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  • richardmitnick 10:07 am on April 25, 2019 Permalink | Reply
    Tags: "Mystery of the Universe's Expansion Rate Widens with New Hubble Data", Astronomers have already hypothesized that dark energy existed during the first seconds after the big bang and pushed matter throughout space starting the initial expansion., , , , Cepheid variables in the Large Magellanic Cloud, , , Dark energy may also be the reason for the universe's accelerated expansion today., DASH (Drift And Shift) using Hubble as a "point-and-shoot" camera, , , , Proposed by astronomers at Johns Hopkins the theory is dubbed "early dark energy" and suggests that the universe evolved like a three-act play., Standard candles, The new estimate of the Hubble constant is 74 kilometers (46 miles) per second per megaparsec., The new theory suggests that there was a third dark-energy episode not long after the big bang which expanded the universe faster than astronomers had predicted., The true explanation is still a mystery.   

    From NASA/ESA Hubble Telescope: “Mystery of the Universe’s Expansion Rate Widens with New Hubble Data” 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope


    From NASA/ESA Hubble Telescope

    Apr 25, 2019

    Adam Riess
    Space Telescope Science Institute, Baltimore, Maryland
    and Johns Hopkins University, Baltimore, Maryland
    410-338-6707
    ariess@stsci.edu

    Donna Weaver
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4493
    dweaver@stsci.edu

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4514
    villard@stsci.edu

    1
    Large Magellanic Cloud (DSS View) with Star Cluster Overlay (Hubble). STScI.
    New physics may be needed to rectify the universe’s past and present behavior.

    2
    Three Steps to the Hubble Constant. STScI.

    4
    Three steps to the Hubble constant | ESA/Hubble

    ________________________________________________________________
    There is something wrong with our universe. Or, more specifically, it is outpacing all expectations for its present rate of expansion.

    Something is amiss in astronomers’ efforts to measure the past and predict the present, according to a discrepancy between the two main techniques for measuring the universe’s expansion rate – a key to understanding its history and physical parameters.

    The inconsistency is between the Hubble Space Telescope measurements of today’s expansion rate of the universe (by looking at stellar milepost markers) and the expansion rate as measured by the European Space Agency’s Planck satellite. Planck observes the conditions of the early universe just 380,000 years after the big bang.

    ESA/Planck 2009 to 2013

    For years, astronomers have been assuming this discrepancy would go away due to some instrumental or observational fluke. Instead, as Hubble astronomers continue to “tighten the bolts” on the accuracy of their measurements, the discordant values remain stubbornly at odds.

    The chances of the disagreement being just a fluke have skyrocketed from 1 in 3,000 to 1 in 100,000.

    Theorists must find an explanation for the disparity that could rattle ideas about the very underpinnings of the universe.
    ________________________________________________________________

    Astronomers using NASA’s Hubble Space Telescope say they have crossed an important threshold in revealing a discrepancy between the two key techniques for measuring the universe’s expansion rate. The recent study strengthens the case that new theories may be needed to explain the forces that have shaped the cosmos.

    A brief recap: The universe is getting bigger every second. The space between galaxies is stretching, like dough rising in the oven. But how fast is the universe expanding? As Hubble and other telescopes seek to answer this question, they have run into an intriguing difference between what scientists predict and what they observe.

    Hubble measurements suggest a faster expansion rate in the modern universe than expected, based on how the universe appeared more than 13 billion years ago. These measurements of the early universe come from the European Space Agency’s Planck satellite. This discrepancy has been identified in scientific papers over the last several years, but it has been unclear whether differences in measurement techniques are to blame, or whether the difference could result from unlucky measurements.

    The latest Hubble data lower the possibility that the discrepancy is only a fluke to 1 in 100,000. This is a significant gain from an earlier estimate, less than a year ago, of a chance of 1 in 3,000.

    These most precise Hubble measurements to date bolster the idea that new physics may be needed to explain the mismatch.

    “The Hubble tension between the early and late universe may be the most exciting development in cosmology in decades,” said lead researcher and Nobel laureate Adam Riess of the Space Telescope Science Institute (STScI) and Johns Hopkins University, in Baltimore, Maryland. “This mismatch has been growing and has now reached a point that is really impossible to dismiss as a fluke. This disparity could not plausibly occur just by chance.”

    Tightening the bolts on the ‘cosmic distance ladder’

    Scientists use a “cosmic distance ladder” to determine how far away things are in the universe.

    Cosmic Distance Ladder, skynetblogs

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

    This method depends on making accurate measurements of distances to nearby galaxies and then moving to galaxies farther and farther away, using their stars as milepost markers. Astronomers use these values, along with other measurements of the galaxies’ light that reddens as it passes through a stretching universe, to calculate how fast the cosmos expands with time, a value known as the Hubble constant.

