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  • richardmitnick 8:50 am on November 30, 2017 Permalink | Reply
    Tags: , , , , Here’s what really happened to Hanny’s Voorwerp, How the activity of supermassive black holes varies on superhuman time scales, ScienceNews   

    From ScienceNews: “Here’s what really happened to Hanny’s Voorwerp” 

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    ScienceNews

    November 27, 2017
    Lisa Grossman

    Astronomers can finally explain a gas cloud’s strange glow.

    1
    GLOWING GAS Hanny’s Voorwerp, the greenish smudge at the bottom of this image, is glowing thanks to photons from a feasting black hole in the galaxy above. NASA, ESA, W. Keel (Univ. Alabama), et al., Galaxy Zoo Team.

    The weird glowing blob of gas known as Hanny’s Voorwerp was a 10-year-old mystery. Now, Lia Sartori of ETH Zürich and colleagues have come to a two-pronged solution.

    Hanny van Arkel, then a teacher in the Netherlands, discovered the strange bluish-green voorwerp, Dutch for “object,” in 2008 as she was categorizing pictures of galaxies as part of the Galaxy Zoo citizen science project.

    Further observations showed that the voorwerp was a glowing cloud of gas that stretched some 100,000 light-years from the core of a massive nearby galaxy called IC 2497. The glow came from radiation emitted by an actively feeding black hole in the galaxy.

    To excite the voorwerp’s glow, the black hole should have had the brightness of about 2.5 trillion suns; its radio emission, however, suggested the black hole emitted the equivalent of a relatively paltry 25,000 suns. Either the black hole was obscured by dust, or it stopped eating around 100,000 years ago, causing its brightness to plunge.

    Sartori and colleagues made the first direct measurement of the black hole’s intrinsic brightness using NASA’s NuSTAR telescope, which observed IC 2497 in high-energy X-rays that cut through the dust.

    NASA NuSTAR X-ray telescope

    They found that, yes, the black hole is obscured by dust, and yes, it is dimmer than expected. The team reported on arXiv.org on November 20 that IC 2497’s heart is as bright as 50 billion to 100 billion suns, meaning it dropped in brightness by a factor of 50 in the past 100,000 years — a less dramatic drop than previously thought.

    “Both hypotheses that we thought before are true,” Sartori says.

    Sartori plans to analyze NuSTAR observations of other voorwerpjes to see if their galaxies’ black holes are also in the process of shutting down — or even booting up.

    “If you look at these clouds, you get information on how the black hole was in the past,” she says. “So we have a way to study how the activity of supermassive black holes varies on superhuman time scales.”

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  • richardmitnick 8:04 am on November 27, 2017 Permalink | Reply
    Tags: , , , , DESI spectroscopic instrument, , , ScienceNews, Simulating the universe using Einstein’s theory of gravity may solve cosmic puzzles   

    From ScienceNews: “Simulating the universe using Einstein’s theory of gravity may solve cosmic puzzles” 

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    ScienceNews

    November 25, 2017
    Emily Conover

    Until recently, simulations of the universe haven’t given its lumps their due.

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    UNEVEN TERRAIN Universe simulations that consider general relativity (one shown) may shift knowledge of the cosmos. James Mertens

    If the universe were a soup, it would be more of a chunky minestrone than a silky-smooth tomato bisque.

    Sprinkled with matter that clumps together due to the insatiable pull of gravity, the universe is a network of dense galaxy clusters and filaments — the hearty beans and vegetables of the cosmic stew. Meanwhile, relatively desolate pockets of the cosmos, known as voids, make up a thin, watery broth in between.

    Until recently, simulations of the cosmos’s history haven’t given the lumps their due. The physics of those lumps is described by general relativity, Albert Einstein’s theory of gravity. But that theory’s equations are devilishly complicated to solve. To simulate how the universe’s clumps grow and change, scientists have fallen back on approximations, such as the simpler but less accurate theory of gravity devised by Isaac Newton.

    Relying on such approximations, some physicists suggest, could be mucking with measurements, resulting in a not-quite-right inventory of the cosmos’s contents. A rogue band of physicists suggests that a proper accounting of the universe’s clumps could explain one of the deepest mysteries in physics: Why is the universe expanding at an increasingly rapid rate?

    The accepted explanation for that accelerating expansion is an invisible pressure called dark energy. In the standard theory of the universe, dark energy makes up about 70 percent of the universe’s “stuff” — its matter and energy. Yet scientists still aren’t sure what dark energy is, and finding its source is one of the most vexing problems of cosmology.

    Perhaps, the dark energy doubters suggest, the speeding up of the expansion has nothing to do with dark energy. Instead, the universe’s clumpiness may be mimicking the presence of such an ethereal phenomenon.

    Most physicists, however, feel that proper accounting for the clumps won’t have such a drastic impact. Robert Wald of the University of Chicago, an expert in general relativity, says that lumpiness is “never going to contribute anything that looks like dark energy.” So far, observations of the universe have been remarkably consistent with predictions based on simulations that rely on approximations.

    _____________________________________________________________________________

    Growing a lumpy universe

    The universe has gradually grown lumpier throughout its history. During inflation, rapid expansion magnified tiny quantum fluctuations into minute density variations. Over time, additional matter glommed on to dense spots due to the stronger gravitational pull from the extra mass. After 380,000 years, those blips were imprinted as hot and cold spots in the cosmic microwave background, the oldest light in the universe. Lumps continued growing for billions of years, forming stars, planets, galaxies and galaxy clusters.

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    _____________________________________________________________________________

    As observations become more detailed, though, even slight inaccuracies in simulations could become troublesome. Already, astronomers are charting wide swaths of the sky in great detail, and planning more extensive surveys. To translate telescope images of starry skies into estimates of properties such as the amount of matter in the universe, scientists need accurate simulations of the cosmos’s history. If the detailed physics of clumps is important, then simulations could go slightly astray, sending estimates off-kilter. Some scientists already suggest that the lumpiness is behind a puzzling mismatch of two estimates of how fast the universe is expanding.

    Researchers are attempting to clear up the debate by conquering the complexities of general relativity and simulating the cosmos in its full, lumpy glory. “That is really the new frontier,” says cosmologist Sabino Matarrese of the University of Padua in Italy, “something that until a few years ago was considered to be science fiction.” In the past, he says, scientists didn’t have the tools to complete such simulations. Now researchers are sorting out the implications of the first published results of the new simulations. So far, dark energy hasn’t been explained away, but some simulations suggest that certain especially sensitive measurements of how light is bent by matter in the universe might be off by as much as 10 percent.

