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  • richardmitnick 2:56 pm on December 18, 2018 Permalink | Reply
    Tags: , ESA Gaia, Gaia 17bpi, , The star belongs to a class of fitful stars known as FU Ori's, Young Star Caught in a Fit of Growth   

    From Caltech: “Young Star Caught in a Fit of Growth” 

    Caltech Logo

    From Caltech

    12/18/2018

    Whitney Clavin
    (626) 395-1856
    wclavin@caltech.edu

    1
    This illustration shows a young star undergoing a growth spurt. Top panel: Material from the dusty and gas-rich disk (orange) plus hot gas (blue) mildly flows onto the star, creating a hot spot. Middle panel: The outburst begins—the inner disk is heated, more material flows to the star, and the disk creeps inward. Lower panel: The outburst is in full throttle, with the inner disk merging into the star and gas flowing outward (green).

    2
    The location of Gaia 17bpi, which lies in the Sagitta constellation, is indicated in the center of this image taken by NASA’s Spitzer Space Telescope. Credit: NASA/JPL-Caltech/M. Kuhn (Caltech)

    New visible and infrared observations of young star reveal clues about how it bulks up.

    Researchers have discovered a young star in the midst of a rare growth spurt—a dramatic phase of stellar evolution when matter swirling around a star falls onto the star, bulking up its mass. The star belongs to a class of fitful stars known as FU Ori’s, named after the original member of the group, FU Orionis (the capital letters represent a naming scheme for variable stars, and Orionis refers to its location in the Orion constellation). Typically, these stars, which are less than a few million years old, are hidden behind thick clouds of dust and hard to observe. This new object is only the 25th member of this class found to date and one of only about a dozen caught in the act of an outburst.

    “These FU Ori events are extremely important in our current understanding of the process of star formation but have remained almost mythical because they have been so difficult to observe,” says Lynne Hillenbrand, professor of astronomy at Caltech and lead author of a new report on the findings appearing in The Astrophysical Journal. “This is actually the first time we’ve ever seen one of these events as it happens in both optical and infrared light, and these data have let us map the movement of material through the disk and onto the star.”

    The newfound star, called Gaia 17bpi, was first spotted by the European Space Agency’s Gaia satellite, which scans the sky continuously, making precise measurements of stars in visible light.

    ESA/GAIA satellite

    When Gaia spots a change in a star’s brightness, an alert goes out to the astronomy community. A graduate student at the University of Exeter and co-author of the new study, Sam Morrell, was the first to notice that the star had brightened. Other members of the team then followed up and discovered that the star’s brightening had been serendipitously captured in infrared light by NASA’s asteroid-hunting NEOWISE satellite at the same time that Gaia saw it, as well as one-and-a-half-years earlier.

    NASA Wise Telescope

    “While NEOWISE’s primary mission is detecting nearby solar system objects, it also images all of the background stars and galaxies as it sweeps around the sky every six months,” says co-author Roc Cutri, lead scientist for the NEOWISE Data Center at IPAC, an astronomy and data center at Caltech. “NEOWISE has been surveying in this way for five years now, so it is very effective for detecting changes in the brightness of objects.”

    NASA’s infrared-sensing Spitzer Space Telescope also happened to have witnessed the beginning of the star’s brightening phase twice back in 2014, giving the researchers a bonanza of infrared data.

    NASA/Spitzer Infrared Telescope

    The new findings shine light on some of the longstanding mysteries surrounding the evolution of young stars. One unanswered question is: How does a star acquire all of its mass? Stars form from collapsing balls of gas and dust. With time, a disk of material forms around the star, and the star continues to siphon material from this disk. But, according to previous observations, stars do not pull material onto themselves fast enough to reach their final masses.

    Theorists believe that FU Ori events—in which mass is dumped from the disk onto the star over a total period of about 100 years—may help solve the riddle. The scientists think that all stars undergo around 10 to 20 or so of these FU Ori events in their lifetimes but, because this stellar phase is often hidden behind dust, the data are limited. “Somebody sketched this scenario on the back of an envelope in the 1980s, and, after all this time, we still haven’t done much better at determining the event rates,” says Hillenbrand.

    The new study shows, with the most detail yet, how material moves from the midrange of a disk, in a region located around 1 astronomical unit from the star, to the star itself. (An astronomical unit is the distance between Earth and the sun.) NEOWISE and Spitzer were the first to pick up signs of the buildup of material in the middle of the disk. As the material started to accumulate in the disk, it warmed up, giving off infrared light. Then, as this material fell onto the star, it heated up even more, giving off visible light, which is what Gaia detected.

    “The material in the middle of the disk builds up in density and becomes unstable,” says Hillenbrand. “Then it drains onto the star, manifesting as an outburst.”

    The researchers used the W. M. Keck Observatory and Caltech’s Palomar Observatory to help confirm the FU Ori nature of the newfound star. Says Hillenbrand, “You can think of Gaia as discovering the initial crime scene, while Keck and Palomar pointed us to the smoking gun.”


    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft), above sea level,


    Caltech Palomar Observatory, located in San Diego County, California, US, at 1,712 m (5,617 ft)

    The study is titled, “Gaia 17bpi: An FU Ori Type Outburst.” Other authors include: Carlos Contreras Peña and Tim Naylor of the University of Exeter; Michael Kuhn and Luisa Rebull of Caltech; Simon Hodgkin of Cambridge University; Dirk Froebrich of the University of Kent; and Amy Mainzer of JPL.

    See the full article here .


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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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  • richardmitnick 1:04 pm on November 3, 2018 Permalink | Reply
    Tags: , , , , ESA Gaia, , , Unbound and Out: Boosted by Black Holes Stars Speed Off Leaving Clues Behind   

    From Discover Magazine: “Unbound and Out: Boosted by Black Holes, Stars Speed Off, Leaving Clues Behind” 

    DiscoverMag

    From Discover Magazine

    November 2, 2018
    Stephen Ornes

    1
    Astronomers say the galactic center is home to a black hole (illustration shown) with as much mass as 4 million suns. Its entourage likely includes clusters of stars — many of them orbiting each other in two- or three-star systems — as well as smaller black holes. (Credit: NASA/Dana Berry/SkyWorks Digital)

    In April, the European Space Agency released the second massive trove of data from Gaia, a spinning, scanning satellite that for nearly five years has been spying on a billion stars.

    ESA GAIA Release 2 map

    ESA/GAIA satellite

    Its goal is to produce a three-dimensional stellar map, enabling a new age of precision astronomy. Like other stargazers, Warren Brown of the Harvard-Smithsonian Center for Astrophysics has plunged headfirst into Gaia’s data. He’s hoping to find space oddities.

    He has found some notable ones before. In 2005, Brown identified a young star speeding at 850 kilometers per second through the Milky Way’s lonely hinterland, called the halo.

    MIlky Way Halo NASA ESA STScI

    The star is traveling so fast that it’s unbound, which means that eventually, it will escape the galaxy. Brown coined the term “hypervelocity star” to refer to this breed of superfast stellar travelers.

    Brown suspects that the star was flung by the enormous black hole that lies at the center of the Milky Way, SGR A*.

    Sgr A* from ESO VLT


    SgrA* NASA/Chandra


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

    The black hole, about 4 million times the mass of the sun, is so powerful that astronomers classify it as supermassive. Black holes are usually thought of as pulling things toward themselves, but they can also act like cosmic slingshots, Brown says. And their ammo can be as big as stars. Once shot, tossed stars may get a one-way ticket out of the galaxy’s grasp.

    Since that initial discovery, surveys by Brown and by other astronomers have identified more than 20 unbound, hypervelocity stars of various origins zipping around, including one traveling away from our galaxy that was probably ejected from the Large Magellanic Cloud, a dwarf galaxy companion of the Milky Way [MNRAS].

