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  • richardmitnick 4:07 pm on October 25, 2014 Permalink | Reply
    Tags: , , , Cosmology, ,   

    From Quanta: “Dwarf Galaxies Dim Hopes of Dark Matter” 

    Quanta Magazine
    Quanta Magazine

    October 25, 2014
    Natalie Wolchover

    Once again, a shadow of a signal that scientists hoped would amplify into conclusive evidence of dark matter has instead flatlined, repeating a maddening refrain in the search for the invisible, omnipresent particles.

    The Fermi Large Area Telescope (LAT) failed to detect the glow of gamma rays emitted by annihilating dark matter in miniature “dwarf” galaxies that orbit the Milky Way, scientists reported Friday at a meeting in Nagoya, Japan. The hint of such a glow showed up in a Fermi analysis last year, but the statistical bump disappeared as more data accumulated.

    NASA Fermi Telescope
    NASA/Fermi Gamma Ray Spacecraft

    LAT
    LAT cutaway

    “We were obviously somewhat disappointed not to see a signal,” said Matthew Wood, a postdoctoral researcher at Stanford University who was centrally involved the Fermi-LAT collaboration’s new analysis, in an email.

    Scientists homed in on the dwarf galaxies after Dan Hooper, a theoretical astrophysicist at the Fermi National Accelerator Laboratory in Batavia, Ill., and Lisa Goodenough, his graduate student at the time, detected an unexplained gamma-ray signal coming from the center of the Milky Way in 2009. Hooper and several collaborators proposed that the gamma rays might be due to dark matter in the form of WIMPs, or weakly interacting massive particles, which are the leading candidates for the invisible substance that comprises six-sevenths of the universe’s mass. When two WIMPs collide in the dense galactic center, they should annihilate, with gamma rays as the fallout. Over the past five years the intriguing gamma-ray signal has seemed more and more likely to be the detritus of annihilating WIMPs.

    However, scientists knew that the same glow could also originate from an unknown population of millisecond pulsars in the galactic center — bright, rapidly spinning stars that spew gamma rays into space.

    Looking for ways to distinguish the two possibilities, scientists turned to dwarf galaxies, which are thought to be rich in dark matter but free of pulsars. If researchers found gamma rays pouring out of dwarf galaxies, the observation would rule out alternative explanations and provide emphatic evidence of WIMPs.

    Yet no such signal has been detected in five years’ worth of the highest-quality data from 15 nearby dwarfs, Wood and his colleagues report. “The case for the dark-matter interpretation of the galactic-center excess is substantially weakened,” he said.

    graph
    Olena Shmahalo/Quanta Magazine; data courtesy of Matthew Wood

    Under the most generous assumptions about the density of dark matter, new observations of dwarf galaxies exclude some, but not all, models of dark-matter particles that could be producing a signal coming from the center of the Milky Way. The range of particle properties proposed in a 2014 paper by Dan Hooper and colleagues (purple) is still viable, while a model proposed by Francesca Calore et al. (orange), which experts consider the most comprehensive, predicts a range of properties that is cut exactly in half. Under less generous assumptions, all except the Calore model are excluded.

    The possibility remains that the signal from the Milky Way’s center does come from dark matter, but only if the density of dark matter in the galaxy is at the high end of researchers’ estimates. If dark matter is sufficiently dense, it doesn’t have to annihilate at a very high rate to explain the signal from the galactic center. And if dark matter annihilates at a low rate, then researchers shouldn’t be surprised when they don’t see a signal coming from the more-diffuse dwarfs.

    “At this stage we do not entirely exclude all of the dark-matter models proposed to explain the reported excess,” Wood said.

    Hooper, whose model barely survives the blow of the new dwarf-galaxy findings, seems unfazed, and he maintains his position that the signal from the galactic center most likely comes from colliding WIMPs that vanish in puffs of gamma rays. “That’s where my money is,” he told Quanta Magazine in March. Speaking from the meeting in Japan, he said, “That hasn’t changed in any significant way.”

    Other scientists agree that the dark-matter explanation of the gamma-ray excess is still viable, for now. “It is what it is,” said Savvas Koushiappas, a physicist at Brown University and co-author of another recent analysis of gamma rays from the dwarfs. “There is a dark-matter interpretation, and the dwarfs at the moment did not rule it out, or confirm it. However, we are close.”

    Tracy Slatyer, a physicist at the Massachusetts Institute of Technology who has collaborated with Hooper on models of the galactic-center excess, said she finds the new results “really encouraging.”

    “Of course, I would like the galactic-center excess to come from annihilating dark matter, but I would much rather know one way or the other,” she said. “This result increases the probability that we will know for sure in the near future.”