    Soon, simulations may finally answer the question: How much do lumps matter? The idea that cosmologists might have been missing a simple answer to a central problem of cosmology incessantly nags some skeptics. For them, results of the improved simulations can’t come soon enough. “It haunts me. I can’t let it go,” says cosmologist Rocky Kolb of the University of Chicago.

    Smooth universe

    By observing light from different eras in the history of the cosmos, cosmologists can compute the properties of the universe, such as its age and expansion rate. But to do this, researchers need a model, or framework, that describes the universe’s contents and how those ingredients evolve over time. Using this framework, cosmologists can perform computer simulations of the universe to make predictions that can be compared with actual observations.

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    COSMIC WEB Clumps and filaments of matter thread through a simulated universe 2 billion light years across. This simulation incorporates some aspects of Einstein’s theory of general relativity, allowing for detailed results while avoiding the difficulties of the full-fledged theory.

    After Einstein introduced his theory in 1915, physicists set about figuring out how to use it to explain the universe. It wasn’t easy, thanks to general relativity’s unwieldy, difficult-to-solve suite of equations. Meanwhile, observations made in the 1920s indicated that the universe wasn’t static as previously expected; it was expanding. Eventually, researchers converged on a solution to Einstein’s equations known as the Friedmann-Lemaître-Robertson-Walker metric. Named after its discoverers, the FLRW metric describes a simplified universe that is homogeneous and isotropic, meaning that it appears identical at every point in the universe and in every direction. In this idealized cosmos, matter would be evenly distributed, no clumps. Such a smooth universe would expand or contract over time.

    A smooth-universe approximation is sensible, because when we look at the big picture, averaging over the structures of galaxy clusters and voids, the universe is remarkably uniform. It’s similar to the way that a single spoonful of minestrone soup might be mostly broth or mostly beans, but from bowl to bowl, the overall bean-to-broth ratios match.

    In 1998, cosmologists revealed that not only was the universe expanding, but its expansion was also accelerating (SN: 2/2/08, p. 74). Observations of distant exploding stars, or supernovas, indicated that the space between us and them was expanding at an increasing clip. But gravity should slow the expansion of a universe evenly filled with matter. To account for the observed acceleration, scientists needed another ingredient, one that would speed up the expansion. So they added dark energy to their smooth-universe framework.

    Now, many cosmologists follow a basic recipe to simulate the universe — treating the cosmos as if it has been run through an imaginary blender to smooth out its lumps, adding dark energy and calculating the expansion via general relativity. On top of the expanding slurry, scientists add clumps and track their growth using approximations, such as Newtonian gravity, which simplifies the calculations.

    In most situations, Newtonian gravity and general relativity are near-twins. Throw a ball while standing on the surface of the Earth, and it doesn’t matter whether you use general relativity or Newtonian mechanics to calculate where the ball will land — you’ll get the same answer. But there are subtle differences. In Newtonian gravity, matter directly attracts other matter. In general relativity, gravity is the result of matter and energy warping spacetime, creating curves that alter the motion of objects (SN: 10/17/15, p. 16). The two theories diverge in extreme gravitational environments. In general relativity, for example, hulking black holes produce inescapable pits that reel in light and matter (SN: 5/31/14, p. 16). The question, then, is whether the difference between the two theories has any impact in lumpy-universe simulations.

    Most cosmologists are comfortable with the status quo simulations because observations of the heavens seem to fit neatly together like interlocking jigsaw puzzle pieces. Predictions based on the standard framework agree remarkably well with observations of the cosmic microwave background — ancient light released when the universe was just 380,000 years old (SN: 3/21/15, p. 7). And measurements of cosmological parameters — the fraction of dark energy and matter, for example — are generally consistent, whether they are made using the light from galaxies or the cosmic microwave background [CMB].

    CMB per ESA/Planck


    ESA/Planck

    3
    An image from the Two-Micron All Sky Survey of 1.6 million galaxies in infrared light reveals how matter clumps into galaxy clusters and filaments. Future large-scale surveys may require improved simulations that use general relativity to track the evolution of lumps over time. T.H. Jarrett, J. Carpenter & R. Hurt, obtained as part of 2MASS, a joint project of Univ. of Massachusetts and the Infrared Processing and Analysis Center/Caltech, funded by NASA and NSF.


    Caltech 2MASS Telescopes, a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center (IPAC) at Caltech, at the Whipple Observatory on Mt. Hopkins south of Tucson, AZ, and at the Cerro Tololo Inter-American Observatory near La Serena, Chile.

    Dethroning dark energy

    Some cosmologists hope to explain the universe’s accelerating expansion by fully accounting for the universe’s lumpiness, with no need for the mysterious dark energy.

    These researchers argue that clumps of matter can alter how the universe expands, when the clumps’ influence is tallied up over wide swaths of the cosmos. That’s because, in general relativity, the expansion of each local region of space depends on how much matter is within. Voids expand faster than average; dense regions expand more slowly. Because the universe is mostly made up of voids, this effect could produce an overall expansion and potentially an acceleration. Known as backreaction, this idea has lingered in obscure corners of physics departments for decades, despite many claims that backreaction’s effect is small or nonexistent.

    Backreaction continues to appeal to some researchers because they don’t have to invent new laws of physics to explain the acceleration of the universe. “If there is an alternative which is based only upon traditional physics, why throw that away completely?” Matarrese asks.

    Most cosmologists, however, think explaining away dark energy just based on the universe’s lumps is unlikely. Previous calculations have indicated any effect would be too small to account for dark energy, and would produce an acceleration that changes in time in a way that disagrees with observations.

    “My personal view is that it’s a much smaller effect,” says astrophysicist Hayley Macpherson of Monash University in Melbourne, Australia. “That’s just basically a gut feeling.” Theories that include dark energy explain the universe extremely well, she points out. How could that be if the whole approach is flawed?

    New simulations by Macpherson and others that model how lumps evolve in general relativity may be able to gauge the importance of backreaction once and for all. “Up until now, it’s just been too hard,” says cosmologist Tom Giblin of Kenyon College in Gambier, Ohio.

    To perform the simulations, researchers needed to get their hands on supercomputers capable of grinding through the equations of general relativity as the simulated universe evolves over time. Because general relativity is so complex, such simulations are much more challenging than those that use approximations, such as Newtonian gravity. But, a seemingly distinct topic helped lay some of the groundwork: gravitational waves, or ripples in the fabric of spacetime.

