at 7:41 a.m. CDT by two of LIGO’s three detectors — a find further corroborated by a gamma-ray burst detected by NASA’s Fermi Gamma-ray Space Telescope at roughly the same time — they sent out a target of opportunity observation notice that Marshall quickly seized upon.

    As she was observing at Blanco, Marshall was simultaneously collaborating via Skype with fellow DES scientists Marcelle Soares-Santos (Fermilab/Brandeis University), the DES principal investigator in charge of gravitational wave observations, and Daniel Holtz (University of Chicago), who is a member of both LIGO and DES. Coincidentally, Marshall also was sharing some of those nights via remote with Ting Li ’16, who earned her doctorate in astronomy at Texas A&M in 2016 working with Marshall and currently is a Lederman Fellow in Experimental Physics at Fermilab.

    “LIGO tells you the equivalent of, ‘If you look in this area of the sky, there might be something,'” Marshall explained. “Virgo helped narrow that area down to the extent that, instead of 100 square degrees, it was only 30. DECam has a large field of view of three square degrees, so we only had to look at 30 telescope pointings. I was there with Erika Cook, our Munnerlyn Astronomical Laboratory control systems engineer, and Marcus Sauseda, an undergraduate aerospace engineering major here at Texas A&M, and we took some quick, short exposures — a total of roughly one hour. I sent the data off, then went to bed. I woke up to an ecstatic email from Edo Berger at Harvard, who happens to be a longtime colleague from our postdoc days at The Observatories of the Carnegie Institution of Washington.”

    Armed with the crystal-clear images from DECam, for which Texas A&M astronomer Darren DePoy served as project scientist, Berger’s team went to work analyzing the phenomenon using several different resources, including NASA’s Hubble Space Telescope and Chandra X-ray Observatory. For her part, Marshall continued imaging the galaxy for five more nights at CTIO, watching the event fade rapidly and change in color from blue to red as the explosion quickly cooled down. She then spent a seventh night at Las Campanas, doing follow-up observation with the Magellan telescope, using a different spectrometer to enable more detailed study of the event in collaboration with Carnegie Observatories scientists Maria Drout and Ben Shappee.

    Jennifer Marshall may have been one of many astronomers observing GW170817 from both ground- and space-based telescopes on Aug. 17, but she likely was the only one who happened to have a film crew in tow. Check out this video produced by NOVA PBS, present at CTIO at the time, shooting footage for an upcoming segment on the Dark Energy Survey. Catch Marshall at the 0:45, 1:10 and 1:42 marks!

    Byproducts of a Binary Star Merger

    Understandable excitement aside, Marshall says this event is particularly interesting to her because it is directly related her research on r-process elements — the heavy elements that exist on Earth and are produced in theory as the byproducts of neutron star collisions and mergers. These observations show that the theory is accurate, providing the final piece of the puzzle regarding the origin of r-process elements.

    “This was the first time anyone has ever watched such an event play out from beginning to end, all thanks to LIGO,” Marshall said. “It was truly amazing. Watching science happen in real time is not something most astronomers get to experience. With the exception of supernovae and exoplanet studies, most things we work on take billions of years to play out. I felt so fortunate to be in the right place at the right time to help make perhaps one of the most significant observations of my career.”

    Marshall said one indication of just how well LIGO/Virgo is working is the amount of event follow-up requests, which are so numerous as a result of its second and most recent observing run since being upgraded via a program called Advanced LIGO that astronomers have been forced to prioritize.

    “There were actually several binary black hole mergers that same week that we didn’t bother to look at because the neutron star source was so much more important,” Marshall said. “We had absolutely no idea this was going to happen. Everyone was shocked, and understandably so, because it was truly unbelievable.”

    In addition to Marshall and DePoy, fellow Texas A&M astronomers and Mitchell Institute members Lucas Macri, Casey Papovich, Nicholas Suntzeff and Louis Strigari are full members of the 400-plus-member international DES collaboration that spans 26 institutions and seven countries as well as the gamut of science and engineering in the search for answers regarding the universe’s accelerated expansion. Texas A&M statistician James Long and Mitchell Institute Postdoctoral Fellow Peter Brown also are external collaborators.

