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  • richardmitnick 2:19 pm on January 14, 2020 Permalink | Reply
    Tags: "Have Dark Forces Been Messing With the Cosmos?", Alan Guth MIT "Inflation", , , , , CMB per Planck, , , Dark Energy Survey, Discrepancy in how fast the niverse is expanding., Edwin Hubble in 1929 discovers the Universe is Expanding, , , Saul Perlmutter [The Supernova Cosmology Project] shared the 2006 Shaw Prize in Astronom; the 2011 Nobel Prize in Physics; and the 2015 Breakthrough Prize in Fundamental Physics with Brian P. Schmidt ,   

    From The New York Times: “Have Dark Forces Been Messing With the Cosmos?” 


    From The New York Times

    Feb. 25, 2019 [Sorry, missed the first time around. Picked up from another article found today by Dennis Overbye]
    Dennis Overbye

    1
    Brian Stauffer

    There was, you might say, a disturbance in the Force.

    Long, long ago, when the universe was only about 100,000 years old — a buzzing, expanding mass of particles and radiation — a strange new energy field switched on. That energy suffused space with a kind of cosmic antigravity, delivering a not-so-gentle boost to the expansion of the universe.

    Then, after another 100,000 years or so, the new field simply winked off, leaving no trace other than a speeded-up universe.

    So goes the strange-sounding story being promulgated by a handful of astronomers from Johns Hopkins University. In a bold and speculative leap into the past, the team has posited the existence of this field to explain an astronomical puzzle: the universe seems to be expanding faster than it should be.

    The cosmos is expanding only about 9 percent more quickly than theory prescribes. But this slight-sounding discrepancy has intrigued astronomers, who think it might be revealing something new about the universe.

    And so, for the last couple of years, they have been gathering in workshops and conferences to search for a mistake or loophole in their previous measurements and calculations, so far to no avail.

    “If we’re going to be serious about cosmology, this is the kind of thing we have to be able to take seriously,” said Lisa Randall, a Harvard theorist who has been pondering the problem.

    At a recent meeting in Chicago, Josh Frieman, a theorist at the Fermi National Accelerator Laboratory [FNAL] in Batavia, Ill., asked: “At what point do we claim the discovery of new physics?”

    Now ideas are popping up. Some researchers say the problem could be solved by inferring the existence of previously unknown subatomic particles. Others, such as the Johns Hopkins group, are invoking new kinds of energy fields.

    Adding to the confusion, there already is a force field — called dark energy — making the universe expand faster.

    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

    Timeline of the Inflationary Universe WMAP

    The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

    According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

    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 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

    Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

    And a new, controversial report suggests that this dark energy might be getting stronger and denser, leading to a future in which atoms are ripped apart and time ends.

    Thus far, there is no evidence for most of these ideas. If any turn out to be right, scientists may have to rewrite the story of the origin, history and, perhaps, fate of the universe.

    Or it could all be a mistake. Astronomers have rigorous methods to estimate the effects of statistical noise and other random errors on their results; not so for the unexamined biases called systematic errors.

    As Wendy L. Freedman, of the University of Chicago, said at the Chicago meeting, “The unknown systematic is what gets you in the end.”

    Edwin Hubble looking through a 100-inch Hooker telescope at Mount Wilson in Southern California, 1929 discovers the Universe is Expanding

    Edwin Hubble in 1949, two decades after he discovered that the universe is expanding.Credit…Boyer/Roger Viollet, via Getty Images (credit: Emilio Segre Visual Archives/AIP/SPL)

    Hubble trouble

    Generations of great astronomers have come to grief trying to measure the universe. At issue is a number called the Hubble constant, named after Edwin Hubble, the Mount Wilson astronomer who in 1929 discovered that the universe is expanding.

    As space expands, it carries galaxies away from each other like the raisins in a rising cake. The farther apart two galaxies are, the faster they will fly away from each other. The Hubble constant simply says by how much.

    But to calibrate the Hubble constant, astronomers depend on so-called standard candles: objects, such as supernova explosions and certain variable stars, whose distances can be estimated by luminosity or some other feature. This is where the arguing begins.

    Standard Candles to measure age and distance of the universe from supernovae. NASA

    Until a few decades ago, astronomers could not agree on the value of the Hubble constant within a factor of two: either 50 or 100 kilometers per second per megaparsec. (A megaparsec is 3.26 million light years.)

    But in 2001, a team using the Hubble Space Telescope, and led by Dr. Freedman, reported a value of 72. For every megaparsec farther away from us that a galaxy is, it is moving 72 kilometers per second faster.

    More recent efforts by Adam G. Riess [The Astrophysical Journal], of Johns Hopkins and the Space Telescope Science Institute, and others have obtained similar numbers, and astronomers now say they have narrowed the uncertainty in the Hubble constant to just 2.4 percent.

    But new precision has brought new trouble. These results are so good that they now disagree with results from the European Planck spacecraft, which predict a Hubble constant of 67.

    The discrepancy — 9 percent — sounds fatal but may not be, astronomers contend, because Planck and human astronomers do very different kinds of observations.

    Planck is considered the gold standard of cosmology. It spent four years studying the cosmic bath of microwaves [CMB] left over from the end of the Big Bang, when the universe was just 380,000 years old.

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    But it did not measure the Hubble constant directly. Rather, the Planck group derived the value of the constant, and other cosmic parameters, from a mathematical model largely based on those microwaves.

    In short, Planck’s Hubble constant is based on a cosmic baby picture. In contrast, the classical astronomical value is derived from what cosmologists modestly call “local measurements,” a few billion light-years deep into a middle-aged universe.

    What if that baby picture left out or obscured some important feature of the universe?

    ‘Cosmological Whac-a-Mole’

    And so cosmologists are off to the game that Lloyd Knox, an astrophysicist from the University of California, Davis, called “cosmological Whac-a-Mole” at the recent Chicago meeting: attempting to fix the model of the early universe, to make it expand a little faster without breaking what the model already does well.

    One approach, some astrophysicists suggest, is to add more species of lightweight subatomic particles, such as the ghostlike neutrinos, to the early universe. (Physicists already recognize three kinds of neutrinos, and argue whether there is evidence for a fourth variety.) These would give the universe more room to stash energy, in the same way that more drawers in your dresser allow you to own more pairs of socks. Thus invigorated, the universe would expand faster, according to the Big Bang math, and hopefully not mess up the microwave baby picture.