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    SPECKLED SPACETIME A lumpy universe, recently simulated using general relativity, shows clumps of matter (pink and yellow) that beget stars and galaxies. H. Macpherson, Paul Lasky, Daniel Price.

    The Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, searches for the tremors of cosmic dustups such as colliding black holes (SN: 10/28/17, p. 8).


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

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    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)

    In preparation for this search, physicists honed their general relativity skills on simulations of the spacetime storm kicked up by black holes, predicting what LIGO might see and building up the computational machinery to solve the equations of general relativity. Now, cosmologists have adapted those techniques and unleashed them on entire, lumpy universes.

    The first lumpy universe simulations to use full general relativity were unveiled in the June 2016 Physical Review Letters. Giblin and colleagues reported their results simultaneously with Eloisa Bentivegna of the University of Catania in Italy and Marco Bruni of the University of Portsmouth in England.

    So far, the simulations have not been able to account for the universe’s acceleration. “Nearly everybody is convinced [the effect] is too small to explain away the need for dark energy,” says cosmologist Martin Kunz of the University of Geneva. Kunz and colleagues reached the same conclusion in their lumpy-universe simulations, which have one foot in general relativity and one in Newtonian gravity. They reported their first results in Nature Physics in March 2016.

    Backreaction aficionados still aren’t dissuaded. “Before saying the effect is too small to be relevant, I would, frankly, wait a little bit more,” Matarrese says. And the new simulations have potential caveats. For example, some simulated universes behave like an old arcade game — if you walk to one edge of the universe, you cross back over to the other side, like Pac-Man exiting the right side of the screen and reappearing on the left. That geometry would suppress the effects of backreaction in the simulation, says Thomas Buchert of the University of Lyon in France. “This is a good beginning,” he says, but there is more work to do on the simulations. “We are in infancy.”

    Different assumptions in a simulation can lead to disparate results, Bentivegna says. As a result, she doesn’t think that her lumpy, general-relativistic simulations have fully closed the door on efforts to dethrone dark energy. For example, tricks of light might be making it seem like the universe’s expansion is accelerating, when in fact it isn’t.

    When astronomers observe far-away sources like supernovas, the light has to travel past all of the lumps of matter between the source and Earth. That journey could make it look like there’s an acceleration when none exists. “It’s an optical illusion,” Bentivegna says. She and colleagues see such an effect in a simulation reported in March in the Journal of Cosmology and Astroparticle Physics. But, she notes, this work simulated an unusual universe, in which matter sits on a grid — not a particularly realistic scenario.

    For most other simulations, the effect of optical illusions remains small. That leaves many cosmologists, including Giblin, even more skeptical of the possibility of explaining away dark energy: “I feel a little like a downer,” he admits.

    6
    Lumps (gray) within this simulated universe change the path light takes (yellow lines), potentially affecting observations. Matter bends space, slightly altering the light’s trajectory from that in a smooth universe. James Mertens.

    Surveying the skies

    Subtle effects of lumps could still be important. In Hans Christian Andersen’s The Princess and the Pea, the princess felt a tiny pea beneath an impossibly tall stack of mattresses. Likewise, cosmologists’ surveys are now so sensitive that even if the universe’s lumps have a small impact, estimates could be thrown out of whack.

    The Dark Energy Survey, for example, has charted 26 million galaxies using the Victor M. Blanco Telescope in Chile, measuring how the light from those galaxies is distorted by the intervening matter on the journey to Earth.

    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

    In a set of papers posted online August 4 at arXiv.org, scientists with the Dark Energy Survey reported new measurements of the universe’s properties, including the amount of matter (both dark and normal) and how clumpy that matter is (SN: 9/2/17, p. 32). The results are consistent with those from the cosmic microwave background [CMB] — light emitted billions of years earlier.

    To make the comparison, cosmologists took the measurements from the cosmic microwave background, early in the universe, and used simulations to extrapolate to what galaxies should look like later in the universe’s history. It’s like taking a baby’s photograph, precisely computing the number and size of wrinkles that should emerge as the child ages and finding that your picture agrees with a snapshot taken decades later. The matching results so far confirm cosmologists’ standard picture of the universe — dark energy and all.

    “So far, it has not yet been important for the measurements that we’ve made to actually include general relativity in those simulations,” says Risa Wechsler, a cosmologist at Stanford University and a founding member of the Dark Energy Survey. But, she says, for future measurements, “these effects could become more important.” Cosmologists are edging closer to Princess and the Pea territory.

    Those future surveys include the Dark Energy Spectroscopic Instrument, DESI, set to kick off in 2019 at Kitt Peak National Observatory near Tucson; the European Space Agency’s Euclid satellite, launching in 2021; and the Large Synoptic Survey Telescope in Chile, which is set to begin collecting data in 2023.

    LBNL/DESI spectroscopic instrument on the Mayall 4-meter telescope at Kitt Peak National Observatory, Altitude 2,120 m (6,960 ft)

    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)

    ESA/Euclid spacecraft

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    If cosmologists keep relying on simulations that don’t use general relativity to account for lumps, certain kinds of measurements of weak lensing — the bending of light due to matter acting like a lens — could be off by up to 10 percent, Giblin and colleagues reported at arXiv.org in July. “There is something that we’ve been ignoring by making approximations,” he says.

    That 10 percent could screw up all kinds of estimates, from how dark energy changes over the universe’s history to how fast the universe is currently expanding, to the calculations of the masses of ethereal particles known as neutrinos. “You have to be extremely certain that you don’t get some subtle effect that gets you the wrong answers,” Geneva’s Kunz says, “otherwise the particle physicists are going to be very angry with the cosmologists.”

    Some estimates may already be showing problem signs, such as the conflicting estimates of the cosmic expansion rate (SN: 8/6/16, p. 10). Using the cosmic microwave background, cosmologists find a slower expansion rate than they do from measurements of supernovas. If this discrepancy is real, it could indicate that dark energy changes over time. But before jumping to that conclusion, there are other possible causes to rule out, including the universe’s lumps.

    Until the issue of lumps is smoothed out, scientists won’t know how much lumpiness matters to the cosmos at large. “I think it’s rather likely that it will turn out to be an important effect,” Kolb says. Whether it explains away dark energy is less certain. “I want to know the answer so I can get on with my life.”