    Large Magellanic Cloud. Adrian Pingstone December 2003

    Discussing these discoveries and their implications in the 2015 Annual Review of Astronomy and Astrophysics, Brown explains that, beyond their own interesting origin tales, such exotic stars may also be useful as tools.

    Knowable Magazine spoke with Brown about what it takes to escape the galaxy, what Gaia tells us about space oddities and how stellar travelers can help reveal clues about one of the most fundamental mysteries in astronomy — the invisible dark matter that holds the Milky Way together but remains impossible to detect directly.

    Milky Way Dark Matter Halo Credit ESO L. Calçada

    This conversation has been edited for clarity and length.

    Where do hypervelocity stars come from?

    The fastest ones we’ve found all seem to point back to the galactic center. The measurements aren’t definitive, but with Gaia’s data, I found that the fastest stars are best explained by galactic center ejection. However, I also found that half [of known high-speed stars] did not come from the galactic center. I think that’s cool. There’s a mix of things going on in the Milky Way.

    How do you think a star would get ejected from the center of the galaxy?

    You have to have at least three things, and one of them has to be a supermassive black hole. If you have a supermassive black hole, then you have a lot of energy, and there are a lot of stars around it that interact.

    Then if you have a binary — two stars orbiting each other — approaching a black hole, the gravitational tidal field is so extreme it can pull the pair of stars apart. The capture or ejection depends on the direction of each star’s motion relative to the black hole. Physicists call this a three-body exchange: One star exchanges partners — it gets captured and loses energy. The other escapes, and gains all that energy and just shoots out. That’s the slingshot.

    It’s a conservation of energy problem.

    3
    In 1988, theorist Jack G. Hills at Los Alamos National Laboratory predicted that stars could be ejected from the Milky Way after an interaction with the black hole at the galactic center. Here’s how it works: A binary star system — two stars spinning around each other – approach a black hole. The closer star gets captured, and its energy is transferred to its former companion, which travels outward so fast that it can escape the gravitational pull of the galaxy. (Credit: Adapted from W.R. Brown/AR Astronomy & Astrophysics 2015/Knowable Magazine)

    How do you find a hypervelocity star?

    The single answer is speed. They’re not orbiting with everything else in the Milky Way. They’re unbound, and they’re never coming back. That’s what makes them different. There are 100 billion stars that look like every other star, that you don’t care about. It’s very much a needle in a haystack.

    When we designed our [2008] survey, which I think is fair to say is the only successful survey of unbound stars in the galaxy, we were looking for young stars — blue stars, hot stars — at very large distances from the center, where they shouldn’t exist, unless they were ejected. And that approach worked, because there are very few young stars out in the outer parts of the Milky Way.

    Are you using Gaia to study the hypervelocity stars you already knew about, or are you looking for new discoveries?

    Both. A paper we just had accepted was on the 20-some odd, unbound stars found previous to Gaia. We’re also looking at outliers in the Gaia catalog that might be hypervelocity stars. It’s one of these things where we find candidates, but we need follow-up observations to decide.

    How does Gaia look at stars?

    It’s hard to identify a star other than by its motion. Gaia is trying to measure the tangential motion of the star on the plane of the sky. That’s hard. It’s the product of distance times the angular change over time. In astronomy, you don’t observe distance, you can infer it. And it’s a very small angular change — the angular motion is milliarcseconds in one year, or something. It’s a very tiny angle on the sky that’s changing.

    You’ve used Gaia’s data to study halo stars and runaway stars, too. Why are these other space oddities interesting?

    Runaway stars were discovered [more than] 50 years ago. They’re interesting because they’re very young, massive stars like the hypervelocity stars we’ve found, but they’re ejected from the disk of the Milky Way — instead of from the center — through binary ejections. Its companion explodes. Well, its former companion explodes, releasing energy. If the star’s direction lines up with the rotation of the galaxy, it suddenly has a speed that can exceed the escape velocity. Those are rare — the ones with those speeds — but they can mimic hypervelocity stars. That’s pretty cool.

    Halo stars are normal stars orbiting in the outer parts of the Milky Way. There aren’t a lot of stars way out there. The halo is believed to contain about 1 percent of the Milky Way’s stars, or about 1 billion stars. Halo stars were discovered by Oort and others from the unusual motions of a few stars near the Sun. They orbit in their own way and can appear to have a very different velocity with respect to us. When you’re looking for velocity outsiders, things like halo stars show up. The GAIA Data Release 2 catalog is estimated to have 70 million to 80 million halo stars in its catalog.

    Why do you want better measures on unbound stars?

    Good measures on the trajectory of hypervelocity stars tell you about how these things were ejected. Was it a single black hole or a binary black hole? It’s fun to think about. The really interesting work is not just in studying the stars themselves but learning what you can do with them and how to use them as tools.

    How can a star be useful?

    Hypervelocity stars are the ultimate test particle for the gravitational potential of the Milky Way, which is the pull of all the Milky Way’s matter: its stars, gas and dark matter [the invisible matter thought to hold galaxies together]. The gravitational pull varies with position [in the galaxy] because all the matter is distributed across hundreds of thousands of light years of space.

    How can hypervelocity stars map the gravitational potential?

    If we’re right about where the stars come from, then their arc out of the galaxy tells you the potential of the Milky Way.

    We look at the stars at different moments in time. We look at where the star is today, the specific direction its path is following. We can ask: How much does that differ from a straight line to the center? If you know exactly where the star comes from, then any deviation in the measurement of its position tells you how everything else is affecting its path.

    4
    In September, after searching Gaia’s data for hypervelocity stars — like the ones predicted by Jack Hills and first discovered by Warren Brown — astronomers not only found stars headed out of the galaxy (shown in red) but also, to their surprise, fast stars traveling toward the galactic center (yellow). These inbound travelers may have been ejected from other galaxies, and are now passing through the Milky Way. (Credit: ESA; Marchetti et al. 2018; NASA/ESA Hubble)

    Imagine the simple case that the galaxy was a perfectly spherical ball. These hypervelocity stars launch in the center and follow a straight line out, but they get pulled down by the pull of the galaxy. The stars in the galactic disk will pull on the star and decelerate it.

    How is dark matter distributed in the galaxy?

    No one knows, but theoretical simulations predict that the dark matter is not spherical, but distributed with a different length in every direction, like an American football. It’s mostly in the exterior of the galaxy, farther out from the sun.

    No one can see the distribution of dark matter directly, but it seems different than that of ordinary matter. Hypervelocity stars can test this, if you can measure their trajectories well enough. These stars are going off in different directions, and in principle each star is a completely independent tracer.

    Gaia is still in the midst of its mission. What do you want to see in five years, after the final data release, and in future missions?

    Its measurements get better with time, and every star gets measured 70, 80, 100 times. What we have currently is a lot of very good evidence that, taken together, says you have to have stars ejected by a black hole to explain the observations. Presumably, at the end, we’ll have three times better measurements, which means we’ll have three times smaller error bars. Some of the candidates will probably go away, but the end-of-mission Gaia measurements should definitively tell us that these hypervelocity stars are ejected by our galactic center black hole. If they do come from the galactic center, then they can tell us what stars in that region are like. Ironically, hypervelocity stars are easier for us to see than stars that are still in the center of the galaxy, because there’s so much dust and stars in between.

    Gaia is not the final piece of evidence, though. We’ll still need spectroscopy to determine the nature of each star. Is it a white dwarf? A main sequence star? An old evolved star?

    How else can Gaia’s data help you study hypervelocity stars?

    Presumably, we’ll also see stars that we didn’t know about.

    See the full article here .

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  • richardmitnick 6:18 pm on October 2, 2018 Permalink | Reply
    Tags: , , , , ESA Gaia, Gaia detects stars traveling between galaxies   

    From ESA via Manu Garcia at IAC: “Gaia detects stars traveling between galaxies” 


    Manu Garcia, a friend from IAC.

    The universe around us.
    Astronomy, everything you wanted to know about our local universe and never dared to ask.