    Riess and his SH0ES (Supernovae H0 for the Equation of State) team have been on a quest since 2005 to refine those distance measurements with Hubble and fine-tune the Hubble constant.

    In this new study, astronomers used Hubble to observe 70 pulsating stars called Cepheid variables in the Large Magellanic Cloud. The observations helped the astronomers “rebuild” the distance ladder by improving the comparison between those Cepheids and their more distant cousins in the galactic hosts of supernovas. Riess’s team reduced the uncertainty in their Hubble constant value to 1.9% from an earlier estimate of 2.2%.

    As the team’s measurements have become more precise, their calculation of the Hubble constant has remained at odds with the expected value derived from observations of the early universe’s expansion. Those measurements were made by Planck, which maps the cosmic microwave background [CMB], a relic afterglow from 380,000 years after the big bang.

    CMB per ESA/Planck

    The measurements have been thoroughly vetted, so astronomers cannot currently dismiss the gap between the two results as due to an error in any single measurement or method. Both values have been tested multiple ways.

    “This is not just two experiments disagreeing,” Riess explained. “We are measuring something fundamentally different. One is a measurement of how fast the universe is expanding today, as we see it. The other is a prediction based on the physics of the early universe and on measurements of how fast it ought to be expanding. If these values don’t agree, there becomes a very strong likelihood that we’re missing something in the cosmological model that connects the two eras.”

    How the new study was done

    Astronomers have been using Cepheid variables as cosmic yardsticks to gauge nearby intergalactic distances for more than a century. But trying to harvest a bunch of these stars was so time-consuming as to be nearly unachievable. So, the team employed a clever new method, called DASH (Drift And Shift), using Hubble as a “point-and-shoot” camera to snap quick images of the extremely bright pulsating stars, which eliminates the time-consuming need for precise pointing.

    “When Hubble uses precise pointing by locking onto guide stars, it can only observe one Cepheid per each 90-minute Hubble orbit around Earth. So, it would be very costly for the telescope to observe each Cepheid,” explained team member Stefano Casertano, also of STScI and Johns Hopkins. “Instead, we searched for groups of Cepheids close enough to each other that we could move between them without recalibrating the telescope pointing. These Cepheids are so bright, we only need to observe them for two seconds. This technique is allowing us to observe a dozen Cepheids for the duration of one orbit. So, we stay on gyroscope control and keep ‘DASHing’ around very fast.”

    The Hubble astronomers then combined their result with another set of observations, made by the Araucaria Project, a collaboration between astronomers from institutions in Chile, the U.S., and Europe. This group made distance measurements to the Large Magellanic Cloud by observing the dimming of light as one star passes in front of its partner in eclipsing binary-star systems.

    The combined measurements helped the SH0ES Team refine the Cepheids’ true brightness. With this more accurate result, the team could then “tighten the bolts” of the rest of the distance ladder that extends deeper into space.

    The new estimate of the Hubble constant is 74 kilometers (46 miles) per second per megaparsec. This means that for every 3.3 million light-years farther away a galaxy is from us, it appears to be moving 74 kilometers (46 miles) per second faster, as a result of the expansion of the universe. The number indicates that the universe is expanding at a 9% faster rate than the prediction of 67 kilometers (41.6 miles) per second per megaparsec, which comes from Planck’s observations of the early universe, coupled with our present understanding of the universe.

    So, what could explain this discrepancy?

    One explanation for the mismatch involves an unexpected appearance of dark energy in the young universe, which is thought to now comprise 70% of the universe’s contents. Proposed by astronomers at Johns Hopkins, the theory is dubbed “early dark energy,” and suggests that the universe evolved like a three-act play.

    Astronomers have already hypothesized that dark energy existed during the first seconds after the big bang and pushed matter throughout space, starting the initial expansion. Dark energy may also be the reason for the universe’s accelerated expansion today. The new theory suggests that there was a third dark-energy episode not long after the big bang, which expanded the universe faster than astronomers had predicted. The existence of this “early dark energy” could account for the tension between the two Hubble constant values, Riess said.

    Another idea is that the universe contains a new subatomic particle that travels close to the speed of light. Such speedy particles are collectively called “dark radiation” and include previously known particles like neutrinos, which are created in nuclear reactions and radioactive decays.

    Yet another attractive possibility is that dark matter (an invisible form of matter not made up of protons, neutrons, and electrons) interacts more strongly with normal matter or radiation than previously assumed.

    But the true explanation is still a mystery.

    Riess doesn’t have an answer to this vexing problem, but his team will continue to use Hubble to reduce the uncertainties in the Hubble constant. Their goal is to decrease the uncertainty to 1%, which should help astronomers identify the cause of the discrepancy.

