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  • richardmitnick 2:43 pm on October 25, 2016 Permalink | Reply
    Tags: , , ESA Gaia, Four luminous blue variables found to be much closer than previously assumed,   

    From phys.org: “Four luminous blue variables found to be much closer than previously assumed” 

    physdotorg
    phys.org

    1
    AG Carinae (AG Car) – an example of a Luminous Blue Variable (LBV) star. Credit: Judy Schmidt/Hubble Space Telescope.

    A new study based on the first Gaia data release (DR1) reveals more accurate measurements of the distance of four canonical luminous blue variables (LBVs) in the Milky Way galaxy.

    ESA/GAIA satellite
    ESA/GAIA satellite

    According to a research paper published Oct. 20 on the arXiv server, they are much closer to Earth than previously thought.

    Published on Sept. 14, 2016, DR1 contains a catalog of over 1 billion stars with precise measurements of their brightness and positions in the sky. These data were obtained by ESA’s Gaia satellite, which is completing the first-ever “galactic census”—the most detailed three-dimensional map of the Milky Way ever made. The release of DR1 offers the scientific community an excellent opportunity to improve knowledge of our stellar environment and to redefine some previous calculations.

    Combing through the data obtained by Gaia, Nathan Smith of the Steward Observatory in Arizona and Keivan Stassun of Vanderbilt University in Nashville, Tennessee, have searched for LBVs and LBV candidates. These massive evolved stars showcase unpredictable and sometimes dramatic variations in both their spectra and their brightness. Their strong mass loss is believed to play a critical role in the evolution of massive stars, however the exact role LBVs play and the physics of their instability are still uncertain.

    Four canonical LBVs in the Milky Way were of special interest for Smith and Stassun, namely: AG Car, HR Car, HD 168607 and Hen 3-519 (an LBV candidate).

    “Here, we report direct distances and space motions of four canonical Milky Way LBVs—AG Car, HR Car, HD 168607, and (the LBV candidate) Hen 3-519 – whose parallaxes and proper motions have been provided by the Gaia first data release,” the researchers wrote in the paper.

    The most important findings were made regarding the distance of these LBVs. The clue to understanding their peculiar instability is their high observed luminosity, which, in the case of those stars, often depends on an uncertain distance calculations.

    According to the paper, the distance of HD 168607 was re-calculated from about 7,000 to 3,800 light years. Similar correction was made in the case of HR Car, as its distance from Earth, previously thought to be approximately 16,000 light years, also turned out to be only half of the value – about 7,500 light years.

    The astronomers found more surprising results regarding AG Car and Hen 3-519. DR1 data reveal that AG Car is located just 6,400 light years away, replacing earlier calculations indicating a distance over a three times larger, approximately 21,500 light years.

    Finally, the study finds that the distance of Hen 3-519 shows the biggest discrepancy between the previous and latest estimates. The new measurements reveal that its distance is 5,200 light years from the Earth, while the previously adopted distance was 26,000 light years.

    “The distances to all four objects are closer than traditionally assumed in the literature, lowering their intrinsic luminosities,” the paper reads.

    The researchers noted that the lower luminosities suggest that AG Car and Hen 3-519 passed through a previous red supergiant phase. They also imply that binary evolution could explain their peculiar properties. Moreover, the scientists concluded that the new results may initiate a re-evaluation of our current understanding of LBVs.

    “More precise values of the parallax for a larger number of Galactic LBVs will be available soon; the results reported here may signal upheaval in our understanding of massive star evolution, even if they are regarded as preliminary,” the astronomers wrote.

    See the full article here .

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    About Phys.org in 100 Words

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

     
  • richardmitnick 10:06 am on October 20, 2016 Permalink | Reply
    Tags: , , , ESA Gaia, , , How far away are the stars?, The parallax method   

    From Ethan Siegel: “How far away are the stars?” 

    10.20.16
    Ethan Siegel

    1
    This is the Milky Way from Concordia Camp, in Pakistan’s Karakoram Range. To the right is Mitre Peak, and to the far left is the beginning of Broad Peak. Photograph by Anne Dirkse, of http://www.annedirkse.com under a c.c.-by-s.a.-4.0 license.

    Scientists still don’t know, but the answer could hold the key to the expanding, accelerating Universe.

    “Scratch a cynic and you’ll find a disappointed idealist.” -Jon F. Merz

    When you look up at the night sky and see the glittering stars overhead, your first thought might be to wonder what, exactly, they are. Once you know they’re very distant suns, however, with different masses, brightnesses, temperatures and colors, your next thought might be to wonder just how far away they are. It might surprise you to learn that despite centuries of advancement in astronomy and astrophysics, from telescopes to cameras to CCDs to observatories in space, we still don’t have a satisfying answer. When you consider that much of our understanding of the Universe today — how it was born, how it came to be the way it is and what it’s made of — is based on the distances to the stars, it highlights just how important this problem is.

    2
    Stars that appear to be at the same distance, like the ones in the constellation of Orion, may in fact be many hundreds or even thousands of light years more-or-less distant than one another. Image credit: La bitacora de Galileo, via http://www.bitacoradegalileo.com/2010/02/07/orion-la-catedral-del-cielo/.

    If you want to know how fast the Universe is expanding at any point in time, you need to know how fast the distant galaxies are moving away from us and how far away they are. Measuring a galaxy’s recession speed is straightforward — just measure its redshift and you’re done — but distances are a tricky thing. There needs to be some type of relationship between a quantity you can measure, like observed brightness, angular size, periodicity of a particular signal, etc., and something that will tell you an object’s intrinsic brightness or size. You can then calculate its distance. That’s how we figure out a whole slew of properties about the Universe, including:

    how fast it’s expanding today,
    how the expansion rate has changed over time,
    and what makes up the Universe, including matter, radiation and dark energy.

    3
    The construction of the cosmic distance ladder involves going from our Solar System to the stars to nearby galaxies to distant ones. Each “step” carries along its own uncertainties. Image credit: NASA,ESA, A. Feild (STScI), and A. Riess (STScI/JHU).

    But all of that knowledge requires a starting point for measuring cosmic distances. All of our measurement methods are dependent on knowing how these objects we’re measuring operate nearby: they all require an understanding of the closer star or galaxy types that we also find at great distances. No matter how you go about it, there’s one key step we need to begin with, and that’s an assumption-free method to measure the distances to the nearest stars. We only know of one, and we’ve known of it since before the time of Galileo.

    4
    The parallax method, employed since the 1800s, involves noting the apparent change in position of a nearby star relative to the more distant, background ones. Image credit: ESA/ATG medialab.

    It’s the idea of parallax, which is a purely geometrical way to measure the distances to the stars. Regardless of what type of star you have, what its brightness is or how it’s moving through space, measuring parallax is exactly the same.