    ESA Space For Europe Banner

    From European Space Agency

    2.10.18

    Maria Elena Rossi
    Leiden Observatory, Leiden University
    Leiden, The Netherlands
    Tel: +31 6 8112 1440
    Email: emr@strw.leidenuniv.nl

    Tommaso Marchetti
    Leiden Observatory, Leiden University
    Leiden, The Netherlands
    Tel: +31 6 4776 9205
    Email: marchetti@strw.leidenuniv.nl

    Anthony Brown
    Leiden Observatory, Leiden University
    Leiden, The Netherlands
    Email: brown@strw.leidenuniv.nl

    Timo Prusti
    Gaia Project Scientist
    European Space Agency
    Email: timo.prusti@esa.int

    Markus Bauer
    ESA Science Communication Officer
    Tel: +31 71 565 6799
    Mob: +31 61 594 3 954
    Email: markus.bauer@esa.int

    1
    Fast stars in the Milky Way. The positions and orbits of 20 stars reconstructed high – speed represented at the top of an artistic view of our galaxy, the Milky Way. These stars were identified using data from the second launch of the ESA Gaia mission. The seven stars displayed in red are away from the galaxy and could travel fast enough to eventually escape their gravity. Surprisingly, the study also revealed thirteen stars, shown in orange, running toward the Milky Way could be stars in another galaxy that are close to ours. Copyright ESA (printing and composition of the artist); Marchetti et al 2018 (star positions and trajectories); NASA / ESA / Hubble (background galaxies),CC BY-SA 3.0 IGO.

    ESA/GAIA satellite


    The ESA ‘s Gaia. The ESA ‘s Gaia is a space telescope designed to measure the positions of thousands of millions of stars with a precision without precedents. Gaia was launched on December 19, 2013 and is on the point L2 Lagrange, the same location as will the next space telescope, the James Webb NASA / ESA / CSA James Webb. Credit: ESA / Medialab ATG.

    NASA/ESA Hubble Telescope

    While searching hypervelocity stars escaping the Milky Way with the latest set of data from the Gaia mission for ESA , a team of astronomers discovered by surprise how a series of stars traveling into our galaxy, perhaps from a different galaxy .

    In April, ESA’s astrometric published a catalog unprecedented over a billion stars. Astronomers from around the world have been working tirelessly in recent months with this extraordinary set of data, searching the properties and motions of the stars in our galaxy and beyond with unprecedented accuracy, which has resulted in a multitude of new and interesting studies.

    The Milky Way contains more than a hundred billion stars. Most are located on a disk with a thick, bulky center, in the middle of which there is a supermassive black hole. The rest spans a much larger spherical halo.

    The stars circulate around the Milky Way at hundreds of kilometers per second, and its movements contain vast amounts of information about the past of the galaxy. The fastest stars are so-called “hypervelocity stars”. It is believed to be born near the galactic center, which escape into the limits of the Milky Way by its interaction with the black hole.

    So far only it has been discovered a small number of hypervelocity stars, so the second data catalog Gaia offers a unique opportunity to find more stars of this type.

    2
    Gaia sky color. Credit: ESA / Gaia / DPAC

    Nothing published the new data set, several groups of astronomers penetrated into him for hypervelocity stars. Including three scientists from the University of Leiden (Netherlands), which catalog a big surprise in store.

    Gaia has measured the positions, parallaxes (indicating its distance) and two-dimensional movement in the plane of the sky of 1300 million stars. And for a subset of seven million of the brightest stars, it has also measured how fast away from us.

    “Among those seven million stars in Gaia with full speed three-dimensional measurements, we find twenty traveling fast enough to finish escaping the Milky Way,” explains Maria Elena Rossi, author of the new study.

    Elena and her colleagues, who last year had already discovered several hypervelocity stars in an exploratory study based on the first data catalog of Gaia, were pleasantly surprised as they expected to find as much a star that escaped from the Galaxy between Seven million. But there’s more.

    “Instead of moving away from the galactic center, most detected hypervelocity stars seem to approach him,” adds Tommaso Marchetti, co-author of the study.
    “It could be stars in another galaxy, who are going through the Milky Way.”

    4
    The Large Magellanic Cloud (LMC) , one of the closest galaxies to our Milky Way, seen by ESA ‘s Gaia, which uses information from thesecond release of data from the mission. This view is not a photograph, butthat has been compiled by mapping the total amount of radiation detected by Gaia in each pixel, combined with radiation measurements taken through different
    filters on the spacecraft to generate color information. The image is dominated by the brightest and most massive stars, greatly eclipsing its weaker and less massive counterparts. In this view, the LMC bar is outlined in great detail, along with individual regions of star formation as the giant 30 Doradus, visible just above the center of the galaxy.
    Recognition: Gaia Data Processing and Analysis Consortium (DPAC);
    A. Moitinho / AF Silva / M. Barros / C. Barata, University of Lisbon, Portugal;
    H. Savietto, Research Fork, Portugal.
    Copyright: ESA / Gaia / DPAC.

    It is possible that these intergalactic interlopers originate in the Large Magellanic Cloud, a relatively small galaxy that orbits the Milky Way, although they could also come from an even more distant galaxy. If that is the case, they carry the imprint of their place of origin, and their study at distances much closer than your galaxy parent can provide unique information about the nature of stars in other galaxies, similar to what happens when studying Martian material brought to our planet by meteorites.

    “The stars can be accelerated to high speeds when interacting with a supermassive black hole” said Elena.

    “Thus, the presence of these stars could be a sign of such black holes in nearby galaxies. But the stars also could have been part of a binary system, and have been thrown into the Milky Way when its companion exploded as a supernova. In any case, study allow us to know more about these processes in neighboring galaxies. ”

    Another explanation is that the newly identified stars could be native to the halo of our Galaxy, and have accelerated and moved inwardly by interaction with one of the dwarfs that fell into the Milky Way during its formation. Having additional information about the age and composition of the stars could help astronomers to clarify its origin.

    “A star halo of the Milky Way probably quite old and is made up mostly of hydrogen, while the stars of other galaxies might contain large amounts of heavier elements,” says Tommaso.

    “Observe the colors of the stars gives us more information about their composition”.

    New data will help clarify the nature and origin of these stars, and the team used ground-based telescopes to learn more about them. Meanwhile, Gaia will continue to monitor the entire sky, including stars analyzed in this study.

    In addition to investigating the nature of these stellar interlopers possible, the team is also delving into the dataset of the second release of Gaia in search of hypervelocity stars, but their hopes are also placed in the future. There are at least two other data repositories of Gaia planned for the 2020s and each of them will provide new more accurate over a larger set of data and information stars.

    “In the future we hope to have complete measurements of three-dimensional speed of up to one hundred fifty million stars,” forward Anthony Brown, co-author of the study and chairman of the executive committee of the Consortium for Data Processing and Analysis of Gaia (DPACE).

    “This will help locate hundreds or thousands of hypervelocity stars, much better understanding their origin and use them to investigate the environment of the galactic center and the history of our galaxy,” he adds.

    “This fantastic discovery shows that Gaia is an entire machine that paves the way for new and unexpected discoveries about our galaxy,” says Timo Prusti, Gaia project scientist at ESA.

    Science paper:
    Gaia DR2 in 6D: Searching for the fastest stars in the Galaxy
    MNRAS

    See the full article in Englsh here .


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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 8:26 am on August 30, 2018 Permalink | Reply
    Tags: , , , , Dyson spheres, Dyson spheres are hypothetical megastructures built by extraterrestrials for the purpose of harvesting all of a star’s energy, ESA Gaia, , , The star TYC 6111-1162-1   

    From ESA GAIA Mission via EarthSky: “How Gaia could help find Dyson spheres” 

    ESA/GAIA satellite

    From ESA GAIA Mission

    via

    EarthSky

    August 30, 2018
    Paul Scott Anderson

    Dyson spheres are hypothetical megastructures built by extraterrestrials for the purpose of harvesting all of a star’s energy. Here’s how the European Space Agency’s Gaia mission might help find one.