    The team’s results have been accepted for publication in The Astrophysical Journal.

    See the full HubbleSite article here .
    See the ESA/Hubble article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

    ESA50 Logo large

    AURA Icon

     
  • richardmitnick 1:16 pm on April 4, 2019 Permalink | Reply
    Tags: , , , , , , Standard candles, The Hubble Constant discrepency, UC Banta Barbra   

    From UC Santa Barbara: “The Standard Siren” 

    UC Santa Barbara Name bloc
    From UC Santa Barbara

    Ten years before the detection of gravitational waves, two KITP postdocs at UC Santa Barbara had a novel idea.

    April 2, 2019
    Harrison Tasoff

    1
    Two neutron stars collide, sending out gravitational waves and electromagnetic radiation detected on Earth in 2017. Photo Credit: Fermilab

    2
    Scott Hughesz. Photo Credit: MIT

    The history of science is filled with stories of enthusiastic researchers slowly winning over skeptical colleagues to their point of view. Astrophysicist Scott Hughes can relate to these tales.

    “For the first 15 or 16 years of my career I was speaking to astronomers, and I always had the impression that they were politely interested in what I had to say, but regarded me as a little bit of a wild-eyed enthusiast who was telling them about a herd of unicorns that my friends and I were raising,” said Hughes.

    “Now,” he continued, “there are people who are going, ‘Ooh, all those unicorns you found, can I use them to solve my problem? Do your unicorns have wings? Are they sparkly?’”

    3
    Daniel Holz. Photo Credit: University of Chicago

    These unicorns are gravitational waves, an area of physics in which Hughes specializes. While working as postdoctoral researchers at UC Santa Barbara’s Kavli Institute for Theoretical Physics (KITP), Hughes and his colleague, Daniel Holz, were among the first to propose using the phenomena, in combination with telescope-based observations, to measure the Hubble constant, a fundamental quantity involved in describing the expansion of the universe.

    As the universe expands, it carries celestial objects away from us. This stretches out the wavelength of light we detect from these objects, causing it to drop in frequency just like a siren on a passing ambulance. The faster the object is receding, the more its light will shift toward the red end of the spectrum. The Hubble constant relates an object’s distance from Earth to this redshift, and thus the object’s speed as it’s carried away.

    One of an astronomer’s best tools for calculating this is a standard candle, any class of objects that always have the same, standard brightness.

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

    If scientists know the brightness of an object, they can determine its distance by measuring how dim it appears to us on Earth.

    For decades scientists have tried to get accurate measurements of the Hubble constant in order to investigate why the universe is expanding, and, in fact, accelerating. This ultimately resolves to measuring objects’ redshifts and matching them with independent measurements of the objects’ distances from us. However, these two most accurate measurements scientists currently have for the Hubble constant disagree — an endless source of frustration for cosmologists.

    A Proposal

    This was the cosmological landscape in the early 2000s when Holz and Hughes held positions as postdoctoral researchers at KITP. “Scott had been thinking about gravitational waves for a while,” said Holz. “He was the expert, and I was much more focused on cosmological questions.” But Hughes’ enthusiasm soon piqued Holz’s curiosity, and the two began to talk about gravitational wave cosmology in the office and on walks along the Santa Barbara bluffs.

    Holz and Hughes credit their close collaboration to the construction of the new wing of Kohn Hall in 2001. Initially, all postdocs at KITP had their own offices, explained Hughes, but the construction forced them to double-up. “Suddenly we were spending a lot more time with each other.”

    A 2002 KITP program on cosmological data fanned the flames of their interest in the topic. By the time Hughes left to join the faculty at MIT, they had finished the first draft of their paper detailing how to calculate the Hubble constant with gravitational waves. After two years gestating they finally published the study in The Astrophysical Journal.

    “I had a great time writing that paper with Scott,” said Holz. “I learned an incredible amount. So much that I was convinced that gravitational waves were the future, and that I should get involved.”

    The idea of using gravitational wave sources to measure the Hubble constant was not new. The concept was first proposed in a visionary paper back in 1986 by Bernard Schutz [Nature]. And a number of other notions regarding gravitational waves were also floating around the literature in the early 2000s. But what Holz and Hughes did was synthesize all these ideas and emphasize the feasibility of combining data from gravitational waves with follow-up observations using light.

    The study also was the first to use the term “standard siren [Nature].” Hughes recalled discussing the paper with Caltech astrophysicist Sterl Phinney, who remarked, “Hmm. Kind of like a standard candle, but you hear it. You should call it a standard siren.” Holz independently had an almost identical conversation with physicist Sean Carroll, a former KITP postdoc himself. Holz and Hughes included the term in their paper, and it stuck. The phrase has since become ubiquitous in cosmology.