    The paradigm that dark matter is likely composed of WIMPs has long reigned among physicists because of the “WIMP miracle,” or the fact that the same hypothetical particle could account for mysteries of both the cosmic and the quantum worlds. With roughly the same mass as many of the known particles in nature, WIMPs would counteract the effects of those particles in quantum equations in a way that would make apparently faulty calculations work. And the presence of a halo of WIMPs around galaxies would explain why the galaxies rotate faster than expected at their outskirts — the most compelling indirect evidence that dark matter exists.

    But the fact that WIMPs would represent an elegant solution to deep questions doesn’t mean they’re real. Scientists have spent the past decade monitoring ultra-cooled vats of liquid chemicals located deep underground in repurposed mine shafts all over the world, hoping that WIMPs would occasionally leave traces of energy as they traversed the liquids. But the search has not produced a single convincing signal.

    As the experiments become ever more sensitive, they eat away at the abstract space of all viable WIMP models, giving it the look of Swiss cheese. The discouraging results have pushed researchers to get more creative. “Even though many people are working very hard on the WIMP paradigm, people are starting to think more broadly,” said Mark Trodden, a professor of theoretical physics at the University of Pennsylvania.

    Dwarf galaxies have already inspired alternatives to the standard WIMP picture. If dark-matter particles can interact with one another (instead of “weakly interacting” only with ordinary matter, as in conventional WIMP models), they will transfer heat as they collide. “When you transfer heat, you get a less dense center,” explained David Spergel, an astrophysicist at Princeton University who, along with his colleague Paul Steinhardt, first proposed the self-interacting dark-matter scenario in 2000. Indeed, astronomers have observed that the cores of dwarf galaxies are less dense than would be expected based on simulations of galaxy formation that use WIMPs.

    map
    J. Bullock, M. Geha, R. Powell
    A map of dwarf galaxies orbiting the Milky Way Galaxy. Each dwarf contains up to several billion stars, compared to several hundred billion in the Milky Way.

    Self-interacting dark matter has attracted growing interest among scientists, but not everyone feels comfortable postulating a new property to patch over the problems with current models.

    “We’re just making this invisible particle increasingly complicated,” said Justin Khoury, a theoretical physicist at the University of Pennsylvania. “I’m torn about that.”

    Meanwhile, new and improved simulations by Alyson Brooks of Rutgers University and colleagues suggest that dwarf galaxies can be modeled correctly without dark matter self-interactions after all, if the simulations include the effects of ordinary particles — the one-seventh of all matter that we actually see, but which models often ignore for the sake of simplicity. When stars go supernova, Brooks explained, they produce hot bubbles of gas that rapidly expand. “It turns out that process gives energy to the dark matter in the center of galaxies and pushes it out,” she said.

    Although Brooks’ simulations match observations, some other leading modelers can’t get the effects of ordinary matter to fix the discrepancy in their own simulations, fueling the interest in self-interacting dark matter.

    Complicating the debate is the fact that if dark-matter particles self-interact, that means they don’t annihilate upon contact in bursts of gamma rays. In that case, the signal from the Milky Way’s center would not come from dark matter.

    “If this all sounds lively and contradictory and confused, you have the right idea,” Steinhardt said.

    Khoury has moved the furthest from the WIMP picture with a recent paper postulating that dark matter may not be composed of particles at all. His theory revamps an old idea called modified Newtonian dynamics, or MOND, which proposes a change to the law of gravity. In Khoury’s theory, dark matter is a fluidlike field that permeates space, interacting with the gravitational fields of galaxies in a way that alters their rotation.

    Erik Verlinde, a theoretical physicist at the University of Amsterdam in the Netherlands, has proposed a different modified-gravity theory, one in which dark matter doesn’t exist at all and the rotational speeds of galaxies reflect the entropy, or disorder, of space and time.

    At this stage, one theorist’s guess seems as good as another’s.

    “There are many, many, many things that dark matter could be,” Trodden said. “If you gave me license to write down particle physics [models] that could give me dark matter, I could write down 10 that haven’t been thought about before.” As for which ones hold the most promise, the universe isn’t telling.

    See the full article here.

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

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  • richardmitnick 7:37 am on October 25, 2014 Permalink | Reply
    Tags: , , , Cosmology, ,   

    From Frontier Fields: “First Galaxy Field Complete: Abell 2744″ 

    Frontier Fields
    Frontier Fields

    October 23, 2014
    Tony Darnell

    This past summer, the Hubble Frontier Fields team completed observations of the first cluster on its list: Abell 2744! The second set of observations — astronomers call them epochs — consisted of 70 orbits and marks the completion of the first Frontier Fields galaxy cluster. During this set, Hubble’s Advanced Camera for Surveys (ACS) was pointed at the main galaxy cluster and studied the visible-light portions of the spectrum, while the Wide Field Camera 3 (WFC3) looked at the parallel field in the infrared.

    NASA Hubble ACS
    ACS

    NASA Hubble WFC3
    WFC3

    Remember that Hubble will visit each field multiple times, with Hubble oriented such that one set of observations will point WFC3 at the cluster and ACS at a parallel field adjacent to the cluster (that’s one epoch). The telescope will then come back and do another set of observations with the cameras switched: ACS pointing at the cluster and WFC3 pointing to the parallel field (that’s the second one).

