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  • richardmitnick 10:23 am on December 2, 2019 Permalink | Reply
    Tags: , , , Cosmic inflation yields pristine flatness, , ESA/Planck CMB, ΛCDM does not predict any curvature; it says the universe is flat., ΛCDM model, perhaps the universe is really closed., , What Shape Is the Universe?   

    From Quanta Magazine: “What Shape Is the Universe? A New Study Suggests We’ve Got It All Wrong” 

    Quanta Magazine
    From Quanta Magazine

    November 4, 2019
    Natalie Wolchover

    When researchers reanalyzed the gold-standard data set of the early universe, they concluded that the cosmos must be “closed,” or curled up like a ball. Most others remain unconvinced.

    1
    Lucy Reading-Ikkanda/Quanta Magazine
    In a flat universe, as seen on the left, a straight line will extend out to infinity. A closed universe, right, is curled up like the surface of a sphere. In it, a straight line will eventually return to its starting point.

    A provocative paper published today in the journal Nature Astronomy argues that the universe may curve around and close in on itself like a sphere, rather than lying flat like a sheet of paper as the standard theory of cosmology predicts. The authors reanalyzed a major cosmological data set and concluded that the data favors a closed universe with 99% certainty — even as other evidence suggests the universe is flat.

    The data in question — the Planck space telescope’s observations of ancient light called the cosmic microwave background (CMB) — “clearly points towards a closed model,” said Alessandro Melchiorri of Sapienza University of Rome.

    CMB per ESA/Planck

    ESA/Planck 2009 to 2013

    He co-authored the new paper with Eleonora di Valentino of the University of Manchester and Joseph Silk, principally of the University of Oxford. In their view, the discordance between the CMB data, which suggests the universe is closed, and other data pointing to flatness represents a “cosmological crisis” that calls for “drastic rethinking.”

    However, the team of scientists behind the Planck telescope reached different conclusions in their 2018 analysis. Antony Lewis, a cosmologist at the University of Sussex and a member of the Planck team who worked on that analysis, said the simplest explanation for the specific feature in the CMB data that di Valentino, Melchiorri and Silk interpreted as evidence for a closed universe “is that it is just a statistical fluke.” Lewis and other experts say they’ve already closely scrutinized the issue, along with related puzzles in the data.

    “There is no dispute that these symptoms exist at some level,” said Graeme Addison, a cosmologist at Johns Hopkins University who was not involved in the Planck analysis or the new research. “There is only disagreement as to the interpretation.”

    Whether the universe is flat — that is, whether two light beams shooting side by side through space will stay parallel forever, rather than eventually crossing and swinging back around to where they started, as in a closed universe — critically depends on the universe’s density. If all the matter and energy in the universe, including dark matter and dark energy, adds up to exactly the concentration at which the energy of the outward expansion balances the energy of the inward gravitational pull, space will extend flatly in all directions.

    The leading theory of the universe’s birth, known as cosmic inflation, yields pristine flatness.

    Inflation

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

    HPHS Owls

    Alan Guth’s notes:

    Alan Guth’s original notes on inflation

    And various observations since the early 2000s have shown that our universe is very nearly flat and must therefore come within a hair of this critical density — which is calculated to be about 5.7 hydrogen atoms’ worth of stuff per cubic meter of space, much of it invisible.

    The Planck telescope measures the density of the universe by gauging how much the CMB light has been deflected or “gravitationally lensed” while passing through the universe over the past 13.8 billion years. The more matter these CMB photons encounter on their journey to Earth, the more lensed they get, so that their direction no longer crisply reflects their starting point in the early universe. This shows up in the data as a blurring effect, which smooths out certain peaks and dips in the spatial pattern of the light. According to the new analysis, the large amount of lensing of the CMB suggests that the universe may be about 5% denser than the critical density, averaging something like six hydrogen atoms per cubic meter instead of 5.7, so that gravity wins and the cosmos closes in on itself.

