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  • richardmitnick 2:49 pm on December 9, 2017 Permalink | Reply
    Tags: , , , , , Milky Way   

    From aeon: “Galactic position system” 

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    aeon

    12.9.17
    Sarah Scoles

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    Detail from Starry Night (1888) by Vincent Van Gogh, Musée D’Orsay, Paris. Photo by Getty Images

    Credits: NASA/JPL-Caltech/R. Hurt (SSC/Caltech)

    Every few months, the artist Jon Lomberg kneels next to a croton plant, removes the cheap earring that pierces a speckle on one of its leaves, and fastens a new yellow stud into the same hole. This, he says, pointing to the stud, represents the Sun. He is standing 30ft from the middle of the 100-ft-wide Galaxy Garden in the Captain Cook district of western Hawai’i. The highly manicured garden is an accurate scale model of the Milky Way galaxy, where every step takes you 2,000 light years from where you stood before. Here, the speckles on the leaves of ‘gold dust’ crotons stand in for stars. The plants reach out in spiral arms from the garden’s centre, where a spouting fountain plays the part of a monster black hole. Along the spiral limbs crowd hibiscus, vincas and red and black crotons where nebulae, gas and dust belong.

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    Jon Lomberg’s Galaxy Garden. Photo by Heidy and Pierre Lesage© 2010/www.galaxygarden.net

    When Lomberg stands up, his Milky Way makeover finished, he looks down at our yellow star. The garden’s opposing edge is 70ft away, the distance filled with other speckled leaves. ‘You put a basketball around where Earth is, and everything you’re going to see in the night sky is in that ball,’ he says, adding that other stars are too distant and dust-dimmed. ‘When you see the whole garden,’ Lomberg continues, ‘without any math, or any need for explanation, the scale becomes apparent.’

    It is difficult to picture ourselves in the Milky Way. We have no problem placing ourselves within, say, California, or the United States. Even second-graders can point to a spot on a globe and say: ‘I live there.’ And by third grade, they can position that globe in a neat line of planets, telling you smugly that those worlds orbit the Sun, a next-door version of the points of light in the night sky. But beyond that, what? Everything is so distant that we often lump it all into the ‘out there’ category, so that Pluto and Polaris might as well be in the same spot. Perhaps that’s why, as Lomberg says, many people erroneously use galaxy and solar system as synonyms.

    Only in the past few decades have we become scientifically and technologically advanced enough to situate ourselves within the 100,000-light-year-wide wilderness we call home (where one light year is a distance equivalent to 6 trillion miles). But making heads or tails of galactic latitude and longitude isn’t easy for anyone, including astronomers. We were born inside the Milky Way, and (spoiler alert) we will all die inside the Milky Way. Imagine being trapped inside a building and trying to determine what it looks like from the outside – its layout, when it was last painted, tin roof or shingled? You can catalogue half baths, peer out of a window and describe awnings. But assembling those pieces into a gestalt is like trying to understand your brain using your brain. You’ll never have an aerial view.

    Now imagine you’ve never heard of this strange concept of ‘building’. That’s the situation astronomers found themselves in until the 1920s. The Milky Way has always streaked our sky, a diffuse stripe spreading from horizon to horizon. Its Latin name – Via Lactea – comes from this fuzzy lane-like appearance. But it wasn’t until Galileo Galilei trained his telescope on it 400 years ago that we knew for sure that it was made of stars – stars just like Sirius, but much further away.

    As centuries passed, telescopes grew larger, allowing astronomers to detect fainter objects. Looking deeper into space than ever before, they began to see strange helical clouds. Thinking that they were just baroque clouds of gas within our own galaxy, astronomers called them ‘spiral nebulae’. After all, if you don’t know an object’s true size, it could be small and nearby, or distant and huge. And in the late 19th century, the proximate cosmos was the whole cosmos.

    We had long ago learned that Earth is not the hub of the solar system, but it was the helical clouds, and an argument known as the Great Debate, that pushed the Milky Way off its pedestal. Heber Curtis, director of the Allegheny Observatory in Pittsburgh, suggested in 1920 that the galaxy is just another spiral nebula – simply the one we happen to inhabit. Each other nebula is an ‘island universe’, a Milky Way beyond the Milky Way.

    On the other side of the debate was Harlow Shapley of the Mount Wilson Observatory in California.

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    Edwin Hubble at the 100 inch Hooker telescope at Mt Wilson


    Mt Wilson 100 inch Hooker Telescope, perched atop the San Gabriel Mountains outside Los Angeles, CA, USA

    If each nebula is an ‘island universe’, he said, the closest – Andromeda – would be millions of light years away.

    Andromeda Galaxy NASA/ESA Hubble

    We now know, of course, that Andromeda is an island universe, and that it houses more than a trillion suns. So do other galaxies 13 million, even 13 billion, light years away. Not only is the Milky Way not the entirety of the Universe, it’s not even a remarkable galaxy. The good news is, this ordinariness is what gives us a chance to describe our ‘building’ from the outside.

    We can count on the Milky Way to look and behave like an average spiral galaxy, and the Universe contains tens of billions of those. Wherever we look in the Universe, we see the laws of physics – the strong and weak nuclear forces that make atoms tick; the electromagnetics that attract opposites; the gravity that orders orbits – moulding gas into stars, and stars into galaxies. Peering out of our cosmic window, we can survey these structures to learn about our own. If the spiral nebulae we see have arms and bulges, perhaps the Milky Way sports them, too.

    From the side, the Milky Way is a thin disk with a bulge in the middle. From above or below, it resembles a hurricane, with spiral arms where rain bands would be. Four of them curl from the eye of the storm. The Perseus Arm and, interior to it, the Sagittarius Arm wrap around our side of the Milky Way, while the Scutum-Centaurus and Norma-Cygnus arms form a near-mirror-image on the other side.

    A stream of stars forms a curved lane between Perseus and Sagittarius. It is on this 15,000-light-year-long branch, called the Orion Arm, that our Sun sits. For a long time, astronomers believed the Orion Arm was insubstantial. Last June, however, they discovered our arm is a major appendage in its own right, more like Perseus and Sagittarius than like a minor spur.

    That’s a pretty basic discovery to make so late in the game. But nearly all knowledge of galactic limbs comes from invisible parts of the light spectrum, studies of which are – relative to the optical astronomy that began with Galileo’s telescope – in their infancy. Until extrasensory telescopes augmented our anatomy, we couldn’t sense the spiral arms. Scientists didn’t discover them until the 1950s, with the first radio surveys of hydrogen gas. From these simplest atoms, radio waves 21cm long cut through the thick curtain of particles that stands between us and the other side of the Milky Way. Those particles block the visible light, but longer-wavelength radiation zips right past them, just as FM transmissions pass right through the walls of your house.

    Radio waves and infrared radiation also shed light on how spiral arms move and why they exist in the first place. Although their shape suggests that they rotate with the galaxy, carrying stars along with them, they move at their own pace, like terrestrial traffic jams. While cars bottleneck, they eventually crawl out the other side. The traffic overdensity itself, however, persists. And so do spiral arms, which contain about 10 per cent more stars and gas than the rest of the galaxy. The Sun’s slow passage through the Perseus-Orion jam will take some 10 million years in total. After that, our star will be in a limbless space for 100 million years.