    Publications Aplenty

    The LIGO-Virgo results are published today in the journal Physical Review Letters, while additional papers from the LIGO and Virgo collaborations and the astronomical community either have been submitted or accepted for publication in various journals.

    Six papers relating to the DECam discovery of the optical counterpart are planned for publication in The Astrophysical Journal. Preprints of all papers are available online.

    Marshall’s observations made during that fateful August week in Chile appear in a total of nine publications making their debut today, including the mega paper from LIGO that includes citations for 75 associated papers, in addition to two DES-related papers appearing in The Astrophysical Journal as well as two papers in the journal Science featuring the Las Campanas spectra and images. Beyond those, she is an author on three additional DES papers, including one that uses the binary neutron star merger event to derive the Hubble constant. DePoy and Li join her as co-authors on several of those papers by virtue of their status as fellow DES Builders. Finally, she is an author on the Transient Optical Robotic Observatory of the South (TOROS) Collaboration paper in The Astrophysical Journal Letters.

    “The August 17 binary neutron star merger event occurred in nearby galaxy NGC 4993, located at a distance of 39.5 megaparsecs from the Milky Way,” Marshall said. “This event will surely usher in a new field of science, the direct observational study of the formation of r-process elements starting now and being fueled by future discovery of similar events by LIGO and follow-up study by astronomers.”

    Read more on today’s announcement and its broader significance in the official press releases from LIGO/Virgo , DES/Fermilab, which include additional images along with animations and videos and from From UCSC: “Neutron stars, gravitational waves, and all the gold in the universe”, which tells the optical astronomy part of the story. This last, written by Tim Stephens is quite a production, complete with a 2.5 hour video of the press conference is not to be missed.

    Learn more about the Texas A&M Astronomy Group’s broader role in the imaging and analyses.

    For more information about Texas A&M astronomy, visit http://astronomy.tamu.edu.

    See the full article here .

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    Located in College Station, Texas, about 90 miles northwest of Houston and within a two to three-hour drive from Austin and Dallas.
    Home to more than 50,000 students, ranking as the sixth-largest university in the country, with more than 370,000 former students worldwide.
    Holds membership in the prestigious Association of American Universities, one of only 62 institutions with this distinction.
    More than $820 million in research expenditures generated by faculty-researchers
    Has an endowment valued at more than $5 billion, which ranks fourth among U.S. public universities and 10th overall.

     
  • richardmitnick 3:28 pm on October 16, 2017 Permalink | Reply
    Tags: , , , , Dark Energy Survey, ,   

    From Symmetry: “Scientists observe first verified neutron-star collision” 


    Symmetry

    10/16/17
    Sarah Charley

    1
    Fermilab

    Today scientists announced the first verified observation of a neutron star collision. LIGO detected gravitational waves radiating from two neutron stars as they circled and merged, triggering 50 additional observational groups to jump into action and find the glimmer of this ancient explosion.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    This observation represents the first time experiments have seen both light and gravitational waves from a single celestial crash, unlocking a new era of multi-messenger astronomy.

    On August 17 at 7:41 a.m. Eastern Time, NASA astronomer Julie McEnery had just returned from an early morning row on the Anacostia River when her experiment, the Fermi Gamma Ray Space Telescope, sent out an automatic alert that it had just recorded a burst of gamma rays coming from the southern constellation Hydra.

    NASA/Fermi Telescope


    NASA/Fermi LAT

    By itself, this wasn’t novel; the Gamma-ray Burst Monitor instrument on Fermi has seen approximately 2 gamma-ray outbursts per day since its launch in 2008.

    “Forty minutes later, I got an email from a colleague at LIGO saying that our trigger has a friend and that we should buckle up,” McEnery says.

    Most astronomy experiments, including the Fermi Gamma Ray Space Telescope, watch for light or other particles emanating from distant stars and galaxies. The LIGO experiment, on the other hand, listens for gravitational waves. Gravitational waves are the equivalent of cosmic tremors, but instead of rippling through layers of rock and dirt, they stretch and compress space-time itself.