    The Frontier Fields team does this to allow for complete wavelength coverage in both infrared and visible light for the galaxy cluster and the parallel field.

    The first epoch, completed in November 2013, consisted of 87 orbits. This brings the total amount of time Hubble looked at this cluster to 157 orbits.

    a2744
    Final mosaic of the Frontier Fields galaxy cluster Abell 2744. This image is the culmination of both epochs totaling 157 Hubble orbits. The numbers prefixed with “F” are the Hubble filters used by the ACS and WFC3 cameras to take the image. The scale bar of 30″ is approximately 2% the angular size of the full moon as seen from Earth – very small! Credit: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)

    Final mosaic of the Frontier Fields galaxy cluster Abell 2744. This image is the culmination of both epochs totaling 157 Hubble orbits. The numbers prefixed with “F” are the Hubble filters used by the ACS and WFC3 cameras to take the image. The scale bar of 30″ is approximately 2% the angular size of the full moon as seen from Earth – very small!
    Credit: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)

    par
    Parallel field of Frontier Field Abell 2744

    This is the completed composite mosaic of the Parallel Fields observed with galaxy cluster Abell 2744.
    Credit: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)

    See? Epic! Er, I mean epoch.

    Once the second epoch was completed, some of the faintest galaxies ever seen were measured for the first time. Astronomers have been working on these images since their release, and we are anxiously awaiting to hear what they find.

    See the full article here.

    Frontier Fields draws on the power of massive clusters of galaxies to unleash the full potential of the Hubble Space Telescope. The gravity of these clusters warps and magnifies the faint light of the distant galaxies behind them. Hubble captures the boosted light, revealing the farthest galaxies humanity has ever encountered, and giving us a glimpse of the cosmos to be unveiled by the James Webb Space Telescope.

    NASA Hubble Telescope
    Hubble
    NASA James Webb Telescope
    Webb
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  • richardmitnick 1:35 pm on October 24, 2014 Permalink | Reply
    Tags: , , , Cosmology,   

    From Daily Californian: “Senate meets to support observatory, proposition, research campus” 

    Daily Californian

    The Daily Californian

    October 24, 2014
    Heyun Jeong

    The ASUC Senate passed bills supporting the preservation of Lick Observatory, a state proposition and a new research campus on Wednesday evening.

    UCO Lick Observatory
    Lick Observatory

    Adopted with unanimous consent, the bills establish the ASUC’s support for the different issues and order executives to write up letters or public statements on behalf of the ASUC.

    In response to talks of terminating UC funding for Lick Observatory by 2018, CalSERVE Senator Lavanya Jawaharlal sponsored SB 25 to show support in continuing the observatory’s operations. The bill establishes a committee of students to raise awareness and propose alternative funding options and urges the UC Office of the President to recommit funds.

    The talks of disinvestment make it “difficult to get outside funding, when private donors are wondering why they should invest money when the UC is cutting funding,” Jawaharlal said.

    The committee, which will be made up of two senators and five appointed students, will work on increasing communication with the campus administration and raising student awareness not only on the UC Berkeley campus, but also across the entire UC system.

    “It’s a UC-system owned observatory and not just Berkeley,” she said. “It affects all campuses. … It’s important to raise student awareness and mobilize all of the UC system students.”

    According to Jawaharlal, the ASUC is the first student government to pass such a bill or create a special committee for the observatory.

    The senate also passed a bill in support of Proposition 47, which would reclassify certain crimes to misdemeanors instead of felonies.

    Sponsored by CalSERVE Senator Yordanos Dejen, the bill states that the proposition “will ensure that prison spending is focused on violent and serious offenses and will maximize alternatives for non-serious, nonviolent crime.”

    The senate also showed support for plans of a research campus to be built in Richmond.

    The Richmond Bay Campus, which will be developed in phases over the next 40 years, will provide additional research facilities for both UC Berkeley and the Lawrence Berkeley National Laboratory. By having the second campus in Richmond, bill sponsor and CalSERVE Senator Austin Pritzkat said he envisions that the campus will provide a much-needed revitalization of the economy for the surrounding neighborhood.

    Finance officer Dennis Lee was also confirmed as one of the two undergraduate representatives to the Student Union Board. He will replace Arushi Saxena and serve for the rest of the year with Ismael Contreras.

    Lee said he hopes to increase transparency by connecting the Student Union and the ASUC as the board focuses on overseeing commercial activities concerning the new Student Union, set to open next fall.

    See the full article here.