    The Planck scientists noticed the larger-than-expected lensing effect years ago; the anomaly showed up most prominently in their final analysis of the full data set, released last year. If the universe is flat, cosmologists expect a curvature measurement to fall within about one “standard deviation” of zero, due to random statistical fluctuations in the data. But both the Planck team and the authors of the new paper found that the CMB data deviates by 3.4 standard deviations. Assuming that the universe is flat, this is a major fluke — about equivalent to getting heads in a coin toss 11 times in a row, which happens less than 1% of the time. The Planck team attributes the measurement to just such a fluke, or to some unaccounted-for effect that blurs the CMB light, mimicking the effect of extra matter.

    Or perhaps the universe is really closed. Di Valentino and co-authors point out that a closed model resolves other anomalous findings in the CMB. For instance, researchers deduce the values of key ingredients of our universe, such as the amount of dark matter and dark energy, by measuring variations in the color of the CMB light coming from different regions of the sky. But curiously, they get different answers when they compare small regions of the sky and when they compare large regions. The authors point out that when you recalculate these values assuming a closed universe, they don’t differ.

    Will Kinney, a cosmologist at the University at Buffalo in New York, called this bonus benefit of the closed universe model “really interesting.” But he noted that the discrepancies between small and large-scale variations seen in the CMB light could easily be statistical fluctuations themselves, or they might stem from the same unidentified error that may affect the lensing measurement.

    There are only six of these key properties that shape the universe, according to the standard theory of cosmology, which is known as ΛCDM (named for dark energy, represented by the Greek letter Λ, or lambda, and cold dark matter).

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

    With only six numbers, ΛCDM accurately describes almost all features of the cosmos. And ΛCDM does not predict any curvature; it says the universe is flat.

    The new paper effectively argues that we may need to add a seventh parameter to ΛCDM: a number that describes the curvature of the universe. For the lensing measurement, adding a seventh number improves the fit with the data.

    But other cosmologists argue that before taking an anomaly seriously enough to add a seventh parameter to the theory, we need to take into account all the other things that ΛCDM gets right. Sure, we can focus on this one anomaly — a coin coming up heads 11 times in a row — and say that something’s off. But the CMB is such a huge data set that it’s like flipping a coin hundreds or thousands of times. It’s not too hard to imagine that in doing so, we’ll encounter one random run of 11 heads. Physicists call this the “look elsewhere” effect.

    Furthermore, researchers note that the seventh parameter isn’t needed for most other measurements. There’s a second way of gleaning the spatial curvature from the CMB, by measuring correlations between light from sets of four points in the sky; this “lensing reconstruction” measurement indicates that the universe is flat, with no seventh parameter needed. In addition, the BOSS survey’s independent observations of cosmological signals called baryon acoustic oscillations also point to flatness. Planck, in their 2018 analysis, combined their lensing measurement with these two other measurements and arrived at an overall value for the spatial curvature within one standard deviation of zero.

    Di Valentino, Melchiorri and Silk think that pulling these three different data sets together masks the fact that the different data sets don’t actually agree. “The point here is not that the universe is closed,” Melchiorri said by email. “The problem is the inconsistency between the data. This indicates that there is currently no concordance model and that we are missing something.” In other words, ΛCDM is wrong or incomplete.

    All other researchers consulted for this article think the weight of the evidence points to the universe being flat. “Given the other measurements,” Addison said, “the clearest interpretation of this behavior of the Planck data is that it’s a statistical fluctuation. Maybe it’s caused by some slight inaccuracy in the Planck analysis, or maybe it’s completely just noise fluctuations or random chance. But either way, there’s not really a reason to take this closed model seriously.”

    That’s not to say pieces aren’t missing from the cosmological picture. ΛCDM seemingly predicts the wrong value for the current expansion rate of the universe, causing a controversy known as the Hubble constant problem. But assuming the universe is closed doesn’t fix this problem — in fact, adding curvature worsens the prediction of the expansion rate. Other than Planck’s anomalous lensing measurement, there’s no reason to think the universe is closed.

    “Time will tell, but I am not, personally, terribly worried about this one,” Kinney said, referring to the suggestion of curvature in the CMB data. “It’s of a kind with similar anomalies that have proven to be vapor.”