    1
    Artists’ concept of a Dyson sphere. Notice the little moon or planet on the left side, being ravaged for raw materials. This image – called Shield World Construction – is by Adam Burn. Via http://www.FantasyWallpapers.com.

    When contemplating extraterrestrial intelligence, one of the most tantalizing ideas is that a super-advanced alien civilization could build an enormous structure around its home star, to collect a significant portion of the star’s energy. This hypothetical megastructure is popularly known as a Dyson sphere. It’s a sci-fi-sounding concept, but some scientists have also seriously considered it. This week, a story emerged about how the European Space Agency’s Gaia mission – whose primary purpose is to create a 3D map of our Milky Way galaxy – might be instrumental in the search for Dyson spheres.

    In the past, searches for Dyson spheres have focused on looking for signs of excess infrared or heat radiation in the vicinity of a star. That would be a telltale signature, but those attempts have come up empty, so far. The new peer-reviewed study – which was published in The Astrophysical Journal on July 18, 2018, and later described in Astrobites – proposes looking for Dyson spheres with little or no infrared excess. In other words, it describes a technique not attempted before.

    Erik Zackrisson at Uppsala University in Sweden led the new study. It focuses on a type of Dyson sphere that would’ve been missed by prior searches focused on infrared radiation.

    Suppose you were looking toward a Dyson sphere. What would you see? The visible light of the star would be reduced significantly since the Dyson sphere itself – by its nature – would mostly surround the star for purposes of energy collection. The star would continue shining; it would be shining on the inner portion of the Dyson sphere. Presumably, the star’s radiation would heat the sphere. According to earlier thoughts by scientists on the subject, a Dyson sphere should have a temperature between 50 and 1,000 Kelvin (-370 to 1300 degrees Fahrenheit; -220 to 730 degrees Celsius). At that temperature, radiation from the sphere would peak in infrared wavelengths.

    That was the earlier idea, until Zackrisson’s study.

    2
    An all-sky view of the Milky Way and neighboring galaxies from the Gaia mission. This view includes measurements of nearly 1.7 billion stars. Image via Gaia Data Processing and Analysis Consortium (DPAC)/A. Moitinho/A. F. Silva/M. Barros/C. Barata – University of Lisbon, Portugal/H. Savietto – Fork Research, Portugal.

    His study suggests the possibility that the sphere might be composed of a different kind of material than what had been previously supposed. Suppose this material had the ability to dim the star’s light equally at all wavelengths? That would make it a so-called gray absorber and would significantly affect methods used to search for Dyson spheres. If you measured the star’s distance spectrophotometrically – by comparing the star’s observed flux and spectrum to standard stellar emission models – then the measurements would suggest that the star is farther away than it actually is.

    But then if you measured the star’s distance using the parallax method, you’d get a different number.

    Parallax method ESA

    The parallax method compares the apparent movement of a nearby star against the stellar background, as Earth moves from one side of its orbit to another across a period of, say, six months.

    The size of a Dyson sphere could be determined by comparing the difference in distances between these two methods. The greater the difference, the greater the amount of the star’s surface that is being obscured by the sphere.

    Now, thanks to new data from the Gaia mission, astronomers can do these kinds of comparisons, which could – in theory – detect a Dyson sphere. From the new study:

    “A star enshrouded in a Dyson sphere with a high covering fraction may manifest itself as an optically subluminous object with a spectrophotometric distance estimate significantly in excess of its parallax distance. Using this criterion, the Gaia mission will in coming years allow for Dyson sphere searches that are complementary to searches based on waste-heat signatures at infrared wavelengths. A limited search of this type is also possible at the current time, by combining Gaia parallax distances with spectrophotometric distances from ground-based surveys. Here, we discuss the merits and shortcomings of this technique and carry out a limited search for Dyson sphere candidates in the sample of stars common to Gaia Data Release 1 and Radial Velocity Experiment (RAVE) Data Release 5. We find that a small fraction of stars indeed display distance discrepancies of the type expected for nearly complete Dyson spheres.”

    In other words, using this new method, astronomers have found candidate Dyson sphere stars.

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    Graph showing distribution of covering fractions for all stars in the Gaia-RAVE database overlap (left) and just those stars with less than 10 percent error in their Gaia parallax distance and less than 20 percent error in their RAVE spectrophotometric distance (right). If the parallax distance is smaller than the spectrophotometric distance, that is interpreted this as a negative covering fraction, and could be an indication of a Dyson sphere surrounding that star. Image via Zackrisson et al. 2018.

    The Gaia mission is currently charting a three-dimensional map of our galaxy, providing unprecedented positional and radial velocity measurements with the highest accuracy ever. The goal is to produce a stereoscopic and kinematic census of about one billion stars in the Milky Way galaxy and throughout the Local Group of galaxies.

    As it happens, these data are very useful when searching for Dyson spheres.

    Using the parallax distances from the first data release of Gaia, Zackrisson and his colleagues compared that data to previously measured spectrophotometric distances from the Radial Velocity Experiment (RAVE), which takes spectra of stars in the Milky Way. This resulted in an estimate of what percentage of each star could be blocked by Dyson sphere material.

    Radial Velociity Method. ESO


    Radial velocity Image via SuperWasp http:// http://www.superwasp.org/exoplanets.htm


    Radial Velocity Method-Las Cumbres Observatory

    4
    Illustration of how Gaia is measuring the distances to most stars in the Milky Way with unprecedented accuracy. Image via S. Brunier/ESO; Graphic source: ESA.

    Of course, figuring out if any of these could actually be Dyson sphere candidates required further analysis. Zackrisson and his team decided to focus on main-sequence stars (like the sun), spectral types F, G and K, and narrowed those down to those which displayed a potential blocking fraction greater than 0.7. Larger giant stars were removed from the data set since their spectrophotometric distances tend to be overestimated compared to main-sequence stars.

    This alone left only six possible candidates. Those in turn were then narrowed down to only two, after eliminating four candidates due to problems with the data itself. One of those, the star TYC 6111-1162-1, was then considered to be the best remaining candidate.

    So … has the first Dyson Sphere been found? The simple answer is we don’t know yet. The star, a garden-variety late-F dwarf, seems to exhibit the sought-after characteristics, but more data is needed. No other glitch-related weirdness was found in the data, but the star was also found to be a binary system consisting of two stars (the other being a small white dwarf) which might explain the results – but none of that is certain yet. Additional study of the star will be required, including using future Gaia data releases, to determine what is really happening here. From the new study:

    “To shed light on the properties of objects in this outlier population, we present follow-up high-resolution spectroscopy for one of these stars, the late F-type dwarf TYC 6111-1162-1. The spectrophotometric distance of this object is about twice that derived from its Gaia parallax, and there is no detectable infrared excess. While our analysis largely confirms the stellar parameters and the spectrophotometric distance inferred by RAVE, a plausible explanation for the discrepant distance estimates of this object is that the astrometric solution has been compromised by an unseen binary companion, possibly a rather massive white dwarf. This scenario can be further tested through upcoming Gaia data releases.”

    5

    See the full article here .


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    Objective
    A global space astrometry mission, Gaia will make the largest, most precise three-dimensional map of our Galaxy by surveying more than a thousand million stars.

    Mission
    Gaia will monitor each of its target stars about 70 times over a five-year period. It will precisely chart their positions, distances, movements, and changes in brightness. It is expected to discover hundreds of thousands of new celestial objects, such as extra-solar planets and brown dwarfs, and observe hundreds of thousands of asteroids within our own Solar System. The mission will also study about 500 000 distant quasars and will provide stringent new tests of Albert Einstein’s General Theory of Relativity.