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  • richardmitnick 7:32 am on October 29, 2017 Permalink | Reply
    Tags: , , , , , , ScienceNews   

    From ScienceNews: “What detecting gravitational waves means for the expansion of the universe” 

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    ScienceNews

    October 24, 2017
    Lisa Grossman

    Speed of spacetime ripples rules out some alternatives to dark energy.

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    BANG, FLASH Light waves and gravitational waves from a pair of colliding neutron stars reached Earth at almost the same time, ruling out theories about the universe based on predictions that the two kinds of waves might travel at different speeds. Illustration by Robin Dienel courtesy of the Carnegie Institution for Science.

    Ripples in spacetime travel at the speed of light. That fact, confirmed by the recent detection of a pair of colliding stellar corpses, kills a whole category of theories that mess with the laws of gravity to explain why the universe is expanding as fast as it is.

    On October 16, physicists announced that the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, had detected gravitational waves from a neutron star merger (SN Online: 10/16/17).


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

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

    Also, the neutron stars emitted high-energy light shortly after merging. The Fermi space telescope spotted that light coming from the same region of the sky 1.7 seconds after the gravitational wave detection.

    NASA/Fermi Telescope


    NASA/Fermi LAT

    That observation showed for the first time that gravitational waves, the shivers in spacetime set off when massive bodies move, travel at the speed of light to within a tenth of a trillionth of a percent.

    Within a day, five papers were posted at arXiv.org mourning hundreds of expanding universe theories that predicted gravitational waves should travel faster than light — an impossibility without changes to Einstein’s laws of gravity. These theories “are very, very dead,” says the coauthor of one of the papers, cosmologist Miguel Zumalacárregui of the Nordic Institute for Theoretical Physics, or NORDITA, in Stockholm. “We need to go back to our blackboards and start thinking of other alternatives.”

    In the 1990s, observations of exploding stars showed that more distant explosions were dimmer than existing theories predicted. That suggested that the universe is expanding at an ever-increasing rate (SN: 10/22/11, p. 13). Cosmologists have struggled ever since to explain why.

    The most popular explanation for the speedup is that spacetime is filled with a peculiar entity dubbed dark energy. “You can think of it like a mysterious fluid that pushes everything apart and counteracts gravity,” says cosmologist Jeremy Sakstein of the University of Pennsylvania, coauthor of another new paper.

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

    In the simplest version of this theory, the density of this dark energy has not changed over the history of the universe, so physicists call it a cosmological constant. This doesn’t require any changes to gravity — which is good, because gravity has been well-tested inside the solar system.

    The cosmological constant idea matches observations of the wider universe, but it has some theoretical difficulties. Dark energy is about 120 orders of magnitude weaker than theorists calculate it should be (SN Online: 11/18/13), a mismatch that makes scientists uncomfortable.

    Also, different methods for measuring the rate of expansion come up with slightly different numbers (SN: 8/6/16, p. 10). Measurements based on exploding stars suggest that distant galaxies are speeding away from each other at 73 kilometers per second for each megaparsec (about 3.3 million light-years) of space between them. But observations based on the cosmic microwave background, ancient light that encodes information about the conditions of the early universe, found that the expansion rate is 67 km/s per megaparsec. The disagreement suggests that either one of the measurements is wrong, or the theory behind dark energy needs a tweak.

    So instead of invoking a substance to counteract gravity, theorists tried to explain the expanding universe by weakening gravity itself. Any modifications to gravity need to leave the solar system intact. “It’s quite hard to build a theory that accelerates the universe and also doesn’t mess up the solar system,” says cosmologist Tessa Baker of the University of Oxford, coauthor of still another paper.

    These theories take hundreds of forms. “This field of modified gravity theories is a zoo,” says Baker. Some suggest that gravity leaks out into extra dimensions of space and time. Many others account for the universe’s speedy spreading by adding a different mysterious entity — some unknown particle perhaps — that drains gravity’s strength as the universe evolves.

    But the new entity would have another crucial effect: It could slow the speed of light waves, similar to the way light travels more slowly through water than through air. That means that the best alternatives to dark energy required gravitational waves to travel faster than light — which they don’t.

    Justin Khoury, a theoretical physicist at the University of Pennsylvania who has worked on several of the alternative gravity theories but was not involved in the new papers, was surprised that one gravitational-wave observation ruled out so many theories at once. He’s hardly disappointed, though.

    “The fact that we’re learning something about dark energy because of this measurement is incredibly exciting,” he says.

    Observing gravitational waves and light waves at the same time offers a third, independent way to measure how fast the universe is expanding. For now, that rate lies frustratingly right between the two clashing measurements scientists already had, at 70 km/s per megaparsec. But it’s still imprecise. Once LIGO and other observatories have seen 10 or 20 more neutron star collisions, researchers should be able to tell which measurement is correct and figure out whether dark energy needs an update, Zumalacárregui says.

    “Gravitational waves may kill these models, but eventually they have the potential to tell us if this discrepancy is for real,” he says. “That’s something that is in itself very beautiful.”

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  • richardmitnick 1:47 pm on October 27, 2017 Permalink | Reply
    Tags: An interstellar asteroid might have just been spotted for the first time, , , , , ScienceNews   

    From ScienceNews: “An interstellar asteroid might have just been spotted for the first time” 

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    ScienceNews

    October 27, 2017
    Lisa Grossman

    The interloper could carry information about the makeup of alien planet systems.

    1
    INTERSTELLAR INTERLOPER? The unusual trajectory of an asteroid, called A/2017 U1, suggests it came from outside the solar system and is now on its way out again. JPL-Caltech/NASA

    Astronomers may have just spotted the first asteroid caught visiting the solar system from another star.

    The Pan-STARRS 1 telescope in Hawaii discovered the object, dubbed A/2017 U1, on October 18.

    Pan-STARRS1 located on Haleakala, Maui, HI, USA

    More observations from other telescopes around the world suggest the object’s trajectory is at an unusually steep angle to the plane on which all the planets lie, and it does not orbit the sun. A/2017 U1’s slingshot route suggests it is a recent visitor to the solar system — and is now on its way out again. The discovery was announced in a bulletin published October 25 by the International Astronomical Union’s Minor Planet Center.

    All asteroids previously seen come from within the solar system and circle the sun. Even comets, which come from a distant reservoir of icy rocks in the solar system called the Oort cloud and can have highly titled orbits, still orbit the sun.

    Astronomers first pegged the object as a comet thanks to its elongated path, but additional telescope observations October 25 indicate it’s more likely that A/2017 U1 is an asteroid. Those observations revealed that the object looked like a single, sharp point of light, suggesting it is not a comet, which would have an extended icy halo. The asteroid is probably no more than 400 meters across and is zooming through the solar system at 25.5 kilometers per second.

