Tagged: ESA/Gaia Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 11:55 am on May 3, 2019 Permalink | Reply
    Tags: "Observing Gaia from Earth to improve its star maps", Astronomers have been regularly monitoring the satellite’s position in the sky with telescopes across the world, , , , , ESA/Gaia, , ,   

    From European Space Agency: “Observing Gaia from Earth to improve its star maps” 

    ESA Space For Europe Banner

    From European Space Agency

    2 May 2019

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

    Martin Altmann
    Astronomisches Rechen-Institut
    Centre for Astronomy of Heidelberg University, Germany
    Email: maltmann@ari.uni-heidelberg.de

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

    Calum Turner
    ESO Public Information Officer
    Garching bei München, Germany
    Tel: +49 89 3200 6670
    Email: pio@eso.org

    1
    Gaia among the stars

    ESA/GAIA satellite

    While ESA’s Gaia mission has been surveying more than one billion stars from space, astronomers have been regularly monitoring the satellite’s position in the sky with telescopes across the world, including the European Southern Observatory in Chile, to further refine Gaia’s orbit and ultimately improve the accuracy of its stellar census.

    One year ago, the Gaia mission released its much-awaited second set of data, which included high-precision measurements – positions, distance indicators and proper motions – of more than one billion stars in our Milky Way galaxy.

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

    The catalogue, based on less than two years of observations and almost four years of data processing and analysis by a collaboration of about 450 scientists and software engineers, has enabled transformational studies in many fields of astronomy, generating more than 1000 scientific publications in the past twelve months.

    Meanwhile in space, Gaia keeps scanning the sky and gathering data that is being crunched for future releases to achieve even higher precision on the position and motion of stars and enable ever deeper and more detailed studies into our place in the cosmos. But to reach the accuracy expected for Gaia’s final catalogue, it is crucial to pinpoint the position and motion of the satellite from Earth.

    To this aim, the flight dynamics experts at ESA’s operations centre make use of a combination of techniques, from traditional radio tracking and ranging to simultaneous observing using two radio antennas – the so-called delta-DOR method.

    3
    The Cebreros station, DSA 2 (Deep Space Antenna 2), is located 77 kms west of Madrid, Spain. It hosts a 35-metre antenna with transmission and reception in X-band and reception in Ka-band. It provides routine support to deep-space missions including Mars Express, Gaia and Rosetta.

    ESA Mars Express Orbiter

    ESA/Rosetta spacecraft, European Space Agency’s legendary comet explorer Rosetta

    In a unique and novel approach for ESA, the ground-based tracking of Gaia also includes optical observations provided by a network of medium-size telescopes across the planet.

    The European Southern Observatory’s (ESO) 2.6-metre VLT Survey Telescope (VST) in Chile records Gaia’s position in the sky for about 180 nights every year.


    Part of ESO’s Paranal Observatory, the VLT Survey Telescope (VISTA) 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, with an elevation of 2,635 metres (8,645 ft) above sea level

    “This is an exciting ground-space collaboration, using one of ESO’s world-class telescopes to anchor the trailblazing observations of ESA’s billion star surveyor,” says Timo Prusti, Gaia project scientist at ESA.

    “The VST is the perfect tool for picking out the motion of Gaia,” adds Ferdinando Patat, head of the ESO’s Observing Programmes Office. “Using one of ESO’s first-rate ground-based facilities to bolster cutting-edge space observations is a fine example of scientific cooperation.”

    In addition, the two-metre Liverpool telescope located on La Palma, Canary Islands, Spain, and the Las Cumbres Optical Global Telescope Network, which operates two-metre telescopes in Australia and the US, have also been observing Gaia over the past five years as part of the Ground Based Optical Tracking (GBOT) campaign.


    Liverpool Telescope at the Observatorio del Roque de los Muchachos, altitude 2,363 m (7,753 ft)

    LCOGT Las Cumbres Observatory Global Telescope Network, Haleakala Hawaii, USA, Elevation 10,023 ft (3,055 m)

    “Gaia observations require a special observing procedure,” explains Monika Petr-Gotzens, who has coordinated the execution of ESO’s observations of Gaia since 2013. “The spacecraft is what we call a ‘moving target’, as it is moving quickly relative to background stars – tracking Gaia is quite the challenge!”

    In these images Gaia is a mere dot of light among the many stars that the satellite itself has been measuring, so painstaking calibration is needed to transform this body of observations into meaningful data that can be included in the determination of the satellite’s orbit.