    Gaia will create an extraordinarily precise three-dimensional map of more than a thousand million stars throughout our Galaxy and beyond, mapping their motions, luminosity, temperature and composition. This huge stellar census will provide the data needed to tackle an enormous range of important problems related to the origin, structure and evolutionary history of our Galaxy.

    For example, Gaia will identify which stars are relics from smaller galaxies long ago ‘swallowed’ by the Milky Way. By watching for the large-scale motion of stars in our Galaxy, it will also probe the distribution of dark matter, the invisible substance thought to hold our Galaxy together.

    Gaia will achieve its goals by repeatedly measuring the positions of all objects down to magnitude 20 (about 400 000 times fainter than can be seen with the naked eye).

    For all objects brighter than magnitude 15 (4000 times fainter than the naked eye limit), Gaia will measure their positions to an accuracy of 24 microarcseconds. This is comparable to measuring the diameter of a human hair at a distance of 1000 km.

    It will allow the nearest stars to have their distances measured to the extraordinary accuracy of 0.001%. Even stars near the Galactic centre, some 30 000 light-years away, will have their distances measured to within an accuracy of 20%.

    The vast catalogue of celestial objects expected from Gaia’s scientific haul will not only benefit studies of our own Solar System and Galaxy, but also the fundamental physics that underpins our entire Universe.

     
  • richardmitnick 11:11 am on June 26, 2018 Permalink | Reply
    Tags: , , , , , ESA Gaia   

    From astrobites: ” Clearing Up Stellar Streams with Gaia” 

    Astrobites bloc

    From astrobites

    26 June 2018
    Nora Shipp

    Title: Off the beaten path: Gaia reveals GD-1 stars outside of the main stream
    Author: Adrian M. Price-Whelan, Ana Bonaca
    First Author’s Institution: Princeton University

    Status: Submitted to ApJL

    1
    Figure 1: An illustration of the Gaia space telescope measuring positions and velocities of stars in the Milky Way. [ESA]

    The Gaia space telescope is revolutionizing our understanding of the Milky Way. This European satellite (Figure 1) is carefully tracking the positions of over a billion stars over five years, providing us with an evolving map of stellar locations and velocities. Just a couple months ago the second Gaia data catalog was released, including brand new information about the motions of many times more stars than in previous datasets to accuracies never before achieved, launching a scramble to see what exciting surprises this new data would reveal about our galaxy. (For more examples of exciting Gaia science see these Astrobites.)

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 9:51 am on May 27, 2018 Permalink | Reply
    Tags: , , , , ESA Gaia, ,   

    From ESOblog: “Astronomer Henri Boffin on ESO’s collaboration in the Gaia mission” 

    ESO 50 Large

    From ESOblog

    25 May 2018

    1
    From ESA/GAIA

    ESA/GAIA satellite

    Mapping the sky has been one of humanity’s quests since the dawn of time, and ESA’s Gaia satellite is taking our understanding of our stellar neighbourhood to a whole new level. But it can’t do this alone. ESA has a close collaboration with ESO to use our ground-based expertise to help Gaia excel up in space. We talked to ESO astronomer Henri Boffin to find out more.

    Q: Firstly, could you explain what Gaia is and what kind of data it collects?

    A: Gaia is an astrometric mission from the European Space Agency that has been in the making for decades. It was launched at the end of 2013 and since then it has been using its two telescopes to very precisely measure the position, motion and brightness of more than a billion stars in our galaxy, the Milky Way. At the end of the mission, it will provide us with the most precise 3D map of our galaxy ever made.

    Q: In 2016, ESA released the first data set from Gaia. In April this year, the second data set was released — how does it differ?

    A: In Gaia data release 1, only the positions of most of the objects that Gaia could detect were provided. In data release 2, however, things start to become much more interesting, as Gaia is now providing estimates of the distance, the motion and the brightness for a large subset of stars. The dataset has information on the position and brightness of 1.7 billion stars, the parallax and motion of 1.3 billion stars, the surface temperature of over 100 million stars and the effect of interstellar dust on 87 million stars. Gaia has even given us some information about other objects like asteroids within our Solar System, far-off quasars, globular clusters within our own galaxy and dwarf galaxies orbiting it.


    A virtual journey from our Solar System through our Milky Way, based on data from the first (left) and second (right) release of ESA’s Gaia satellite. The journey starts by looking back at the Sun, moving away and travelling between the stars.
    Credit: ESA/Gaia/DPAC

    Q: Why is this extra information so important to astronomers?

    A: Knowing the distance to a star is a crucial piece of information — without a star’s distance, it is hard to do any astronomy. In fact, one could say that astronomy has always been about tackling the challenges of measuring astronomical distances! If you only see the brightness of a star but don’t know how far away it is, it’s hard to understand what kind of object it is. It’s like when you see a light at night time. It could be someone walking with a small flashlight a few metres away or it could be a lighthouse located tens of kilometres away!

    Once you know the distance to a star, it is possible to know if it is intrinsically bright or faint. You can also determine other properties such as the star’s mass, whether it is still in its infancy or if it will soon explode as a supernova. Distances are also needed to know the size of the Universe, whether it is expanding, and by how much.

    Q: What role does ESO play in the Gaia mission?

    A: ESO has been involved in the Gaia mission in several ways. The first one is the Ground-Based Optical Tracking programme, or GBOT. This involves tracking the position of the Gaia satellite using the 2.4-metre VLT Survey Telescope (VST) at ESO’s Paranal Observatory in Chile.

    The second major involvement of ESO telescopes is in the Gaia–ESO public spectroscopic survey.

    Moreover, ESO astronomers are interested in using Gaia data not only for their science, but also for operations. For example, it’s planned that the Gaia catalogue will be used as the basis of guide stars for ESO’s Very Large Telescope and Extremely Large Telescope. These telescopes need to use guide stars to precisely track the movement of the sky and keep their desired targets fixed in their field of view.

    Finally, ESO is also co-organising a scientific workshop in September 2018 that will focus on the advances in our understanding of stellar physical processes, made possible by combining the astrometry and photometry of Gaia with data from other large photometric, spectroscopic, and asteroseismic stellar surveys.

    Q: Could you explain further about the Ground-Based Optical Tracking programme?

    A: Gaia is the most accurate astrometric device ever built, but in order for its observations to be useful astronomers analysing the data need to know exactly where it is in the Universe. Its position needs to be known to an accuracy of 150 metres (a challenge given that it is 1.5 million kilometres away) and the velocity needs to be measured with an accuracy of 0.009 km/h!

    The only way to know the velocity and position of the spacecraft with very high precision is to observe it on a daily basis from the ground. But the usual ESA tracking stations are not sufficient for this, so the consortium turned to the VST to track the satellite. So, since the launch of Gaia at the end of 2013, the VST has been taking images of Gaia every other night.

    3
    These images from ESO’s VST show ESA’s Gaia spacecraft in its position some 1.5 million kilometres beyond Earth’s orbit. The VST captured these images using OmegaCAM on 23 January 2014, taken about 6.5 minutes apart. Gaia is clearly visible as a small spot moving against a background of stars. Its location is circled in red. In these images, the spacecraft is about a million times fainter than is detectable by the naked eye.
    Credit: ESO

    ESO OmegaCAM on VST at ESO’s Cerro Paranal observatory,with an elevation of 2,635 metres (8,645 ft) above sea level


    ESO OmegaCAM on VST at ESO’s Cerro Paranal observatory,with an elevation of 2,635 metres (8,645 ft) above sea level

    Q: Why is the VST used instead of other ESA tracking stations?

    A: The ESA tracking stations are radars that rely on measuring the radial velocity of the satellites. They are extremely precise, but only for the motion towards us. In order to obtain the real position of an object in space, one would need to combine observations of two such tracking stations. This is, however, very time consuming — and these tracking stations are required for all the other satellites of ESA as well. So it’s not possible to monopolise them for Gaia.