    A more drastic approach, from the Johns Hopkins group, invokes fields of exotic anti-gravitational energy. The idea exploits an aspect of string theory, the putative but unproven “theory of everything” that posits that the elementary constituents of reality are very tiny, wriggling strings.

    String theory suggests that space could be laced with exotic energy fields associated with lightweight particles or forces yet undiscovered. Those fields, collectively called quintessence, could act in opposition to gravity, and could change over time — popping up, decaying or altering their effect, switching from repulsive to attractive.

    The team focused in particular on the effects of fields associated with hypothetical particles called axions. Had one such field arisen when the universe was about 100,000 years old, it could have produced just the right amount of energy to fix the Hubble discrepancy, the team reported in a paper late last year. They refer to this theoretical force as “early dark energy.”

    “I was surprised how it came out,” said Marc Kamionkowski, a Johns Hopkins cosmologist who was part of the study. “This works.”

    The jury is still out. Dr. Riess said that the idea seems to work, which is not to say that he agrees with it, or that it is right. Nature, manifest in future observations, will have the final say.

    Dr. Knox called the Johns Hopkins paper “an existence proof” that the Hubble problem could be solved. “I think that’s new,” he said.

    Dr. Randall, however, has taken issue with aspects of the Johns Hopkins calculations. She and a trio of Harvard postdocs are working on a similar idea that she says works as well and is mathematically consistent. “It’s novel and very cool,” Dr. Randall said.

    So far, the smart money is still on cosmic confusion. Michael Turner, a veteran cosmologist at the University of Chicago and the organizer of a recent airing of the Hubble tensions, said, “Indeed, all of this is going over all of our heads. We are confused and hoping that the confusion will lead to something good!”

    Doomsday? Nah, nevermind

    Early dark energy appeals to some cosmologists because it hints at a link to, or between, two mysterious episodes in the history of the universe. As Dr. Riess said, “This is not the first time the universe has been expanding too fast.”

    The first episode occurred when the universe was less than a trillionth of a trillionth of a second old. At that moment, cosmologists surmise, a violent ballooning propelled the Big Bang; in a fraction of a trillionth of a second, this event — named “inflation” by the cosmologist Alan Guth, of M.I.T. — smoothed and flattened the initial chaos into the more orderly universe observed today.

    Inflation

    4
    Alan Guth, from Highland Park High School and M.I.T., who first proposed cosmic inflation

    HPHS Owls

    Lamda Cold Dark Matter Accerated Expansion of The universe http scinotions.com the-cosmic-inflation-suggests-the-existence-of-parallel-universes
    Alex Mittelmann, Coldcreation

    Alan Guth’s notes:

    Alan Guth’s original notes on inflation

    Nobody knows what drove inflation.

    The second episode is unfolding today: cosmic expansion is speeding up. But why? The issue came to light in 1998, when two competing teams of astronomers asked whether the collective gravity of the galaxies might be slowing the expansion enough to one day drag everything together into a Big Crunch.

    To great surprise, they discovered the opposite: the expansion was accelerating under the influence of an anti-gravitational force later called dark energy. The two teams won a Nobel Prize.

    Saul Perlmutter [The Supernova Cosmology Project] shared the 2006 Shaw Prize in Astronomy, the 2011 Nobel Prize in Physics, and the 2015 Breakthrough Prize in Fundamental Physics with Brian P. Schmidt and Adam Riess [The High-z Supernova Search Team] for providing evidence that the expansion of the universe is accelerating.

    Dark energy comprises 70 percent of the mass-energy of the universe. And, spookily, it behaves very much like a fudge factor known as the cosmological constant, a cosmic repulsive force that Einstein inserted in his equations a century ago thinking it would keep the universe from collapsing under its own weight. He later abandoned the idea, perhaps too soon.

    Under the influence of dark energy, the cosmos is now doubling in size every 10 billion years — to what end, nobody knows.

    Early dark energy, the force invoked by the Johns Hopkins group, might represent a third episode of antigravity taking over the universe and speeding it up. Perhaps all three episodes are different manifestations of the same underlying tendency of the universe to go rogue and speed up occasionally. In an email, Dr. Riess said, “Maybe the universe does this from time-to-time?”

    If so, it would mean that the current manifestation of dark energy is not Einstein’s constant after all. It might wink off one day. That would relieve astronomers, and everybody else, of an existential nightmare regarding the future of the universe. If dark energy remains constant, everything outside our galaxy eventually will be moving away from us faster than the speed of light, and will no longer be visible. The universe will become lifeless and utterly dark.

    But if dark energy is temporary — if one day it switches off — cosmologists and metaphysicians can all go back to contemplating a sensible tomorrow.

    “An appealing feature of this is that there might be a future for humanity,” said Scott Dodelson, a theorist at Carnegie Mellon who has explored similar scenarios.

    The phantom cosmos

    But the future is still up for grabs.

    Far from switching off, the dark energy currently in the universe actually has increased over cosmic time, according to a recent report in Nature Astronomy. If this keeps up, the universe could end one day in what astronomers call the Big Rip, with atoms and elementary particles torn asunder — perhaps the ultimate cosmic catastrophe.

    This dire scenario emerges from the work of Guido Risaliti, of the University of Florence in Italy, and Elisabeta Lusso, of Durham University in England. For the last four years, they have plumbed the deep history of the universe, using violent, faraway cataclysms called quasars as distance markers.

    Quasars arise from supermassive black holes at the centers of galaxies; they are the brightest objects in nature, and can be seen clear across the universe. As standard candles, quasars aren’t ideal because their masses vary widely. Nevertheless, the researchers identified some regularities in the emissions from quasars, allowing the history of the cosmos to be traced back nearly 12 billion years. The team found that the rate of cosmic expansion deviated from expectations over that time span.

    One interpretation of the results is that dark energy is not constant after all, but is changing, growing denser and thus stronger over cosmic time. It so happens that this increase in dark energy also would be just enough to resolve the discrepancy in measurements of the Hubble constant.

    The bad news is that, if this model is right, dark energy may be in a particularly virulent and — most physicists say — implausible form called phantom energy. Its existence would imply that things can lose energy by speeding up, for instance. Robert Caldwell, a Dartmouth physicist, has referred to it as “bad news stuff.”