    The new data also supported the wacky trajectory, suggesting the object truly is a visitor from beyond. “It’s now looking very promising,” says planetary scientist Michele Bannister of Queen’s University Belfast in Northern Ireland, although she would still like to get more data to be sure. Astronomers are already planning to measure the colors in the asteroid’s reflected light to figure out what it’s made of, a clue to its origins.

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    VISITOR FROM BEYOND The dot in the center of this image is A/2017 U1, which may be the first asteroid caught visiting from another solar system. The image was taken with the William Herschel Telescope in La Palma, Spain.


    ING 4 meter William Herschel Telescope at Roque de los Muchachos Observatory on La Palma in the Canary Islands, 2,396 m (7,861 ft)

    See the full article here .

    Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

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    • Matthew Wright 3:02 pm on October 27, 2017 Permalink | Reply

      It would be a real coup to get science data from an interstellar asteroid. Should we call it Rama?

      Like

  • richardmitnick 9:11 am on October 11, 2017 Permalink | Reply
    Tags: , , , , ESA Planck All Sky Map 1, How to make the cosmic web give up the matter it’s hiding, ScienceNews   

    From ScienceNews: “How to make the cosmic web give up the matter it’s hiding” 

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    ScienceNews

    October 11, 2017
    Lisa Grossman

    Half the universe’s ordinary matter is missing. This new technique might have found it.

    1
    A TANGLED SKEIN This computer simulation of the universe highlights its structure: long filaments of dark matter (blue) with galaxies strung along them like beads (pink). Most of the regular matter is probably stored in gas (orange). Illustris Collaboration

    Evidence is piling up that much of the universe’s missing matter is lurking along the strands of a vast cosmic web.

    A pair of papers report some of the best signs yet of hot gas in the spaces between galaxy clusters, possibly enough to represent the half of all ordinary matter previously unaccounted for. Previous studies have hinted at this missing matter, but a new search technique is helping to fill in the gaps in the cosmic census where other efforts fell short. The papers were published online at arXiv.org on September 15 and September 29.

    Two independent teams stacked images of hundreds of thousands of galaxies on top of one another to reveal diffuse filaments of gas connecting pairs of galaxies across millions of light-years. Measuring how the gas distorted the background light of the universe let the researchers determine the mass of ordinary matter, or baryons, that it held — the protons and neutrons that make up atoms.

    “It’s a very important problem,” says Dominique Eckert of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, who has searched for the missing matter via X-rays emitted by individual strands. “If you want to understand how galaxies form and how everything forms within a galaxy, you have to understand the evolution of the baryon content.” That starts with knowing where it is.

    About 85 percent of the matter in the universe is mysterious, invisible stuff called dark matter, which physicists have yet to find (SN Online: 9/6/17).

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

    Weirdly, about half of the ordinary matter is also unaccounted for. When astronomers look around at the galaxies in the nearest few billion light-years, they find only about half the baryons that should have been produced in the Big Bang.

    The rest is probably hiding in long filaments of gas that connect galaxy clusters in a vast cosmic web (SN: 3/8/14, p. 8). Previous attempts to find the baryons focused on X-rays emitted by gas in the filaments (SN Online: 8/4/15) or on the light of distant quasars filtering through these cobwebby strands (SN: 5/13/00, p. 310). But those efforts were either inconclusive, or were sensitive to such a narrow range of gas temperatures that they missed much of the matter.

    Now there might be a way to find the rest. Two groups — cosmologist Hideki Tanimura, who did the work while at the University of British Columbia in Vancouver, and his colleagues, and Anna de Graaff of the University of Edinburgh and her colleagues — have sought the missing matter in a new way. Both teams found a way to look through the gas all the way back to the oldest light in the universe.

    “Filamentary gas is very difficult to detect, but now we have a technique to detect it,” says Tanimura, now with the Institute of Space Astrophysics in Orsay, France.

    That ancient light, called the cosmic microwave background, was emitted 380,000 years after the Big Bang. When this light passes though clouds of electrons in space — such as those found in filaments of hot gas — it gets deflected and distorted in a specific way. The Planck satellite released an all-sky map of these distortions in 2015 (SN: 3/21/15, p. 7).

    ESA Planck All Sky Map 1

    Tanimura and de Graaff separately figured that there would be more distortion along the filaments than in empty space. To locate the filaments, both teams chose pairs of galaxies from the Sloan Digital Sky Survey catalog that were at least 20 million light-years apart. De Graaff’s team chose roughly a million pairs, and Tanimura’s team chose 262,864 pairs. Both teams assumed that the galaxies were not part of the same cluster, but that they should be connected by a filament.

    The filaments were still too faint to see individually, so the teams used software to layer all the images and subtracted out distortion from electrons in the galaxies to see what was left. Both saw a residual distortion in the cosmic microwave background, which they attribute to the filaments.

    Next, de Graaff’s team calculated that those filaments account for 30 percent of the total baryon content of the universe. That’s surely an underestimate, since they didn’t examine every filament in the universe, the team writes — the rest of the missing matter is probably there too.

    “Both groups here took the obvious first step,” says Michael Shull of the University of Colorado Boulder, who was not involved in the new studies. “I think they’re on the right track.” But he worries that the gas they see might have been ejected from galaxies at high speeds, and so not actually the missing matter at all.

    Eckert also worries that the gas may belong more to the galaxies than to their intergalactic tethers. Future observations of the composition of the gas, as well as more sensitive X-ray observations, could help solve that part of the puzzle.

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  • richardmitnick 1:45 pm on October 10, 2017 Permalink | Reply
    Tags: , Antibiotics spiked with quantum dots fought off bacteria as effectively as 1000 times as much antibiotic alone, , , , , ScienceNews, Various superbugs are evolving too rapidly to be counteracted by traditional drugs   

    From ScienceNews: “Superbugs may meet their match in these nanoparticles” 

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    Science News

    October 9, 2017
    Maria Temming

    ‘Quantum dots’ mess with bacteria’s defenses, allowing antibiotics to work.

    1
    ARMED AND DANGEROUS By producing a chemical that makes bacteria more vulnerable to antibiotic attack, quantum dots could help reboot medications that have lost their edge against hard-to-kill microbes. Kateryna Kon/Shutterstock

    Antibiotics may have a new teammate in the fight against drug-resistant infections.