    All spiral arms lead to the Milky Way’s centre. There, a bar of stars in long, looping orbits forms the tapered shape of a cat’s pupil. This eye is 27,000 light years across – nearly as wide as the distance between Earth and the galactic centre – and pokes out of the galaxy’s plane at a 45º angle. Above and below this midsection, nearly 200 spheres, each packed with hundreds of thousands of ancient stars, orbit. Out of the Milky Way’s plane, these ‘globular clusters’ live their long lives in isolation from each other and the rest of the galaxy. If Earth were inside one of them, our night sky would beam down thousands of stars as bright as Sirius.

    At the very centre of the galaxy, 27,190 light years from Earth, sits the Milky Way’s most significant object.

    SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory

    Our fastest spacecraft would take 475 million years to arrive at its boundary, beyond which 4 million suns-worth of mass is squished into a singularity. This supermassive black hole, called Sagittarius A*, appears to orchestrate galactic motions, making every last atom its satellite, but this is an illusion. Everything orbits the centre of mass – the point at which the gravitation from all directions is the same. Just as the Earth spins on its axis and revolves around the Sun, the whole Milky Way whirls around the centre of mass. Even Sagittarius A*, very slightly offset from the galaxy’s true centre, does a delicate jig.

    The region around the black hole is dense with dust, which blocks and scatters visible light. Because no optical telescopes could see to the centre, astronomers did not find evidence of Sagittarius A*’s existence until 1974, when radio telescopes became powerful enough to nail the precise location of a strangely compact source of radiation that coincided with the galactic bull’s-eye.

    Ohio State Big Ear Radio Telescope, Construction of the Big Ear began in 1956 and was completed in 1961, and it was finally turned on for the first time in 1963

    A disk of swirling material surrounds Sagittarius A*. Stripped from stars and gas clouds, these rub against each other as they move. The friction heats things up, causing the disk to glow with radiation. Sometimes, an unfortunate clump of matter falls past the black hole’s event horizon – the point of no return – and the only memorial is a burst of photons. In the 10,000 light years right around the black hole, 10 billion stars bulge in a peanut shape. When astronomers look at the farther-out orbits, such as that of our Sun, the motions don’t perform as expected. The speeds depend on distance from the galactic centre and the amount of mass inside the orbit. Given that we’re in the podunk part of the Milky Way, low-density and far from the middle, our orbit should be slower. But the Milky Way’s farthest-flung suburbs have the same pace as its New York Cities.

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    Vera Rubin in the 1970s, NYT
    Vera Rubin, a researcher at the Carnegie Institution for Science in Washington DC, observed the same surprising motions in other galaxies in 1970. Here, dark matter enters the picture. To generate enough gravity to make the Sun orbit so fast, 80 per cent of the galaxy’s mass must be missing. Black as space, this dark matter pervades the Milky Way – including the solar system and maybe the space next to you right now – and forms a huge halo around the visible galaxy.

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

    And while this invisible cloak might be the most mysterious of the Milky Way’s shrouds, it is not the only one. A balloon of gas also envelops us, extending hundreds of thousands of light years beyond the galaxy’s visible borders – farther from the galaxy’s edges than the galaxy itself measures from edge to edge. If you could ball up this hydrogen, you could create at least 10 billion new stars.

    Even more hydrogen streams in from extragalactic space. Clouds of high-velocity gas come from smaller, nearby galaxies after the Milky Way’s immense gravity re-routes them. One known as Smith’s Cloud weighs more than a million suns, but it’s spread so thin that it fills as much sky (or it would, if you had radio-sensing eyes) as the Orion constellation.

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    When it arrives 30 million years from now, it will set off a burst of star formation. Snacks such as the Smith Cloud will allow the Milky Way to continue making new stars, even after it has consumed the food on its own plate.

    The Milky Way sometimes likes to steal sustenance from the Large and Small Magellanic Clouds, which can be seen orbiting our galaxy on dark, clear nights in the Southern Hemisphere.

    Large Magellanic Cloud. Adrian Pingstone December 2003

    Small Magellanic Cloud. NASA/ESA Hubble and ESO/Digitized Sky Survey 2

    Magellanic Bridge ESA_Gaia satellite. Image credit V. Belokurov D. Erkal A. Mellinger.

    But the theft does not go unavenged: the Magellanic Clouds might have turned the Milky Way into a warped and vibrating thing. As they move through space-time, they create a wake, just like rocks skipped across water. The undulations bump into our dark matter, bending the galaxy. Its edges flap and wave on timescales we can never experience.

    The Berkeley astronomer Leo Blitz theorised the cause of this warp. A renowned galactic researcher, he also is the scientific consultant for the Galaxy Garden. Before Lomberg broke ground, he sought out Blitz to ensure the floral Milky Way would be accurate. Each landscaping choice he made represents years of graduate students’ lives, scientific collaborations spanning continents and decades, and terabytes (and terabytes) of archived data. This Hawai’ian garden is the only place where you can truly feel that you’re in the Milky Way, because here you are in the Milky Way. ‘You’re walking around, bending down, looking down, then looking up,’ he says. ‘It’s a sensory experience.’

    If you stand where the Sun’s earring is and survey the fecundity around you, it’s easy to believe that you actually do live inside something larger than your world. Lomberg believes this cosmic swaddling – and the accompanying smallness – should be part of our mental toolkit.

    While acknowledging that your speckishness in the galaxy can make you feel trivial, Lomberg insists that the crushing scale doesn’t have to squash your importance. ‘There’s really no such thing as big or small,’ he says. ‘There’s only bigger or smaller. In some contexts, the galaxy is a tiny insignificant thing. So if the galaxy is not significant, then is anything significant? I think that the answer is that either nothing is or everything is.’

    If you zoom out of the Milky Way entirely, you’ll find 26 known dwarf galaxies orbiting us. It’s likely that 1,000 more are hiding out there, some nearly invisible, and made mostly of dark matter or cold hydrogen gas. Beyond them lie the other members of the Local Group.

    Local Group. Andrew Z. Colvin 3 March 2011

    These galaxies, 54 of which are known, travel together through space, and their gravitational centre lies between our galaxy and its nearest large neighbour, the Andromeda galaxy. Around the Milky Way and Andromeda, 12 other large galaxies form a protective circle known as the Council of Giants.

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    Council of Giants
    Date 28 February 2016
    Source http://www.atlasoftheuniverse.com/galgrps.gif

    The gravitational tethers that bind these galaxies are strong enough to resist the dark energy that is pushing everything apart, and getting faster every femtosecond (or one quadrillionth of a second).

    The Local Group is part of the Virgo Supercluster, which contains more than 100 galaxy groups and clusters, but even this structure is cosmically insignificant. Just as Earth is one of many planets, the Sun is an average star, and just as the Milky Way is a predictable spiral galaxy, the Virgo Supercluster has 10 million massive siblings.