    As the universe expands, the push from phantom energy would grow without bounds, eventually overcoming gravity and tearing apart first Earth, then atoms.

    The Hubble-constant community responded to the new report with caution. “If it holds up, this is a very interesting result,” said Dr. Freedman.

    Astronomers have been trying to take the measure of this dark energy for two decades. Two space missions — the European Space Agency’s Euclid and NASA’s Wfirst — have been designed to study dark energy and hopefully deliver definitive answers in the coming decade. The fate of the universe is at stake.

    ESA/Euclid spacecraft depiction

    NASA/WFIRST

    In the meantime, everything, including phantom energy, is up for consideration, according to Dr. Riess.

    “In a list of possible solutions to the tension via new physics, mentioning weird dark energy like this would seem appropriate,” he wrote in an email. “Heck, at least their dark energy goes in the right direction to solve the tension. It could have gone the other way and made it worse!”

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

     
  • richardmitnick 1:07 pm on January 14, 2020 Permalink | Reply
    Tags: A pursuit that stretches from underground particle colliders to orbiting telescopes with all manner of ground-based observatories in between., , , , , Dark Energy Survey, , , , , The astronomer missed her Nobel Prize [in my view a crime of old white men], ,   

    From The New York Times: Women in STEM-“Vera Rubin Gets a Telescope of Her Own” 

    From The New York Times

    Jan. 11, 2020
    Dennis Overbye

    The astronomer missed her Nobel Prize [in my view a crime of old white men]. But she now has a whole new observatory to her name.

    1
    The astronomer Vera Rubin at the Lowell Observatory in Flagstaff, Ariz., in 1965.Credit: via Carnegie Institution of Science

    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)

    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970.

    Vera Rubin, a young astronomer at the Carnegie Institution in Washington, was on the run in the 1970s when she overturned the universe.

    Seeking refuge from the controversies and ego-bashing of cosmology, she decided to immerse herself in the pearly swirlings of spiral galaxies, only to find that there was more to them than she and almost everybody else had thought.

    For millenniums, humans had presumed that when we gaze out at the universe, what we see is a fair representation of reality. Dr. Rubin, with her colleague Kent Ford, discovered that was not true. The universe — all those galaxies and the vast spaces between — was awash with dark matter, an invisible something with sufficient gravity to mold the large scale structures of the universe.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Coma cluster via NASA/ESA Hubble, the original example of Dark Matter discovered during observations by Fritz Zwicky and confirmed by Vera Rubin

    Esteemed astronomers dismissed her findings at first. But half a century later, the still futile quest to identify this “dark matter” is a burning question for both particle physics and astronomy. It’s a pursuit that stretches from underground particle colliders to orbiting telescopes, with all manner of ground-based observatories in between.

    Last week the National Science Foundation announced that the newest observatory joining this cause will be named the Vera C. Rubin Observatory. The name replaces the mouthful by which the project was previously known: the Large Synoptic Survey Telescope, or L.S.S.T.

    2
    The Vera C. Rubin Observatory, formerly the Large Synoptic Survey Telescope, under construction in Cerro Pachon, Chile. Credit: LSST Project/NSF/AURA

    The Rubin Observatory joins a handful of smaller astronomical facilities that have been named for women. The Maria Mitchell Observatories in Nantucket, Mass., is named after the first American woman to discover a comet. The Swope telescope, at Carnegie’s Las Campanas Observatory in Chile, is named after Henrietta Swope, who worked at the Harvard College Observatory in the early 20th century. She used a relationship between the luminosities and periodicities of variable stars to measure distances to galaxies.

    And finally there is the new Annie Maunder Astrographic Telescope at the venerable Royal Greenwich Observatory, just outside London. It is named after Annie Maunder, who with her husband Walter made pioneering observations of the sun and solar cycle of sunspots in the late 1800s.

    Heros of science, all of them.

    In a field known for grandiloquent statements and frightening intellectual ambitions, Dr. Rubin was known for simple statements about how stupid we are. In an interview in 2000 posted on the American Museum of Natural History website, Dr. Rubin said:

    “In a spiral galaxy, the ratio of dark-to-light matter is about a factor of 10. That’s probably a good number for the ratio of our ignorance to knowledge. We’re out of kindergarten, but only in about third grade.”

    Once upon a time cosmologists thought there might be enough dark matter in the universe for its gravity to stop the expansion of the cosmos and pull everything back together in a Big Crunch. Then astronomers discovered an even more exotic feature of the universe, now called dark energy, which is pushing the galaxies apart and speeding up the cosmic expansion.

    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

    Timeline of the Inflationary Universe WMAP

    The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

    According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

    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 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

    Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

    These discoveries have transformed cosmology still further, into a kind of Marvel Comics super-struggle between invisible, titanic forces. One, dark matter, pulls everything together toward its final doom; the other, dark energy, pushes everything apart toward the ultimate dispersal, some times termed the Big Rip. The rest of us, the terrified populace looking up at this cosmic war, are bystanders, made of atoms, which are definitely a minority population of the universe. Which force will ultimately prevail? Which side should we root for?

    Until recently the money was on dark energy and eventual dissolution of the cosmos. But lately cracks have appeared in the data, suggesting that additional forces may be at work beneath the surface of our present knowledge.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

     
  • richardmitnick 9:51 am on January 5, 2020 Permalink | Reply
    Tags: Analysis of data from hundreds of supernovas—the stellar explosions that provided the first evidence for cosmic acceleration, , , , , , Dark Energy Survey,   

    From WIRED: “Does Dark Energy Really Exist? Cosmologists Battle It Out” 

    Wired logo

    From WIRED

    December 17, 2019
    Natalie Wolchover

    1
    The supernova SN 2007af shines clearly near the lower-right edge of the spiral galaxy NGC 5584. ESO

    Dark energy, mysterious as it sounds, has become part of the furniture in cosmology. The evidence that this repulsive energy infuses space has stacked up since 1998. That was the year astronomers first discovered that the expansion of the universe has been speeding up over time, with dark energy acting as the accelerator. As space expands, new space arises, and with it more of this repulsive energy, causing space to expand even faster.