    Measure the star you’re trying to observe today from your location, at its current position relative to the other objects in the sky.
    Measure the star from a different position in space, and note how the star’s apparent position appears to change relative to the other points of light you can identify.
    Use simple geometry — knowing the difference in your position from those first two measurements and the apparent change in angle — to determine the distance to the star.

    We’ve been using this method since the mid-1800s to measure the distances to the nearest stars, including Alpha Centauri, Vega and 61 Cygni, which has the distinction of being the first star to ever have its parallax measured back in 1838.

    5
    61 Cygni was the first star to have its parallax measured, but also is a difficult case due to its large proper motion. These two images, stacked in red and blue and taken almost exactly one year apart, show this binary star system’s fantastic speed. Image credit: Lorenzo2 of the forums at http://forum.astrofili.org/viewtopic.php?f=4&t=27548.

    But as straightforward as this method is, it comes along with its own inherent flaws. For starters, these angles are always very small: about 1 arcsecond (or 1/3600th of a degree) for a star that’s 3.26 light years away. For comparison, our nearest star, Proxima Centauri, is 4.24 light years away and has a parallax of just 0.77 arcsec. Stars more distant than perhaps one or two hundred light years can’t have their parallaxes measured from the ground at all, since the atmospheric turbulence contributes too greatly to uncertainties. In 1989, the European Space Agency attempted to overcome all of these difficulties by launching the Hipparcos satellite, which — from space — could measure precisions down to an accuracy of just 0.001 arcsec.

    12
    ESA/Hipparcos satellite

    6
    Testing the Hipparcos satellite in the Large Solar Simulator, ESTEC, February 1988. Image credit: Michael Perryman.

    Ideally, this would have meant that we could get accurate parallaxes for stars up to 1,600 light years away: about 100,000 stars total. The brightest and closest stars would be able to have their distances measured to better than 1% precision, which would then mean we’d be able to measure things like the expansion of the Universe throughout its history to that precision level as well. But a number of difficulties prevented that.

    The Earth doesn’t just move throughout the year; the Sun moves through the galaxy as well.
    Because parallax measurements aren’t simultaneous, other stars move relative to the Earth-Sun system as well.
    The more distant stars are not “fixed” in the sky, but exhibit relative motions as well. All stars have their own parallax, dependent on their distance.
    And the influence of gravitational bodies in our Solar System and throughout the galaxy can cause small deflections in starlight due to General Relativity.

    When you take all of these uncertainties into account, we wound up with uncertainties in positions that were much greater than 1%. In fact, if you expected a known nearby, bright star to simply have its position change the same way your thumb’s position, held at arm’s length, changed when you switched which eye you looked at it with, the actual data would be a rude awakening to you.

    7
    The “real” motion of Vega, just 26 light years away, as made from three years of Hipparcos data. Image credit: Michael Richmond of RIT, under a creative commons license, via http://spiff.rit.edu/classes/phys301/lectures/parallax/parallax.html.

    Over a period of three years, Hipparcos taught us a great deal about the motion of stars in our Milky Way, which is a combination of parallax and a series of true proper motions. The way to overcome these constraints is to take continuous measurements of stars as the Earth moves around the Sun and the Sun moves through space, with clearly identified, bright, distant “reference stars” which won’t show any discernible parallax. If you heard about the ESA’s Gaia mission, this is exactly what it’s attempting to do.

    ESA/GAIA satellite
    ESA/GAIA satellite

    With much greater accuracy and precision than Hipparcos, Gaia is undertaking an all-sky survey of the galaxy to measure the positions and motions of approximately 1 billion stars within the Milky Way.

    8
    A map of star density in the Milky Way and surrounding sky, clearly showing the Milky Way, large and small Magellanic Clouds, and if you look more closely, NGC 104 to the left of the SMC, NGC 6205 slightly above and to the left of the galactic core, and NGC 7078 slightly below. Image credit: ESA/GAIA.

    Parallaxes should be available for hundreds of millions of these stars, with a precision of just 10 µas (0.00001 arcsec) at maximum. We should be able to get significantly better than 1% precision for all of the Hipparcos stars, and — at last — should get outstanding parallax measurements for the closest Cepheid variable stars: Polaris and Delta Cephei. If we can understand the distances to this type of variable star within our own galaxy, we should be able to much better constrain our measurements of the cosmic distance ladder, and therefore, better understand how the Universe has expanded over its history and what makes it up.

    9
    Image credit: NASA/JPL-Caltech, of the (symbolic) cosmic distance ladder.

    It’s a bold, ambitious plan, and after hundreds of years of uncertainty in the distances to the stars, we’ll finally have the answer. By the year 2020, when Gaia’s data catalog is complete, we should know whether our various methods of measuring extragalactic distances have flaws or tensions, or whether all the pieces fall into place. We might not know exactly how far away the stars are today, but thanks to our greatest space observatories, we’re finally about to find out!

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 11:40 am on October 14, 2016 Permalink | Reply
    Tags: Astrometry, , , ESA Gaia, , , 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

    1
    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.

    2
    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 9:14 am on September 17, 2016 Permalink | Reply
    Tags: , , ESA Gaia, ,   

    From Science Node: “Gaia, Hipparcos, and 3D star maps” 

    Science Node bloc
    Science Node

    12 Sep, 2016
    Lance Farrell

    The European Space Agency just published the first catalog of stars from the Gaia mission. Before Gaia, there was Hipparcos.

    1
    ESA/Hipparcos, launched in 1989

    The European Space Agency (ESA) released long awaited galactic images from the Global Astrometric Interferometer for Astrophysics (GAIA) on September 15.

    ESA/GAIA satellite
    ESA/GAIA satellite


    Gaia’s view. A visualization of how Gaia scanned the sky during its first 14 months of operations, between July 2014 and September 2015.The oval represents a projection of the celestial sphere, with different portions of the sky gradually appearing, according to when and how frequently they were scanned by Gaia. Courtesy ESA

    Thanks to Gaia – and the supercomputers and 400 or so humans in the associated Data Processing and Analysis Consortium (DPAC) helping to process the massive datasets – we now have the best map of our home galaxy every made.

    So far GAIA has charted about one billion stars, and will assemble the most detailed 3D visualization of the Milky Way in the months to come.

    Launched in late 2013 and currently orbiting the sun nearly 1.5 million km away from Earth, Gaia streams back about 40 Gigabytes per day. Over the full life of the mission, Gaia will amass 73 Terabytes.

    But before Gaia, there was Hipparcos. Hipparcos was launched in 1989 and remained in operation until 1993. In 2015, Hervé Bouy from the Center for Astrobiology (CSIC-INTA) in Spain and João Alves from the University of Vienna, Austria brought the Hipparcos data to life, rendering the star maps in 3D.