    “The term ‘standard siren’ might be our most lasting contribution, Scott,” Holz remarked. “I’ll take it,” laughed Hughes.

    Using gravitational waves to measure the Hubble constant has many advantages over other methods. Certain supernovae provide decent standard candles, “but, as a standard candle, supernovae are not very well understood,” said Holz. “The main thing that makes standard sirens interesting is that they’re understood from first principles, directly from the theory of general relativity.”

    When using standard candles, scientists have to calibrate the distances of certain classes of objects using the information from other ones, effectively leapfrogging their way to a proper distance measurement. Astronomers call this method a “distance ladder,” and errors and uncertainty can creep in at many points in the calculations.

    3
    Getting accurate measurements of distance requires building up a distance ladder using a number of different techniques for various ranges. Photo Credit: MATT PERKO.

    In contrast, gravitational waves can provide a direct measurement of an object’s distance. “You just write down the equations and solve them, and then you’re done,” said Holz. “We’ve tested general relativity for a hundred years; it really works, and it says ‘here’s how far that source is.’ There’s no distance ladder, there’s none of that fiddling around.”

    All the early papers on measuring the Hubble constant using gravitational waves were somewhat speculative, according to Holz. They were proposals for the far future. “We hadn’t even detected gravitational waves yet, much less waves from two neutron stars, much less with an optical counterpart,” he said. But interest and enthusiasm for the technique were growing.

    Hughes remembers colleagues coming up to him after his talks and asking about the likelihood of observing a standard siren in the next decade. He didn’t know, but he did say that with a better understanding of the optical counterpart, they could probably localize an event to within 10-20 square degrees. “And I think if you have that, every piece of large glass on Earth is going to stare at that spot on the sky,” Hughes had said. “And, in the end, that is exactly what happened.”

    And Then It Happened

    On August 17, 2017, less than two years after detecting the first gravitational waves, the LIGO and Virgo observatories recorded a signal from merging neutron stars. Thanks to an alert system, which Holz helped establish, a flurry of activity followed as nearly every major ground and space-based observatory trained their sights on the event. Scientists collected data on the merger in every region of the electromagnetic spectrum.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    Gravity is talking. Lisa will listen. Dialogos of Eide

    ESA/eLISA the future of gravitational wave research

    Localizations of gravitational-wave signals detected by LIGO in 2015 (GW150914, LVT151012, GW151226, GW170104), more recently, by the LIGO-Virgo network (GW170814, GW170817). After Virgo came online in August 2018


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

    “It really is one of those things where, if it had happened before I retired, I would have been happy,” said Hughes. “But it actually happened before I turned 50.”

    Suddenly, gravitational wave cosmology was a real field, and standard sirens were another part of the toolkit. “But for something to become part of the toolkit so quickly? That’s extraordinarily unusual,” said Holz.

    It turns out that cosmologists need another tool, because they currently have two different values for the Hubble constant. Methods using the cosmic microwave background [CMB] — faint light left over from the big bang — yields a value of around 68. Meanwhile, calculations that use Type Ia supernovae — a variety of standard candle [above] — yield a bit more than 73.

    CMB per ESA/Planck

    Although they appear close, the two values actually differ by three standard deviations, and both have fairly tight error bars. The disagreement has cosmologists increasingly concerned as the error bars on these two values only get tighter. It could signal a fundamental problem in our understanding of the universe, and is the subject of a KITP conference this July.

    There are a few intrinsic differences between the two techniques, though. The cosmic microwave background reflects the conditions of the early universe, while the supernovae paint a picture of the current universe. “There’s a chance that maybe something very strange and unexpected has happened between the early and late days of the universe, and that’s why these values don’t agree,” said Holz. But cosmologists simply don’t know for sure.

    Getting another, independent value for the Hubble constant will help clear up this conundrum. “Because it’s so clean and so direct, that measurement will be a very compelling number,” Holz explained. “At the very least, it’ll inform this discussion, if not just completely resolve it.”

    Holz and his colleagues, Hsin-Yu Chen and Maya Fishbach, have just published a paper in the journal Nature, finding that 20 to 30 observations would allow scientists to calculate the Hubble constant to within 2 percent accuracy, tight enough to begin comparing it to the two values from the cosmic microwave background and supernovae.

    This summer, Holz is co-organizing a KITP program on the new era of gravitational wave physics and astrophysics, and the new field of standard siren cosmology will be a major topic of discussion. In fact, Holz also helped organize the KITP rapid response program that brought researchers together shortly after LIGO’s first detection of gravitational waves.