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

    Saul Perlmutter [The Supernova Cosmology Project] shared the 2006 Shaw Prize in Astronomy, the 2011 Nobel Prize in Physics, and the 2015 Breakthrough Prize in Fundamental Physics with Brian P. Schmidt and Adam Riess [The High-z Supernova Search Team] for providing evidence that the expansion of the universe is accelerating.

    Two decades later, multiple independent measurements agree that dark energy comprises about 70 percent of the universe’s contents. It is so baked into our current understanding of the cosmos that it came as a surprise when a recent paper published in the journal Astronomy & Astrophysics questioned whether it’s there at all.

    The four authors, including the Oxford physicist Subir Sarkar, performed their own analysis of data from hundreds of supernovas—the stellar explosions that provided the first evidence for cosmic acceleration, a discovery that earned three astronomers the 2011 Nobel Prize in Physics. When Sarkar and his colleagues looked at supernovas, they didn’t see a universe that’s accelerating uniformly in all directions due to dark energy. Rather, they say supernovas look the way they do because our region of the cosmos is accelerating in a particular direction—roughly toward the constellation Centaurus in the southern sky.

    Standard Candles to measure age and distance of the universe from supernovae NASA

    Outside experts almost immediately began picking the paper apart, finding apparent flaws in its methodology. Now, two cosmologists have formalized those arguments and others in a paper that was posted online on December 6 and submitted to The Astrophysical Journal. The authors, David Rubin and his student Jessica Heitlauf of the University of Hawaii, Manoa, detail four main problems with Sarkar and company’s data handling. “Is the expansion of the universe accelerating?” their paper title asks. “All signs still point to yes.”

    Outside researchers praised the thorough dissection. “The arguments by Rubin et al. are very convincing,” said Dragan Huterer, a cosmologist at the University of Michigan. “Some of them I was aware of upon looking at the original [Astronomy & Astrophysics paper], and others are new to me but make a lot of sense.”

    However, Sarkar and his co-authors—Jacques Colin and Roya Mohayaee of the Paris Institute of Astrophysics and Mohamed Rameez of the University of Copenhagen—don’t agree with the criticisms. Days after Rubin and Heitlauf’s paper appeared, they posted a rebuttal of the rebuttal.

    The cosmology community remains unmoved. Huterer said this latest response at times “misses the point” and attempts to debate statistical principles that are “not negotiable.” Dan Scolnic, a supernova cosmologist at Duke University, reaffirmed that “the evidence for dark energy from supernovas alone is significant and secure.”

    A Moving Shot

    The expansion of space stretches light, reddening its color. Supernovas appear more “redshifted” the farther away they are, because their light has to travel farther through expanding space. If space expanded at a constant rate, a supernova’s redshift would be directly proportional to its distance, and thus to its brightness.

    But in an accelerating universe filled with dark energy, space expanded less quickly in the past than it does now. This means a supernova’s light will have stretched less during its long journey to Earth, given how slowly space expanded during much of the time. A supernova located at a given distance away (indicated by its brightness) will appear significantly less redshifted than it would in a universe without dark energy. Indeed, researchers find that the redshift and brightness of supernovas scales in just this way.

    3
    Illustration: Dillon Brout

    In their recent paper, Sarkar and collaborators took an unconventional approach to the analysis. Normally, any study of supernova data has to account for Earth’s movement: As Earth orbits the sun, which orbits the galaxy, which orbits the local group of galaxies, we and our telescopes hurtle through space at around 600 kilometers per second. Our net motion is toward a dense region near Centaurus. Consequently, light coming from that direction is subject to the Doppler shift, which makes it look bluer than the light from the opposite side of the sky.

    It’s standard to correct for this motion and to transform supernova data into a stationary reference frame. But Sarkar and company did not. “If you don’t subtract that [motion], then it puts the same Doppler shift into the supernova data,” Rubin explained in an interview. “Our claim is that most of the effect is due to the solar system’s motion.”

    Another problem with the paper, according to Rubin and Heitlauf, is that Sarkar and colleagues made a “plainly incorrect assumption”: They failed to account for the fact that cosmic dust absorbs more blue light than red.

    Because of this, a supernova in a relatively “clean,” dust-free region looks especially blue, since there’s less dust that would otherwise absorb its blue light. The lack of dust also means that it will appear brighter. Thus, the faraway supernovas we spot with our telescopes are disproportionately blue and bright. If you don’t control for the color-dependent effect of dust, you will infer less difference between the brightness of nearby supernovas (on average, dustier and redder) and faraway supernovas (on average, bluer and brighter)—and as a result, you will infer less cosmic acceleration.

    The combination of these and other unusual decisions allowed Sarkar’s group to model their supernova data with a “dipole” term, an acceleration that points in a single direction, and only a small, or possibly zero, “monopole” term describing the kind of uniform acceleration that signifies dark energy.

    This dipole model has two other problems, said Rubin and Heitlauf. First, the model includes a term that says how quickly the dipole acceleration drops to zero as you move away from Earth; Sarkar and company made this distance small, which means that their model isn’t tested by a large sampling of supernovas. And second, the model doesn’t satisfy a consistency check involving the relationship between the dipole and monopole terms in the equations.

    Not All the Same

    The day Rubin and Heitlauf’s paper appeared, Sarkar said by email, “We do not think any revisions need to be made to our analysis.” He and his team soon posted their rebuttal of the duo’s four points, mostly rehashing earlier justifications. They cited research by Natallia Karpenka, a cosmologist who has left academia for a career in finance, to support one of their choices, but they misconstrued her work, Rubin said. Four other cosmologists contacted by Quanta said the group’s response doesn’t change their view.

    Those who find the back-and-forth about data analysis hard to follow should note that the data from supernovas matches other evidence of cosmic acceleration. Over the years, dark energy has been inferred from the ancient light called the cosmic microwave background, fluctuations in the density of the universe called baryon acoustic oscillations, the gravitationally distorted shapes of galaxies, and the clustering of matter in the universe.

    Sarkar and colleagues ground their work in a respectable body of research on the “cosmological fitting problem.” Calculations of cosmological parameters like the density of dark energy (which is represented in Albert Einstein’s gravity equations by the Greek letter lambda) tend to treat the universe as smooth, averaging over the universe’s inhomogeneities, such as its galaxies and voids. The fitting problem asks whether this approximation might lead to incorrect inferences about the values of constants like lambda, or if it might even suggest the presence of a lambda that doesn’t exist.