    Virgo Supercluster, Wikipedia

    That number hardly means anything to those of us who are five or six feet tall, perhaps travel to a foreign continent once, and die when we’re 85 if we’re lucky. But imagine that the Galaxy Garden really is the galaxy: the visible Universe would be the size of Earth, and it would be immaculately landscaped with hundreds of billions of Galaxy Garden clones, all congregating in clusters and superclusters. Long filaments of gas and dark matter bridge superclusters, connecting them across voids. If you could see it from afar, the cosmos would look a lot like a brain: a collection of neurons, where each supercluster is a bright dendrite, and each filament an axon.

    Our brains have fewer synapses than the visible Universe, but they’ve enabled us to situate ourselves within it. Lomberg envisions a world in which every third-grader knows where the ‘You are here’ label goes on a galactic map and can give you directions from there to the Scutum-Centaurus Arm. ‘The Milky Way is as important to your self-identification as the fact that you live on planet Earth, or you live in the solar system,’ he says. ‘We may be insignificant, but we figured out that we’re in a galaxy. For insignificant nothings, that’s pretty good.’

    See the full article here .

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    Since 2012, Aeon has established itself as a unique digital magazine, publishing some of the most profound and provocative thinking on the web. We ask the big questions and find the freshest, most original answers, provided by leading thinkers on science, philosophy, society and the arts.

    Aeon has three channels, and all are completely free to enjoy:

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  • richardmitnick 2:46 pm on August 3, 2017 Permalink | Reply
    Tags: , , , , , Milky Way, The Outer Galaxy   

    From CfA: “The Outer Galaxy” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    July 28, 2017
    No writer credit

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

    The Sun is located inside one of the spiral arms of the Milky Way galaxy, roughly two-thirds of the way from the galactic center to the outer regions. Because we are inside the galaxy, obscuration by dust and the confusion of sources along our lines-of-sight make mapping the galaxy a difficult task. Astronomers think that the galaxy is a symmetric spiral, and about ten years ago CfA astronomers Tom Dame and Pat Thaddeus using millimeter observations of the gas carbon monoxide discovered symmetric components to the spiral arms deep in the inner galaxy that lent support to this model.

    The galaxy is not perfectly flat. It has a slight warp that allows some distant structures, at least in the direction of the constellations of Scutum and Centaurus, to be seen more distinctly above much of the foreground confusion. In 2011 the same CfA astronomers were the first to discover a large-scale spiral feature within this distant warp which they called the “Outer Scutum–Centaurus Arm (OSC).” Subsequent studies placed the OSC at a distance from the galactic center of over forty thousand light-years; it appears to be a symmetric counterpart to a spiral arm on the opposite side, in the direction of Perseus.

    CfA astronomer Tom Dame has joined with a set of collaborators to probe the extent of massive star formation in the OSC; sadly, his colleague Pat Thaddeus passed away earlier this year. Using radio measurements of ionized gas, which traces the hot ultraviolet from massive young stars, as well as bright emission from masers associated with massive star formation, the scientists observed 140 candidate locations and discovered evidence for massive young stars in about sixty percent of them. The study shows that the OSC is forming new stars, some with as much as forty solar masses each. These stars and their associated ionized environments, at least as far as we know now, mark the outer boundary for massive star formation in the Milky Way.

    Science paper:
    High-mass Star Formation in the Outer Scutum–Centaurus Arm, ApJ

    See the full article here .

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    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.

     
  • richardmitnick 2:53 pm on October 28, 2016 Permalink | Reply
    Tags: , Milky Way, , Our Galactic Arm May Have a Longer Reach Than We Thought   

    From SPACE.com: “Our Galactic Arm May Have a Longer Reach Than We Thought” 

    space-dot-com logo

    SPACE.com

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    An artist’s impression of the Milky Way as seen from the outside. New research suggests that the Orion Spur, or Arm, is almost twice as long as scientists had previously thought. Credit: NASA/JPL-Caltech/ESO/R. Hurt

    The sun’s galactic neighborhood just became a bit more significant. New research reveals that the sun’s branch of the Milky Way may be several times longer than previously measured, which would make it a significant contender in the structure of the galaxy.

    Spiral galaxies like the Milky Way contain several massive structures known as arms, which unwind from the galaxy’s center. The sun’s neighborhood is called the Orion Arm, though scientists often refer to it as the Local Arm. Despite its name, it is classified as a spur — a collection of dust and gas that lies between the more massive arms.

    “Our study reveals that the Local Arm is not only a tiny spur of the Milky Way. In includes a prominent major arm nearly extending to the Perseus Arm and a long spur branching between the Local and Sagittarius Arms,” astronomer Ye Xu of the Chinese Academy of Sciences told Space.com by email. Xu led a team that identified eight new features in the Orion Arm and determined that it is much longer than scientists have previously estimated, Xu said.

    According to Xu, characteristics of the Local Arm “are comparable to those of the Galaxy’s major spiral arms such as Sagittarius and Perseus.”

    Mapping from within

    With their gently unfurling arms and ongoing star formation, spiral galaxies are some of the most beautiful star collections in the universe. But it is far easier to calculate the characteristics of distant galaxies than it is to understand the features of our own Milky Way.

    “Determining the structure of the Milky Way has been a long-standing problem for astronomers because we are inside of it,” Xu said. “While astronomers agree that our galaxy has a spiral structure, there are disagreements on how many arms it has and on their specific location.”

    Mark Reid, a researcher at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts who was not involved in the study, compares the Milky Way to a dinner plate with an interesting design on its face. While the pattern is easy to spot from above, it can be difficult to interpret when the plate is edge-on.

    “All of the structures are projected on top of each other, and without accurate distances to these structures, it is impossible to infer the design,” Reid told Space.com by email.

    “All of the structures are projected on top of each other, and without accurate distances to these structures, it is impossible to infer the design,” Reid told Space.com by email.

    To measure how far parts of the arm sit from the sun, scientists search for telltale signals in star-forming regions. As gas enters galactic arms, gravitational forces squeeze the gas to produce newborn stars. In other galaxies, blobs of bluish light that are produced by the birth of stars trace out spiral arms.

    In the Milky Way, star-forming regions are more challenging to map. As part of the new research, the scientists identified bright spots of radio emission known as masers, whose shift in light researchers can measure to identify their movement and distance from Earth. Masers can be made up of clouds of gas that contain trace amounts of molecules such as water and methyl alcohol.

    Reid compared the microwave emissions produced by masers to the spots of red light streaming from a hand-held laser.

    “All they need is a source of energy — analogous to the battery in a laser pointer — and long path-lengths to amplify the emission,” Reid said. “In star-forming regions, the more massive and very young stars provide the energy.”

    Using the National Radio Astronomy Observatory’s Very Long Baseline Array (VLBA), a suite of 10 telescopes operating in Socorro, New Mexico, the scientists identified and measured eight new masers in the Orion Arm, setting its new length at about 25,000 light-years long.

    NRAO VLBA
    NRAO VLBA

    (A light-year is the distance light travels in a year.) Although measurements of the arm vary, Xu’s team set the distance as being just over 16,000 light-years in 2013.

    “This characterization of the Local Arm will change the image of the Milky Way,” Xu said.