    Holz and Hughes credit their success to their experiences at KITP. “While working together at the KITP the two of us got excited about measuring the Hubble constant using gravitational waves,” said Holz. “And that’s exactly what the KITP is about: bringing different people together with different backgrounds, stirring the pot and seeing what happens.”

    For the past decade Holz’s career has focused on standard siren cosmology. “And the amazing thing is we’ve actually done it,” he said. “I helped write the paper that did the first standard siren measurement ever. This was exactly what Scott and I had hypothesized about years before.”

    “If both of us hadn’t been at the KITP there’s no way I’d be spending a good fraction of my life on LIGO teleconferences right now,” said Holz. “But I wouldn’t have it any other way.”

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    UC Santa Barbara Seal
    The University of California, Santa Barbara (commonly referred to as UC Santa Barbara or UCSB) is a public research university and one of the 10 general campuses of the University of California system. Founded in 1891 as an independent teachers’ college, UCSB joined the University of California system in 1944 and is the third-oldest general-education campus in the system. The university is a comprehensive doctoral university and is organized into five colleges offering 87 undergraduate degrees and 55 graduate degrees. In 2012, UCSB was ranked 41st among “National Universities” and 10th among public universities by U.S. News & World Report. UCSB houses twelve national research centers, including the renowned Kavli Institute for Theoretical Physics.

     
  • richardmitnick 10:28 am on January 29, 2019 Permalink | Reply
    Tags: , , , , , , Quasars are brilliant enough to be seen from a universe less than a billion years old making them prime targets for reaching earlier epochs, , Standard candles, Two decades ago astronomers discovered that the universe was not only expanding but accelerating in its expansion, Type Ia supernovae have long been the brightest of standard candles, What Quasar Cosmology Can Teach Us About Dark Energy   

    From Sky & Telescope: “What Quasar Cosmology Can Teach Us About Dark Energy” 

    SKY&Telescope bloc

    From Sky & Telescope

    January 28, 2019
    Monica Young

    Astronomers have found a way to turn quasars into standard candles, with potentially far-reaching implications for the nature of mysterious dark energy.

    Standard Candles to measure age and distance of the universe NASA

    National Science Foundation (NASA, JPL, Keck Foundation, Moore Foundation, related) — Funded BICEP2 Program; modifications by E. Siegel.

    Two decades ago astronomers discovered that the universe was not only expanding but accelerating in its expansion. They dubbed the cause of this acceleration dark energy, but what that actually is remains as ineffable now as it was then.

    The weird repulsive force has left its fingerprints on the earliest photons we can see, the ones emitted as part of the cosmic microwave background (CMB), when the infant universe was only 370,000 years old. Yet dark energy only began to dominate expansion as the universe entered middle age, after 9 billion years or so.

    Now, Guido Risaliti (University of Florence and INAF-Astrophysical Observatory of Arcetri, Italy) and Elisabeta Lusso (Durham University, UK) are using quasars to probe the cosmology of our universe’s relatively unexplored adolescence. The results, appearing in the January 28th Nature Astronomy, promise to reveal dark energy’s true nature.

    The leading explanation for dark energy has long been the cosmological constant, also known as vacuum energy. This energy inherent to empty space arises from quantum theory, which says that even when space appears empty of particles, it’s actually filled with quantum fields. These fields exert a negative pressure that counteracts the attractive force of gravity. However, calculations of vacuum energy overpredict the measured dark energy density by an astounding 120 orders of magnitude (that’s a 1 followed by 120 zeroes!). That the cosmological constant remains the favorite theory speaks to how little we understand dark energy — and how difficult the measurements involved are.

    Studying the universe at any age starts with gauging cosmological distance — the farther we look, the further back in time we see­­ ­— but we can’t just roll out a tape measure to the stars. Enter standard candles, objects for which we can measure an intrinsic luminosity. By comparing how bright a standard candle appears to be with how bright it really is, we can determine its distance without knowing anything about cosmology.

    Type Ia supernovae have long been the brightest of standard candles. Observations of these detonating white dwarfs led to the Nobel-winning discovery of accelerating expansion announced back in 1998. The supernovae extended our reach to when the universe was a third of its current age. That’s a pretty good tape measure! Nevertheless, it only probes the era when dark energy began to dominate the universe’s expansion. To see farther back, and probe the era when dark energy overtook matter, astronomers need something even more luminous.

    Quasars as Standard Candles

    2
    Understanding the physics of quasar accretion disks (blue-white) and X-ray-emitting coronae (yellow) can help astronomers use quasars as standard candles.
    NASA / CXC / M. Weiss.

    What’s more luminous than an exploding star? A gas-guzzling supermassive black hole would do the trick. After all, quasars are brilliant enough to be seen from a universe less than a billion years old, making them prime targets for reaching earlier epochs.