    This required using data from Gaia’s second release to identify the stars in each of the images collected over the past five years and calculate the satellite’s position in the sky with a precision of 20 milliarcseconds or better (one arcsecond is equivalent to the size of a Euro coin seen from a distance of about four kilometres).

    “This is a challenging process: we are using Gaia’s measurements of the stars to calibrate the position of the Gaia spacecraft and ultimately improve its measurements of the stars,” explains Timo.

    3
    Gaia’s sky in colour

    The ground-based observations also provide key information to improve the determination of Gaia’s velocity through space, which must be known to the precision of a few millimetres per second. This is necessary to correct for a phenomenon known as aberration of light – an apparent distortion in the direction of incoming light due to the relative motion between the source and an observer – in a way similar to tilting one’s umbrella while walking through the rain.

    “After careful and lengthy data processing, we have now achieved the accuracy required for the ground-based observations of Gaia to be implemented as part of the orbit determination,” says Martin Altmann, lead of the GBOT campaign from the Astronomisches Rechen-Institut, Centre for Astronomy of Heidelberg University, Germany, who works in close collaboration with colleagues from the Paris Observatory in France.

    The GBOT information will be used to improve our knowledge of Gaia’s orbit not only in observations to come, but also for all the data that have been gathered from Earth in the previous years, leading to improvements in the data products that will be included in future releases.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.

    ESA50 Logo large

     
  • richardmitnick 11:18 am on March 13, 2019 Permalink | Reply
    Tags: "Streams of Stars Snaking Through the Galaxy Could Help Shine a Light on Dark Matter", Adrian Price-Whelan calls GD-1 "the Goldilocks stream" because it's in just the right place., , , At about 33000 light-years (10 kiloparsecs) GD-1 is the longest stellar stream in the galactic halo, , , Dark matter makes up the bulk of the mass in the universe but it has never been directly observed, ESA/Gaia, , , scores of dark matter seeds are scattered through galaxies like the Milky Way, , The stellar stream known as GD-1 is a thin flow of material tucked inside the Galactic halo   

    From smithsonian.com: “Streams of Stars Snaking Through the Galaxy Could Help Shine a Light on Dark Matter” 

    smithsonian
    From smithsonian.com

    March 12, 2019
    Nola Taylor Redd

    When the Milky Way consumes another galaxy, tendrils of stellar streams survive the merger, containing clues about the universe’s mysterious unseen matter.

    1
    An ultraviolet image of the Andromeda galaxy, the closest major galaxy to the Milky Way, taken by NASA’s Galaxy Evolution Explorer space telescope. Like our own galaxy, Andromeda is a spiral galaxy with a flat rotating disk of stars and gas and a concentrated bulge of stars at the center. (NASA/JPL-Caltech)

    When a small galaxy strays too close to the Milky Way, the gravity from our larger galaxy reels it in. Gas and stars are ripped from the passing galaxy as it falls inward toward its doom, creating streams of material that stretch between the galactic pair. These streams continue to tear away stars until the infalling object has been completely consumed. After the merger is over, some of the only remaining signs of the devoured object are the stellar streams snaking through the Milky Way, a small sample of stars from a galaxy long gone.

    In addition to being a record of the past, one of these streams may provide the first direct evidence for small scale clusters of dark matter—the elusive material that is believed to account for 85 percent of all matter in the universe. A recent analysis of a trail of stars reveals that it interacted with a dense object in the last few hundred million years. After ruling out the most likely suspects, the researchers determined that the relatively recently made gap in the stream may have been caused by a small clump of dark matter. If confirmed, the eddies of this stellar stream could help scientists sort through the competing theories about dark matter and perhaps even close in on the characteristics of the mysterious material.

    The stellar stream known as GD-1 is a thin flow of material tucked inside the Galactic halo, the loose collection of stars and gases surrounding the disk of the Milky Way. Using data released last April from the European Space Agency’s Gaia space telescope, which is in the process of assembling the most detailed map of the Milky Way’s stars ever made, astronomers were able to use precise positional data to reconstruct the movement of the stars in GD-1.

    ESA/GAIA satellite

    Torn from a cloud of material, the stream is the last remnant of an object that was likely consumed by our galaxy in the last 300 million years—an eyeblink on astronomical timescales.

    Gaia found two small breaks in the stream, the first unambiguous observation of gaps in a stellar stream, as well as a dense collection of stars called a spur. Together, these features suggest that a small but massive object shook up the material of the stream.