    Star maps. 100,000 stars is an interactive visualization of our stellar neighborhood. It shows the location of 119,617 nearby stars derived from multiple sources, including the 1989 Hipparcos mission. Courtesy Chrome Experiments; ESA.

    Among many advantages, a 3D view eliminates the interference brought by companion stars, bringing hidden structures into focus. The 3D visualization includes all the stars within 1500 light years of our sun.

    So while we wait for Gaia’s update, take a look at this Chrome experiment, and let’s fly through the 100,000 stars in our immediate stellar neighborhood.

    But be warned: Do not use this visualization for interstellar navigation.

    See the full article here .

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    Science Node is an international weekly online publication that covers distributed computing and the research it enables.

    “We report on all aspects of distributed computing technology, such as grids and clouds. We also regularly feature articles on distributed computing-enabled research in a large variety of disciplines, including physics, biology, sociology, earth sciences, archaeology, medicine, disaster management, crime, and art. (Note that we do not cover stories that are purely about commercial technology.)

    In its current incarnation, Science Node is also an online destination where you can host a profile and blog, and find and disseminate announcements and information about events, deadlines, and jobs. In the near future it will also be a place where you can network with colleagues.

    You can read Science Node via our homepage, RSS, or email. For the complete iSGTW experience, sign up for an account or log in with OpenID and manage your email subscription from your account preferences. If you do not wish to access the website’s features, you can just subscribe to the weekly email.”

     
  • richardmitnick 4:57 pm on September 13, 2016 Permalink | Reply
    Tags: , , , Cosmic distance ladder, , , ESA Gaia   

    From Ethan Siegel: “GAIA Satellite To Find Out If We’re Wrong About Dark Energy And The Expanding Universe” 

    From Ethan Siegel

    Sep 13, 2016

    ESA/Gaia satellite
    ESA/Gaia satellite

    How far away are the most distant objects in the Universe? How has the Universe expanded over the course of its history? And therefore, how big and how old is the Universe since the Big Bang? Through a number of ingenious developments, humanity has come up with two separate ways to answer these questions:

    To look at the minuscule fluctuations on all scales in the leftover glow from the Big Bang — the Cosmic Microwave Background — and to reconstruct the Universe’s composition and expansion history from that.
    To measure the distances to the stars, the nearby galaxies, and the more distant galaxies individually, and reconstruct the Universe’s expansion rate and history from this progressive “cosmic distance ladder.”

    1
    The Gaia Deployable Sunshield Assembly (DSA) during deployment testing in the S1B integration building at Europe’s spaceport in Kourou, French Guiana, two months before launch. Image credit: ESA-M. Pedoussaut.

    Interestingly enough, these two methods disagree by a significant amount, and the European Space Agency’s GAIA satellite, poised for its first data release tomorrow, September 14th, intends to resolve it one way or another.

    2
    Image credit: ESA and the Planck Collaboration, of the best-ever map of the fluctuations in the cosmic microwave background.

    The leftover glow from the Big Bang is only one data set, but it’s perhaps the most powerful data set we could have asked for nature to provide us with. It tells us the Universe expands with a Hubble constant of 67 km/s/Mpc, meaning that for every Megaparsec (about 3.26 million light years) a galaxy is apart from another, the expanding Universe pushes them apart at 67 km/s. The Cosmic Microwave Background also tells us how the Universe has expanded over its history, giving us a Universe that’s 68% dark energy, 32% dark-and-normal matter combined, and with an age of 13.81 billion years. Beginning with COBE and heavily refined later by BOOMERanG, WMAP and now Planck, this is perhaps the best data humanity has ever obtained for precision cosmology.

    NASA/WMAP
    NASA/WMAP

    ESA/Planck
    ESA/Planck

    3
    The construction of the cosmic distance ladder involves going from our Solar System to the stars to nearby galaxies to distant ones. Each “step” carries along its own uncertainties. Image credit: NASA,ESA, A. Feild (STScI), and A. Riess (STScI/JHU).

    But there’s another way to measure how the Universe has expanded over its history: by constructing a cosmic distance ladder. One cannot simply look at a distant galaxy and know how far away it is from us; it took hundreds of years of astronomy just to learn that the sky’s great spirals and ellipticals weren’t even contained within the Milky Way! It took a tremendous series of steps to figure out how to measure astronomical distances accurately:

    We needed to learn how to measure Solar System distances, which took the developments of Newton and Kepler, plus the invention of the telescope.
    We needed to learn how to measure the distances to the stars, which relied on a geometric technique known as parallax, as a function of Earth’s motion in its orbit.
    We needed to learn how to classify stars and use properties that we could measure from those parallax stars in other galaxies, thereby learning our first galactic distances.
    And finally, we needed to identify other galactic properties that were measurable, such as surface brightness fluctuations, rotation speeds or supernovae within them, to measure the distances to the farthest galaxies.

    This latter method is older, more straightforward and requires far fewer assumptions. But it also disagrees with the Cosmic Microwave Background method, and has for a long time. In particular, the expansion rate looks to be about 10% faster: 74 km/s/Mpc instead of 67, meaning — if the distance ladder method is right — that the Universe is either younger and smaller than we thought, or that the amount of dark energy is different from what the other method indicates. There’s a big uncertainty there, however, and the largest component comes in the parallax measurement of the stars nearest to Earth.

    5
    The parallax method, employed by GAIA, involves noting the apparent change in position of a nearby star relative to the more distant, background ones. Image credit: ESA/ATG medialab.

    This is where the GAIA satellite comes into play. Outstripping all previous efforts, GAIA will measure the brightnesses and positions of over one billion stars in the Milky Way, the largest survey ever undertaken of our own galaxy. It expects to do parallax measurements for millions of these to an accuracy of 20 micro-arc-seconds (µas), and for hundreds of millions more to an accuracy of 200 µas. All of the stars visible with the naked eye will do even better, with as little as 7 µas precision for everything visible to a human through a pair of binoculars.

    6
    A map of star density in the Milky Way and surrounding sky, clearly showing the Milky Way, large and small Magellanic Clouds, and if you look more closely, NGC 104 to the left of the SMC, NGC 6205 slightly above and to the left of the galactic core, and NGC 7078 slightly below. Image credit: ESA/GAIA.

    GAIA was launched in 2013 and has been operational for nearly two full years at this point, meaning it’s collected data on all of these stars at many different points in our planet’s orbit around the Sun. Obtaining parallax measurements means we can get the full three-dimensional positions of these stars in space, and can even infer their proper motions at these accuracies, meaning we can dramatically reduce the uncertainties in the distances to the stars. What’s most spectacular is that many of these stars will be of the same types that we can measure in other star clusters and galaxies, enabling us to build a better, more robust cosmic distance ladder. When the GAIA results come out — and have been fully analyzed by the astronomical community — we’ll have our best-ever understanding of the Universe’s expansion history and of the distances to the farthest galaxies in the Universe, all because we measured what’s happening right here at home.