    See the full article here .


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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 11:18 am on March 13, 2019 Permalink | Reply
    Tags: "Streams of Stars Snaking Through the Galaxy Could Help Shine a Light on Dark Matter", Adrian Price-Whelan calls GD-1 "the Goldilocks stream" because it's in just the right place., , , At about 33000 light-years (10 kiloparsecs) GD-1 is the longest stellar stream in the galactic halo, , , Dark matter makes up the bulk of the mass in the universe but it has never been directly observed, , ΛCDM model, , scores of dark matter seeds are scattered through galaxies like the Milky Way, , The stellar stream known as GD-1 is a thin flow of material tucked inside the Galactic halo   

    From smithsonian.com: “Streams of Stars Snaking Through the Galaxy Could Help Shine a Light on Dark Matter” 

    smithsonian
    From smithsonian.com

    March 12, 2019
    Nola Taylor Redd

    When the Milky Way consumes another galaxy, tendrils of stellar streams survive the merger, containing clues about the universe’s mysterious unseen matter.

    1
    An ultraviolet image of the Andromeda galaxy, the closest major galaxy to the Milky Way, taken by NASA’s Galaxy Evolution Explorer space telescope. Like our own galaxy, Andromeda is a spiral galaxy with a flat rotating disk of stars and gas and a concentrated bulge of stars at the center. (NASA/JPL-Caltech)

    When a small galaxy strays too close to the Milky Way, the gravity from our larger galaxy reels it in. Gas and stars are ripped from the passing galaxy as it falls inward toward its doom, creating streams of material that stretch between the galactic pair. These streams continue to tear away stars until the infalling object has been completely consumed. After the merger is over, some of the only remaining signs of the devoured object are the stellar streams snaking through the Milky Way, a small sample of stars from a galaxy long gone.

    In addition to being a record of the past, one of these streams may provide the first direct evidence for small scale clusters of dark matter—the elusive material that is believed to account for 85 percent of all matter in the universe. A recent analysis of a trail of stars reveals that it interacted with a dense object in the last few hundred million years. After ruling out the most likely suspects, the researchers determined that the relatively recently made gap in the stream may have been caused by a small clump of dark matter. If confirmed, the eddies of this stellar stream could help scientists sort through the competing theories about dark matter and perhaps even close in on the characteristics of the mysterious material.

    The stellar stream known as GD-1 is a thin flow of material tucked inside the Galactic halo, the loose collection of stars and gases surrounding the disk of the Milky Way. Using data released last April from the European Space Agency’s Gaia space telescope, which is in the process of assembling the most detailed map of the Milky Way’s stars ever made, astronomers were able to use precise positional data to reconstruct the movement of the stars in GD-1.

    ESA/GAIA satellite

    Torn from a cloud of material, the stream is the last remnant of an object that was likely consumed by our galaxy in the last 300 million years—an eyeblink on astronomical timescales.

    Gaia found two small breaks in the stream, the first unambiguous observation of gaps in a stellar stream, as well as a dense collection of stars called a spur. Together, these features suggest that a small but massive object shook up the material of the stream.

    “I think this is the first direct dynamical evidence for the small-scale [structure] of dark matter,” says Adrian Price-Whelan, an astronomer at the Flatiron Institute in New York. Working with Ana Bonaca of the Harvard-Smithsonian Center for Astrophysics, Price-Whelan investigated the newfound structures in GD-1 to determine their source and presented the results earlier this year at the winter meeting of the American Astronomical Society.

    At about 33,000 light-years (10 kiloparsecs), GD-1 is the longest stellar stream in the galactic halo. While Price-Whelan and his colleagues were able to use models to show that one of the gaps formed during the generation of the stream, the other gap remained a mystery. However, along with the puzzle, Gaia also revealed a solution: the spur.