    The consortium of astronomers in charge of analysing the Gaia data came up with another solution — using a 2-metre class telescope to track the satellite. They mostly use the VST for this, as well as the Liverpool Telescope located on the Canary island of La Palma, Spain.

    2-metre Liverpool Telescope at La Palma in the Canary Islands, Altitude 2,363 m (7,753 ft)

    The VST is particularly suited for this task because it can take images of a very large area of the sky. In fact, as an aside, because of this capability, the VST takes images of dozens of asteroids every time it captures the Gaia satellite! In three years, it has discovered almost 9000 asteroids.

    Q: Tell us more about the Gaia–ESO public spectroscopic survey. What value does it add to the Gaia data?

    A: The Gaia–ESO public spectroscopic survey obtained high-quality spectroscopy of about 100 000 stars in the Milky Way with the FLAMES instrument on the VLT.

    ESO/FLAMES on The VLT. FLAMES is the multi-object, intermediate and high resolution spectrograph of the VLT. Mounted at UT2, FLAMES can access targets over a field of view 25 arcmin in diameter. FLAMES feeds two different spectrograph covering the whole visual spectral range:GIRAFFE and UVES.

    The survey spanned six years and used more than 300 nights of telescope time. These spectra allow astronomers to determine the chemical composition and the radial velocities of the stars. Although Gaia is able to take spectra, it can only do so for the brightest stars and in a very limited spectral range. So there was a need to obtain more precise data for fainter stars, in order to systematically cover all major components of the Milky Way, from the halo to clusters of stars to star-forming regions. When combined with the distances measured by Gaia, the survey will quantify the formation history and evolution of young, mature and ancient galactic populations, providing unprecedented knowledge of the evolution of our galaxy and its stars. This creates a legacy dataset that adds enormous value to the Gaia mission.

    Q: What will the future role of ESO be in relation to the Gaia mission?

    A: ESO will of course continue to track the Gaia satellite for several years, but ESO telescopes will be needed for following up many of the targets that Gaia has found to be particularly interesting (and there will be many!). Gaia should lead to the discovery of thousands of exoplanets, tens of thousands of brown dwarfs, more than 20 000 exploding stars, and countless numbers of variable and binary stars, as well as 500 000 distant quasars. Astronomers will most likely want to study many of these in detail. This will require high-multiplex instruments, so the future MOONS on the VLT and 4MOST on VISTA are going to play an important role. And of course, for many decades to come, astronomers will use the distances provided by Gaia to better understand their favourite objects.

    4
    This conceptual engineering drawing shows MOONS, a unique new instrument for ESO’s Very Large Telescope. MOONS will be able to tackle some of the most compelling astronomical questions such as probing the structure of the Milky Way and tracing how stars and galaxies form and evolve.
    Credit: ESO/MOONS Consortium

    Q: What excites you most about Gaia, and in particular about ESO’s involvement?

    A: The sheer amount of data that comes out of Gaia is truly amazing. To know that we will soon have a full understanding of our own galaxy and the myriad stars it contains is mind-blowing!

    I am rather proud that ESO is playing a role in this by tracking the satellite, but as an astronomer I am also very keen to use the Gaia data. In fact, together with colleagues here at ESO, I am currently finishing a study that relies on Gaia data to analyse the well-known star-forming region of Orion in great detail. When we first saw what we could do with these stars using Gaia, we could hardly believe our eyes. With Gaia, we can clearly distinguish where the youngest stars are located as a function of their age, and thus see the structure of this stellar nursery in 3D.

    Q: When is the next data release and what can we expect it to add to our knowledge?

    A: The third data release should come out at the end of 2020. It will improve on the parameters of the stars, distances and motions, as well as provide a catalogue of all the stars that are part of binary or multiple systems. But astronomers will be keen to wait for the final data release, hopefully around 2022, as it will provide orbits for many binary stars and objects in our Solar System, light curves of many variable stars, and a list of all the exoplanets found. This immense amount of data will create work for at least the next generation of astronomers, and perhaps further generations too.

    See the full article here .


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    ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

    ESO LaSilla
    ESO/Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres.

    ESO VLT
    VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level.

    ESO Vista Telescope
    ESO/Vista Telescope at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level.

    ESO NTT
    ESO/NTT at Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres.

    ESO VLT Survey telescope
    Part of ESO’s Paranal Observatory, the VLT Survey Telescope (VST) observes the brilliantly clear skies above the Atacama Desert of Chile. It is the largest survey telescope in the world in visible light.
    Credit: ESO/Y. Beletsky

    ALMA Array
    ALMA on the Chajnantor plateau at 5,000 metres.

    ESO E-ELT
    ESO/E-ELT to be built at Cerro Armazones at 3,060 m.

    ESO APEX
    APEX Atacama Pathfinder 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert.

    Leiden MASCARA instrument, La Silla, located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    Leiden MASCARA cabinet at ESO Cerro la Silla located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    ESO Next Generation Transit Survey at Cerro Paranel, 2,635 metres (8,645 ft) above sea level

    SPECULOOS four 1m-diameter robotic telescopes 2016 in the ESO Paranal Observatory, 2,635 metres (8,645 ft) above sea level

    ESO TAROT telescope at Paranal, 2,635 metres (8,645 ft) above sea level

    ESO ExTrA telescopes at Cerro LaSilla at an altitude of 2400 metres

     
  • richardmitnick 7:22 am on May 27, 2018 Permalink | Reply
    Tags: , , , , ESA Gaia, Gaia and the 14000 (white) dwarfs   

    From astrobites: “Gaia and the 14000 (white) dwarfs” 

    Astrobites bloc

    From astrobites

    Title: Gaia reveals evidence for merged white dwarfs
    Authors: Mukremin Kilic, N.C.Hambly, P.Bergeron and N. Rowell
    First Author’s Institution: Department of Physics and Astronomy, University of Oklahoma
    1
    Status: Submitted to MNRAS, open access

    Unless you’ve been avoiding the internet for fear of Avengers spoilers, you may have noticed that everyone’s favourite star-tracker, Gaia, has recently released its second catalogue containing the precise location of around 1.7 billion stars in our own galaxy and beyond.

    ESA/GAIA satellite

    1
    Figure 1: Gaia’s all-sky view of the Milky Way produced from tracking 1.7 billion stars in our galaxy. Credit: ESA/Gaia/DPAC

    Until now, we only had access to around 250 white dwarf stars in our local galaxy, making it difficult to look for common properties and understand the population as a whole. But, thanks to Gaia, today’s authors had a sample of almost 14,000 white dwarf stars to play with – here’s what they discovered.

    See the full article here .


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    Please help promote STEM in your local schools.
    stem
    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 9:42 pm on May 18, 2018 Permalink | Reply
    Tags: , , , , ESA Gaia, Know Thy Star Know Thy Planet: How Gaia is Helping Nail Down Planet Sizes,   

    From Many Worlds: “Know Thy Star, Know Thy Planet: How Gaia is Helping Nail Down Planet Sizes” 

    NASA NExSS bloc

    NASA NExSS

    Many Words icon

    From Many Worlds

    2018-05-17
    (This column was written by my colleague Elizabeth Tasker, now at the Japan Aerospace Exploration Agency (JAXA), Institute of Space and Astronautical Sciences (ISAS). Trained as an astrophysicist, she researches planet and galaxy formation and also writes on space science topics. Her book, The Planet Factory, came out last year.)

    1
    Gaia’s all-sky view of our Milky Way and neighboring galaxies. (ESA/Gaia/DPAC) [Small and Large Magelaic Clouds are visible]

    Last month, the European Space Agency’s Gaia mission released the most accurate catalogue to date of positions and motions for a staggering 1.3 billion stars.

    ESA/GAIA satellite

    Let’s do a few comparisons so we can be suitably amazed. The total number of stars you can see without a telescope is less than 10,000. This includes visible stars in both the northern and southern hemispheres, so looking up on a very dark night will allow you to count only about half this number.