    Unfortunately, quasars also exhibit a bewildering variety of forms — astronomers have long thought they were anything but standard. Case in point: Astronomers have known for the past 30 years that more visibly luminous quasars emit relatively fewer X-rays, but there was too much variance from one quasar to another to pin down any one quasar’s intrinsic brightness.

    Risaliti and Lusso realized that this relation between the emission of X-rays and visible light must arise from the physics of quasar accretion disks. The disk itself emits visible light, while a hot, gaseous corona emits the X-rays. The two are intertwined by straightforward physics; it’s just that previously, contaminants had been mucking things up. So for this study, Risaliti and Lusso removed any sources where disk emission is obscured (by dust or gas) or contaminated (by emission from a fast-flowing black hole jet). Their careful selection results in a much tighter, more useful relation. Using data from the Sloan Digital Sky Survey and the XMM-Newton, Chandra, and Swift space telescopes, the duo then apply the relation to turn 1,600 quasars into standard candles.

    SDSS 2.5 meter Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

    ESA/XMM Newton

    NASA/Chandra X-ray Telescope

    NASA Neil Gehrels Swift Observatory

    3
    The history of the universe shows a crucial time when the expansion switched from decelerating to accelerating. But the future still hangs in the balance, depending on the behavior of dark energy. If dark energy increases, everything will be torn apart; if it changes direction, the cosmos could end in a big crunch.
    NASA / CXC / M.Weiss

    The quasars help Risaliti and Lusso fill in the gap along the cosmic timeline, looking back to an adolescent universe only a billion years old. From this data, the team finds that dark energy is actually increasing over cosmic time.

    The results appear to rule out the cosmological constant, which predicts a constant energy density. That’s a bit of a relief given that vacuum energy overpredicts the observations so badly. (Did I mention the 120 orders of magnitude?) Evolving dark energy may also help resolve an ongoing tension between measurements of the universe’s current expansion rate.

    Nevertheless, the results are unsettling from a philosophical standpoint: If dark energy density really does increase over time, then so does the repulsive force it exerts, potentially ending our universe in a Big Rip.

    Too Early To Tell

    Let’s not give up on the universe just yet, though. Phil Hopkins (Caltech), who wasn’t involved in the study, urges caution in interpreting its results. The relation that Lusso and Risaliti use to turn quasars into standard candles may itself evolve over time, making those quasars not so standard. For example, if quasars slow their gas-guzzling as mergers become less frequent, that might change the shape of the relation between the emission of X-rays and visible light. “[The relation] only needs to evolve a little bit to explain these observations,” he adds.

    That said, Hopkins agrees the results are interesting and worth following up with even bigger and better samples. The authors also note that other studies probing the adolescent universe are forthcoming. The bar is high these days for disproving the standard cosmological model, and only time and additional study will tell if this is the method that will do it.

    See the full article here .
    See also from Chandra here.

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Sky & Telescope magazine, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 3:06 pm on October 24, 2018 Permalink | Reply
    Tags: A double-degenerate model in which a one white dwarf explodes in a binary pair flinging the other one out into space, , , , , , Dynamically driven double-degenerate double-detonation” model — or D6 for short, Speeding White Dwarfs May Point to Past Explosions, Standard candles,   

    From AAS NOVA: “Speeding White Dwarfs May Point to Past Explosions” 

    AASNOVA

    From AAS NOVA

    24 October 2018
    Susanna Kohler

    1
    A new study suggests that binary white dwarfs be the key to understanding Type Ia supernovae like the explosion featured in this artist’s impression. [ESO/M. Kornmesser]

    A recent study has discovered three of the fastest stars known in the Milky Way. But these stars may be more than just speeders — they might also be evidence of how Type Ia supernovae occur.

    1
    Two competing theoretical models for the progenitors of Type Ia supernova explosions: the single-degenerate model (top) and the double-degenerate model (bottom). Today’s study focuses on a double-degenerate model in which a one white dwarf explodes in a binary pair, flinging the other one out into space. [NASA/CXC/SAO and GSFC/D. Berry]

    Seeking a Source

    Given the extent to which we rely on Type Ia supernovae as standard candles used to measure vast distances, you might think that we’ve got them fairly well figured out. But these stellar explosions are complicated, and it turns out that we don’t know some of the most fundamental things about them! Scientists are still working hard to find answers about what systems Type Ia supernovae originate from, and how the explosions are caused.

    Led by astronomer Ken Shen (University of California, Berkeley), a team of astronomers has explored one particular model for Type Ia supernovae further: the “dynamically driven double-degenerate double-detonation” model — or D6, for short. In this scenario, a pair of white dwarfs orbit each other in a binary system. Two back-to-back detonations then cause one of the white dwarfs to explode as a supernova while the other white dwarf survives and is flung free of the explosion site.