    The new research, which was published in the journal Science Advances in September, reveals the Milky Way as more complex than scientists have previously estimated. The galaxy is typically classified as a grand-design spiral, which Reid said is often very symmetrical, often boasting only two arms.

    “The Milky Way, while probably a ‘pretty galaxy,’ has significant irregularities,” Reid said. “Based on our observations, it is clear that there are four major spiral arms and some non-symmetric structures like the Local Arm.”

    Further studies are needed to determine how irregular the Milky Way might be: “Without a complete map of the Milky Way, however, it is not clear how symmetric the four arms are,” Reid said.

    Instruments like the VLBA, located in the northern hemisphere, are limited in their ability to study the Milky Way. According to Reid, they can only map a bit more than half of the galaxy.

    “We need more observations, particularly from the Southern Hemisphere, so that we can map the entire Milky Way,” Reid said.

    See the full article
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  • richardmitnick 11:40 am on October 14, 2016 Permalink | Reply
    Tags: Astrometry, , , , , Milky Way, Parallaxes   

    From nationalgeographics.com: “New Milky Way Map Is a Spectacular Billion-Star Atlas” 

    National Geographic

    National Geographics

    September 14, 2016 [This just now appeared in social media.]
    Michael Greshko

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    The Milky Way, Scorpius, Sagittarius, Lagoon Nebula, Sagittarius Star Cloud, and Antares. From Atacama Desert, Chile.
    Photograph by Babak Tafreshi, National Geographic Creative

    After more than two years spent gluing its eyes to the heavens, an advanced celestial mapmaker has released its first results—wowing astronomers with the most accurate view of our Milky Way ever assembled.

    The announcement marks the first release of data from Gaia, a spacecraft operated by the European Space Agency (ESA).

    ESA/GAIA satellite
    ESA/GAIA satellite

    Launched in December 2013, the spacecraft currently sits a million miles away from Earth in the gravitational parking spot known as L2.

    LaGrange Points map. NASA
    LaGrange Points map. NASA

    From this unique vantage point, the craft has been cataloging stars and looking for shifts in their apparent positions caused by the spacecraft’s orbital motion around the sun.

    Measuring these shifts, or parallaxes, lets astronomers calculate the stars’ actual positions and movements through the galaxy with great precision, a field of study called astrometry that Gaia and its predecessor Hipparcos have revitalized.

    For thousands of years, astronomers from the ancient Babylonians to Tycho Brahe had preoccupied themselves with noting the stars’ precise locations, a crucial foundation to understanding the cosmos. But the field sputtered in the 1960s, when scientists reached the smallest parallaxes that Earth-based telescopes could measure, stymied by interference from our rippling atmosphere.

    It wasn’t until the 1980s and 1990s that the ESA satellite Hipparcos took astrometry to space, where it ultimately measured the precise distances of more than 100,000 stars. Gaia is even better: Hipparcos’s gaze reached only as far as 1,600 light-years away, barely leaving our celestial backyard, but Gaia is able to spy on stars up to 30,000 light-years away.

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    This all-sky view of the stars in our galaxy and its neighbors is based on the first year of observations from ESA’s Gaia satellite, taken from July 2014 to September 2015. Map by ESA

    Revolutionary Mapping

    With the new data release, Gaia has tracked the positions and motions of the brightest two million stars in the Milky Way, smashing the 100,000-star mark set by Hipparcos.

    The release, the first of five planned through 2022, also contains an atlas detailing the positions and brightnesses of some 1.1 billion stars in the Milky Way, based on 14 months of observations starting in July 2014. Over 400 million of these stars have never been seen before. (Also see “How Much Does the Milky Way Weigh?”)

    “It’s the largest-ever map made [of the Milky Way] from a single survey, and it’s also the most accurate map ever made,” says Anthony Brown of Leiden University, a member of the Gaia Data Processing and Analysis Consortium. He notes that while the map will improve dramatically in the coming years, it already pinpoints a star’s location to within 10 milliarcseconds—equivalent to determining an object’s position to within a hair’s breadth from more than a mile away.

    “Gaia is at the forefront of astrometry, charting the sky at precisions that have never been achieved before,” Alvaro Giménez, ESA’s director of science, says in a statement. “Today’s release gives us a first impression of the extraordinary data that await us and that will revolutionize our understanding of how stars are distributed and move across our galaxy.”

    What’s more, the data release adds hundreds of variable stars to astronomers’ toolkits. These stars regularly dim and brighten in predictable ways, allowing astronomers to measure vast cosmological distances. Having more of them to work with is akin to getting a larger, more precise yardstick.

    And Gaia is just getting started. By the end of its scheduled observation run, the spacecraft will have tracked the accurate positions and motions of roughly a billion stars, or one percent of the Milky Way’s estimated stellar population.

    “[Gaia] is going to give you this sort of three-dimensional movie of the galaxy, which is absolutely unprecedented,” says astronomer Michael Perryman of University College Dublin, who worked on Hipparcos before becoming Gaia’s lead project scientist from 1993 to 2007.

    “It’s very unusual, very revolutionary, and very spectacular—and it’s going to keep thousands of scientists busy for years.”

    And Gaia, which sports a billion-pixel camera and optics that rival those aboard the Hubble Space Telescope, isn’t just for tracking stars. The final survey will contain 250,000 new solar system objects, a million distant galaxies, 500,000 quasars—and about 20,000 exoplanets, says Gaia lead project scientist Timo Prusti.

    It’s no small wonder, then, that astronomers are agog. Columbia University astronomer Kathryn Johnston calls Gaia “the data set for galactic science for my generation of astronomers.”

    See the full article here .

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    The National Geographic Society has been inspiring people to care about the planet since 1888. It is one of the largest nonprofit scientific and educational institutions in the world. Its interests include geography, archaeology and natural science, and the promotion of environmental and historical conservation.

     
  • richardmitnick 3:34 pm on August 30, 2016 Permalink | Reply
    Tags: , , , , Milky Way,   

    From Symmetry: “Our galactic neighborhood” 

    Symmetry Mag

    Symmetry

    08/30/16
    Molly Olmstead

    What can our cosmic neighbors tell us about dark matter and the early universe?

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

    Imagine a mansion.

    Now picture that mansion at the heart of a neighborhood that stretches irregularly around it, featuring other houses of different sizes—but all considerably smaller. Cloak the neighborhood in darkness, and the houses appear as clusters of lights. Many of the clusters are bright and easy to see from the mansion, but some can just barely be distinguished from the darkness.

    This is our galactic neighborhood. The mansion is the Milky Way, our 100,000-light-years-across home in the universe. Stretching roughly a million light years from the center of the Milky Way, our galactic neighborhood is composed of galaxies, star clusters and large roving gas clouds that are gravitationally bound to us.

    The largest satellite galaxy, the Large Magellanic Cloud [LMC], is also one of the closest.

    2
    LMC

    It is visible to the naked eye from areas clear of light pollution in the Southern Hemisphere. If the Large Magellanic Cloud were around the size of the average American home—about 2,500 square feet—then by a conservative estimate the Milky Way mansion would occupy more than a full city block. On that scale, our most diminutive neighbors would occupy the same amount of space as a toaster.

    Our cosmic neighbors promise answers to questions about hidden matter and the ancient universe. Scientists are setting out to find them.