    The data just released from Gaia is accurate to 0.04 milli-arcseconds. This is a measurement of the angle on the sky, and corresponds to the width of a human hair at a distance of over 300 miles (500 km.) These results are from 22 months of observations and Gaia will ultimately whittle down the stellar positions to within 0.025 milli-arcseconds, the width of a human hair at nearly 680 miles (1000 km.)

    OK, so we are now impressed. But why is knowing the precise location of stars exciting to planet hunters?

    The reason is that when we claim to measure the radius or mass of a planet, we are almost always measuring the relative size compared to the star. This is true for all planets discovered via the radial velocity and transit techniques — the most common exoplanet detection methods that account for over 95% of planet discoveries.

    It means that if we underestimate the star size, our true planet size may balloon from being a close match to the Earth to a giant the size of Jupiter. If this is true for many observed planets, then all our formation and evolution theories will be a mess.

    The size of a star is estimated from its brightness. Brightness depends on distance, as a small, close star can appear as bright as a distant giant. Errors in the precise location of stars therefore make a big mess of exoplanet data.

    This issue has been playing on the minds of exoplanet hunters.

    In 2014, a journal paper authored by Fabienne Bastien [The Astrophysical Journal] from Vanderbilt University suggested that nearly half of the brightest stars observed by the Kepler Space Telescope are not regular stars like our sun, but actually are distant and much larger sub-giant stars. Such an error would mean planets around these stars are 20 – 30% larger than estimated, a particularly hard punch for the exoplanet community as planets around bright stars are prime targets for follow-up studies.

    Previous improvements in the accuracy of the measured radii and other properties of stars have already proved their worth. In 2017, a journal paper led by Benjamin Fulton [The Astrophysical Journal]at the University of Hawaii revealed the presence of a gap in the distribution of sizes of super Earths orbiting close to their star. Planets 20% and 140% larger than the Earth appeared to be common, but there was a notable dearth of planets around twice the size of our own.

    2
    Super Earth planets with orbits of less than 100 days seem to come in two different sizes. (NASA/Ames/Caltech/University of Hawaii. (B.J.Fulton))

    The most popular theory for this gap is that the peaks belong to planets with similar core sizes, but the planets with larger radii have deep atmospheres of hydrogen and helium. This would make the planets belonging to the smaller radii peak true rocky worlds, whereas the second peak would be mini Neptunes: the first evidence of a size distinction between these two regimes.

    This split in the small planet population was spotted due to improved measurements of planet radii based on higher precision stellar observations made using the Keck Observatory.


    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft), above sea level, showing also NASA’s IRTF and NAOJ Subaru

    With a gap size of only half an Earth-radius, it had previously gone unnoticed due to the uncertainty in planet size measurements.

    Both the concern of a significant error in planet sizes and the tantalizing glimpse at the insights that could be achieved with more accurate data is why Gaia is so exciting.

    Launched on December 19, 2013, Gaia is a European Space Agency (ESA) space telescope for astrometry; the measurement of the position and motion of stars. The mission has the modest goal of creating a three-dimensional map of our galaxy to unprecedented precision.

    Gaia measures the position of stars using a technique known as parallax, which involves looking at an object from different perspectives.

    Parallax is easily demonstrated by holding up your finger and looking at it with one eye open and the other closed. Switch eyes, and you will see your finger moves in relation to the background. This movement is because you have viewed your finger from two different locations: the position of your left eye and that of your right.

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    Parallax is the apparent shift in the position of stars as the Earth orbits the sun. It can be used to determine distances between stars. (ESA/ATG medialab)

    The degree of motion depends on the separation between your eyes and the distance to your finger: if you move your finger further from your eyes, its parallax motion will be less. By measuring the separation of your viewing locations and the amount of movement you see, the distance to an object can therefore be calculated.

    Since stars are far more distant than a raised finger, we need widely separated viewing locations to detect the parallax. This can be done by observing the sky when the Earth is on opposite sides of its orbit. By measuring how far stars seem to move over a six month interval, we can calculate their distance and precisely estimate their size.

    This measurement was first achieved by Friedrich Wilhelm Bessel in 1838, who calculated the distance to the star 61 Cygni. Bessel estimated the star was 10.3 light years from the Earth, just 10% lower than modern measurements which place the star at a distance of 11.4 light years.

    However, measuring parallax from Earth can be challenging even with powerful telescopes. The first issue is that our atmosphere distorts light, making it difficult to measure tiny shifts in the position of more distant stars. The second problem is that the measured motion is always relative to other background stars. These more distant stars will also have a parallax motion, albeit smaller than stars closer to Earth.

    As a result, the motion measured and hence the distance to a star, will depend on the parallax of the more distant stars in the same field of view. This background parallax varies over the sky, leaving no way on Earth of creating a consistent catalogue of stellar positions.

    4
    The Gaia spacecraft’s billion-pixel camera maps stars and other objects in the Milky Way. (C. Carreau/ESA)

    These two conundrums are where Gaia has the advantage. Orbiting in space, Gaia simply avoids atmospheric distortion. The second issue of the background stars is tackled by a clever instrument design.

    Gaia has two telescopes that point 106.4 degrees apart but project their images onto the same detector. This allows Gaia to see stars from different parts of the sky simultaneously. The telescopes slowly rotate so that each field of view is seen once by each telescope and overlaid with a field 106.4 degrees either clockwise or counter-clockwise to its position. The parallax motion of stars during Gaia’s orbit can therefore be compared both with stars in the same field of view, and with stars in two different directions.

    Gaia repeats this across the sky, linking the fields of view together to globally compare stellar positions. This removes the problem of a parallax measurement depending on the motion of stars that just happen to be in the background.

    The result is the relative position of all stars with respect to one another, but a reference point is needed to turn this into true distances. For this, Gaia compares the parallax motion to distant quasars.

    Quasars are black holes that populate the center of galaxies and are surrounded by immensely luminous discs of gas. Being outside our Milky Way, the distance to quasars is so great that their parallax during the Earth’s orbit is negligibly small. Quasars are too rare to be within the field of view of most stars, but with stellar positions calibrated across the whole sky, Gaia can use any visible quasars to give the absolute distances to the stars.

    What did these precisely measured stellar motions do to the properties of the orbiting planets? Did our small worlds vanish or the intriguing division in the sizes of super Earths disappear?

    This was bravely investigated in a journal paper this month led by Travis Berger from the University of Hawaii. By matching the stars observed by Kepler to those in the Gaia catalogue, Berger confirmed that the majority of bright stars were indeed sun-like and not the suspected sub-giant population. However, the more precise stellar sizes were slightly larger on average, causing a small shift in the observed small planet radii towards bigger planets.

    5
    Planet radii derived from the new Gaia data and the Kepler (DR25) Stellar Properties Catalogue. Red points are confirmed planets while black points are planet candidates. Bottom panel shows the ratio between the two data sets. There is a small shift towards larger planets in the new Gaia data. (Figure 6 in Berger et al, 2018.)

    The same result was found in a parallel study led by Fulton, who found a 0.4% increase in planet radii from Gaia compared with the (higher precision than Kepler, but less precision than Gaia) results using Keck.

    The papers authored by Berger and Fulton investigated the split in super Earth sizes on short orbits, confirming that the two planet populations was still evident with the high precision Gaia data. Further exploration also revealed interesting new trends.

    Fulton noticed that two peaks in the super Earth population appear at slightly larger radii for planets orbiting more massive stars. This is true irrespective of the level radiation the planets are receiving from the star, ruling out the possibility that more massive stars are simply better at evaporating away atmospheres on bigger planets. Instead, this trend implies that bigger stars build bigger planets.

    Models proposed by Sheng Jin (Chinese Academy of Sciences) and Christoph Mordasini (the Max Planck Institute for Astronomy) in a paper last year [The Astrophysical Journal] proposed that the location of the split in the super Earth population could be linked to composition.