    The Daily Californian is an independent, student-run newspaper published by the Independent Berkeley Students Publishing Company, Inc. The newspaper serves the UC Berkeley campus and its surrounding community, publishing Monday through Friday during the academic year and twice a week during the summer. Established in 1871, The Daily Californian is one of the oldest newspapers on the West Coast and one of the oldest college newspapers in the country. Daily Cal staffers have the unique opportunity of gaining daily metro news experience in the lively city of Berkeley. The newspaper has consistently covered the city and its institutions since its establishment, allowing student journalists to report on campus as well as city news. The Daily Cal also operates Best of Berkeley, a city guide and local arts Web site for the city of Berkeley.

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  • richardmitnick 11:04 am on October 24, 2014 Permalink | Reply
    Tags: , , , Cosmology, , ,   

    From CfA: “Accreting Supermassive Black Holes in the Early Universe” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    October 24, 2014
    No Writer Credit

    Supermassive black holes containing millions or even billions of solar-masses of material are found at the nuclei of galaxies. Our Milky Way, for example, has a nucleus with a black hole with about four million solar masses of material. Around the black hole, according to theories, is a torus of dust and gas, and when material falls toward the black hole (a process called accretion) the inner edge of the disk can be heated to millions of degrees. Such accretion heating can power dramatic phenomena like bipolar jets of rapidly moving charged particles. Such actively accreting supermassive black holes in galaxies are called active galactic nuclei (AGN).

    torus
    Torus

    The evolution of AGN in cosmic time provides a picture of their role in the formation and co-evolution of galaxies. Recently, for example, there has been some evidence that AGN with more modest luminosities and accretion rates (compared to the most dramatic cases) developed later in cosmic history (dubbed “downsizing”), although the reasons for and implications of this effect are debated. CfA astronomers Eleni Kalfontzou, Francesca Civano, Martin Elvis and Paul Green and a colleague have just published the largest study of X-ray selected AGN in the universe from the time when it was only 2.5 billion years old, with the most distant AGN in their sample dating from when the universe was about 1.2 billion years old.

    The astronomers studied 209 AGN detected with the Chandra X-ray Observatory.

    NASA Chandra Telescope
    NASA/Chandra

    image
    A multicolor image of galaxies in the field of the Chandra Cosmic Evolution Survey. A large, new study of 209 galaxies in the early universe with X-ray bright supermassive black holes finds that more modest AGN tend to peak later in cosmic history, and that obscured and unobscured AGN evolve in similar ways.
    X-ray: NASA/CXC/SAO/F.Civano et al. Optical: NASA/STScI

    They note that the X-ray observations are less contaminated by host galaxy emission than optical surveys, and consequently that they span a wider, more representative range of physical conditions. The team’s analysis confirms the proposed trend towards downsizing, while it also can effectively rule out some alternative proposals. The scientists also find, among other things, that this sample of AGN represents nuclei with a wide range of molecular gas and dust extinction. Combined with the range of AGN dates, this result enables them to conclude that obscured and unobscured phases of AGN evolve in similar ways.

    See the full article here.

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

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  • richardmitnick 10:43 am on October 24, 2014 Permalink | Reply
    Tags: , , , , , , Cosmology   

    From astrobio.net: “The Abundance of Water in Asteroid Fragments” 

    Astrobiology Magazine

    Astrobiology Magazine

    Oct 24, 2014
    Aaron L. Gronstal

    A new study could provide insights about the abundance of water in fragments from a famous asteroid.

    two
    These colorful images are of thin slices of meteorites viewed through a polarizing microscope. Part of the group classified as HED meteorites for their mineral content (Howardite, Eucrite, Diogenite), they likely fell to Earth from 4 Vesta. Credit: NASA / JPL-Caltech / Hap McSween (Univ. Tennessee), A. Beck and T. McCoy (Smithsonian Inst.)

    The study focused on a mineral called apatite, which can act as a record of the volatiles in materials, including things like magma and lunar rocks. Volatiles are chemical elements with low boiling points (like water), and are usually associated with a celestial bodies’ crust or atmosphere.

    By looking at the apatite in meteorites, the team was able to determine the history of water in these rocks from space.

    The meteorites they chose to study are known as the Howardite-Eucrite-Diogenite (HED) meteorites. These meteorites are a subset of the achondrite meteorites, which are stony meteorites that do not have any chondrites (round grains that were formed from molten droplets of material floating around in space before being incorporated into an asteroid).

    vesta
    Vesta closeup. Credit: NASA

    Studying the composition of meteorites can provide important clues about how asteroids and other rocky bodies form and evolve. Volatile elements influence processes important to planet formation, such as melting and eruption processes.

    HED meteorites are especially interesting because scientists think they originated from the crust of the asteroid Vesta – a large body in the main asteroid belt that was recently visited by NASA’s Dawn spacecraft. Behind Ceres, Vesta is the second largest object in the asteroid belt and is sometimes referred to as a protoplanet.

    Vesta is a relic of the ancient Solar System and can help astrobiologists understand our system’s formation and evolution. This information provides clues about conditions in the Solar System that led to the formation of a habitable planet – the Earth.