    What makes a neighbor

    If we are the mansion, the neighboring houses are dwarf galaxies. Scientists have identified about 50 possible galaxies orbiting the Milky Way and have confirmed the identities of roughly 30 of them. These galaxies range in size from several billion stars to only a few hundred. For perspective, the Milky Way contains somewhere between 100 billion to a trillion stars.

    Dwarf galaxies are the most dark-matter-dense objects known in the universe. In fact, they have far more dark matter than regular matter. Segue 1, our smallest confirmed neighbor, is made of 99.97 percent dark matter.

    Dark matter is key to galaxy formation. A galaxy forms when enough regular matter is attracted to a single area by the gravitational pull of a clump of dark matter.

    Dark matter halo  Image credit: Virgo consortium / A. Amblard / ESA
    Dark matter halo Image credit: Virgo consortium / A. Amblard / ESA

    Projects such as the Dark Energy Survey, or DES, find these galaxies by snapping images of a segment of the sky with a powerful telescope camera. Scientists analyze the resulting images, looking for the pattern of color and brightness characteristic of galaxies.

    Dark Energy Icon
    Dark Energy Camera,  built at FNAL
    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile
    Dark Energy Camera, built at FNAL; NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile

    Scientists can find dark matter clumps by measuring the motion and chemical composition of stars. If a smaller galaxy seems to be behaving like a more massive galaxy, observers can conclude a considerable amount of dark matter must anchor the galaxy.

    “Essentially, they are nearby clouds of dark matter with just enough stars to detect them,” says Keith Bechtol, a postdoctoral researcher at the University of Wisconsin-Madison and a member of the Dark Energy Survey.

    Through these methods of identification (and thanks to the new capabilities of digital cameras), the Sloan Digital Sky Survey kicked off the modern hunt for dwarf galaxies in the early 2000s.

    SDSS Telescope at Apache Point, NM, USA
    SDSS Telescope at Apache Point, NM, USA

    The survey, which looked at the northern part of the sky, more than doubled the number of known satellite dwarf galaxies from 11 to 26 galaxies between 2005 and 2010.

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

    Now DES, along with some other surveys, is leading the search. In the last few years DES and its Dark Energy Camera, which maps the southern part of the sky, brought the total to 50 probable galaxies.

    Dark matter mysteries

    Dwarf galaxies serve as ideal tools for studying dark matter. While scientists haven’t yet directly discovered dark matter, in studying dwarf galaxies they’ve been able to draw more and more conclusions about how it behaves and, therefore, what it could be.

    “Dwarf galaxies tell us about the small-scale structure of how dark matter clumps,” says Alex Drlica-Wagner of Fermi National Accelerator Laboratory, one of the leaders of the DES analysis. “They are excellent probes for cosmology at the smallest scales.”

    Dwarf galaxies also present useful targets for gamma-ray telescopes, which could tell us more about how dark matter particles behave.

    NASA/Fermi Telescope
    NASA/Fermi Gamma-ray Telescope

    ESA/Integral
    ESA/Integral Gamma-ray telescope

    Some models posit that dark matter is its own antiparticle. If that were so, it could annihilate when it meets other dark matter particles, releasing gamma rays. Scientists are looking for those gamma rays.

    But while studying these neighbors provides clues about the nature of dark matter, they also raise more and more questions. The prevailing cosmological theory of dark matter has accurately described much of what scientists observe in the universe. But when scientists looked to our neighbors, some of the predictions didn’t hold up.

    The number of galaxies appears to be lower than expected from calculations, for example, and those that are around seem to be too small. While some of the solutions to these problems may lie in the capabilities of the telescopes or the simulations themselves, we may also need to reconsider the way we think dark matter interacts.

    The elements of the neighborhood

    Dwarf galaxies don’t just tell us about dark matter: They also present a window into the ancient past. Most dwarf galaxies’ stars formed more than 10 billion years ago, not long after the Big Bang. Our current understanding of galaxy formation, according to Bechtol, is that after small galaxies formed, some of them merged over billions of years into larger galaxies.

    If we didn’t have these ancient neighbors, we’d have to peer all the way across the universe to see far enough back in time to glimpse galaxies that formed soon after the big bang. While the Milky Way and other large galaxies bustle with activity and new star formation, the satellite galaxies remain mostly static—snapshots of galaxies soon after their birth.

    “They’ve mostly been sitting there, waiting for us to study them,” says Josh Simon, an astronomer at the Carnegie Institution for Science.

    The abundance of certain elements in stars in dwarf galaxies can tell scientists about the conditions and mechanisms that produce them. Scientists can also look to the elements to learn about even older stars.

    The first generation of stars are thought to have looked very different than those formed afterward. When they exploded as supernovae, they released new elements that would later appear in stars of the next generation, some of which are found in our neighboring galaxies.

    “They do give us the most direct fingerprint we can get as to what those first stars might have been like,” Simon says.

    Scientists have learned a lot about our satellites in just the past few years, but there’s always more to learn. DES will begin its fourth year of data collection in August. Several other surveys are also underway. And the Large Synoptic Survey Telescope, an ambitious international project currently under construction in Chile, will begin operating fully in 2022.

    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile
    LSST/Camera, built at SLAC; SST telescope, currently under construction at Cerro Pachón Chile

    LSST will create a more detailed map than any of the previous surveys’ combined.

    From NatGeo, Inside the Milky Way, possibly the best science video ever made.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:11 am on August 29, 2016 Permalink | Reply
    Tags: , , , Milky Way   

    From CfA: “Milky Way Had a Blowout Bash 6 Million Years Ago” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    August 29, 2016

    Christine Pulliam
    Media Relations Manager
    Harvard-Smithsonian Center for Astrophysics
    617-495-7463
    cpulliam@cfa.harvard.edu

    1
    This artist’s impression shows the Milky Way as it may have appeared 6 million years ago during a “quasar” phase of activity. A wispy orange bubble extends from the galactic center out to a radius of about 20,000 light-years. Outside of that bubble, a pervasive “fog” of million-degree gas might account for the galaxy’s missing matter of 130 billion solar masses. Mark A. Garlick/CfA

    The center of the Milky Way galaxy is currently a quiet place where a supermassive black hole slumbers, only occasionally slurping small sips of hydrogen gas.

    Sag A*  NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way
    Sag A* NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way

    But it wasn’t always this way. A new study shows that 6 million years ago, when the first human ancestors known as hominins walked the Earth, our galaxy’s core blazed forth furiously. The evidence for this active phase came from a search for the galaxy’s missing mass.

    Measurements show that the Milky Way galaxy weighs about 1-2 trillion times as much as our Sun. About five-sixths of that is in the form of invisible and mysterious dark matter. The remaining one-sixth of our galaxy’s heft, or 150-300 billion solar masses, is normal matter. However, if you count up all the stars, gas and dust we can see, you only find about 65 billion solar masses. The rest of the normal matter – stuff made of neutrons, protons, and electrons – seems to be missing.

    “We played a cosmic game of hide-and-seek. And we asked ourselves, where could the missing mass be hiding?” says lead author Fabrizio Nicastro, a research associate at the Harvard-Smithsonian Center for Astrophysics (CfA) and astrophysicist at the Italian National Institute of Astrophysics (INAF).