    When an object travels past or through a stellar stream, it disrupts the stars. Price-Whelan compares the disruption to a strong jet of air blowing across a stream of water. The water—or stars—plume outward along the path of the disruptor, creating a gap. Some move so fast that they escape the stream and go flying off into space, lost forever. Others are pulled back into the stream to form eddy-like features astronomers call spurs. After a few hundred million years, most spurs merge back into the stream, and only the gap remains, though some can be longer-lived.

    When it comes to spotting structures in stellar streams, Price-Whelan calls GD-1 “the Goldilocks stream” because it’s in just the right place. GD-1 is within the stars of the Milky Way, but moving in the opposite direction, making it easier for astronomers to pick out the stars in the stream from the surrounding objects. “At any given location, it’s moving differently from the way most of the other stars in that part of the sky are moving,” Price-Whelan says.

    The researchers modeled what type of objects could be responsible for the relatively newborn spur spotted in GD-1. They determined that the responsible object had to weigh in with a mass somewhere between 1 million and 100 million times the mass of the sun. Stretching only about 65 light-years (20 pc) in length, the object would have been incredibly dense. The interaction between the stream and the dense object would have likely happened within the last few hundred million years out of the 13.8-billion-year lifetime of the universe.

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

    Dark matter isn’t the only object that could have disrupted the stellar stream. A globular cluster or dwarf galaxy swooping nearby could also have created the gap and spur. Price-Whelan and his colleagues turned their eyes toward all known such objects and calculated their orbits, finding that none came close enough to GD-1 in the last billion years to shake things up. A chance encounter with a primordial black hole could have sent the stream’s stars flying, but it would have been an extremely rare event.

    According to dark matter simulations that allow for small structures, scores of dark matter seeds are scattered through galaxies like the Milky Way. A stream like GD-1 is expected to encounter at least one such seed within the last 8 billion years, making dark matter a far more likely perturber based on encounter rates than any other object.

    Dark matter makes up the bulk of the mass in the universe, but it has never been directly observed. The two leading theories for its existence are the warm dark matter model and the Lambda cold dark matter model (ΛCDM), which is the model preferred by most scientists.

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

    Under ΛCDM, dark matter forms clumps that can be as large as a galaxy or as small as a soda can. Warm dark matter models suggest that the material has less massive particles and lacks the can-sized structures that the ΛCDM model suggests. Finding evidence for small scale structures of dark matter could help weed out certain models and start to narrow in on some of the characteristics of the tantalizing stuff.

    “Streams might be the only avenue that we could [use to] study the lowest mass end of what dark matter is doing,” Price-Whelan says. “If we want to be able to confirm or reject or rule out different theories of dark matter, we really need to know what’s happening at [the low] end.”

    Gaia’s data helped identify the stars of the spur, but it’s not detailed enough to compare the velocity differences between them and the stars in the stream, which could help confirm that dark matter perturbed the structure. Price-Whelan and his colleagues want to use NASA’s Hubble Space Telescope to further study the movement of the faint stars in GD-1. Although Gaia has opened the door to wide-scale examination of the movement of stars across the Milky Way, Price-Whelan says that it can’t compete with the HST when it comes to very faint stars. “You can drill much deeper when you have a dedicated telescope like Hubble,” he says.

    The differences in how the stars of the stream and spur move could help astronomers determine how much energy the perturbing object carried, as well as allow researchers to calculate its orbit. These pieces of information could be used to track down the disruptive dark matter clump and study its immediate environment.

    In addition to making a more in-depth study of GD-1, astronomers plan to apply the same techniques enabled by Gaia’s data to some of the more than 40 other streams surrounding the Milky Way. Spotting spurs and gaps in other streams and tying them to dark matter could further improve our understanding of how the mysterious substance interacts with the visible galaxy.

    After decades of puzzling over the mystery of dark matter, the gaps and spurs in stellar streams like GD-1 may finally help to reveal the secrets of the substance that makes up most of the universe. “This is one of the most exciting things that has come out of Gaia,” Price-Whelan says.

    See the full article here .

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    Smithsonian magazine and Smithsonian.com place a Smithsonian lens on the world, looking at the topics and subject matters researched, studied and exhibited by the Smithsonian Institution — science, history, art, popular culture and innovation — and chronicling them every day for our diverse readership.