    Interestingly, the team’s results from the HED meteorites are similar to studies on the Earth and Moon, and could support theories that water in all three objects (Vesta, the Earth, and the Moon) came from the same source.

    See the full article here.

    NASA

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  • richardmitnick 9:42 am on October 24, 2014 Permalink | Reply
    Tags: , , , Cosmology, ,   

    From SPACE.com: “Einstein’s Gravity Waves Could Be Found with New Method” 

    space-dot-com logo

    SPACE.com

    October 24, 2014
    Charles Q. Choi

    Gravitational waves, invisible ripples in the fabric of space and time, might be detected by looking for the brightening of stars, researchers say.

    gw
    This illustration depicts the gravitational waves generated by two black holes orbiting each other.
    Credit: NASA

    These mysterious ripples were first proposed by Albert Einstein as part of his theory of general relativity. The waves’ size depends on the mass of the objects creating them.

    “Gravitational waves are emitted by accelerating masses,” said lead study author Barry McKernan, an astrophysicist at the American Museum of Natural History in New York. Really big waves are emitted by really big masses, such as systems containing black holes merging with each other.

    Scientists have still not made direct observations of gravitational waves, although researchers continue to endeavor to detect them using experiments involving lasers on the ground and in space. The waves interact very weakly with matter, which partly explains why seeing these ripples in spacetime is difficult.

    Now, McKernan and his colleagues suggest that gravitational waves could have more of an effect on matter than previously thought, with their influence potentially brightening stars.

    “It’s neat that nearly 100 years after Einstein proposed his theory of general relativity, there are still interesting surprises it can turn up,” McKernan told Space.com. “We’re brought up as astronomers thinking the interaction between matter and gravitational waves is very weak, essentially negligible, and that turns out not to be true.”

    The researchers suggest that stars that vibrate at the same frequency as gravitational waves passing through them can absorb a large amount of energy from the ripples.

    “You can imagine gravitational waves as sounds from a piano, and stars as a vibrating violin string held near that piano,” McKernan said. “If the frequency of the sounds matches the frequency of the violin string, the string can resonate with the sound.” If a star gets pumped up with large amounts of energy from gravitational waves in this way, “the star can puff up and look brighter than it normally would,” McKernan said.

    One challenge is determining whether any star brightening astronomers detect is from gravitational waves or some other factor. The researchers suggest the key to spotting the effects of gravitational waves involves looking at large groups of stars.

    “When a population of stars is near a system of merging black holes and is getting pounded by gravitational waves, we think that the more massive stars will light up first,” McKernan said. “It’s like playing keys on a piano and starting with low pitches.” As the black holes get closer together, the frequency of the gravitational waves they generate will increase, “and we’d expect to see brightening of smaller stars,” he added. “If we see a population of stars where the smaller stars are brightening after the bigger stars in a collective way, that might be a sign of gravitational waves.”

    This research also suggests a different way to indirectly detect gravitational waves. If scientists develop working gravitational wave detectors on Earth or in space, when a star passes in front of powerful sources of gravitational waves such as merging black holes, the detector may see a drop in the intensity of those waves. This will happen if the eclipsing star is vibrating at the right frequency.

    “You usually think of stars as being eclipsed by something, not the other way around,” McKernan said in a statement.

    McKernan and his colleagues Saavik Ford, Bence Kocsis and Zoltan Haiman detailed their findings online Sept. 22 in the journal Monthly Notices of the Royal Astronomical Society: Letters.

    See the full article here.

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  • richardmitnick 9:20 am on October 24, 2014 Permalink | Reply
    Tags: , , , , Cosmology, , POLARBEAR Collaboration   

    From phys.org: “POLARBEAR detects curls in the universe’s oldest light” 

    physdotorg
    phys.org

    Oct 21, 2014
    Susan Brown

    Cosmologists have made the most sensitive and precise measurements yet of the polarization of the cosmic microwave background.

    image

    The report, published October 20 in the Astrophysical Journal, marks an early success for POLARBEAR, a collaboration of more than 70 scientists using a telescope high in Chile’s Atacama desert designed to capture the universe’s oldest light.

    “It’s a really important milestone,” said Kam Arnold, the corresponding author of the report who has been working on the instrument for a decade. “We’re in a new regime of more powerful, precision cosmology.” Arnold is a research scientist at UC San Diego’s Center for Astrophysics and Space Sciences and part of the cosmology group led by physics professor Brian Keating.

    POLARBEAR measures remnant radiation from the Big Bang, which has cooled and stretched with the expansion of the universe to microwave lengths. This cosmic microwave background, the CMB, acts as an enormous backlight, illuminating the large-scale structure of the universe and carrying an imprint of cosmic history.

    Cosmic Background Radiation Planck
    CMB from Planck

    Arnold and many others have developed sensitive instruments called bolometers to measure this light. Arrayed in the telescope, the bolometers record the direction of the light’s electrical field from multiple points in the sky.