    Researchers have engineered nanoparticles to produce chemicals that render bacteria more vulnerable to antibiotics. These quantum dots, described online October 4 in Science Advances, could help combat pathogens that have developed resistance to antibiotics (SN: 10/15/16, p. 11).

    “Various superbugs are evolving too rapidly to be counteracted by traditional drugs,” says Zhengtao Deng, a chemist at Nanjing University in China not involved in the research. “Drug resistant infections will kill an extra 10 million people a year worldwide by 2050 unless action is taken.”

    In the study, antibiotics spiked with quantum dots fought off bacteria as effectively as 1,000 times as much antibiotic alone. That’s “really impressive,” says Chao Zhong, a materials scientist at ShanghaiTech University who was not involved in the study. “This is a really comprehensive study.”

    Quantum dots, previously investigated as a tool to trace drug delivery throughout the body or to take snapshots of cells, are made of semiconductors — the same kind of material in such electronics as laptops and cellphones (SN: 7/11/15, p. 22). The new quantum dots are tiny chunks of cadmium telluride just 3 nanometers across, or about as wide as a strand of DNA.

    When illuminated by a specific frequency of green light, the nanoparticles’ electrons can pop off and glom onto nearby oxygen molecules — which are dissolved in water throughout the body — to create a chemical called superoxide. When a bacterial cell absorbs this superoxide, it throws the microbe’s internal chemistry so off-balance that the pathogen can’t defend itself against antibiotics, explains study coauthor Anushree Chatterjee, a chemical engineer at the University of Colorado Boulder.

    Chatterjee and colleagues mixed various amounts of quantum dots into different concentrations of each of five antibiotics, and then added these concoctions to samples of five drug-resistant bacterial strains, such as Salmonella and methicillin-resistant Staphylococcus aureus, or MRSA. In more than 75 percent of 480 tests of different antibiotic combinations on different bacteria, the researchers found that lower doses of antibiotics were required to kill or curb the growth of bacteria when the medicine was combined with quantum dots.

    One limitation of this treatment is that the green light that activates the nanoparticles can shine through only a few millimeters of flesh, says coauthor Prashant Nagpal, a chemical engineer also at the University of Colorado Boulder. So these quantum dots could probably be used only to treat skin or accessible wound infections.

    The researchers are now designing nanoparticles that absorb infrared light, which can pass through the body. “That could be really effective in deep tissue and bone infections,” Nagpal says.

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  • richardmitnick 1:31 pm on October 5, 2017 Permalink | Reply
    Tags: An early interest in tricks of light led Dionne to begin wielding it as a tool during graduate school at Caltech and then her postdoc at UC Berkeley, , Jennifer Dionne, , ScienceNews,   

    From ScienceNews: Women in STEM – “Jennifer Dionne harnesses light to illuminate nano landscapes” 

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    ScienceNews

    October 4, 2017
    Emily Conover

    Tiny particles could light the way to improved cancer tests or drugs with fewer side effects.

    1
    LEADING LIGHT Jennifer Dionne, 35 Materials scientist, Stanford University.
    Materials scientist Jennifer Dionne melds purpose and play in her work with matter and light. Timothy Archibald

    To choose her research goals, Jennifer Dionne envisions conversations with hypothetical grandchildren, 50 years down the line. What would she want to tell them she had accomplished? Then, to chart a path to that future, “I work backward to figure out what are the milestones en route,” she says.

    That long-term vision has led the 35-year-old materials scientist on a quest to wrangle light and convince it to do her bidding in interactions with nanoparticles and various materials. Already, Dionne has created new nanomaterials that steer light in ways that are impossible with natural substances. Her new projects could eventually lead to light-based technologies used to improve drugs or to create new tests to find cancerous cells. There are even applications for renewable energy, for example, designing materials that help solar cells absorb more light.

    But the route to a scientific vision may not always be clear, so Dionne makes time for diversions. “A lot of the really amazing discoveries that we enjoy today came from just playing in the lab,” she says. Dionne encourages her team to let creativity be a guide, melding a serious sense of purpose with play.

    “She’s a very curious person, so she’s always learning new things,” says Paul Alivisatos, the vice chancellor for research at the University of California, Berkeley, who mentored Dionne when she was a postdoc there. Plus, “she’s an extremely deep and rigorous thinker.”

    Dionne, now at Stanford University, studies nanophotonics, the way that light interacts with matter on very small scales. Her interest in light and materials began in childhood, she recalls, when she was fascinated by the blue morpho butterfly.

    The insect’s wings sport an azure hue that comes not from pigments, like most colors found in living things, but from tiny nanostructures on the wings’ surface (SN: 6/7/08, p. 26). When light reflects off the structures, blue wavelengths are amplified, while wavelengths corresponding to other colors are canceled out.

    That early interest in tricks of light led Dionne to begin wielding it as a tool during graduate school at Caltech and then her postdoc at UC Berkeley. Then and now, says Alivisatos, “she has consistently done very beautiful work.”

    At Caltech, Dionne and colleagues created a bizarre optical material in which light bends backward. As light passes from one material to another — say, from air to water — the rays are deflected due to a property called the index of refraction. (That’s why a straw in a drinking glass appears to be broken at the water’s surface.) In natural materials, light always bends in the same direction. But that rule gets flipped around in oddball nanomaterials with a negative index of refraction.

    2
    G. Dolling et al/Optics Express 2006
    Light rays bend as they pass from air into water, making a drinking straw look broken (illustrated in a computer-generated image, left). In materials with a negative index of refraction (right), light rays bend in the opposite direction they normally do, so that the straw appears flipped around.

    Dionne’s material, reported in Science in 2007, was the first that worked with visible light (SN: 3/24/07, p. 180). Because they can steer light around objects to hide the objects from view, such materials could be used to create rudimentary versions of invisibility cloaks — though so far all attempts are a far cry from Harry Potter’s version. Dionne is now working on a “squid skin” with an adjustable refractive index, which would mimic the shifting camouflage patterns of the stealthy cephalopod.

    Another focal point of Dionne’s research is harnessing light to separate mixtures of mirror-image molecules. Right- and left-handed versions of these molecules are perfect reflections of each other, like a person’s right and left hands. The two types are so similar that scientists struggle to separate them, which can cause problems for drugmakers. In drugs, these molecules can be two-faced; one might relieve pain, while the other causes unwanted side effects.