    Inflationary Universe. NASA/WMAP
    Inflationary Universe. NASA/WMAP

    Right now, the Cosmic Microwave Background and the cosmic distance ladder are giving us two different answers to the question of the age, expansion rate and composition of our Universe. They’re not very different, but the fact that they disagree points to one of two possible things. Either one (or both) of the measurements are in error, or there’s a fundamental tension between these two types of measurement that might mean our Universe is a funnier place than we’ve realized to date. When the results from GAIA come out tomorrow, the great hope of most astronomers is that the previous parallax measurements will be shown to have been in error, and our best understanding of the Universe will hold up and be vindicated. But nature has surprised us before, and — if you’re hoping for something new — keep in mind that it just might do so again.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 6:51 am on September 10, 2016 Permalink | Reply
    Tags: , , ESA Gaia,   

    From Nature- “Milky Way mapper: 6 ways the Gaia spacecraft will change astronomy” 

    Nature Mag
    Nature

    09 September 2016
    Davide Castelvecchi

    1
    The Gaia spacecraft’s billion-pixel camera maps stars and other objects in the Milky Way. C. Carreau/ESA

    Astronomers the world over are about to get their first taste of a tool that will transform their working lives.

    Gaia, a space telescope launched by the European Space Agency (ESA) in late 2013, will release its first map of the Milky Way on 14 September. The catalogue will show the 3D positions of 2,057,050 stars and other objects, and how those positions have changed over the past two decades. Eventually, the map will contain one billion objects or more and will be 1,000 times more extensive and at least 10 times more precise than anything that came before.

    The release next week will also include 19 papers by Gaia astronomers who have already seen the data. But independent teams are getting ready for their first glimpse. Lennart Lindegren, an astronomer at the Lund Observatory in Sweden and a major driving force in the Gaia project since it was first proposed in 1993, expects astronomers to produce 100 or so papers just in the weeks following the draft catalogue release.

    Some groups have planned ‘Gaia hacking’ and ‘Gaia sprint’ events, at which researchers will collectively work out how best to exploit the sudden manna. “Gaia is going to revolutionize what we know about stars and the Galaxy,” says David Hogg, an astronomer at New York University who is leading some of these efforts. So what are some of the revelations that Gaia could make?

    Milky Way archaeology
    2
    The structure of the Milky Way (artist’s impression) may soon be better understood. NASA/JPL

    Gaia’s 3D view of Milky Way in motion will reveal how stars move under its combined gravitational pull. This will add to knowledge of the Galaxy’s structure, including parts that are not directly visible from Earth, such as the ‘bar’ — two arms that stick straight out of the Galactic Centre and join it to the spiral arms.

    Researchers will be able to identify ‘outlier’ groups of stars which stream together at high speeds, and which are thought to be remnants of mergers with smaller galaxies, says Michael Perryman, an astronomer at University College Dublin and a former senior scientist for Gaia at ESA. Combined with existing information about factors including stars’ colour, temperature and chemical composition, this detailed map will enable researchers to reconstruct the Galaxy’s archaeology: how it got to its present state over the past 13 billion years. “Over its lifetime, Gaia is going to radically impact our understanding of the structure of the Milky Way and its evolutionary history,” says Monica Valluri, an astronomer at the University of Michigan in Ann Arbor.

    Where is the Milky Way’s dark matter?

    The details of star trajectories inside the Galaxy will reveal the distribution not only of visible matter, but also of dark matter, which constitutes the bulk of most galaxies’ mass. And that in turn could help to reveal what dark matter is.

    Gaia might also put some exotic theories to the test. Standard dark-matter theory predicts that the gravitational field of the Galaxy is spherically symmetrical near the Galactic Centre but then becomes elongated “like an American football” farther out, Valluri explains. But an alternative theory called MOND (modified Newtonian dynamics) implies that the field is shaped more like a pancake. By looking at the velocities of stars, which depend on the gravitational field, Gaia will be able to test which theory is right.

    The probe’s data might even reveal evidence for the idea that dark matter killed the dinosaurs. If dark matter is concentrated in a relatively thin ‘dark disk’ near the Galactic plane, says the audacious theory, it could trigger asteroid impacts that cause mass extinctions when the Solar System periodically crosses the disk.

    Disputed stellar distances
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    How far is the Pleiades star cluster from the Sun? NASA, ESA and AURA/Caltech

    Precise measurements of how far individual stars lie from the Sun will enable astrophysicists to fine-tune their models of how stars evolve. That is because current theories rely heavily on estimates of distance to understand how a star’s intrinsic brightness changes during its lifetime.

    One of the first groups of stars that researchers will want to check is the Pleiades, a cluster in the constellation Taurus. Most observations, including one [1] made with the Hubble Space Telescope, put the cluster about 135 parsecs (440 light years) away. But results based on data from Hipparcos, an ESA space mission that preceded Gaia, suggest [2] that it is only 120 parsecs away.

    Some have said that the discrepancy casts doubt on the accuracy of Hipparcos. Gaia uses a similar, but much more evolved, method to Hipparcos, so astronomers will be watching its observations closely. “I believe that the Hipparcos result will very likely be proved wrong by Gaia,” says David Soderblom of the Space Telescope Science Institute in Baltimore, Maryland, who is an author on the Hubble study.

    Thousands of new worlds

    Astronomers have discovered thousands of planets orbiting other stars, in most cases by detecting tiny dips in a star’s brightness when an orbiting planet passes in front of, or ‘transits’, it. Gaia will detect planets using another method: measuring slight wobbles in the star’s position caused by a planet’s gravitational pull.

    “It seems like a good bet that the mission will reveal thousands of new worlds,” says Gregory Laughlin, an astronomer at Yale University in New Haven, Connecticut.

    Gaia’s technique is best suited to detecting large planets in relatively wide orbits, says Alessandro Sozzetti, a Gaia researcher at the Astrophysical Observatory of Turin in Italy. And unlike the transit method, it directly measures a planet’s mass. If it works, it will be a striking comeback for a technique that has seen many false starts.

    But finding planets in this way will require several years of observation, with a sneak preview expected by 2018, Sozzetti says.

    How fast the Universe is expanding
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    Variable star RS Pup, located in the Milky Way, is used as a standard candle. NASA

    Although Gaia is primarily an explorer of the Milky Way, its influence will reach across the entire observable Universe.

    Gaia’s direct distance measurements work only for objects in the Galaxy or its immediate vicinity; to estimate the distances to faraway galaxies, astronomers typically wait for stellar explosions called Type Ia supernovae. The apparent brightness of such a supernova reveals how far away the corresponding galaxy is. Such signposts, or ‘standard candles’, have been the main tool for estimating the rate of expansion of the Universe. The measurements have led astronomers to propose that a mysterious ‘dark energy’ has been accelerating that expansion.