    “It’s a map of all these little directions that the light’s electric field is pointing,” Arnold explained.

    POLARBEAR has now mapped these angles with resolution on a scale of about 3 arcminutes, just one-tenth the diameter of the full moon..

    The team found telling twists called B-Modes in the patterns of polarization, signs that this cosmic backlight has been warped by intervening structures in the universe, including such mysteries as dark matter, composed of substance that remains unknown, and the famously aloof particles called neutrinos, which elude capture making them difficult to study.

    This initial report, the result of the first season of observation, maps B-modes in three small patches of sky.

    Dust in our own galaxy also emits polarized radiation like the CMB and has influenced other measurements. But these patches are relatively clean, Arnold says. And variations in the CMB polarization due to dust occur on so broad a scale that they do not significantly influence the finer resolution B-modes in this report.

    “We are confident that these B-modes are cosmological rather than galactic in origin,” Arnold said.

    Observations continue, and the data stream will ultimately be fed by additional telescopes comprising the Simons Array. Together they will map wider swaths of the sky, making fundamental discoveries possible.

    Simmons Array

    “POLARBEAR is a real tour de force. With a relatively small, but strong, UC-led team we have surpassed the next-nearest competitors by an order of magnitude in sensitivity. We have paved the way towards solving the deepest mysteries in the quest to understand matter and energy at the beginning of time,” said Brian Keating.

    POLARBEAR is a collaboration of scientists from many institutions including experiment founder, Adrian Lee, professor of physics at UC Berkeley.

    See the full article here.

    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

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  • richardmitnick 8:17 am on October 24, 2014 Permalink | Reply
    Tags: , , , Cosmology, , ,   

    From SPACE.com:”Saturn’s ‘Death Star’ Moon Mimas Is Weird Inside” 

    space-dot-com logo

    SPACE.com

    October 16, 2014
    Kelly Dickerson

    There’s something strange going on below the surface of Saturn’s Death Star-looking moon Mimas, a new study suggests.

    star

    Mimas’ rotation and its orbit around Saturn make the moon look like it’s rocking and back forth and oscillating similar to the way a pendulum swings. The rocking motion is called libration, and it’s commonly observed in moons that are influenced by the gravity from neighboring planets. However, using images of the moon captured by the Cassini spacecraft, Radwan Tajeddine, a research associate at Cornell University, discovered that the satellite’s libration was much more exaggerated in one spot than predicted. He expects it must be caused by the moon’s weird interior.

    NASA Cassini Spacecraft
    NASA/ Cassini

    “We’re very excited about this measurement because it may indicate much about the satellite’s insides,” Tajeddine said in a statement. “Nature is essentially allowing us to do the same thing that a child does when she shakes a wrapped gift in hopes of figuring out what’s hidden inside.”

    Feel the libration

    Astronomers have long been using the rotation and orbit of celestial bodies to guess what their interiors might be like. Most of the rocking is explained by the interacting forces from Mimas’ rotation and orbit, but one libration was much larger than expected.

    Tajeddine and the team tested five different models of what Mimas might look like below the surface to see which one could explain the exaggerated rocking. They quickly ruled out the possibility that Mimas has a uniform interior, an interior with two different layers or an abnormal mass under the moon’s 88-mile-long (142 kilometers) crater that makes it look like the Death Star from the “Star Wars” franchise.

    However, the last two models could both explain Mimas’ extreme libration. One idea is that the moon has an elongated, oval-shaped core. This elongation might have happened as the moon formed under the push and pull of Saturn’s rings. The teeter tottering could also come from a subsurface ocean, similar to the one on Jupiter’s moon Europa.

    While it’s still a possibility, Tajeddine thinks the subsurface ocean is an unlikely explanation. Astronomers have not observed any evidence of liquid water on Mimas, unlike some of Saturn’s other moons. The heat radiating from the core escapes through the moon’s ice-covered shell and would cause any subsurface ocean that existed to quickly freeze.

    3D Mimas map

    Mimas is the smallest and closest of Saturn’s main eight moons. Its giant crater covers almost one-third of the moon’s icy surface.

    For the past 10 years,the Cassini space probe has been collecting data on Mimas, Saturn and the ringed wonder’s other natural satellites. The Imaging Science Subsystem (ISS) onboard Cassini is a two-camera system that captures ultraviolet and infrared images of Saturn and its moons.

    Tajeddine and a team of researchers sifted through dozens of images captured by ISS and created a 3D map of the moon from the photos to study how Mimas spins and orbits Saturn.

    The new research was published this week in the journal Science.

    See the full article here.