    But the latest research on the question—including a major cosmological simulation published this summer—rejects that possibility. Inhomogeneities “could change lambda by 1 or 2 percent,” said Ruth Durrer of the University of Geneva, a co-author on that paper, “but could not get rid of it. It’s simply impossible.”

    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

    Timeline of the Inflationary Universe WMAP

    The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

    According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

    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 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

    Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

     
  • richardmitnick 7:02 am on December 19, 2019 Permalink | Reply
    Tags: "ESO Observations Reveal Black Holes' Breakfast at the Cosmic Dawn", , , , , Dark Energy Survey,   

    From European Southern Observatory: “ESO Observations Reveal Black Holes’ Breakfast at the Cosmic Dawn” 

    ESO 50 Large

    From European Southern Observatory

    19 December 2019
    Emanuele Paolo Farina
    Max Planck Institute for Astronomy and Max Planck Institute for Astrophysics
    Heidelberg and Garching bei München, Germany
    Tel: +49 89 3000 02297
    Email: emanuele.paolo.farina@gmail.com

    Bárbara Ferreira
    ESO Public Information Officer
    Garching bei München, Germany
    Tel: +49 89 3200 6670
    Cell: +49 151 241 664 00
    Email: pio@eso.org

    1
    “Astronomers using ESO’s Very Large Telescope [below] have observed reservoirs of cool gas around some of the earliest galaxies in the Universe. These gas halos are the perfect food for supermassive black holes at the centre of these galaxies, which are now seen as they were over 12.5 billion years ago. This food storage might explain how these cosmic monsters grew so fast during a period in the Universe’s history known as the Cosmic Dawn.”

    Dark Energy Camera Enables Astronomers a Glimpse at the Cosmic Dawn. CREDIT National Astronomical Observatory of Japan

    ____________________________________________________________
    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

    Timeline of the Inflationary Universe WMAP

    The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

    According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

    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 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

    Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.
    ____________________________________________________________

    “We are now able to demonstrate, for the first time, that primordial galaxies do have enough food in their environments to sustain both the growth of supermassive black holes and vigorous star formation,” says Emanuele Paolo Farina, of the Max Planck Institute for Astronomy in Heidelberg, Germany, who led the research published today in The Astrophysical Journal. “This adds a fundamental piece to the puzzle that astronomers are building to picture how cosmic structures formed more than 12 billion years ago.”

    Astronomers have wondered how supermassive black holes were able to grow so large so early on in the history of the Universe.

    4
    Supermassive black hole Messier 87 imaged by the EHT

    “The presence of these early monsters, with masses several billion times the mass of our Sun, is a big mystery,” says Farina, who is also affiliated with the Max Planck Institute for Astrophysics in Garching bei München. It means that the first black holes, which might have formed from the collapse of the first stars, must have grown very fast. But, until now, astronomers had not spotted ‘black hole food’ — gas and dust — in large enough quantities to explain this rapid growth.

    To complicate matters further, previous observations with ALMA, the Atacama Large Millimeter/submillimeter Array, revealed a lot of dust and gas in these early galaxies that fuelled rapid star formation.

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

    These ALMA observations suggested that there could be little left over to feed a black hole.

    To solve this mystery, Farina and his colleagues used the MUSE instrument on ESO’s Very Large Telescope (VLT) in the Chilean Atacama Desert to study quasars — extremely bright objects powered by supermassive black holes which lie at the centre of massive galaxies.

    ESO MUSE on the VLT on Yepun (UT4)

    The study surveyed 31 quasars that are seen as they were more than 12.5 billion years ago, at a time when the Universe was still an infant, only about 870 million years old. This is one of the largest samples of quasars from this early on in the history of the Universe to be surveyed.

    The astronomers found that 12 quasars were surrounded by enormous gas reservoirs: halos of cool, dense hydrogen gas extending 100 000 light years from the central black holes and with billions of times the mass of the Sun. The team, from Germany, the US, Italy and Chile, also found that these gas halos were tightly bound to the galaxies, providing the perfect food source to sustain both the growth of supermassive black holes and vigorous star formation.


    3D view of gas halo observed by MUSE surrounding a galaxy merger seen by ALMA

    The research was possible thanks to the superb sensitivity of MUSE, the Multi Unit Spectroscopic Explorer, on ESO’s VLT, which Farina says was “a game changer” in the study of quasars. “In a matter of a few hours per target, we were able to delve into the surroundings of the most massive and voracious black holes present in the young Universe,” he adds. While quasars are bright, the gas reservoirs around them are much harder to observe. But MUSE could detect the faint glow of the hydrogen gas in the halos, allowing astronomers to finally reveal the food stashes that power supermassive black holes in the early Universe.

    In the future, ESO’s Extremely Large Telescope (ELT) will help scientists reveal even more details about galaxies and supermassive black holes in the first couple of billion years after the Big Bang.

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile. located at the summit of the mountain at an altitude of 3,060 metres (10,040 ft).

    “With the power of the ELT, we will be able to delve even deeper into the early Universe to find many more such gas nebulae,” Farina concludes.

    More information

    This research is presented in a paper to appear in The Astrophysical Journal.

    The team is composed of Emanuele Paolo Farina (Max Planck Institute for Astronomy [MPIA], Heidelberg, Germany and Max Planck Institute for Astrophysics [MPA], Garching bei München, Germany), Fabrizio Arrigoni-Battaia (MPA), Tiago Costa (MPA), Fabian Walter (MPIA), Joseph F. Hennawi (MPIA and Department of Physics, University of California, Santa Barbara, US [UCSB Physics]), Anna-Christina Eilers (MPIA), Alyssa B. Drake (MPIA), Roberto Decarli (Astrophysics and Space Science Observatory of Bologna, Italian National Institute for Astrophysics [INAF], Bologna, Italy), Thales A. Gutcke (MPA), Chiara Mazzucchelli (European Southern Observatory, Vitacura, Chile), Marcel Neeleman (MPIA), Iskren Georgiev (MPIA), Eduardo Bañados (MPIA), Frederick B. Davies (UCSB Physics), Xiaohui Fan (Steward Observatory, University of Arizona, Tucson, US [Steward]), Masafusa Onoue (MPIA), Jan-Torge Schindler (MPIA), Bram P. Venemans (MPIA), Feige Wang (UCSB Physics), Jinyi Yang (Steward), Sebastian Rabien (Max Planck Institute for Extraterrestrial Physics, Garching bei München, Germany), and Lorenzo Busoni (INAF-Arcetri Astrophysical Observatory, Florence, Italy).