    But to use supernovae as signposts, astronomers must compare them with other types of standard candle in our Galaxy. In its first release, Gaia will measure the distances of thousands of such stars to high accuracy. Eventually, the probe’s measurements will enable cosmologists to improve their maps of the entire Universe and perhaps to resolve some conflicting estimates of its rate of expansion.

    Invisible asteroid threats

    As it constantly scans the sky, Gaia will also track and discover things much closer to home. It is ultimately expected to find some 350,000 asteroids inside the Solar System, says Gaia astronomer Paolo Tanga of the Côte d’Azur Observatory in Nice, France. These will include near-Earth objects (NEOs), those whose orbits bring them within about 200 million kilometres of Earth.

    When it spots an NEO, Gaia can alert observatories, which can then use ground-based telescopes to establish whether the object is a threat. From its vantage point in space, Gaia will scan nearly the entire sky and so might reveal objects that, during certain times, are too close to the Sun to be observed from Earth, says Anthony Brown, an astronomer at the Leiden Observatory in the Netherlands who chairs Gaia’s data-processing collaboration. “We can observe in areas you cannot normally reach from the ground at the same time.”

    By tracking the way certain asteroids orbit the Sun over several years, Gaia will also be able to perform sensitive tests of Albert Einstein’s description of gravity, his general theory of relativity.

    See the full article here .

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    Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.

     
  • richardmitnick 10:18 am on December 24, 2015 Permalink | Reply
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    From ESA: “Stellar density map” 

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    1
    Credits: ESA/Gaia – CC BY-SA 3.0 IGO

    The outline of our Galaxy, the Milky Way, and of its neighbouring Magellanic Clouds, in an image based on housekeeping data from ESA’s Gaia satellite, indicating the total number of stars detected every second in each of the satellite’s fields of view.

    ESA Gaia satellite
    Gaia

    2
    Seen from the southern skies, the Large and Small Magellanic Clouds (the LMC and SMC, respectively) are bright patches in the sky. These two irregular dwarf galaxies, together with our Milky Way Galaxy, belong to the so-called Local Group of galaxies. Astronomers once thought that the two Magellanic Clouds orbited the Milky Way, but recent research suggests this is not the case, and that they are in fact on their first pass by the Milky Way. The LMC, lying at a distance of 160 000 light-years, and its neighbour the SMC, some 200 000 light-years away, are among the largest distant objects we can observe with the unaided eye. Both galaxies have notable bar features across their central discs, although the very strong tidal forces exerted by the Milky Way have distorted the galaxies considerably. The mutual gravitational pull of the three interacting galaxies has drawn out long streams of neutral hydrogen that interlink the three galaxies.
    Date 27 August 2009
    Source ESO

    3
    Local Group. Andrew Z. Colvin

    Brighter regions indicate higher concentrations of stars, while darker regions correspond to patches of the sky where fewer stars are observed.

    The plane of the Milky Way, where most of the Galaxy’s stars reside, is evidently the brightest portion of this image, running horizontally and especially bright at the centre. Darker regions across this broad strip of stars, known as the Galactic Plane, correspond to dense, interstellar clouds of gas and dust that absorb starlight along the line of sight.

    The Galactic Plane is the projection on the sky of the Galactic disc, a flattened structure with a diameter of about 100 000 light-years and a vertical height of only 1000 light-years.

    Beyond the plane, only a few objects are visible, most notably the Large and Small Magellanic Clouds, two dwarf galaxies orbiting the Milky Way, which stand out in the lower right part of the image. A few globular clusters – large assemblies up to millions of stars held together by their mutual gravity – are also sprinkled around the Galactic Plane.

    Acknowledgement: this image was prepared by Edmund Serpell, a Gaia Operations Engineer working in the Mission Operations Centre at ESA’s European Space Operations Centre in Darmstadt, Germany.

    This work is licenced under the Creative Commons Attribution-ShareAlike 3.0 IGO

    See the full article 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 12:11 pm on July 3, 2015 Permalink | Reply
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    From ESA: “Counting stars with Gaia” 

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    European Space Agency

    3 July 2015
    No Writer Credit

    1`
    Stellar density map (Edmund Serpell)

    This image, based on housekeeping data from ESA’s Gaia satellite, is no ordinary depiction of the heavens. While the image portrays the outline of our Galaxy, the Milky Way, and of its neighbouring Magellanic Clouds, it was obtained in a rather unusual way.

    2
    Large Magellanic Cloud

    3
    Small Magellanic Cloud

    ESA Gaia satellite
    GAIA
    ESA Gaia Camera
    GAIA Camera

    As Gaia scans the sky to measure positions and velocities of a billion stars with unprecedented accuracy, for some stars it also determines their speed across the camera’s sensor. This information is used in real time by the attitude and orbit control system to ensure the satellite’s orientation is maintained with the desired precision.

    These speed statistics are routinely sent to Earth, along with the science data, in the form of housekeeping data. They include the total number of stars, used in the attitude-control loop, that is detected every second in each of Gaia’s fields of view.

    It is the latter – which is basically an indication of the density of stars across the sky – that was used to produce this uncommon visualisation of the celestial sphere. Brighter regions indicate higher concentrations of stars, while darker regions correspond to patches of the sky where fewer stars are observed.

    The plane of the Milky Way, where most of the Galaxy’s stars reside, is evidently the brightest portion of this image, running horizontally and especially bright at the centre. Darker regions across this broad strip of stars, known as the Galactic Plane, correspond to dense, interstellar clouds of gas and dust that absorb starlight along the line of sight.

    The Galactic Plane is the projection on the sky of the Galactic disc, a flattened structure with a diameter of about 100 000 light-years and a vertical height of only 1000 light-years.

    Beyond the plane, only a few objects are visible, most notably the Large and Small Magellanic Clouds, two dwarf galaxies orbiting the Milky Way, which stand out in the lower right part of the image.

    2
    Annotated map

    A few globular clusters – large assemblies up to millions of stars held together by their mutual gravity – are also sprinkled around the Galactic Plane. Globular clusters, the oldest population of stars in the Galaxy, sit mainly in a spherical halo extending up to 100 000 light-years from the centre of the Milky Way.

    The globular cluster NGC 104 is easily visible in the image, to the immediate left of the Small Magellanic Cloud.


    NGC 104

    Other globular clusters are highlighted in an annotated version of this image.

    Interestingly, the majority of bright stars that are visible to the naked eye and that form the familiar constellations of the sky are not accounted for in this image because they are too bright to be used by Gaia’s control system. Similarly, the Andromeda galaxy – the largest galactic neighbour of the Milky Way – also does not stand out here.