    “We analyzed archival X-ray observations from the XMM-Newton spacecraft and found that the missing mass is in the form of a million-degree gaseous fog permeating our galaxy. That fog absorbs X-rays from more distant background sources,” Nicastro continues.

    ESA/XMM Newton
    ESA/XMM Newton

    The astronomers used the amount of absorption to calculate how much normal matter was there, and how it was distributed. They applied computer models but learned that they couldn’t match the observations with a smooth, uniform distribution of gas. Instead, they found that there is a “bubble” in the center of our galaxy that extends two-thirds of the way to Earth.

    Clearing out that bubble required a tremendous amount of energy. That energy, the authors surmise, came from the feeding black hole. While some infalling gas was swallowed by the black hole, other gas was pumped out at speeds of 2 million miles per hour (1,000 km/sec).

    Six million years later, the shock wave created by that phase of activity has crossed 20,000 light-years of space. Meanwhile, the black hole has run out of nearby food and gone into hibernation.

    This timeline is corroborated by the presence of 6-million-year-old stars near the galactic center. Those stars formed from some of the same material that once flowed toward the black hole.

    “The different lines of evidence all tie together very well,” says Smithsonian co-author Martin Elvis (CfA). “This active phase lasted for 4 to 8 million years, which is reasonable for a quasar.”

    The observations and associated computer models also show that the hot, million-degree gas can account for up to 130 billion solar masses of material. Thus, it just might explain where all of the galaxy’s missing matter was hiding: it was too hot to be seen.

    More answers may come from the proposed next-generation space mission known as X-ray Surveyor. It would be able to map out the bubble by observing fainter sources, and see finer detail to tease out more information about the elusive missing mass. The European Space Agency’s Athena X-ray Observatory, planned for launch in 2028, offers similar promise.

    These results have been accepted for publication in The Astrophysical Journal and are available online.

    Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

    See the full article here .

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    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.

     
  • richardmitnick 12:11 pm on July 20, 2016 Permalink | Reply
    Tags: , , , Do Galactic Bars Buckle to Form Bulges, Milky Way   

    From AAS NOVA: ” Do Galactic Bars Buckle to Form Bulges?” 

    AASNOVA

    American Astronomical Society

    20 July 2016
    Susanna Kohler

    1
    Artist’s impression of a side view of the Milky Way, complete with its central peanut-shaped bulge. A new study has examined how bulges like this might form. [ESO/NASA/JPL-Caltech/M. Kornmesser/R. Hurt]

    Milky Way NASA/JPL-Caltech /ESO R. Hurt
    Artist’s illustration of the Milky Way, including the galactic bar at its center. [NASA/JPL-Caltech/ESO/R. Hurt]

    The Milky Way is one of many galaxies that has a peanut-shaped bulge at its center. A new study has now caught two galaxies in the process of forming similar bulges, yielding insight into how ours was created.

    Unstable Buckling

    Roughly 60-70% of disk galaxies in the local universe have stellar bars at the centers of their disks. Many of these — including our own galaxy — are vertically thickened in their inner regions, giving their bulges a boxy or peanut-shaped appearance in an edge-on view. We call these “B/P bulges”.

    What causes B/P bulges? Twenty years of simulations of galaxy formation and evolution have pointed to an answer: galactic bars in simulations can buckle, due to a vertical instability that can occur in the bar shortly after its formation. When this asymmetric buckling eventually ends, the inner part of the bar settles into a vertically symmetric structure again: the B/P bulge.

    But despite the fact that simulations predict this formation mechanism, we’ve yet to confirm it observationally. Though we’ve observed many examples in the universe of galaxies with boxy bulges that match the outcomes of the simulations, we’ve never yet caught a galactic bar in the act of buckling … until now.

    3
    Top panel: N-body simulations showing the result after a galactic bar buckles. Bottom panels: two examples of real galaxies (NGC 3185 and NGC 3627) with B/P bulges matching simulations. [Adapted from Erwin & Debattista 2016]

    Matching Observation to Simulation

    Scientists Peter Erwin (Max Planck Institute for Extraterrestrial Physics, Germany) and Victor Debattista (University of Central Lancashire, UK) searched through barred disk galaxies with the Spitzer Space Telescope, looking for buckling galactic bars. Their search was successful: two galaxies, NGC 4569 and NGC 3227, have the central characteristics of buckling bars!

    The authors made this identification by comparing their observations of galaxies to simulated galaxies that were undergoing bar buckling. Several characteristics — like trapezoidal bulge structure and spurs that extend symmetrically off of the long end of the trapezoid — are specifically characteristic of bars that are in the process of buckling. NGC 4569 and NGC 3227 both nicely match these morphological predictions from simulations.

    Examining the stellar motions in the center of NGC 4569, Erwin and Debattista additionally find that the stellar kinematics match the specific predictions from simulations of a buckling bar as well.

    4
    N-body simulations showing the result during the buckling of a galactic bar. Bottom panels: the two galaxies discovered in this study (NGC 4569 and NGC 3227), which show characteristics of buckling bars matching simulations. [Adapted from Erwin & Debattista 2016]

    A Common Structure

    Erwin and Debattista’s overall survey results indicate that B/P bulges are extremely common in high-stellar-mass galaxies: they are present in ~80% of the 44 high-stellar-mass barred-disk galaxies they examined. Based on these observations, the fraction of high-mass barred galaxies with bars in the process of buckling is estimated to be ~4.5% in the local universe.

    In contrast, the authors calculate that the fraction of galaxies with buckling bars should be much higher in the earlier universe — the buckling fraction peaks at ~40% at a redshift of z = 0.7. The James Webb Space Telescope should be up to the task of detecting these galaxies, so future observations will provide a useful test of the authors’ model for B/P bulge formation.
    Citation

    Peter Erwin and Victor P. Debattista 2016 ApJ 825 L30. doi:10.3847/2041-8205/825/2/L30

    See the full article here .

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  • richardmitnick 9:22 am on July 20, 2016 Permalink | Reply
    Tags: , , Milky Way,   

    From JPL-Caltech: “X Marks the Spot for Milky Way Formation” 

    NASA JPL Banner

    JPL-Caltech

    July 19, 2016
    Elizabeth Landau
    Jet Propulsion Laboratory, Pasadena, Calif.
    818-354-6425
    elizabeth.landau@jpl.nasa.gov

    1
    To reveal the X shape in the Milky Way’s central bulge, researchers took WISE observations and subtracted a model of how stars would be distributed in a symmetrical bulge. Credit: NASA/JPL-Caltech/D.Lang

    NASA/WISE Telescope
    NASA/WISE Telescope

    2
    X Marks the Spot for Milky Way Formation
    To reveal the X shape in the Milky Way’s central bulge, researchers took WISE observations and subtracted a model of how stars would be distributed in a symmetrical bulge. Credit: NASA/JPL-Caltech/D.Lang

    A new understanding of our galaxy’s structure began in an unlikely way: on Twitter. A research effort sparked by tweets led scientists to confirm that the Milky Way’s central bulge of stars forms an “X” shape. The newly published study uses data from NASA’s Wide-field Infrared Survey Explorer (WISE) mission.