    Shen and collaborators note that if the D6 model proves to be the primary means of producing Type Ia supernovae, then there’s an observable outcome: there should be white dwarfs speeding throughout our galaxy that were suddenly liberated by the supernova explosions of their companions.

    2
    Posterior probability distributions for the total galactocentric velocities for estimated for the three hypervelocity white dwarf candidates: D6-1, D6-2, and D6-3. [Shen et al. 2018]

    Hunt for Speeders

    Based on the estimated supernova rate in our galaxy and the properties of binary white dwarfs, Shen and collaborators predict that there should be ~30 hypervelocity white dwarfs within ~3,000 light-years of us. But how to spot these compact stars speeding across the sky? With one of the best tools in the business: Gaia.

    Shen and collaborators combed through the numbers from the Gaia mission’s second data release, which presents the astrometric parameters of more than a billion stars across the sky. In this treasure trove of information, they discovered seven candidates that they then followed up with ground-based observations. After ruling out four as ordinary stars, the authors were left with three candidate hypervelocity white dwarfs.

    Associated Remnant?

    3

    The three candidates have total galactocentric velocities between 1,000 and 3,000 km/s (that’s 2.2 to 6.7 million miles per hour!), making them some of the fastest known stars in the Milky Way. That alone is enough to qualify them as potential progenitors of Type Ia supernovae via the D6 model — but Shen and collaborators look for one more clue: whether they can be tracked back to a supernova remnant.

    Two of the candidates show no sign of having traveled from a nearby remnant — not necessarily surprising, as the remnants could be very faint, or even have already dissipated completely. But the third candidate can be tracked back to a location within the faint, old supernova remnant G70.0–21.5.

    While not yet a smoking gun, these hypervelocity white dwarfs represent important support for the D6 model. And continued follow-up of additional candidates — as well as new candidates discovered in future Gaia releases — may further confirm this model for how Type Ia supernovae occur.

    Citation

    “Three Hypervelocity White Dwarfs in Gaia DR2: Evidence for Dynamically Driven Double-Degenerate Double-Detonation Type Ia Supernovae,” Ken J. Shen et al 2018 ApJ 865 15.
    http://iopscience.iop.org/article/10.3847/1538-4357/aad55b/meta

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

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    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 7:59 am on September 27, 2017 Permalink | Reply
    Tags: , , , , , , Dark energy may not exist, Standard candles,   

    From COSMOS: “Dark energy may not exist” 

    Cosmos Magazine bloc

    COSMOS Magazine

    27 September 2017
    Stuart Gary

    1
    A model of the universe that takes into account the irregular distribution of galaxies may make dark energy disappear. NASA, H. Ford (JHU), G. Illingworth (UCSC/LO), M. Clampin (STScI), G. Hartig (STScI), the ACS Science Team and ESA

    The accelerating expansion of the universe due to a mysterious quantity called “dark energy” may not be real, according to research claiming it might simply be an artefact caused by the physical structure of the cosmos.

    The findings, reported in the Monthly Notices of the Royal Astronomical Society, claims the fit of Type Ia supernovae to a model universe with no dark energy appears to be slightly better than the fit using the standard dark energy model.

    The study’s lead author David Wiltshire, from the University of Canterbury in New Zealand, says existing dark energy models are based on a homogenous universe in which matter is evenly distributed.

    CMB per ESA/Planck

    ESA/Planck

    “The real universe has a far more complicated structure, comprising galaxies, galaxy clusters, and superclusters arranged in a cosmic web of giant sheets and filaments surrounding vast near-empty voids”, says Wiltshire.

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    Current models of the universe require dark energy to explain the observed acceleration in the rate at which the universe is expanding.

    Scientists base this conclusion on measurements of the distances to Type 1a supernovae in distant galaxies, which appear to be farther away than they would be if the universe’s expansion was not accelerating.

    Type 1a supernovae are powerful explosions bright enough to briefly outshine an entire galaxy. They’re caused by the thermonuclear destruction of a type of star known as a white dwarf – the stellar corpse of a Sun-like star.

    All Type 1a supernovae are thought to explode at around the same mass – a figure known in astrophysics as the Chandrasekhar limit – which equates to about 1.44 times the mass of the Sun.

    Because they all explode at about the same mass, they also explode with about the same level of luminosity.

    This allows astronomers to use them as standard candles to measure cosmic distances across the universe – in the same way you can determine how far away a row of street lights is along a road by how bright each one appears from where you’re standing.

    2
    Standard candles. https://www.extremetech.com

    On a galactic scale, gravity appears to be stronger than scientists can account for, using the normal matter of the universe, the material in the standard model of particle physics, which makes up all the stars, planets, buildings, and people.