    Counterintuitively, while Gaia carries a billion-pixel camera, it is not a mission aimed at imaging the sky: it is making the largest, most precise 3D map of our Galaxy, providing a crucial tool for studying the formation and evolution of the Milky Way.

    Gaia is an ESA mission to survey one billion stars in our Galaxy and local galactic neighbourhood in order to build the most precise 3D map of the Milky Way and answer questions about its origin and evolution.

    Gaia’s scientific operations begun on 25 July 2014 with the special scanning through a narrow region in the sky, while the normal scanning procedure was switched on a month later, on 25 August.

    The mission’s primary scientific product will be a catalogue with the position, motion, brightness and colour of the surveyed stars. An intermediate version of the catalogue will be released in 2016. In the meantime, Gaia’s observing strategy, with repeated scans of the entire sky, will allow the discovery and measurement of transient events across the sky.

    Acknowledgement: this image was prepared by Edmund Serpell, a Gaia Operations Engineer working in the Mission Operations Centre at ESA’s European Space Operations Centre in Darmstadt, Germany.

    This image is licenced under the Creative Commons Attribution-ShareAlike 3.0 IGO (CC BY-SA 3.0 IGO) licence.

    See the full article 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 May 20, 2015 Permalink | Reply
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    From U Heidelberg: “Asteroid Research Benefits From Gaia Satellite Mission” 

    U Heidelberg bloc

    University of Heidelberg

    20 May 2015
    No Writer Credit

    Scientists discover dozens of small celestial bodies every night

    ESA Gaia satellite
    ESA/Gaia

    Astronomical research on asteroids, i.e. minor planets, is also benefiting from the large-scale Gaia mission of the European Space Agency (ESA). Even though the astrometry satellite’s main purpose is to precisely measure nearly one billion stars in the Milky Way, it has tracked down a multitude of minor planets in our solar system. To determine its current position in space and thus ensure Gaia’s extremely high measurement accuracy, images are taken every day of the regions of the sky where the very faint satellite is located. “Each night the images reveal several dozen minor planets. The data are quite valuable for our understanding of the origin of our solar system,” says Dr. Martin Altmann of the Institute for Astronomical Computing (ARI), which is part of the Centre for Astronomy of Heidelberg University. Dr. Altmann heads the observation programme to determine the position of the Gaia satellite for the Data Processing and Analysis Consortium (DPAC), which is responsible for evaluating the data from Gaia.

    The Gaia astrometry satellite, which has been fully operational since August 2014, measures with pinpoint accuracy the positions, movements and distances of stars in the Milky Way, thereby furnishing the basis for a three-dimensional map of our home galaxy. According to Dr. Altmann, it became clear during preparation for the Gaia mission that the ambitious accuracy goals required novel methods to determine the position and velocity of the satellite itself. For this purpose an observation campaign was launched to determine Gaia’s position and velocity from Earth. As early as 2009, Dr. Altmann of the ARI and his colleague Dr. Sebastien Bouquillon of the Observatoire de Paris (France) began planning the programme together with an international team. Among the partners for the implementation, they attracted observatories in Chile and Spain. The Institute for Astronomical Computing is responsible for coordinating the daily observations. Since the launch of Gaia in December 2013, Gaia’s ground-based position measurements are transmitted regularly to mission control, the European Space Operations Centre in Darmstadt.

    Dr. Altmann explains that the astrometry satellite is at a distance of approximately 1.5 million kilometres and is always located in the region of space away from the Sun as viewed from the Earth. “For this reason Gaia’s positioning images are also perfect for observing minor planets. This so-called oppositional position brings these celestial bodies closer to Earth, making them appear brighter than at other times,” continues the Heidelberg researcher. More than 2,000 small planets have been found this way since the beginning of this year, mainly on images from the VST telescope of the European Southern Observatory (ESO) in Chile.

    ESO VST telescope
    ESO VST

    Dr. Altmann indicates that nearly 40 per cent of them are new discoveries. Moreover, these current measurements are especially interesting for already known minor planets as well, precisely because Gaia and the minor planets located in the same part of space are always opposite the sun at the time of observation. Just like with the full moon, the planets’ entire earthward side is completely illuminated only at that location. This allows the researchers to measure the asteroid’s reflectivity very accurately and draw conclusions as to their chemical composition. Up to now only approximately 30 asteroids have their reflectivity sufficiently well-determined, according to Dr. Altmann.

    The Gaia astrometry satellite itself will also discover and accurately measure many asteroids in its survey of the sky, but in totally different regions. “In this respect, the observations from the Gaia mission and the ground-based measurements complement each other extremely well,” says Dr. Altmann. “We hope not only to acquire new insight into the origins of our home galaxy through the Gaia satellite mission. We will certainly learn more about the origins of our solar system,” stresses Prof. Dr. Stefan Jordan of the Institute for Astronomical Computing, whose responsibilities also include public relations for the DPAC Consortium.

    See the full article here.

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    Founded in 1386, Heidelberg University, a state university of BadenWürttemberg, is Germany’s oldest university. In continuing its timehonoured tradition as a research university of international standing the Ruprecht-Karls-University’s mission is guided by the following principles:
    Firmly rooted in its history, the University is committed to expanding and disseminating our knowledge about all aspects of humanity and nature through research and education. The University upholds the principle of freedom of research and education, acknowledging its responsibility to humanity, society, and nature.

     
  • richardmitnick 2:42 pm on January 14, 2015 Permalink | Reply
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    From ESA: “A year on-station for Gaia” 

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    European Space Agency

    ESA’s Gaia mission will produce an unprecedented 3D map of our Galaxy by mapping, with exquisite precision, the position and motion of a billion stars. The key to this is the billion-pixel camera at the heart of its dual telescope. This animation illustrates how the camera works.


    Watch, enjoy, learn.

    ESA Gaia satellite
    ESA/Gaia

    ESA Gaia Camera
    Gaia’ camera

    Today’s update provided by Gaia Spacecraft Operations Manager Dave Milligan at ESOC.

    Time flies when you’re mapping a billion stars!

    One year ago, Gaia performed its last major orbit insertion burn and was stable at ‘L2’ (see What’s an ell-two?).

    Gaia is an ambitious mission to chart a three-dimensional map of our Galaxy, the Milky Way, in the process revealing the composition, formation and evolution of the Galaxy. Credit: ESA–D. Ducros, 2013

    After a smooth, but operationally intense lift-off, LEOP (launch and early orbit phase) and transfer phase, in which Gaia travelled the 1.5 million km from Earth to the point at which the sky survey will be done, the work to start Gaia’s mapping task was only just beginning.

    14 January 2014, 15:55 UTC

    The five thrusters used to perform the orbit insertion are commanded to stop firing and there are smiles in the control room at ESOC as the telemetry on the screens confirm the last planned ‘critical operation’ is successfully completed.