    The unconventional collaboration started in May 2015 when Dustin Lang, an astronomer at the Dunlap Institute of the University of Toronto, posted galaxy maps to Twitter, using data from WISE’s two infrared surveys of the entire sky in 2010. Infrared light allows astronomers to see the structures of galaxies in spite of dust, which blocks crucial details in visible light. Lang was using the WISE data in a project to map the web of galaxies far outside our Milky Way, which he made available through an interactive website.

    But it was the Milky Way’s appearance in the tweets that got the attention of other astronomers. Some chimed in about the appearance of the bulge, a football-shaped central structure that is three-dimensional compared to the galaxy’s flat disk. Within the bulge, the WISE data seemed to show a surprising X structure, which had never been as clearly demonstrated before in the Milky Way. Melissa Ness, a postdoctoral researcher at the Max Planck Institute for Astronomy in Heidelberg, Germany, recognized the significance of the X shape, and contacted Lang.

    The two met a few weeks later at a conference in Michigan, and decided to collaborate on analyzing the bulge using Lang’s WISE maps. Their work resulted in a new study published in the Astronomical Journal confirming an X-shaped distribution of stars in the bulge.

    “The bulge is a key signature of formation of the Milky Way,” said Ness, the study’s lead author. “If we understand the bulge we will understand the key processes that have formed and shaped our galaxy.”

    The Milky Way is an example of a disk galaxy — a collection of stars and gas in a rotating disk. In these kinds of galaxies, when the thin disk of gas and stars is sufficiently massive, a “stellar bar” may form, consisting of stars moving in a box-shaped orbit around the center. Our own Milky Way has a bar, as do nearly two-thirds of all nearby disk galaxies.

    Over time, the bar may become unstable and buckle in the center. The resulting “bulge” would contain stars that move around the galactic center, perpendicular to the plane of the galaxy, and in and out radially. When viewed from the side, the stars would appear distributed in a box-like or peanut-like shape as they orbit. Within that structure, according to the new study, there is a giant X-shaped structure of stars crossing at the center of the galaxy.

    A bulge can also form when galaxies merge, but the Milky Way has not merged with any large galaxy in at least 9 billion years.

    “We see the boxy shape, and the X within it, clearly in the WISE image, which demonstrates that internal formation processes have driven the bulge formation,” Ness said. “This also reinforces the idea that our galaxy has led a fairly quiet life, without major merging events since the bulge was formed, as this shape would have been disrupted if we had any major interactions with other galaxies.”

    The Milky Way’s X-shaped bulge had been reported in previous studies. Images from the NASA Cosmic Background Explorer (COBE) satellite’s Diffuse Infrared Background Experiment suggested a boxy structure for the bulge.

    NASA COBE
    NASA COBE

    In 2013, scientists at the Max Planck Institute for Extraterrestrial Physics published 3-D maps of the Milky Way that also included an X-shaped bulge, but these studies did not show an actual image of the X shape. Ness and Lang’s study uses infrared data to show the clearest indication yet of the X shape.

    Additional research is ongoing to analyze the dynamics and properties of the stars in the Milky Way’s bulge.

    Collaborating on this study was unusual for Lang — his expertise is in using computer science to understand large-scale astronomical phenomena, not the dynamics and structure of the Milky Way. But he was able to enter a new field of research because he posted maps to social media and used openly accessible WISE data.

    “To me, this study is an example of the interesting, serendipitous science that can come from large data sets that are publicly available,” he said. “I’m very pleased to see my WISE sky maps being used to answer questions that I didn’t even know existed.”

    NASA’s Jet Propulsion Laboratory, Pasadena, California, manages and operates WISE for NASA’s Science Mission Directorate in Washington. The spacecraft was put into hibernation mode in 2011, after it scanned the entire sky twice, thereby completing its main objectives. In September 2013, WISE was reactivated, renamed NEOWISE and assigned a new mission to assist NASA’s efforts to identify potentially hazardous near-Earth objects.

    For more information on WISE, visit:

    http://www.nasa.gov/wise

    See the full article here .

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    NASA JPL Campus

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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    NASA image

     
  • richardmitnick 11:28 am on March 29, 2016 Permalink | Reply
    Tags: , , , Milky Way,   

    From Symmetry: “The Milky Way’s hot spot” 

    Symmetry Mag

    Symmetry

    03/29/16
    Ali Sundermier

    Credits: NASA/JPL-Caltech/R. Hurt (SSC/Caltech)
    Milky Way map. Credits: NASA/JPL-Caltech/R. Hurt (SSC/Caltech)

    When you look up at night, the Milky Way appears as a swarm of stars arranged in a misty white band across the sky.

    But from an outside perspective, our galaxy looks more like a disk, with spiral arms of stars reaching out into the universe. At the center of this disk is a small region around which the entire pinwheel of our galaxy rotates, a region packed with exotic astronomical phenomena ranging from dark matter and newborn stars to a supermassive black hole. Astronomers call this region of the Milky Way the galactic center.

    SGR A* NASA's Chandra X-Ray Observatory
    Milky Way’s supermassive black hole SGR A* NASA’s Chandra X-Ray Observatory

    It’s a strange neighborhood, and scientists have reason to believe it’s one of the best places to hunt for dark matter.

    1
    The Spitzer Space Telescope provides an infrared view of the galactic center region.
    Courtesy of: NASA/JPL-Caltech/ESA/CXC/STScI

    NASA/Spitzer Telescope
    NASA/Spitzer Telescope

    Phenomena in our galaxy’s heart

    In the ’70s, scientists hypothesized that a supermassive black hole might be lurking in the center of the Milky Way. Black holes are points of space-time where gravity is so strong that not even light can escape.

    After decades of trying to indirectly identify the mysterious object in the galactic center by tracing the orbits of stars and gas, astronomers were finally able to calculate its mass in 2008. It weighed more than 4 million times as much as the sun, making it a prime supermassive black hole candidate.

    About 10 percent of all new star formation in the galaxy occurs in the galactic center. This is strange because local conditions produce an extreme environment in which it should be difficult for stars to form.

    Scientists believe that at least some of the new stars being formed should explode and transform into pulsars, but they aren’t seeing any. Pulsars emit a regular pulsating signal, like a lighthouse. One early explanation for the apparent lack of pulsars in the galactic center was that the magnetic fields there could be bending their radio waves on their way to us, hiding their pulsating signals. But recently scientists measured the strength of the fields and realized the bending was much less than they had anticipated. The mystery of the missing pulsars remains unsolved.

    The galactic center also has a notably high concentration of cosmic rays, high-energy charged particles that hurtle through outer space. Scientists still don’t understand where these particles come from or how they reach such intense energies.

    2
    The Hubble Space Telescope, though better known for its visible light images, also captured an infrared light picture of the galactic center (the bright patch in the lower right).
    Courtesy of: NASA/JPL-Caltech/ESA/CXC/STScI

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    Hunting for dark matter

    We know that the Milky Way is rotating because when we look along it, we see some stars moving towards us and some stars moving away. But the speed at which our galaxy rotates is faster than it should be for the amount of matter we can see.