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  • richardmitnick 8:01 am on October 24, 2014 Permalink | Reply
    Tags: , , , , Cosmology,   

    From SETI: “New Insights on the Origin of the triple asteroid system (87) Sylvia” 


    SETI Institute

    Oct 24, 2014
    Franck Marchis, Senior Research Scientist

    Combining observations from the world’s largest telescopes with those from smaller instruments used by amateur astronomers, a team of scientists has discovered that the large main-belt asteroid (87) Sylvia has a complex interior. This has been deduced by using the motions of the two moons orbiting the main asteroid as probes of the object’s density distribution. The complex structure is probably linked to the way the multiple system was formed.

    two
    Description Discovery of the two moons Romulus and Remus of the asteroid (87) Sylvia
    Date 24 January 2007
    Adaptive Optics observations of (87) Sylvia, showing its two satellites, Remus and Romulus

    The findings were announced last year at the 45th annual Division of Planetary Sciences meeting in Denver, Colorado and were published last month in the journal Icarus.

    The asteroid (87) Sylvia is the first known to have two moons. One moon was discovered in 2001, and the second was found in 2005 by a team led by Franck Marchis, senior research scientist at the Carl Sagan Center of the SETI Institute. Since then, the team has continued to make new observations of the system using 8 to 10 m-class telescopes, including those at the Keck Observatory, the European Southern Observatory, and Gemini North.

    Keck Observatory
    Keck Observatory Interior
    Keck

    ESO VLT Interferometer
    ESO VLT Interior
    ESO VLT

    Gemini North telescope
    Gemini North Interior
    Gemini North

    syl
    (credit: Danielle Futselaar/SETI Institute).
    An artist’s rendition of the triple system showing the large 270-km asteroid Sylvia surrounded by its two moons – Romulus and Remus – gives a pictorial representation of this intriguing triple system.

    The differentiated interior of the asteroid is shown in a cutaway diagram. The primary asteroid may have a dense, regularly-shaped core, surrounding by fluffy or fractured material. The outer moon, named Romulus, is known to be strongly elongated, possibly having two lobes, as suggested by a recently observed occultation recorded by amateur astronomers.

    “Combined observations from small and large telescopes provide a unique opportunity to understand the nature of this complex and enigmatic triple asteroid system,” Marchis said. “Thanks to the presence of these moons, we can constrain the density and interior structure of an asteroid, without the need for a spacecraft’s visit. Knowledge of the internal structure of asteroids is key to understanding how the planets of our solar system formed.”

    The article Physical and dynamical properties of the main belt triple Asteroid (87) Sylvia, published last month in Icarus, is co-authored by J. Berthier, F. Vachier, B. Carry from IMCCE-Obs de Paris, J. Durech from Charles University, Prague, and F. Marchis from the SETI Institute and Obs. de Paris.

    Reference
    Berthier, J., F. Vachier, F. Marchis, J. Ďurech, and B. Carry. 2014. Physical and Dynamical Properties of the Main Belt Triple Asteroid (87) Sylvia. Icarus 239 (September): 118–30. doi:10.1016/j.icarus.2014.05.046.

    Abstract
    We present the analysis of high angular resolution observations of the triple Asteroid (87) Sylvia collected with three 8-10 m class telescopes (Keck, VLT, Gemini North) and the Hubble Space Telescope. The moons’ mutual orbits were derived individually using a purely Keplerian model. We computed the position of Romulus, the outer moon of the system, at the epoch of a recent stellar occultation which was successfully observed at less than 15 km from our predicted position, within the uncertainty of our model. The occultation data revealed that the Moon, with a surface-area equivalent diameter Ds=23.1±0.7km, is strongly elongated (axes ratio of 2.7±0.32.7±0.3), significantly more than single asteroids of similar size in the main-belt. We concluded that its shape is probably affected by the tides from the primary. A new shape model of the primary was calculated combining adaptive-optics observations with this occultation and 40 archived light-curves recorded since 1978. The difference between the J2=0.024-0.009+0.016 derived from the 3-D shape model assuming an homogeneous distribution of mass for the volume equivalent diameter Dv=273±10km primary and the null J2 implied by the Keplerian orbits suggests a non-homogeneous mass distribution in the asteroid’s interior.

    See the full article here.

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  • richardmitnick 8:09 pm on October 23, 2014 Permalink | Reply
    Tags: Cosmology, , , ,   

    From Frontier Fields: “Recent Guide Star Loss with Abell 2744″ 

    Frontier Fields
    Frontier Fields

    May 30, 2014
    Patricia Royle – Frontier Fields Program Coordinator

    We have just experienced our first non-acquisition of a guide star during Frontier Fields observations. This occurred while in the midst of Abell 2744 observations.

    bel
    Abell 2744, nicknamed Pandora’s Cluster. The galaxies in the cluster make up less than five percent of its mass. The gas (around 20 percent) is so hot that it shines only in X-rays (coloured red in this image). The distribution of invisible dark matter (making up around 75 percent of the cluster’s mass) is coloured here in blue.