    Exactly 1.7 seconds before Fermi noticed the gamma ray burst, a set of extremely loud gravitational waves had shaken LIGO’s dual detectors.

    “The sky positions overlapped, strongly suggesting the two signals were coming from the same astronomical event,” says Daniel Holz, a professor at the University of Chicago and member of LIGO collaboration and the Dark Energy Survey Gravitational Wave group.

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam

    LIGO reconstructed the location and distance of the event and sent an alert to their allied astronomers. About 12 hours later, right after sunset, multiple astronomical surveys found a glowing blue dot just above the horizon in the area LIGO predicted.

    “It lasted for two weeks, and we observed it for about an hour every night,” says Jim Annis, a researcher at the US Department of Energy’s Fermi National Accelerator Laboratory, the lead institution on the Dark Energy Survey. “We used telescopes that could see everything from low-energy radio waves all the way to high-energy X-rays, giving us a detailed image of what happened immediately after the initial collision.”

    Neutron stars are roughly the size of the island of Nantucket but have more mass than the sun. They have such a strong gravitational pull that all their matter has been squeezed and transformed into a single, giant atomic nucleus consisting entirely of neutrons.

    “Right before two neutron stars collide, they circle each other about 100 times a second,” Annis says. “As they collide, huge electromagnetic tornados erupt at the poles and material is sprayed out in all directions at close to the speed of light.”

    As they merge, neutron stars release a quick burst of gamma radiation and then a spray of decompressing neutron star matter. Exotic heavy elements form and decay, dumping enough energy that the surface reaches temperatures of 20,000 degrees Kelvin. That’s almost four times hotter than the surface of the sun and much brighter. Scientists theorize that a good portion of the heavy elements in our universe, such as gold, originated in neutron star collisions and other massively energetic events.

    Since coming online in September 2015, the US-based LIGO collaboration and their Italy-based partners, the Virgo collaboration, have reported detecting five bursts of gravitational waves. Up until now, each of these observations has come from a collision of black holes.

    “When two black holes collide, they emit gravitational waves but no light,” Holz says. “But this event released an enormous amount of light and numerous astronomical surveys saw it. Hearing and seeing the event provides a goldmine of information, and we will be mining the data for years to come.”

    This is a Rosetta Stone-type discovery, Holz says. “We’ve learned about the processes that neutron stars are undergoing as they fling out matter and how this matter synthesizes into some of the elements we find on Earth, such as gold and platinum,” he says. “In addition to teaching us about mysterious gamma-ray bursts, we can use this event to calculate the expansion rate of the universe. We will be able to estimate the age and composition of the universe in an entirely new way.”

    For McEnery, the discovery ushers in a new age of cooperation between gravitational-wave experiments and experiments like her own.

    “The light and gravitational waves from this collision raced each other across the cosmos for 130 million years and hit earth 1.7 seconds apart,” she says. “This shows that both are moving at the speed of light, as predicted by Einstein. This is what we’ve been hoping to see.”

    Editor’s note: See LIGO scientific publications here.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 9:38 am on August 3, 2017 Permalink | Reply
    Tags: , , , , Dark Energy Survey, ,   

    From U Chicago: “Dark Energy Survey reveals most precise measure of universe’s structure” 

    U Chicago bloc

    University of Chicago

    August 3, 2017

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet


    The Dark Energy Survey’s primary instrument, the 570-megapixel Dark Energy Camera, is mounted on the Blanco Telescope in Chile. UChicago, Argonne and Fermilab scientists are members of international Dark Energy Survey collaboration.

    Imagine planting a single seed and, with great precision, being able to predict the exact height of the tree that grows from it. Now imagine traveling to the future and snapping photographic proof that you were right.

    If you think of the seed as the early universe, and the tree as the universe the way it looks now, you have an idea of what the international Dark Energy Survey collaboration has just done. Scientists unveiled their most accurate measurement of the present large-scale structure of the universe at a meeting Aug. 3 at the University of Chicago-affiliated Fermi National Accelerator Laboratory. UChicago, Argonne and Fermilab scientists are members of international Dark Energy Survey collaboration.