    To separate molecules and their mirror images, Dionne is developing techniques that use circularly polarized light, in which the light’s wiggling electromagnetic waves rotate over time. Such light can interact differently with right- and left-handed molecules, for example, breaking apart one version while leaving the other unscathed.

    Normally, the light’s effect is very weak. But in a theoretical study published in ACS Photonics last December, Dionne and colleagues showed that adding nanoparticles to the mix could enhance the process. These tiny particles behave like antennas that concentrate the light onto nearby molecules, helping break them apart. Dionne is now working to implement the technique.

    She and her colleagues have also created nanoparticles that, when illuminated with infrared light, emit visible light. The color of that light changes depending on how tightly the nanoparticle is squeezed, the team reported in Nano Letters in June. In keeping with her penchant for creative exploration in the lab, Dionne and colleagues fed these nanoparticles to roundworms, the nematode Caenorhabditis elegans, to study the forces exerted as a transparent worm squeezed a meal through its digestive tract.

    “You can see the nanoparticles change colors throughout,” Dionne says. She plans to use the technique to reveal more sinister squeezing. Cancer cells exert stronger mechanical forces on their environment than healthy cells, so such nanoparticles could one day be used to test for cancer, she says. Dionne is now cooking up other creative ways to use these nanoparticles. In collaboration with other researchers, she hopes to marshal her color-changing nanoparticles to understand how jellyfish move and how plants take a drink.

    Dionne’s work exploits light to reveal hidden forces — and as a force for good. “She’s done amazing work,” says materials scientist Prineha Narang of Harvard University. Narang was a graduate student at Caltech after Dionne left, and had heard chatter about Dionne before meeting her in person. “The legend of Jen Dionne was definitely all over,” Narang says. So Dionne has made a start at establishing her scientific legacy — even before that chat with her future grandchildren.

    At the full article many citations with links.

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  • richardmitnick 9:46 am on September 28, 2017 Permalink | Reply
    Tags: , , , , ScienceNews, , Technical University of Dresden, The spin Hall effect, The spin Nernst effect, The spin Peltier effect, The spin Seebeck effect, Turning up the heat on electrons reveals an elusive physics phenomenon, When things heat up spinning electrons go their separate ways   

    From ScienceNews: “Turning up the heat on electrons reveals an elusive physics phenomenon” 

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    ScienceNews

    September 26, 2017
    Emily Conover

    Spin Nernst effect could help scientists design new gadgets that store data using quantum property of spin.

    1
    WHIRL AWAY Electrons in platinum move in different directions depending on their spin when the metal is heated at one end. Scientists have observed this phenomenon, called the spin Nernst effect, for the first time. Creativity103/Flickr (CC BY 2.0)

    When things heat up, spinning electrons go their separate ways.

    Warming one end of a strip of platinum shuttles electrons around according to their spin, a quantum property that makes them behave as if they are twirling around. Known as the spin Nernst effect, the newly detected phenomenon was the only one in a cadre of related spin effects that hadn’t previously been spotted, researchers report online September 11 in Nature Materials.

    “The last missing piece in the puzzle was spin Nernst and that’s why we set out to search for this,” says study coauthor Sebastian Goennenwein, a physicist at the Technical University of Dresden in Germany.

    The effect and its brethren — with names like the spin Hall effect, the spin Seebeck effect and the spin Peltier effect — allow scientists to create flows of electron spins, or spin currents. Such research could lead to smaller and more efficient electronic gadgets that use electrons’ spins to store and transmit information instead of electric charge, a technique known as “spintronics.”

    In the spin Nernst effect, named after Nobel laureate chemist Walther Nernst, heating one end of a metal causes electrons to flow toward the other end, bouncing around inside the material as they go. Within certain materials, that bouncing has a preferred direction: Electrons with spins pointing up (as if twirling counterclockwise) go to the right and electrons with spins pointing down (as if twirling clockwise) go to the left, creating an overall spin current. Although the effect had been predicted, no one had yet observed it.

    Finding evidence of the effect required disentangling it from other heat- and charge-related effects that occur in materials. To do so, the researchers coupled the platinum to a layer of a magnetic insulator, a material known as yttrium iron garnet. Then, they altered the direction of the insulator’s magnetization, which changed whether the spin current could flow through the insulator. That change slightly altered a voltage measured along the strip of platinum. The scientists measured how this voltage changed with the direction of the magnetization to isolate the fingerprints of the spin Nernst effect.

    “The measurement was a tour de force; the measurement was ridiculously hard,” says physicist Joseph Heremans of Ohio State University in Columbus, who was not involved with the research. The effect could help scientists to better understand materials that may be useful for building spintronic devices, he says. “It’s really a new set of eyes on the physics of what’s going on inside these devices.”

    A relative of the spin Nernst effect called the spin Hall effect is much studied for its potential use in spintronic devices. In the spin Hall effect, an electric field pushes electrons through a material, and the particles veer off to the left and right depending on their spin. The spin Nernst effect relies on the same basic physics, but uses heat instead of an electric field to get the particles moving.

    “It’s a beautiful experiment. It shows very nicely the spin Nernst effect,” says physicist Greg Fuchs of Cornell University. “It beautifully unifies our understanding of the interrelation between charge, heat and spin transport.”

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  • richardmitnick 7:43 am on May 16, 2017 Permalink | Reply
    Tags: anti-de Sitter space, , , , , , Hypothetical universes, Naked singularity might evade cosmic censor, ScienceNews,   

    From ScienceNews: “Naked singularity might evade cosmic censor” 

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    ScienceNews

    May 15, 2017
    Emily Conover

    Spacetime singularities might exist unhidden in strangely curved universes

    1
    LAID BARE Inside a black hole, the extreme curvature of space (shown) means that the standard rules of physics don’t apply. Such regions, called singularities, are thought to be shrouded by event horizons, but scientists showed that a singularity could be observable under certain conditions in a hypothetical curved spacetime. Henning Dalhoff/Science Source

    Certain stealthy spacetime curiosities might be less hidden than thought, potentially exposing themselves to observers in some curved universes.

    These oddities, known as singularities, are points in space where the standard laws of physics break down. Found at the centers of black holes, singularities are generally expected to be hidden from view, shielding the universe from their problematic properties. Now, scientists report in the May 5 Physical Review Letters that a singularity could be revealed in a hypothetical, saddle-shaped universe.

    Previously, scientists found that singularities might not be concealed in hypothetical universes with more than three spatial dimensions. The new result marks the first time the possibility of such a “naked” singularity has been demonstrated in a three-dimensional universe. “That’s extremely important,” says physicist Gary Horowitz of the University of California, Santa Barbara. Horowitz, who was not involved with the new study, has conducted previous research that implied that a naked singularity could probably appear in such saddle-shaped universes.