    Since HST is in constant motion, pointing is maintained by a set of three Fine Guidance Sensors (FGS) which find and lock on to a pair of guide stars, or a single guide star if pairs are not available. These guide stars are selected by software based on several criteria, including magnitude, relative position to other similar stars, position within the FGS “pickles” (Fields of View) and any pointing constraints on the observation such as ORIENT or POS TARGs within the Phase 2 program. Selected guide stars need to stay within the FGS pickles for the entire orbit, including all pointing changes due to POS TARGs or PATTERNs. If an observation spans more than one visibility interval, the guide stars are reacquired after each interruption either from occultation or SAA passages. A pair of guide stars provides the most accurate and stable pointing since they act as sort of handles for HST to focus on. If two stars are used in two separate FGS pickles, then HST is able to maintain almost perfect pointing throughout the observations. If only one star is used, HST may show some drift around the single star since there is not a second star to keep the telescope from rotating. More information about the accuracy of each type of guiding can be found online at http://www.stsci.edu/hst/acs/faqs/guide_star.html.

    In some cases, a guide star may fail to acquire or it might successfully acquire but can not be maintained. Sometimes this is a result of a telescope problem, but more often, it turns out that a selected guide star fails to meet one of the criteria it initially appeared to pass. This can happen in the case of a variable star, a multi-star system that previously appeared as a single star, or with the presence of a similar star (called a spoiler) nearby that confuses the FGS. When PAIRs are used, it is possible to fail to acquire one star, but succeed with the other, resulting in observations taken with single star guiding which is often good enough for most science. There may also be situations when a star is acquired initially but fails to re-acquire in a subsequent orbit, or lock may be lost on one star during an orbit. This is usually due to the star itself being at the very edge of usability and violating one of the limits set by the telescope to help ensure HST knows where it is pointing. With guide star pairs, science can usually continue as long as one of the stars is acquired. If both stars fail (very unusual) or an observation using single star guiding fails to acquire its one star, the observations default to gyro control. This is often problematic to the science as the observations are likely to show significant drift and rotation, or may be far enough off that the target is completely missed.

    During the first Frontier Fields visit observing Abell 2744 on May 14, one of the two selected guide stars failed to acquire, resulting in the observations continuing on single star guiding instead. As with all failures, the failed star was investigated and was found to be a bad star. It was flagged in the database within 24 hours of the failure, such that future observations would not attempt to use the same bad star. The second Frontier Fields visit of Abell 2744 on May 15 also failed, as it was already on the telescope and set to use the same guide star pair. Several other visits that were scheduled to execute on the telescope the following week, with the same guide star pair, were quickly reworked by the calendar-building team at STScI to use a different guide star pair. The remaining visits in the epoch not yet put on a calendar are unaffected, since the bad star is no longer an option for our software when selecting from available guide star pairs.

    fs
    Figure 1: The HST Field of View of Abell 2744, with Fine Guidance Sensors Fields of View indicated by the large, gray arcs.

    The green boxes in Figure 1 identify potential guide stars. To use guide star pairs, two stars must fall into separate FGS pickles and remain there throughout any shifts in pointing during the visit. If two similar guide stars are too close to each other, neither can be used since the FGS could lock onto the wrong star. Because of the multiple criteria involved and the need for precision, not all guide stars can be used for a given observation, even if the Field of View seems to show stars that could be used.

    The Frontier Fields data products team carried out a detailed examination of all the data from the two visits that were affected by these guidestar issues. For the first visit (number 37), only one of the guidestars was lost, while the other star was successfully acquired and the observations were able to continue in single guide star mode. Analysis of the resulting images showed no measurable impact on the pointing or the PSF quality (consistent with our knowledge that HST is able to perform successfully with a single guide star, when necessary), and all the data from this visit were included in the mosaics.

    For the second visit (number 81), the failure mode was somewhat different. The guide stars were fine during the first two orbits of this 4-orbit visit, but began to show problems during the third orbit and failed the reacquisition for the fourth orbit. Consequently, the ACS shutter was closed at the start of the fourth orbit and the fourth exposure for each filter was not obtained. As a result, we include only the first two exposures for each filter in our fast-turnaround v0.5 products, although we may include the third exposure in future versions. For WFC3/IR, all the exposures were obtained, and analysis revealed that the last exposure was offset by no more than a few tenths of an arcsecond compared to its expected location. Thus, there was no significant evidence of drift during the exposures, indicating that the telescope was able to track successfully in gyro mode during these exposures.

    So, it makes no difference. Two, one, or zero guide stars – we can do great science in any case!

    See the full article here.

    Frontier Fields draws on the power of massive clusters of galaxies to unleash the full potential of the Hubble Space Telescope. The gravity of these clusters warps and magnifies the faint light of the distant galaxies behind them. Hubble captures the boosted light, revealing the farthest galaxies humanity has ever encountered, and giving us a glimpse of the cosmos to be unveiled by the James Webb Space Telescope.

    NASA Hubble Telescope
    Hubble

    NASA James Webb Telescope
    Webb

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