    These measurements of the amount and “clumpiness” (or distribution) of dark matter in the present-day cosmos were made with a precision that, for the first time, rivals that of inferences from the early universe by the European Space Agency’s orbiting Planck observatory. The new Dark Energy Survey result (the tree, in the above metaphor) is close to “forecasts” made from the Planck measurements of the distant past (the seed), allowing scientists to understand more about the ways the universe has evolved over 14 billion years.

    “This result is beyond exciting,” said Fermilab’s Scott Dodelson, a professor in the Department of Astronomy and Astrophysics at UChicago and one of the lead scientists on this result, which was announced at the American Physical Society Division of Particles and Fields meeting. “For the first time, we’re able to see the current structure of the universe with the same clarity that we can see its infancy, and we can follow the threads from one to the other, confirming many predictions along the way.”

    Most notably, this result supports the theory that 26 percent of the universe is in the form of mysterious dark matter and that space is filled with an also-unseen dark energy, which makes up 70 percent and is causing the accelerating expansion of the universe.

    1
    A map of dark matter covering about one-thirtieth of the entire sky and spanning several billion light years—red regions have more dark matter than average, blue regions less dark matter. (Courtesy of Chihway Chang, the DES collaboration)

    Paradoxically, it is easier to measure the large-scale clumpiness of the universe in the distant past than it is to measure it today. In the first 400,000 years following the Big Bang, the universe was filled with a glowing gas, the light from which survives to this day. The Planck observatory’s map of this cosmic microwave background radiation gives us a snapshot of the universe at that very early time. Since then, the gravity of dark matter has pulled mass together and made the universe clumpier over time. But dark energy has been fighting back, pushing matter apart. Using the Planck map as a start, cosmologists can calculate precisely how this battle plays out over 14 billion years.

    “These first major cosmology results are a tribute to the many people who have worked on the project since it began 14 years ago,” said Dark Energy Survey Director Josh Frieman, a scientist at Fermilab and a professor in the Department of Astronomy and Astrophysics at UChicago. “It was an exciting moment when we unveiled the results to ourselves just last month, after carrying out a ‘blind’ analysis to avoid being influenced by our prejudices.”

    The Dark Energy Survey is a collaboration of more than 400 scientists from 26 institutions in seven countries. Its primary instrument is the 570-megapixel Dark Energy Camera, one of the most powerful in existence, which is able to capture digital images of light from galaxies eight billion light years from Earth. The camera was built and tested at Fermilab, the lead laboratory on the Dark Energy Survey, and is mounted on the National Science Foundation’s four-meter Blanco telescope, part of the Cerro Tololo Inter-American Observatory in Chile. The DES data are processed at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.

    Scientists are using the camera to map an eighth of the sky in unprecedented detail over five years. The fifth year of observation will begin this month. The new results draw only from data collected during the survey’s first year, which covers one-thirtieth of the sky.

    Scientists used two methods to measure dark matter. First, they created maps of galaxy positions as tracers, and second, they precisely measured the shapes of 26 million galaxies to directly map the patterns of dark matter over billions of light years, using a technique called gravitational lensing.

    Gravitational Lensing NASA/ESA

    To make these ultra-precise measurements, the team developed new ways to detect the tiny lensing distortions of galaxy images—an effect not even visible to the eye, enabling revolutionary advances in understanding these cosmic signals. In the process, they created the largest guide to spotting dark matter in the cosmos ever drawn. The new dark matter map is ten times the size of the one that the Dark Energy Survey released in 2015 and will eventually be three times larger than it is now.

    “The Dark Energy Survey has already delivered some remarkable discoveries and measurements, and they have barely scratched the surface of their data,” said Fermilab Director Nigel Lockyer. “Today’s world-leading results point forward to the great strides DES will make toward understanding dark energy in the coming years.”

    See the full article here .

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    U Chicago Campus

    An intellectual destination

    One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

     
  • richardmitnick 2:16 pm on June 10, 2017 Permalink | Reply
    Tags: , , , , , Dark Energy Survey, , The largest virtual Universe ever simulated, U Zürich   

    From U Zürich: “The largest virtual Universe ever simulated.” 