    See the full article here .


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    Please help promote STEM in your local schools.


    Stem Education Coalition

    Visit ESO in Social Media-

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    ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre EEuropean Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

    ESO La Silla HELIOS (HARPS Experiment for Light Integrated Over the Sun)

    ESO/HARPS at La Silla

    ESO 3.6m telescope & HARPS at Cerro LaSilla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    MPG/ESO 2.2 meter telescope at Cerro La Silla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres

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

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

    2009 ESO VLTI Interferometer image, Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).

    ESO VLT 4 lasers on Yepun

    Glistening against the awesome backdrop of the night sky above ESO_s Paranal Observatory, four laser beams project out into the darkness from Unit Telescope 4 UT4 of the VLT.

    ESO/NTT at Cerro La Silla, Chile, at an altitude of 2400 metres

    ESO VLT Survey telescope

    Part of ESO’s Paranal Observatory, the VISTA Telescope observes the brilliantly clear skies above the Atacama Desert of Chile. Credit: ESO/Y. Beletsky, with an elevation of 2,635 metres (8,645 ft) above sea level

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

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile. located at the summit of the mountain at an altitude of 3,060 metres (10,040 ft).

    ESO APEXESO/MPIfR APEX high on the Chajnantor plateau in Chile’s Atacama region, at an altitude of over 4,800 m (15,700 ft)at the Llano de Chajnantor Observatory in the Atacama desert.

    Leiden MASCARA instrument, La Silla, located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    Leiden MASCARA cabinet at ESO Cerro la Silla located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    ESO Next Generation Transit Survey at Cerro Paranel, 2,635 metres (8,645 ft) above sea level

    ESO Speculoos telescopes four 1m-diameter robotic telescopes at ESO Paranal Observatory 2635 metres 8645 ft above sea level

    ESO TAROT telescope at Paranal, 2,635 metres (8,645 ft) above sea level

    ESO ExTrA telescopes at Cerro LaSilla at an altitude of 2400 metres

    A novel gamma ray telescope under construction on Mount Hopkins, Arizona. a large project known as the Cherenkov Telescope Array, composed of hundreds of similar telescopes to be situated in the Canary Islands and Chile. The telescope on Mount Hopkins will be fitted with a prototype high-speed camera, assembled at the University of Wisconsin–Madison, and capable of taking pictures at a billion frames per second. Credit: Vladimir Vassiliev

     
  • richardmitnick 11:17 am on July 8, 2019 Permalink | Reply
    Tags: , , , , Dark Energy Survey, , ,   

    From Lawrence Berkeley National Lab: “3 Sky Surveys Completed in Preparation for Dark Energy Spectroscopic Instrument” 

    Berkeley Logo

    From Lawrence Berkeley National Lab

    July 8, 2019

    Glenn Roberts Jr.
    geroberts@lbl.gov
    (510) 486-5582

    Researchers will pick 35 million galaxies and quasars to target during DESI’s 5-year mission

    It took three sky surveys – conducted at telescopes in two continents, covering one-third of the visible sky, and requiring almost 1,000 observing nights – to prepare for a new project that will create the largest 3D map of the universe’s galaxies and glean new insights about the universe’s accelerating expansion.

    This Dark Energy Spectroscopic Instrument (DESI) project will explore this expansion, driven by a mysterious property known as dark energy, in great detail. It could also make unexpected discoveries during its five-year mission.

    LBNL/DESI spectroscopic instrument on the Mayall 4-meter telescope at Kitt Peak National Observatory starting in 2018

    NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA, Altitude 2,120 m (6,960 ft)

    The surveys, which wrapped up in March, have amassed images of more than 1 billion galaxies and are essential in selecting celestial objects to target with DESI, now under construction in Arizona.

    The latest batch of imaging data from these surveys, known as DR8, was publicly released July 8, and an online Sky Viewer tool provides a virtual tour of this data. A final data release from the DESI imaging surveys is planned later this year.

    It took three sky surveys – conducted at telescopes in two continents, covering one-third of the visible sky, and requiring almost 1,000 observing nights – to prepare for a new project that will create the largest 3D map of the universe’s galaxies and glean new insights about the universe’s accelerating expansion.

    This Dark Energy Spectroscopic Instrument (DESI) project will explore this expansion, driven by a mysterious property known as dark energy, in great detail. It could also make unexpected discoveries during its five-year mission.

    The surveys, which wrapped up in March, have amassed images of more than 1 billion galaxies and are essential in selecting celestial objects to target with DESI, now under construction in Arizona.

    The latest batch of imaging data from these surveys, known as DR8, was publicly released July 8, and an online Sky Viewer tool provides a virtual tour of this data. A final data release from the DESI imaging surveys is planned later this year.

    Scientists will select about 33 million galaxies and 2.4 million quasars from the larger set of objects imaged in the three surveys. Quasars are the brightest objects in the universe and are believed to contain supermassive black holes. DESI will target these selected objects for several measurements after its start, which is expected in February 2020.

    DESI will measure each target across a range of different wavelengths of light, known as spectrum, from the selected set of galaxies repeatedly over the course of its mission. These measurements will provide details about their distance and acceleration away from Earth.

    A collection of 5,000 swiveling robots, each carrying a fiber-optic cable, will point at sets of pre-selected sky objects to gather their light (see a related video [below]) so it can be split into different colors and analyzed using a series of devices called spectrographs.

    Three surveys, 980 nights

    “Typically, when you apply for time on a telescope you get up to five nights,” said David Schlegel, a DESI project scientist at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), which is the lead institution in the DESI collaboration. “These three imaging surveys totaled 980 nights, which is a pretty big number.”

    The three imaging surveys for DESI include:

    The Mayall z-band Legacy Survey (MzLS), carried out at the Mayall Telescope at the National Science Foundation’s Kitt Peak National Observatory near Tucson, Arizona, over 401 nights. DESI is now under installation at the Mayall Telescope.