     
  • richardmitnick 12:19 pm on October 5, 2017 Permalink | Reply
    Tags: , , BAO (SDSS-IV) survey, , , , ΛCDM model, , The mysterious repulsive force known as dark energy   

    From Science Alert: “Mysterious Dark Energy Is More Dynamic Than We Thought, Says New Study” 

    ScienceAlert

    Science Alert

    4 OCT 2017
    MIKE MCRAE

    1
    betibup33/Shutterstock

    Not so constant after all.

    For over 20 years, physicists have puzzled over why space appears to be flying apart at the seams.

    New research is adding some deeper insight into the mysterious repulsive force known as dark energy, providing evidence that whatever it might be, its ghostly influence hasn’t been constant over time.

    In 2016, an international team of researchers accurately measured fluctuations in the density of visible matter through the Universe over long periods of its history.

    These shifts – called baryon acoustic oscillations (BAO) – provide something of a yardstick for cosmologists studying relative distances over time.

    Just as astronomers have used light from distant exploding stars to conclude the Universe is spreading out, cosmologists (big picture astronomers) have used BAO.

    Whichever of these two tools we use, it looks as if the Universe has been gaining real estate over the 13.82 billion years of its existence, causing clumps of material in it to spread out.

    Weirder yet, that growth has been speeding up for quite some time.

    The unit used to describe this expansion is called the Hubble Constant, and is thought to be the result of the tension between matter pulling itself together and the swelling of space in between.

    Why is space growing? Nobody is really all that certain, and that’s a problem.

    To help come up with an explanation astrophysicists look at the hum of empty space as if it has qualities, and isn’t just an empty stage for fields and particles.

    The odds-on favourite description at the moment is called the Lambda Cold Dark Matter (ΛCDM) model, which combines what’s referred to as the Friedmann-Lemaitre-Robertson-Walker (FLRW) model of empty space with a distribution of visible and invisible matter within it.

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

    In this model, dark energy is the constant push of emptiness between masses, possibly caused by the hiss of particles popping in and out of virtual existence.

    But the ΛCDM model is built on a number of assumptions, leaving open the question; does dark energy need to be among the fundamental qualities of space, static over time?

    Or could it be influenced by its surroundings, shifting as the Universe changes?

    “Since its discovery at the end of last century, dark energy has been a riddle wrapped in an enigma,” says researcher Bob Nichol from the Institute of Cosmology and Gravitation (ICG) at the University of Portsmouth.

    “We are all desperate to gain some greater insight into its characteristics and origin.”

    Armed with more accurate measures of these tides of matter pulsing like a cosmic heartbeat, the researchers applied their BAO data to a dark energy model developed by Gong-Bo Zhao, from the University of Portsmouth and the National Astronomical Observatories of China (NAOC).

    The study’s results point to a more dynamic description of this mysterious force.

    This conclusion is based in part on a conflict between data produced by the team’s own BAO survey and interpretations based on the cosmic microwave background (CMB) – the echo of light bouncing through the Universe since moments after the Big Bang.

    CMB per ESA/Planck


    ESA/Planck

    This diagram on the BAO (SDSS-IV) survey gives you some idea of how it relates to the CMB.

    4
    Sloan Digital Sky Survey

    One way the researchers found they could resolve this difference is to treat dark energy as if it is dynamic changing with time.

    If true, it would mean dark energy isn’t a force produced by the bubbling of a vacuum.

    The significance of their results isn’t enough to overturn the evidence favouring the static dark energy feature of the ΛCDM model.

    But that could all change with data collected from the Dark Energy Spectroscopic Instrument when it starts its survey next year.

    “We are excited to see that current observations are able to probe the dynamics of dark energy at this level, and we hope that future observations will confirm what we see today,” says Zhao.

    Whatever the outcome, it’ll be worth it – the fate of the Universe is at stake, after all.

    This research was published in Nature Astronomy.

    See the full article here .

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