    University of Zürich

    9 June 2017
    Contact
    Prof. Dr. Romain Teyssier
    romain.teyssier@uzh.ch
    Institute for Computational Science
    University of Zurich
    +41 44 635 60 20

    Dr. Joachim Stadel
    stadel@physik.uzh.ch
    Institute for Computational Science
    University of Zurich
    Phone: +41 44 635 58 16

    Researchers from the University of Zürich have simulated the formation of our entire Universe with a large supercomputer. A gigantic catalogue of about 25 billion virtual galaxies has been generated from 2 trillion digital particles. This catalogue is being used to calibrate the experiments on board the Euclid satellite, that will be launched in 2020 with the objective of investigating the nature of dark matter and dark energy.

    ESA/Euclid spacecraft

    1
    The Cosmic Web: A section of the virtual universe, a billion light years across, showing how dark matter is distributed in space, with dark matter halos the yellow clumps, interconnected by dark filaments. Cosmic void, shown as the white areas, are the lowest density regions in the Universe. (Image: Joachim Stadel, UZH)

    Over a period of three years, a group of astrophysicists from the University of Zürich has developed and optimised a revolutionary code to describe with unprecedented accuracy the dynamics of dark matter and the formation of large-scale structures in the Universe. As Joachim Stadel, Douglas Potter and Romain Teyssier report in their recently published paper [Computational Astrophysics and Cosmology], the code (called PKDGRAV3) has been designed to use optimally the available memory and processing power of modern supercomputing architectures, such as the “Piz Daint” supercomputer of the Swiss National Computing Center (CSCS). The code was executed on this world-leading machine for only 80 hours, and generated a virtual universe of two trillion (i.e., two thousand billion or 2 x 1012) macro-particles representing the dark matter fluid, from which a catalogue of 25 billion virtual galaxies was extracted.

    Cray Piz Daint supercomputer of the Swiss National Supercomputing Center (CSCS)

    Studying the composition of the dark universe

    Thanks to the high precision of their calculation, featuring a dark matter fluid evolving under its own gravity, the researchers have simulated the formation of small concentration of matter, called dark matter halos, in which we believe galaxies like the Milky Way form.

    Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

    The challenge of this simulation was to model galaxies as small as one tenth of the Milky Way, in a volume as large as our entire observable Universe. This was the requirement set by the European Euclid mission, whose main objective is to explore the dark side of the Universe.

    Measuring subtle distortions

    Indeed, about 95 percent of the Universe is dark. The cosmos consists of 23 percent of dark matter and 72 percent of dark energy. “The nature of dark energy remains one of the main unsolved puzzles in modern science,” says Romain Teyssier, UZH professor for computational astrophysics.

    Earthbound science of Dark Energy

    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam

    A puzzle that can be cracked only through indirect observation: When the Euclid satellite will capture the light of billions of galaxies in large areas of the sky, astronomers will measure very subtle distortions that arise from the deflection of light of these background galaxies by a foreground, invisible distribution of mass – dark matter. “That is comparable to the distortion of light by a somewhat uneven glass pane,” says Joachim Stadel from the Institute for Computational Science of the UZH.

    Optimizing observation strategies of the satellite

    This new virtual galaxy catalogue will help optimize the observational strategy of the Euclid experiment and minimize various sources of error, before the satellite embarks on its six-year data collecting mission in 2020. “Euclid will perform a tomographic map of our Universe, tracing back in time more than 10-billion-year of evolution in the cosmos,” Stadel says. From the Euclid data, researchers will obtain new information on the nature of this mysterious dark energy, but also hope to discover new physics beyond the standard model, such as a modified version of general relativity or a new type of particle.

    See the full article here .

    Please help promote STEM in your local schools.

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    The University of Zürich (UZH, German: Universität Zürich), located in the city of Zürich, is the largest university in Switzerland, with over 26,000 students. It was founded in 1833 from the existing colleges of theology, law, medicine and a new faculty of philosophy.

    Currently, the university has seven faculties: Philosophy, Human Medicine, Economic Sciences, Law, Mathematics and Natural Sciences, Theology and Veterinary Medicine. The university offers the widest range of subjects and courses of any Swiss higher education institutions.