    The Dark Energy Camera Legacy Survey (DECaLS) at the Victor Blanco Telescope at NSF’s Cerro Tololo Inter-American Observatory in Chile, which lasted 204 nights.

    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

    Timeline of the Inflationary Universe WMAP

    The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

    According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

    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 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

    Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

    The Beijing-Arizona Sky Survey (BASS), which used the Steward Observatory’s Bok telescope at Kitt Peak National Observatory and lasted 375 nights.

    2.3-metre Bok Telescope at the Steward Observatory at Kitt Peak in Arizona, USA, altitude 2,096 m (6,877 ft)

    4
    This map shows the sky areas covered (blue) by three surveys conducted in preparation for DESI. (Credit: University of Arizona)

    On-site survey crews – typically two DESI project researchers per observing night for each of the surveys – served in a sort of “lifeguard” role, Schlegel said. “When something went wrong they were there to fix it – to keep eyes on the sky,” and researchers working remotely also aided in troubleshooting.

    On the final night of the final survey …

    In early March, Eva-Maria Mueller, a postdoctoral researcher at the U.K.’s University of Portsmouth, and Robert Blum, former deputy director at the National Optical Astronomy Observatory (NOAO) that manages the survey sites, were on duty with a small team in the control room of the NSF’s Victor Blanco Telescope on a mile-high Chilean mountain for the final night of DECaLS survey imaging.

    Seated several stories beneath the telescope, Mueller and Blum viewed images in real time to verify the telescope’s position and focus. Mueller, who was participating in a five-night shift that was her first observing stint for the DESI surveys, said, “This was always kind of a childhood dream.”

    Blum, who had logged many evenings at the Blanco telescope for DECaLS, said, “It’s really exciting to think about finishing this phase.” He noted that this final night was focused on “cleaning up little holes” in the previous imaging. Blum is now serving in a new role as acting operations director for the Large Synoptic Survey Telescope under installation in Chile.

    New software designed for the DESI surveys, and precise positioning equipment on the telescopes, has helped to automate the image-taking process, setting the exposure time and filters and compensating for atmospheric distortions and other factors that can affect the imaging quality, Blum noted. During a productive evening, it was common to produce about 150 to 200 images for the DECaLS survey.

    Cool cosmic cartography experiment

    The data from the surveys was routed to supercomputers at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC), which will be the major storehouse for DESI data.

    NERSC

    NERSC Cray Cori II supercomputer at NERSC at LBNL, named after Gerty Cori, the first American woman to win a Nobel Prize in science

    NERSC Hopper Cray XE6 supercomputer


    LBL NERSC Cray XC30 Edison supercomputer


    The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.

    NERSC PDSF


    PDSF is a networked distributed computing cluster designed primarily to meet the detector simulation and data analysis requirements of physics, astrophysics and nuclear science collaborations.

    Future:

    Cray Shasta Perlmutter SC18 AMD Epyc Nvidia pre-exascale supeercomputer

    NERSC is a DOE Office of Science User Facility.

    More than 100 researchers participated in night shifts to conduct the surveys, said Arjun Dey, the NOAO project scientist for DESI. Dey served as a lead scientist for the MzLS survey and a co-lead scientist on the DECaLS survey with Schlegel.

    “We are building a detailed map of the universe and measuring its expansion history over the last 10 to 12 billion years,” Dey said. “The DESI experiment represents the most detailed – and definitely the coolest – cosmic cartography experiment undertaken to date. Although the imaging was carried out for the DESI project, the data are publicly available so everyone can enjoy the sky and explore the cosmos.”

    BASS survey supported by global team

    Xiaohui Fan, a University of Arizona astronomy professor who was a co-lead on the BASS survey conducted at Kitt Peak’s Bok Telescope, coordinated viewing time by an international group that included co-leads Professor Zhou Xu and Associate Professor Zou Hu, other scientists from the National Astronomical Observatories of China (NAOC), and researchers from the University of Arizona and from across the DESI collaboration.

    4
    The Bok (left) and Mayall telescopes at Kitt Peak National Observatory near Tucson, Arizona. DESI is currently under installation at the Mayall telescope. (Credit: Michael A. Stecker)

    BASS produced about 100,000 images during its four-year run. It scanned a section of sky about 13 times larger than the Big Dipper, part of the Ursa Major constellation.

    “This is a good example of how a collaboration is done,” Fan said. “Through this international partnership we were bringing in people from around the world. This is a nice preview of what observing with DESI will be like.”

    Fan noted the DESI team’s swift response in updating the telescope’s hardware and software during the course of the survey.

    “It improved a lot in terms of automated controls and focusing and data reduction,” he said. Most of the BASS survey imaging concluded in February, with some final images taken in March.

    Next steps toward DESI’s completion

    All of the images gathered will be processed by a mathematical code, called Tractor, that helps to identify all of the galaxies surveyed and measure their brightness.

    With the initial testing of the massive corrector barrel, which houses DESI’s package of six large mirrors, in early April, the next major milestone for the project will be the delivery, installation, and testing of its focal plane, which caps the telescope and houses the robotic positioners.

    Dey, who participated in formative discussions about the need for an experiment like DESI almost 20 years ago, said, “It’s pretty amazing that our small and dedicated team was able to pull off such a large survey in such a short time. We are excited to be turning to the next phase of this project!”

    NERSC is a DOE Office of Science User Facility.

    More:

    Explore Galaxies Far, Far Away at Internet Speeds

    Scientists have released an “expansion pack” for a virtual tour of the universe that you can enjoy from the comfort of your own computer. The latest version of the publicly accessible images of the sky roughly doubles the size of the searchable universe from the project’s original release in May.

    News Center


    In this video, Dark Energy Spectroscopic Instrument (DESI) project participants share their insight and excitement about the project and its potential for new and unexpected discoveries.