    Planets made of lighter materials such as ices would need a larger size to retain their atmospheres, compared to planet cores of denser rock. If the planet size at the population split marks the transition from large rocky worlds without thick atmospheres to mini-Neptunes enveloped in gas, then it corresponds to the size needed to retain that gas.

    Berger suggests that the gap between the planet populations seen in the new Gaia data is best explained by planets with an icy-rich composition. As these planets all have short orbits, this suggests these close-in worlds migrated inwards from a much colder region of the planetary system.

    The high precision planet radii measurements from Gaia seem to leave our planet population intact, but suggest new trends worth exploring. This will be a great job for TESS, NASA’s recently launched planet hunter that is preparing to begin its first science run this summer.

    NASA/TESS

    Gaia’s astrometry catalogue of stars will be ensuring we get the very best from this data.

    See the full article here .

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    About Many Worlds

    There are many worlds out there waiting to fire your imagination.

    Marc Kaufman is an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer, and is the author of two books on searching for life and planetary habitability. While the “Many Worlds” column is supported by the Lunar Planetary Institute/USRA and informed by NASA’s NExSS initiative, any opinions expressed are the author’s alone.

    This site is for everyone interested in the burgeoning field of exoplanet detection and research, from the general public to scientists in the field. It will present columns, news stories and in-depth features, as well as the work of guest writers.

    About NExSS

    The Nexus for Exoplanet System Science (NExSS) is a NASA research coordination network dedicated to the study of planetary habitability. The goals of NExSS are to investigate the diversity of exoplanets and to learn how their history, geology, and climate interact to create the conditions for life. NExSS investigators also strive to put planets into an architectural context — as solar systems built over the eons through dynamical processes and sculpted by stars. Based on our understanding of our own solar system and habitable planet Earth, researchers in the network aim to identify where habitable niches are most likely to occur, which planets are most likely to be habitable. Leveraging current NASA investments in research and missions, NExSS will accelerate the discovery and characterization of other potentially life-bearing worlds in the galaxy, using a systems science approach.
    The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

    President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

    Since that time, most U.S. space exploration efforts have been led by NASA, including the Apollo moon-landing missions, the Skylab space station, and later the Space Shuttle. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle and Commercial Crew vehicles. The agency is also responsible for the Launch Services Program (LSP) which provides oversight of launch operations and countdown management for unmanned NASA launches. Most recently, NASA announced a new Space Launch System that it said would take the agency’s astronauts farther into space than ever before and lay the cornerstone for future human space exploration efforts by the U.S.

    NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate’s Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories [Hubble, Chandra, Spitzer, and associated programs. NASA shares data with various national and international organizations such as from the [JAXA]Greenhouse Gases Observing Satellite.

     
  • richardmitnick 10:01 am on May 7, 2018 Permalink | Reply
    Tags: , , , , , ESA Gaia, , Which Are The Brightest Gravitational Wave Sources In Our Galaxy?   

    From astrobites: “Which Are The Brightest Gravitational Wave Sources In Our Galaxy?” 

    Astrobites bloc

    From astrobites

    May 7, 2018
    Matthew Green

    Title: LISA verification binaries with updated distances from Gaia Data Release 2
    Authors: T. Kupfer, V. Korol, S. Shah, G. Nelemans, T. R. Marsh, G. Ramsay, P. J. Groot, D. T. H Steeghs, E. M. Rossi
    First Author’s Institution: Division of Physics, Mathematics and Astronomy, Caltech, Pasadena, USA.

    Status: Submitted to MNRAS, open access

    A couple of weeks ago, the Gaia satellite released data that it has been collecting since its launch in 2013.

    ESA/GAIA satellite

    Among these data were “parallax” measurements (a property we can use to measure how far away something is) for over a billion stars — a revolution for many fields of astronomy. A couple of astrobites last week talked about some results from this data. In today’s paper, the authors used the data from Gaia to look at a group of gravitational-wave-emitting binary stars, and see how visible they will be to the planned LISA mission.

    2
    Figure 1: The LISA space mission will consist of 3 satellites connected by laser beams, which they will use to monitor for changes to the distance between them. Source: NASA.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 4:32 pm on May 4, 2018 Permalink | Reply
    Tags: , , , , , ESA Gaia, , New Target for an Old Method: Hubble Measures Globular Cluster Parallax   

    From AAS NOVA: “New Target for an Old Method: Hubble Measures Globular Cluster Parallax” 

    AASNOVA

    AAS NOVA

    4 May 2018
    Kerry Hensley

    1
    Globular cluster NGC 6397 dazzles in this optical image from La Silla Observatory.

    ESO WFI LaSilla 2.2-m MPG/ESO telescope at La Silla, 600 km north of Santiago de Chile at an altitude of 2400 metres


    MPG/ESO 2.2 meter telescope at Cerro La Silla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres

    Globular clusters like NGC 6397 are important laboratories for understanding stellar evolution — but measuring the distance to these ancient stellar groups can be challenging. [ESO]

    the Wide-Field-Imager (WFI) camera at the 2.2-m ESO/MPI telescope at the ESO La Silla Observatory

    ESO/Cerro LaSilla, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    Measuring precise distances to faraway objects has long been a challenge in astrophysics. Now, one of the earliest techniques used to measure the distance to astrophysical objects has been applied to a metal-poor globular cluster for the first time.

    ESA/GAIA satellite


    Gaia is on track to map the positions and motions of a billion stars. [ESA]

    A Classic Technique

    Distances to nearby stars are often measured using the parallax technique — tracing the tiny apparent motion of a target star against the background of more distant stars as Earth orbits the Sun. This technique has come a long way since it was first used in the 1800s to measure the distance to stars a few tens of light-years away; with the advent of space observatories like Hipparcos and Gaia, parallax can now be used to map the positions of stars out to thousands of light-years.

    ESA/Hipparcos satellite

    Precise distance measurements aren’t only important for setting the scale of the universe, however; they can also help us better understand stellar evolution over the course of cosmic history. Stellar evolution models are often anchored to a reference star cluster, the properties of which must be known precisely. These precise properties can be readily determined for young, nearby open clusters using parallax measurements. But stellar evolution models that anchor on the more-distant, ancient, metal-poor globular clusters have been hampered by the less-precise indirect methods used to measure distance to these faraway clusters — until now.

    New Measurement to an Old Cluster

    Thomas Brown (Space Telescope Science Institute) and collaborators used the Hubble Space Telescope to determine the distance to NGC 6397, one of the nearest metal-poor globular clusters and anchor for one stellar population model.

    NASA/ESA Hubble Telescope

    Brown and coauthors used a technique called spatial scanning to greatly broaden the reach of the parallax method.

    Spatial scanning was initially developed as a way to increase the signal-to-noise of exoplanet transit observations, but it has also greatly improved the prospects of astrometry — precisely determining the separations between astronomical objects. In spatial scanning, the telescope moves while the exposure is being taken, spreading the light out across many pixels.

    Unprecedented Precision

    This technique allowed the authors to achieve a precision of 20–100 microarcseconds. From the observed parallax angle of just 0.418 milliarcseconds (for reference, the moon’s angular size is about 5 million times larger on the sky!), Brown and collaborators refined the distance to NGC 6397 to 7,795 light-years, with a measurement error of only a few percent.

    Using spatial scanning, Hubble can make parallax measurements of nearby globular clusters, while Gaia has the potential to reach even farther. Looking ahead, the measurement made by Brown and collaborators can be combined with the recently released Gaia data to trim the uncertainty down to just 1%. This highlights the power of space telescopes to make extremely precise measurements of astoundingly large distances — informing our models and helping us measure the universe.

    Citation

    Thomas Brown et al 2018 ApJL 856 L6.http://iopscience.iop.org/article/10.3847/2041-8213/aab55a/meta .

    Related journal articles
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    See the full article for further references with links.

    See the full article here .

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    AAS Mission and Vision Statement

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

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

    Adopted June 7, 2009

     
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