     
  • richardmitnick 9:59 pm on June 6, 2017 Permalink | Reply
    Tags: , , , , Dark Energy Survey, ,   

    From FNAL: “Scientists close in on dark matter using Dark Energy Survey data” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    June 6, 2017
    Troy Rummler

    Scientists exploring data collected by the Fermilab-constructed, Chilean-based Dark Energy Camera (DECam) discovered 20 satellite galaxies of the Milky Way, nearly doubling the number previously known and adding to those identified by the earlier Sloan Digital Sky Survey, another project where Fermilab played a key role. These tiny satellite galaxies can contain hundreds of times more dark matter than normal matter. Whether the mysterious dark matter turns out to be axions, weakly interacting massive particles or something else, DECam has proven itself to be a powerful new tool for the dark matter community.


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam

    See the full article here .

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    FNAL Icon
    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 9:16 am on February 22, 2017 Permalink | Reply
    Tags: , , , , Dark Energy Survey, Paul Sutter,   

    From CBS: “When the lights went out in the universe” 

    CBS News

    CBS News

    February 21, 2017
    Paul Sutter

    1
    Astronomers think that the expansion of the universe is regulated by both the force of gravity, and a mysterious dark energy. In this artist’s conception, dark energy is represented by the purple grid above, and gravity by the green grid below.
    NASA/JPL-Caltech

    About 5 billion years ago, everything changed. The expansion of the universe, which had been gradually decelerating for billions of years, reversed course and entered into a period of unbridled acceleration. (It was sort of like a car that switches from decelerating to accelerating, but is still moving forward the whole time.) The unhurried, deliberate process of structure formation — the gradual buildup of ever-larger assemblies of matter from galaxies to groups to clusters — froze and began to undo itself.

    Map of voids and superclusters within 500 million light years from Milky Way 8/11/09 http://www.atlasoftheuniverse.com/nearsc.html  Richard Powell
    Map of voids and superclusters within 500 million light years from Milky Way 8/11/09 http://www.atlasoftheuniverse.com/nearsc.html Richard Powell

    Five billion years ago, a mysterious force overtook the universe. Hidden in the shadows, it lay dormant, buried underneath fields of matter and radiation. But once it uncovered itself, it worked quickly, bending the entire cosmos to its will.

    Five billion years ago, dark energy awoke.

    The guts of the universe

    To explain what’s going on in this overly dramatic telling of the emergence of dark energy, we need to talk about what the universe is made of and how that affects its expansion.

    Let’s start with the mantra of general relativity: mass and energy tell space-time how to bend, and the bending of space-time tells objects how to move. Usually, we think of this as a local interaction, used to explain the orbits of particular planets or the unusual properties of a black hole.

    But those same mathematics of relativity — which provide the needed accuracy for GPS satellites to tell you how close you are to your coffee fix — also serve as the foundation for understanding the growth and evolution of the entire universe. I mean, it is “general” relativity after all.

    The universe is made of all sorts of stuff, and the properties of that stuff influence the overall curvature of the entire cosmos, which impacts its expansion. It’s the mantra of relativity writ large: the mass and energy of the entire universe is bending the spacetime of the entire universe, which is telling the entire universe how to move.

    If the total density of all the stuff is greater than a very specific value — called “the critical density” and equal to about 4 hydrogen atoms per cubic meter — then the universe’s expansion will slow down, stop and reverse in a Big Crunch. If the universe’s density is less than this critical value, the universe will expand forever. And if it’s exactly equal to the critical value, then the universe will expand forever, but at an ever-diminishing rate.

    Measurements suggest that we live in a contradictory universe, where the total density exactly equals the critical density — but the universe’s expansion is still accelerating as if the density was too low.

    What in Hubble’s ghost is going on?

    An empty argument

    What’s going on is dark energy. Totaling 69.2 percent of the energy density of the universe, it simply behaves … strangely. Dark energy’s most important property is that its density is constant. Its second most important property is that it appears to be tied to the vacuum of empty space.