    Thruster Firings

    Earlier, Gaia’s operators had to perform a number of critical operations in the initial post-launch period: the first autonomous flight activation; sun-shield deployment and three orbit manoeuvres – when the thrusters were heavily used – all between 2 and 27 days after launch.

    Had these gone wrong, the mission operations team would have been in a race against the clock to stop Gaia drifting off into interplanetary space.

    Today we are one year on from the last of these.

    The blue line in the Earth-centered plot below shows the correct trajectory (i.e. the nominal case when the manoeuvre worked) and the green shows what would have happened without this manoeuvre (drift around the Earth-Moon system followed by escape into interplanetary space).

    2
    Gaia L2 arrival – worst case scenario

    Now that this activity was over, the operations team could fully focus on the commissioning phase, testing and configuring the spacecraft and payload operations until system performance was ready to perform science.

    This was not time-critical, but was technically demanding, and this phase would eventually last six months.

    Gaia is a one-off, purpose-built spacecraft that is capable of mapping the positions of one billion stars to unprecedented precision (to the micro-arc-second level, comparable to the width of a smart phone on the Moon as viewed from Earth). This performance is far beyond anything previously achieved, and the Gaia spacecraft is a marvel of engineering in its own right.

    Spacecraft are complex

    Spacecraft such as Gaia are complex machines, which have layered operational modes.

    The spacecraft can be flown and operated, performing the more basic tasks, with a subset of service module units on and working. Just like the tip of a pyramid can only be placed on top after all other stones have been laid, all on-board prime units must be switched on and correctly configured for full performance. This, together with checking a number of redundant units and functions, is the task of teams on ground during the commissioning phase.

    The Gaia spacecraft has a relatively large fraction of ‘bespoke’ units i.e. custom designed, due largely to the incredible precision requirements. Not the least of these are the telescopes and camera.

    Gaia’s camera is the most impressive ever flown in space, containing 106 CCDs, which are around 90% light efficient (a CCD in a typical digital camera is around 20% efficient).

    These have to be linked to the on-board attitude control system to achieve the needed and incredible precision for mapping the stars.

    Gaia must rotate once every 6 hours to scan the heavens and this rate is so precisely controlled that the error is equivalent to one rotation every 410 years. There are (and can be) no moving parts on board, so the data is downlinked through a novel electromagnetically steerable antenna.

    Attitude control is provided by a micro propulsion system that has its first flight use with Gaia. This delivers micro-Newton levels of thrust primarily to oppose the quantum mechanical force exerted by sunlight falling onto the sunshield. An atomic clock is used for precise time-stamping, which in fact allows controllers to see the time dilation effects from Einstein’s Theory of General Relativity.

    Just after entry into the operational orbit, most of these hardware units were either off or had hardly been used at all.

    Solving problems with teamwork

    One year ago, the critical phases were over and the operations team began focusing on the complex task of bringing the spacecraft up to full performance.

    In terms of what was planned, this consisted of an iterative phase where teams on the ground send commands to move the mirrors and adjust the spacecraft spin rate and then industry (i.e. the spacecraft manufacturer) and the mission science teams analysed the results before the next tuning cycle. The other major element planned was the tuning of Gaia’s seven powerful video processing units, each connected to a row of the camera’s CCDs, responsible for identifying and characterizing the stars that will make up Gaia’s map.

    These tasks progressed well, but almost immediately after orbit insertion some problems became apparent.

    First noticed through an apparent dimming of the on-board laser used to track the angle between the telescope mirrors, and later confirmed by data from the stars themselves, ice was unexpectedly building up and had to be dealt with .

    Also apparent was more background light than expected .

    These issues, like many others, were dealt with and solved in a series of brainstorming review meetings between experts, some of which required in-orbit special operations to be developed and executed to provide the necessary data. For example, Gaia’s normally rock-stable sun-attitude was changed twice in special operations designed to characterise the stray-light problem.

    Examples elsewhere from the spacecraft commissioning period included a micro-propulsion thruster with unexpected performance levels and a back-up chemical thruster that had a failed valve (meaning it was permanently lost).

    Teamwork has been critical

    Again, teamwork in brainstorming review meetings was critical to solving these issues. The on-board software could be quickly reprogrammed to match the new performance of the micro-propulsion thruster and the on-board protection software was changed to make sure the system would never try to use the chemical thruster that had failed (for this was a thruster present in case the spacecraft was in trouble and needed to put itself into ‘Safe Mode’).
    An artist’s impression of a Type Ia supernova – the explosion of a white dwarf locked in a binary system with a companion star. Credit: ESA/ATG medialab/C. Carreau

    3
    An artist’s impression of a Type Ia supernova – the explosion of a white dwarf locked in a binary system with a companion star. Credit: ESA/ATG medialab/C. Carreau

    By the end of the commissioning phase, the teamwork between the ESA operations, project and science teams together with the industry experts at AirbusDS and the wider Gaia scientific community organised into the Data Processing and Analysis Consortium (DPAC) had delivered the spacecraft in excellent shape.

    The spacecraft was correctly configured and the software of the majority of on-board units had been changed based on the lessons learned to date. In getting to this stage, approximately 400 000 telecommands had been sent by ground teams.

    Shortly after the commissioning ended, a new Survival Mode was activated on board, using thrusters that are normally used only for orbit manoeuvres. This meant that single failure tolerance had been fully restored, even with a permanently lost thruster.

    The mapping begins

    By July 2014, Gaia was busy mapping parts of the sky that had been calibrated by ground telescopes, before its nominal scanning mode was entered in September.

    At this point Gaia was working so well that it was producing more data than originally foreseen, since it was able to see stars fainter than required. Towards the end of the year, operators had to come up with a method to partially automate ground operations allowing Gaia to take advantage of more ground station time and expand its mapping data set.

    It’s been a busy first year for Gaia, but at the one-year point there’s a good sense of achievement.

    The science data are now coming down in huge quantities (11 billion camera transits were recorded by the one-year launch anniversary), with anticipation slowly building for what Gaia may find in the coming years.

    But even before the first map release next year, Gaia is already making discoveries.

    Gaia discovers its first supernova

    12 September 2014

    For further information, please contact:

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

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

    Simon Hodgkin
    Institute of Astronomy
    Cambridge, UK
    Tel: +44 1223 766657
    Email: sth@ast.cam.ac.uk

    Łukasz Wyrzykowski
    Warsaw University Astronomical Observatory
    Warsaw, Poland
    Tel: +48 608 648817
    Email: lw@astrouw.edu.pl

    Nadejda Blagorodnova
    Institute of Astronomy
    Cambridge, UK
    Tel: +44 1223 337548
    Email: nblago@ast.cam.ac.uk

    While scanning the sky to measure the positions and movements of stars in our Galaxy, Gaia has discovered its first stellar explosion in another galaxy far, far away.