    DESI is supported by the U.S. Department of Energy’s Office of Science; the U.S. National Science Foundation, Division of Astronomical Sciences under contract to the National Optical Astronomy Observatory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the National Council of Science and Technology of Mexico; the Ministry of Economy of Spain; the French Alternative Energies and Atomic Energy Commission (CEA); and DESI member institutions. The DESI scientists are honored to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation. View the full list of DESI collaborating institutions, and learn more about DESI here: desi.lbl.gov.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Bringing Science Solutions to the World

    In the world of science, Lawrence Berkeley National Laboratory (Berkeley Lab) is synonymous with “excellence.” Thirteen Nobel prizes are associated with Berkeley Lab. Seventy Lab scientists are members of the National Academy of Sciences (NAS), one of the highest honors for a scientist in the United States. Thirteen of our scientists have won the National Medal of Science, our nation’s highest award for lifetime achievement in fields of scientific research. Eighteen of our engineers have been elected to the National Academy of Engineering, and three of our scientists have been elected into the Institute of Medicine. In addition, Berkeley Lab has trained thousands of university science and engineering students who are advancing technological innovations across the nation and around the world.

    Berkeley Lab is a member of the national laboratory system supported by the U.S. Department of Energy through its Office of Science. It is managed by the University of California (UC) and is charged with conducting unclassified research across a wide range of scientific disciplines. Located on a 202-acre site in the hills above the UC Berkeley campus that offers spectacular views of the San Francisco Bay, Berkeley Lab employs approximately 3,232 scientists, engineers and support staff. The Lab’s total costs for FY 2014 were $785 million. A recent study estimates the Laboratory’s overall economic impact through direct, indirect and induced spending on the nine counties that make up the San Francisco Bay Area to be nearly $700 million annually. The Lab was also responsible for creating 5,600 jobs locally and 12,000 nationally. The overall economic impact on the national economy is estimated at $1.6 billion a year. Technologies developed at Berkeley Lab have generated billions of dollars in revenues, and thousands of jobs. Savings as a result of Berkeley Lab developments in lighting and windows, and other energy-efficient technologies, have also been in the billions of dollars.

    Berkeley Lab was founded in 1931 by Ernest Orlando Lawrence, a UC Berkeley physicist who won the 1939 Nobel Prize in physics for his invention of the cyclotron, a circular particle accelerator that opened the door to high-energy physics. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab legacy that continues today.

    A U.S. Department of Energy National Laboratory Operated by the University of California.

    University of California Seal

    DOE Seal

     
  • richardmitnick 9:12 am on May 12, 2019 Permalink | Reply
    Tags: , , , , , Dark Energy Survey, Dark nature is observable only indirectly by its effects   

    From COSMOS Magazine: “Multiple measurements close in on dark energy” 

    Cosmos Magazine bloc

    From COSMOS Magazine

    06 May 2019
    Andrew Masterson

    Cerro Tololo Inter-American Observatory, located on Cerro Tololo in the Coquimbo Region of northern Chile, Altitude 2,207 m (7,241 ft)

    An extensive analysis of four different phenomena within the universe points the way to understanding the nature of dark energy, a collaboration between more than 100 scientists reveals.

    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

    Timeline of the Inflationary Universe WMAP

    The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

    According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

    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 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

    Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

    Dark energy – the force that propels the acceleration of the expanding universe – is a mysterious thing. It’s nature, write telescope scientist Timothy Abbott from the Cerro Tololo Inter-American Observatory, in Chile, and colleagues, “is unknown, and understanding its properties and origin is one of the principal challenges in modern physics”.

    Indeed, there is a lot at stake. Current measurements indicate that dark energy can be smoothly incorporated into the theory of general relativity as a cosmological constant; but, the researchers note, those measurements are far from precise and incorporate a wide range of potential variations.

    “Any deviation from this interpretation in space or time would constitute a landmark discovery in fundamental physics,” they note.

    The heart of the problem, of course, is that dark nature is observable only indirectly, by its effects.

    These fall into two categories. First, it deforms galactic architectures through accelerating the expansion of the universe. Second, it suppresses growth in some parts of the cosmic structure.

    However, it is not the only force that can produce such results, and the danger thus always exists that what is assumed to be evidence of dark matter activity may in fact be something else altogether.

    Current approaches to measuring dark matter are problematic. All of them begin with the cosmic microwave background (CMB), the relic radiation that fills space, generated just 400,000 years after the Big Bang.

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    At that point in the history of the universe the influence of dark matter was minimal. It increased significantly as spacetime expanded ever more and ever faster.

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

    The second pillar for measuring it, thus, comprises observations of “low-redshift” phenomena – wavelengths stretched over vast distances, allowing calculations of conditions within the universe the past several billion years.

    Red shift and wave length shift-The Earliest Stars And Galaxies In The Universe Science at ESA

    Combining the two measurements and then extrapolating forwards to the present day, Abbott and colleagues note, “can be a powerful test of our models, but it requires precise, independent constraints from low-redshift experiments”.

    It follows, then, that any increase in the precision of low-redshift measurements will also increase the precision of dark energy calculations, reducing (or perhaps increasing) the chances that a previously undiscovered physics is in play in the universe.

    The researchers approach this challenge by invoking a combination of multiple observational probes for low-redshift phenomena – namely, those measuring Type Ia supernova light curves, fluctuations in the density of visible (or “baryonic”) matter, weak gravitational lensing, and galaxy clustering.

    To do this, they use the results of the Dark Energy Survey (DES), a collaboration of research institutions in the US, South America and Europe that studies observations made by the Victor M Blanco telescope in Chile, which is fitted with specialised instruments for dark energy detection.

    Presenting the first tranche of results from the survey, Abbott and colleagues reveal progress towards constraining the nature of dark energy.

    The DES findings, they report, absolutely – and independent of CMB-based research – rule out a universe in which dark energy doesn’t exist. They also report that the results suggest the universe is spatially flat, and derive a tighter constraint on the density of baryon matter.

    These results, they suggest, constrain the state of “of dark energy and its energy density in the Universe” … “to a precision that is almost a factor of three better than the 7 previous best single-experiment result from the CMB”.

    Further planned DES surveys, they conclude, will likely sharpen up knowledge of the impact of dark energy in the universe by orders of magnitude.

    The research is published in the journal Physical Review Letters.

    See the full article here .


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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.”

    2

    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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    FNAL Icon

    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

    FNAL/MicrobooNE

    FNAL Don Lincoln

    FNAL/MINOS

    FNAL Cryomodule Testing Facility

    FNAL Minos Far Detector

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

    FNAL/NOvA experiment map

    FNAL NOvA Near Detector

    FNAL ICARUS

    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

    1
    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.”

    3
    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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    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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    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.

     
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