    Dark Energy Icon
    Dark Energy Camera. Built at FNAL
    Dark Energy Camera. Built at FNAL
    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile
    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile

    Take a box, and empty out everything, removing all the matter (regular and dark), neutrinos, radiation … everything. If you did it right, you’ll have a box of pure, unadulterated vacuum — which means you’ll have a box of pure dark energy. Double the size of the box, and you’ll have double the dark energy.

    This behavior is the total opposite of the behavior of matter and radiation. If you have a box (or, say, a universe) with a fixed amount of matter and you double that container’s volume, the density of matter is cut in half. Radiation’s energy density goes down even further: Not only does the expansion of the universe dilute radiation, it also stretches out its wavelength.

    But as the universe expands, we continually get more empty space (vacuum) in it, so we continually get more dark energy. If you’re worried that this violates some sort of principle of conservation of energy, you can rest easy tonight: The universe is a dynamic system, and the form of the conservation laws taught in Physics 101 only apply to static systems. The universe is a dynamic place, and the concept of “conservation of energy” still holds but in a more complex, noninuitive way. But that’s an article for another day.

    You may also be wondering how I can talk so confidently about the nature of dark energy, since we don’t seem to understand it at all. You’re right: We don’t understand dark energy. At all. We know it exists, because we directly observe the accelerated expansion of the universe, and a half-dozen other lines of evidence all point to its existence.

    And while we don’t know what’s creating the accelerated expansion, we do know that we can model it as a property of the vacuum of space that has a constant density, so that’s good enough for now.

    A vacuum and an empty place

    The fact that dark energy has constant density means that in the distant past, it simply didn’t matter — because of matter. All the stuff in the universe was crammed into a smaller volume, which means regular and dark matter had very high densities. This high density meant that for a long time, the expansion of the universe was slowing down.


    The day Dark Energy switched on – Ask a Spaceman! by Paul M. Sutter on YouTube

    But as expansion continued, the matter and radiation in the universe became more and more dilute, and they got less and less dense. Eventually, about 5 billion years ago, the density of matter dropped beneath that of dark energy, which had been holding constant all that time. And once dark energy took over, the game changed completely. Because of the constant nature of its density, compared to the lowering density of matter, expansion not only continued but also accelerated. And that accelerated expansion halted the process of structure formation: Galaxies would love to continue gluing onto each other to form larger structures like clusters and superclusters, but the intervening empty space is inexorably pulling them apart.

    Some chance mergers will continue to happen, of course, but the universe’s days of building larger structures are long over.

    A cosmic coincidence

    The emergence of dark energy leaves us with a little puzzle. In the distant past, when matter densities were incredibly high in a compact universe, dark energy didn’t matter at all. In the distant future, matter will be spread so thin — like too little butter over too much bread — that its density will be ridiculously, hilariously, pathetically small compared to dark energy’s.

    Dark energy depiction. Image: Volker Springle/Max Planck Institute for Astrophysics/SP)
    Dark energy depiction. Image: Volker Springle/Max Planck Institute for Astrophysics/SP


    The surprising coincidence between dark matter and dark energy – Ask a Spaceman! by Paul M. Sutter on YouTube

    Right now, we live in the in-between epoch, where dark energy is roughly three-quarters of the total mass-energy of the universe and dark matter is about one-quarter (regular matter is a negligible amount). This seems a bit … coincidental. Considering the grand history of the universe, we just happen to observe it in the tiny slice of time when matter and dark energy are trading places.

    Did we just happen to get lucky? To arise to consciousness and observe the universe where both dark matter and dark energy are of roughly equal strength? Or is the universe telling us something more? Maybe it’s not a coincidence at all. Maybe dark matter and dark energy “talk” to each other and keep in balance via additional forces of nature; forces that simply don’t manifest in Earthly laboratories. Maybe they’re connected and related.

    Or maybe not. We simply don’t know. It’s a little too dark out there to tell.

    Paul Sutter is an astrophysicist at The Ohio State University and the chief scientist at COSI Science Center. Sutter is also host of Ask a Spaceman, RealSpace and COSI Science Now.

    See the full article here .

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