    This leads scientists to believe that there is matter located in the center of our galaxy that we cannot see. Despite all of the other stuff going on there, this makes the inner galaxy the perfect hunting ground for this “dark matter,” an invisible substance that makes up most of the matter in the universe.

    Scientists looking for dark matter take advantage of the fact that it likely interacts with itself. Researchers predict that when dark matter particles run into each other, they annihilate. They believe that this might produce a distinctive spectrum of gamma rays.

    Over the past few years, scientists have detected an excess of gamma rays from the Milky Way’s galactic center. Many scientists believe that this could be a very strong signal for dark matter. The events look the way they would expect dark matter to look, and the energy spectrum and the way the gamma rays are concentrated resemble what scientists would expect from dark matter.

    Other scientists believe that it is pulsars, not dark matter, that create this signal. Because the excess appears clumped, instead of smooth, scientists believe that it could be coming from compact sources like an ancient population of pulsars.

    To determine whether this excess is a dark matter signal, scientists are looking for similar signatures elsewhere in the universe, in places like dwarf galaxies. These small galaxies are cleaner places to look for dark matter with a lot less going on, but the trade-off is that they do not produce as much gamma radiation.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:40 pm on November 18, 2015 Permalink | Reply
    Tags: , , Milky Way,   

    From Science Node: “Chaos mixes the Milky Way” 

    Science Node bloc
    Science Node

    11.18.15
    Lance Farrell

    1
    Galaxies grow by absorbing other stellar masses, with trails of stars tracing the future and past orbits of satellite galaxies consumed. Understanding how these tidal streams evolve will help measure the Milky Way’s gravitational field and the shape of its dark matter halo.

    2
    Whereas the Milky Way was previously thought to have four arms, infrared images from NASA’s Spitzer Space Telescope have helped scientists discover that our galaxy’s spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars. Courtesy Robert Hurt; NASA.

    Our Milky Way has evolved to its present shape after billions of years. Dark matter makes up its unseen bulk, but it now seems that only by embracing chaos will we know its true size. To help correctly track the Milky Way’s dark matter halo, US National Science Foundation (NSF) -funded cosmologists employed supercomputers to model these irregular orbits.

    Think of our planet as a tiny blue fish splashing in a virtually boundless starry ocean. We travel with neighboring fish around a medium sized star, which in turn swims in one of the arms of a barred spiral galaxy we call the Milky Way. These spiral arms appear to be connected strands, but are really discontinuous star nurseries, whipped into line at a cruising speed of roughly 220 kilometers (136 miles) per second.

    With a diameter of around 100,000 to 180,000 light years, the Milky Way transports 200-400 billion stars and 100 billion planets. A large vessel indeed, this galaxy is just one of more than 100 billion galaxies in the universe. Galaxies are thought to grow through absorption — like cosmic leviathans, they consume smaller galaxies. Absorption takes billions of years, and the streams of stars left behind is the evidence marking the remainders of satellite galaxies ripped apart by the Milky Way’s cosmic hunger.

    3
    Three newly-discovered streams arcing high over the Milky Way galaxy are remnants of cannibalized galaxies and star clusters. Though only about 150 globular clusters orbit the Milky Way today, they may once have numbered in the thousands. Once crowded so closely together that they could sometimes actually collide, these stars are now separated by many light-years, trailing one another at half a million miles an hour. Courtesy NASA.

    “The Milky Way is eating many satellite galaxies that leave a sort of trail of breadcrumbs as they get gobbled up,” says Adrian Price-Whelan, NSF graduate research fellow at Columbia University. “The tidal forces from the mass in the Milky Way cause the smaller galaxies to unravel and create long, thin streams of stars called tidal streams. These trace out the future and past orbit of the satellite galaxies, and from a single snapshot in time, we can learn about the orbit of the smaller galaxy and therefore study the distribution of matter around the Milky Way.”

    According to our current understanding, the largest percentage of the cosmos remains unseen (dark), yet is indirectly observable by the effect it wields on visible matter. In similar fashion, we can deduce the mass of our sun from the effect seen on orbiting planets. The Lambda Cold Dark Matter (∆CDM) theory incorporates this understanding of dark matter and offers remarkably precise large-scale predictions of properties of the universe. One of the predictions is that galaxies live in halos of dark matter.

    These halos are thought to be triaxial, but this prediction awaits verification when the European Space Agency Gaia satellite completes its galactic survey.

    ESA Gaia satellite
    ESA/Gaia

    Gaia’s five-year mission ends in 2018, and by measuring the velocities of hundreds of millions of stars around the Milky Way, will give cosmologists a 3D look at the exact shape of our spiral home. But for all of Gaia’s promise, unless chaos theory is integrated into orbital calculations, scientists might not be able to trace the true shape of the dark matter halo surrounding our galaxy.

    4
    The Milky Way arch emerging from the Cerro Paranal, Chile, on the left, and sinking into the Antofagasta’s night lights. The Magellanic Clouds are visible on the left side, and a plane has left a visible trace on the right, along the Vista enclosure. Courtesy Bruno Gilli; ESO. Creative Commons Attribution 4.0.

    If some of the stars in these tidal streams were subject to chaotic orbits, their streams would ‘fan’ out more quickly, making them unrecognizable to Gaia as stellar streams. However, Price-Whelan notes, thus far we’ve only observed thin tidal streams in the Milky Way — so either the dark matter halo around the Milky Way doesn’t contain chaotic orbits, or the thin streams we observe are merely the remaining streams after chaotic ones ‘fanned’ out long ago.

    If this is the case, “there could be many more streams that formed on chaotic orbits that have now dispersed too much for us to detect them. This would also mean that the thin streams we see trace out the regular orbits around the galaxy, which would place limits on the possible configurations of dark matter around the Milky Way,” he says.

    Price-Whelan recently published research in the Monthly Notices of the Royal Astronomical Society, where his team simulated chaotic stellar streams under the ∆CDM. To study how many orbits are expected to be chaotic and where these orbits are, his team had to calculate tens of thousands of orbits for hundreds of thousands of time steps.

    To meet this challenge, Price-Whelan looked for a computer large enough to weather the numerical storm incurred by the tidal stream simulations. The problem lends itself to a parallel approach, so using NSF-funded Extreme Science and Engineering Discovery Environment (XSEDE) resources, researchers distributed the individual orbit integrations over many nodes. They jumped aboard Stampede, one of the XSEDE compute clusters, and Columbia University’s Hotfoot and Yeti compute clusters.

    Price-Whelan’s results indicate that tidal streams around the Milky Way exist only on regular orbits, not chaotic ones, and can thus provide a map to the regular regions of the Milky Way. This suggests a promising new direction using tidal streams to constrain the distribution of dark matter around our galaxy. Cosmologists can now look to the Gaia survey with a new sense of confidence: Understanding how tidal streams form in the Milky Way provides a measure of the galaxy’s gravitational field over vast distances.


    The clearest infrared panorama of our galactic home ever made, courtesy of NASA’s Spitzer Space Telescope. Navigate the panaroma with the Spitzer GLIMPSE360 web tool.
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