    In Einstein’s theory of gravity, the general theory of relativity, spacetime itself can be curved (SN: 10/17/15, p. 16). Massive objects such as stars bend the fabric of space, causing planets to orbit around them. A singularity occurs when the warping is so extreme that the equations of general relativity become nonsensical — as occurs in the center of a black hole. But black holes’ singularities are hidden by an event horizon, which encompasses a region around the singularity from which light can’t escape. The cosmic censorship conjecture, put forth in 1969 by mathematician and physicist Roger Penrose, proposes that all singularities will be similarly cloaked.

    According to general relativity, hypothetical universes can take on various shapes. The known universe is nearly flat on large scales, meaning that the rules of standard textbook geometry apply and light travels in a straight line. But in universes that are curved, those rules go out the window. To demonstrate the violation of cosmic censorship, the researchers started with a curved geometry known as anti-de Sitter space, which is warped such that a light beam sent out into space will eventually return to the spot it came from. The researchers deformed the boundaries of this curved spacetime and observed that a region formed in which the curvature increased over time to arbitrarily large values, producing a naked singularity.

    “I was very surprised,” says physicist Jorge Santos of the University of Cambridge, a coauthor of the study. “I always thought that gravity would somehow find a way” to maintain cosmic censorship.

    Scientists have previously shown that cosmic censorship could be violated if a universe’s conditions were precisely arranged to conspire to produce a naked singularity. But the researchers’ new result is more general. “There’s nothing finely tuned or unnatural about their starting point,” says physicist Ruth Gregory of Durham University in England. That, she says, is “really interesting.”

    But, Horowitz notes, there is a caveat. Because the violation occurs in a curved universe, not a flat one, the result “is not yet a completely convincing counterexample to the original idea.”

    Despite the reliance on a curved universe, the result does have broader implications. That’s because gravity in anti-de Sitter space is thought to have connections to other theories. The physics of gravity in anti-de Sitter space seems to parallel that of some types of particle physics theories, set in fewer dimensions. So cosmic censorship violation in this realm could have consequences for seemingly unrelated ideas.

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  • richardmitnick 1:14 pm on May 9, 2017 Permalink | Reply
    Tags: , , , , , ScienceNews   

    From ScienceNews: “Mars may not have been born alongside the other rocky planets” 

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    ScienceNews

    May 5, 2017
    Thomas Sumner

    New origin story could explain mystery of Red Planet’s makeup.

    1
    FAR OUT Mars may have formed near what’s now the asteroid belt, much farther away from the sun than the other rocky planets. ESA & MPS for OSIRIS Team, UPD, LAM, IAA, RSSD, INTA, UPM, DASP, IDA (CC BY-SA 3.0 IGO)

    Mars may have had a far-out birthplace.

    Simulating the assembly of the solar system around 4.56 billion years ago, researchers propose that the Red Planet didn’t form in the inner solar system alongside the other terrestrial planets as previously thought. Mars instead may have formed around where the asteroid belt is now and migrated inward to its present-day orbit, the scientists report in the June 15 Earth and Planetary Science Letters. The proposal better explains why Mars has such a different chemical composition than Earth, says Stephen Mojzsis, a study coauthor and geologist at the University of Colorado Boulder.

    The new work is an intuitive next step in a years-long rethink of the early solar system, says Kevin Walsh, a planetary scientist at the Southwest Research Institute in Boulder, Colo., who was not involved with the new simulation. “We only became comfortable within the last 10 years with the idea that planets move around, possibly a lot,” he says. “Planets may not have formed where we see them today.”

    Mars, like Mercury, is a runt of the inner solar system, weighing in at only about a ninth of Earth’s mass. One of the reigning theories of planetary formation, the Grand Tack model, blames Jupiter for the Red Planet’s paltry size. In that scenario, the newly formed Jupiter migrated toward the sun until it reached Mars’ present-day orbit. A gravitational tug from Saturn then reversed Jupiter’s course, sending the gas giant back to the outer solar system (SN: 4/2/16, p. 7).

    Gravitational effects of Jupiter’s sunward jaunt acted like a snowplow, scientists believe, causing a pileup of material near where Earth’s orbit is today. The bulk of that material formed Venus and Earth, and the scraps created Mercury and Mars. This explanation predicts that all the terrestrial planets formed largely from the same batch of ingredients (SN: 4/15/17, p. 18). But studies of Martian meteorites suggest that the Red Planet contains a different mix of various elements and isotopes, such as oxygen-17 and oxygen-18, compared with Earth.

    Planetary scientist Ramon Brasser of the Tokyo Institute of Technology, Mojzsis and colleagues reran the Grand Tack simulations, keeping an eye on the materials that went into Mars’ creation to see if they could explain the different mix.

    As with previous studies, the researchers found that the most probable way of creating a solar system with the same planet sizes and positions as seen today is to have Mars form within Earth’s orbit and migrate outward. However, this explanation failed to explain Mars’ strikingly different composition.

    Another possible scenario, though seen in only about 2 percent of the team’s new simulations, is that Mars formed more than twice as far from the sun as its present-day orbit in the region currently inhabited by the asteroid belt. Then as Jupiter moved sunward, its gravitational pull yanked Mars into the inner solar system. Jupiter’s gravity also diverted planet-making material away from Mars, resulting in the planet’s relatively small mass. With Mars forming so far from the planetary feeding frenzy responsible for the other rocky planets, its composition would be distinct. While this scenario isn’t as likely as Mars forming in the inner solar system, it at least matches the reality of Mars’ makeup, Mojzsis says.

    Such a distant origin means that the fledgling Mars would have received far less sunlight than originally thought, a challenge to early Mars’ possible habitability. Without a sustained thick atmosphere of heat-trapping greenhouse gases, the planet would have been too cold to sustain liquid water on its surface for long periods of time, Mojzsis argues. Though large meteorite impacts could have temporarily warmed Mars above freezing, the planet wouldn’t have had a consistently warm and wet youth similar to that of the early Earth, he says.

    Confirming whether Mars really was born that far out in space will require taking a closer look at Venus’ mix of elements and isotopes, which the researchers predict would be similar to Earth’s. Venus’ composition is largely unknown because of a lack of Venusian meteorites found on Earth, and that mystery won’t be unlocked anytime soon: No missions to Venus are planned.

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