    To explain their observations, scientists invented “dark matter”, a mysterious substance which seems to only interact gravitationally with normal matter.

    To explain science’s observations of how galaxies move, there must be about five times as much dark matter as normal matter.

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

    It’s called dark because whatever it is, it cannot emit light. Scientists can only see its effects gravitationally on normal matter.

    On the even larger cosmic scales of an expanding universe, gravity appears to be weaker than expected in a universe containing only normal matter and dark matter.

    And so, scientists invented a new force, called “dark energy”, a sort of anti-gravitational force causing an acceleration in the expansion of the universe out from the big bang 13.8 billion years ago.

    Dark energy isn’t noticeable on small scales, but becomes the dominating force of the universe on the largest cosmic scales: almost four times greater than the gravity of normal and dark matter combined.

    The idea of dark energy isn’t new. Albert Einstein first came up with it to explain a problem he was having when he applied his famous 1915 equations of general relativity theory to the whole universe.

    Like other scientists at the time, Einstein believed the universe was in a steady unchanging state. Yet, when applied to cosmology, his equations showed the universe wanted to expand or contract as matter interacts with the fabric of spacetime: matter tells spacetime how to curve, and spacetime tells matter how to move.

    To resolve the problem, Einstein introduced a dark energy force in 1917 which he called the “cosmological constant”.

    It was a mathematical invention, a fudge factor designed to solve the discrepancies between general relativity theory and the best observational evidence of the day, thus bringing the universe back into a steady state.

    Years later, when astronomer Edwin Hubble discovered that galaxies appeared to be moving away from each other, and the rate at which they were moving was proportional to their distance, Einstein realised his mistake, describing the cosmological constant as the biggest blunder of his life.

    However, the idea has never really gone away, and keeps reappearing to explain strange observations.

    In the mid 1990s two teams of scientists, one led by Brian Schmidt and Adam Riess, and the other by Saul Perlmutter, independently measured distances to Type 1a supernovae in the distant universe, finding that they appeared to be further way than they should be if the universe’s rate of expansion was constant.

    The observations led to the hypothesis that some kind of dark energy anti-gravitational force has caused the expansion of the universe to accelerate over the past six billion years.

    Wiltshire and his colleagues now challenge that reasoning.

    “But these observations are based on an old model of expansion that has not changed since the 1920s”, he says.

    In 1922, Russian physicist Alexander Friedmann used Einstein’s field equations to develop a physical cosmology governing the expansion of space in homogeneous and isotropic models of the universe.

    “Friedmann’s equation assumes an expansion identical to that of a featureless soup, with no complicating structure”, says Wiltshire.

    This has become the basis of the standard Lambda Cold Dark Matter cosmology used to describe the universe.

    “In reality, today’s universe is not homogeneous”, says Wiltshire.

    The earliest snapshot of the universe – called cosmic microwave background radiation – displays only slight temperature variations caused by differences in densities present 370,000 years after the Big Bang.

    However, gravitational instabilities led those tiny density variations to evolve into the stars, galaxies, and clusters of galaxies, which made up the large scale structure of the universe today.

    “The universe has become a vast cosmic web dominated in volume by empty voids, surrounded by sheets of galaxies and threaded by wispy filaments”, says Wiltshire.

    Rather than comparing the supernova observations to the standard Lambda Cold Dark Matter cosmological model, Wiltshire and colleagues used a different model, called ‘timescape cosmology’.

    Timescape cosmology has no dark energy. Instead, it includes variations in the effects of gravity caused by the lumpiness in the structure in the universe.

    Clocks carried by observers in galaxies differ from the clock that best describes average expansion once variations within the universe (known as “inhomogeneity” in the trade) becomes significant.

    Whether or not one infers accelerating expansion then depends crucially on the clock used.

    “Timescape cosmology gives a slightly better fit to the largest supernova data catalogue than Lambda Cold Dark Matter cosmology,” says Wiltshire.

    He admits the statistical evidence is not yet strong enough to definitively rule in favour of one model over the other, and adds that future missions such as the European Space Agency’s Euclid spacecraft will have the power to distinguish between differing cosmology models.

    ESA/Euclid spacecraft

    Another problem involves science’s understanding of Type 1a supernovae. They are not actually perfect standard candles, despite being treated as such in calculations.

    Since timescape cosmology uses a different equation for average expansion, it gives scientists a new way to test for changes in the properties of supernovae over distance.

    Regardless of which model ultimately fits better, better understanding of this will increase the confidence with which scientists can use them as precise distance indicators.

    Answering questions like these will help scientists determine whether dark energy is real or not – an important step in determining the ultimate fate of the universe.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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