    5
    Supernova Gaia14aaa and its host galaxy. Credit: M. Fraser/S. Hodgkin/L. Wyrzykowski/H. Campbell/N. Blagorodnova/Z. Kostrzewa-Rutkowska/Liverpool Telescope/SDSS

    This powerful event, now named Gaia14aaa, took place in a distant galaxy some 500 million light-years away, and was revealed via a sudden rise in the galaxy’s brightness between two Gaia observations separated by one month.

    Gaia, which began its scientific work on 25 July, repeatedly scans the entire sky, so that each of the roughly one billion stars in the final catalogue will be examined an average of 70 times over the next five years.

    “This kind of repeated survey comes in handy for studying the changeable nature of the sky,” comments Simon Hodgkin from the Institute of Astronomy in Cambridge, UK.

    Many astronomical sources are variable: some exhibit a regular pattern, with a periodically rising and declining brightness, while others may undergo sudden and dramatic changes.

    “As Gaia goes back to each patch of the sky over and over, we have a chance to spot thousands of ‘guest stars’ on the celestial tapestry,” notes Dr Hodgkin. “These transient sources can be signposts to some of the most powerful phenomena in the Universe, like this supernova.”

    Dr Hodgkin is part of Gaia’s Science Alert Team, which includes astronomers from the Universities of Cambridge, UK, and Warsaw, Poland, who are combing through the scans in search of unexpected changes.

    6
    Discovery of supernova Gaia14aaa.
    Credit: ESA/Gaia/DPAC/Z. Kostrzewa-Rutkowska (Warsaw University Astronomical Observatory) & G. Rixon (Institute of Astronomy, Cambridge)

    It did not take long until they found the first ‘anomaly’ in the form of a sudden spike in the light coming from a distant galaxy, detected on 30 August. The same galaxy appeared much dimmer when Gaia first looked at it just a month before.

    “We immediately thought it might be a supernova, but needed more clues to back up our claim,” explains Łukasz Wyrzykowski from the Warsaw University Astronomical Observatory, Poland.

    Other powerful cosmic events may resemble a supernova in a distant galaxy, such as outbursts caused by the mass-devouring supermassive black hole at the galaxy centre.

    However, in Gaia14aaa, the position of the bright spot of light was slightly offset from the galaxy’s core, suggesting that it was unlikely to be related to a central black hole.

    So, the astronomers looked for more information in the light of this new source. Besides recording the position and brightness of stars and galaxies, Gaia also splits their light to create a spectrum. In fact, Gaia uses two prisms spanning red and blue wavelength regions to produce a low-resolution spectrum that allows astronomers to seek signatures of the various chemical elements present in the source of that light.

    7
    Gaia spectrum of supernova Gaia14aaa. Credit: ESA/Gaia/DPAC/N. Blagorodnova, M. Fraser, H. Campbell, A. Hall (Institute of Astronomy, Cambridge)

    “In the spectrum of this source, we could already see the presence of iron and other elements that are known to be found in supernovas,” says Nadejda Blagorodnova, a PhD student at the Institute of Astronomy in Cambridge.

    In addition, the blue part of the spectrum appears significantly brighter than the red part, as expected in a supernova. And not just any supernova: the astronomers already suspected it might be a ‘Type Ia’ supernova – the explosion of a white dwarf locked in a binary system with a companion star.

    While other types of supernovas are the explosive demises of massive stars, several times more massive than the Sun, Type Ia supernovas are the end product of their less massive counterparts.

    Low-mass stars, with masses similar to the Sun’s, end their lives gently, puffing up their outer layers and leaving behind a compact white dwarf. Their high density means that white dwarfs can exert an intense gravitational pull on a nearby companion star, accreting mass from it until the white dwarf reaches a critical mass that then sparks a violent explosion.

    To confirm the nature of this supernova, the astronomers complemented the Gaia data with more observations from the ground, using the Isaac Newton Telescope (INT) and the robotic Liverpool Telescope on La Palma, in the Canary Islands, Spain.

    A high-resolution spectrum, obtained on 3 September with the INT, confirmed not only that the explosion corresponds to a Type Ia supernova, but also provided an estimate of its distance. This proved that the supernova happened in the galaxy where it was observed.

    “This is the first supernova in what we expect to be a long series of discoveries with Gaia,” says Timo Prusti, ESA’s Gaia Project Scientist.

    Supernovas are rare events: only a couple of these explosions happen every century in a typical galaxy. But they are not so rare over the whole sky, if we take into account the hundreds of billions of galaxies that populate the Universe.

    Astronomers in the Science Alert Team are currently getting acquainted with the data, testing and optimising their detection software. In a few months, they expect Gaia to discover about three new supernovas every day.

    In addition to supernovas, Gaia will discover thousands of transient sources of other kinds – stellar explosions on smaller scale than supernovas, flares from young stars coming to life, outbursts caused by black holes that disrupt and devour a nearby star, and possibly some entirely new phenomena never seen before.

    “The sky is ablaze with peculiar sources of light, and we are looking forward to probing plenty of those with Gaia in the coming years,” concludes Dr Prusti.
    Background Information

    Gaia is an ESA mission to survey one billion stars in our Galaxy and local galactic neighbourhood in order to build the most precise 3D map of the Milky Way and answer questions about its origin and evolution. Gaia’s scientific operations begun on 25 July 2014 with the special scanning through a narrow region in the sky, while the normal scanning procedure was switched on a month later, on 25 August.

    The mission’s primary scientific product will be a catalogue with the position, motion, brightness and colour of the surveyed stars. An intermediate version of the catalogue will be released in 2016. In the meantime, Gaia’s observing strategy, with repeated scans of the entire sky, will allow the discovery and measurement of transient events across the sky.

    This first such discovery is the Type Ia supernova described in this article, named Gaia14aaa. The name follows the convention used for naming transient astronomical sources, which acknowledges the name of the survey followed by the year of discovery and by a combination of letters to indicate the order of discovery. The supernova’s host galaxy, SDSS J132102.26+453223.8, is about 500 million light-years away.

    Converting the telemetry received from Gaia into scientific data products is the responsibility of the Gaia Data Processing and Analysis Consortium (DPAC). Within the Photometric Processing coordination unit of DPAC, the Science Alert Team is responsible for identifying transient sources.

    During the first few months of Gaia’s scientific operations, astronomers in the Science Alert Team will be compiling a preliminary catalogue of transients on a daily basis, depending on the data availability.

    Follow-up observations from the ground to assess the nature of these sources will be carried out by the collaborating partners from Europe and elsewhere. Schools and amateur astronomers will also be involved in following up these targets.

    Scientists from the Gaia mission and other astronomers studying transient events are gathered this week at the 5th Gaia Science Alerts Workshop, hosted at Warsaw University, Poland from 9 to 12 September 2014.

    See the full article 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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