    “I think this is the first direct dynamical evidence for the small-scale [structure] of dark matter,” says Adrian Price-Whelan, an astronomer at the Flatiron Institute in New York. Working with Ana Bonaca of the Harvard-Smithsonian Center for Astrophysics, Price-Whelan investigated the newfound structures in GD-1 to determine their source and presented the results earlier this year at the winter meeting of the American Astronomical Society.

    At about 33,000 light-years (10 kiloparsecs), GD-1 is the longest stellar stream in the galactic halo. While Price-Whelan and his colleagues were able to use models to show that one of the gaps formed during the generation of the stream, the other gap remained a mystery. However, along with the puzzle, Gaia also revealed a solution: the spur.

    When an object travels past or through a stellar stream, it disrupts the stars. Price-Whelan compares the disruption to a strong jet of air blowing across a stream of water. The water—or stars—plume outward along the path of the disruptor, creating a gap. Some move so fast that they escape the stream and go flying off into space, lost forever. Others are pulled back into the stream to form eddy-like features astronomers call spurs. After a few hundred million years, most spurs merge back into the stream, and only the gap remains, though some can be longer-lived.

    When it comes to spotting structures in stellar streams, Price-Whelan calls GD-1 “the Goldilocks stream” because it’s in just the right place. GD-1 is within the stars of the Milky Way, but moving in the opposite direction, making it easier for astronomers to pick out the stars in the stream from the surrounding objects. “At any given location, it’s moving differently from the way most of the other stars in that part of the sky are moving,” Price-Whelan says.

    The researchers modeled what type of objects could be responsible for the relatively newborn spur spotted in GD-1. They determined that the responsible object had to weigh in with a mass somewhere between 1 million and 100 million times the mass of the sun. Stretching only about 65 light-years (20 pc) in length, the object would have been incredibly dense. The interaction between the stream and the dense object would have likely happened within the last few hundred million years out of the 13.8-billion-year lifetime of the universe.

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

    Dark matter isn’t the only object that could have disrupted the stellar stream. A globular cluster or dwarf galaxy swooping nearby could also have created the gap and spur. Price-Whelan and his colleagues turned their eyes toward all known such objects and calculated their orbits, finding that none came close enough to GD-1 in the last billion years to shake things up. A chance encounter with a primordial black hole could have sent the stream’s stars flying, but it would have been an extremely rare event.

    According to dark matter simulations that allow for small structures, scores of dark matter seeds are scattered through galaxies like the Milky Way. A stream like GD-1 is expected to encounter at least one such seed within the last 8 billion years, making dark matter a far more likely perturber based on encounter rates than any other object.

    Dark matter makes up the bulk of the mass in the universe, but it has never been directly observed. The two leading theories for its existence are the warm dark matter model and the Lambda cold dark matter model (ΛCDM), which is the model preferred by most scientists.

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

    Under ΛCDM, dark matter forms clumps that can be as large as a galaxy or as small as a soda can. Warm dark matter models suggest that the material has less massive particles and lacks the can-sized structures that the ΛCDM model suggests. Finding evidence for small scale structures of dark matter could help weed out certain models and start to narrow in on some of the characteristics of the tantalizing stuff.

    “Streams might be the only avenue that we could [use to] study the lowest mass end of what dark matter is doing,” Price-Whelan says. “If we want to be able to confirm or reject or rule out different theories of dark matter, we really need to know what’s happening at [the low] end.”

    Gaia’s data helped identify the stars of the spur, but it’s not detailed enough to compare the velocity differences between them and the stars in the stream, which could help confirm that dark matter perturbed the structure. Price-Whelan and his colleagues want to use NASA’s Hubble Space Telescope to further study the movement of the faint stars in GD-1. Although Gaia has opened the door to wide-scale examination of the movement of stars across the Milky Way, Price-Whelan says that it can’t compete with the HST when it comes to very faint stars. “You can drill much deeper when you have a dedicated telescope like Hubble,” he says.

    The differences in how the stars of the stream and spur move could help astronomers determine how much energy the perturbing object carried, as well as allow researchers to calculate its orbit. These pieces of information could be used to track down the disruptive dark matter clump and study its immediate environment.

    In addition to making a more in-depth study of GD-1, astronomers plan to apply the same techniques enabled by Gaia’s data to some of the more than 40 other streams surrounding the Milky Way. Spotting spurs and gaps in other streams and tying them to dark matter could further improve our understanding of how the mysterious substance interacts with the visible galaxy.

    After decades of puzzling over the mystery of dark matter, the gaps and spurs in stellar streams like GD-1 may finally help to reveal the secrets of the substance that makes up most of the universe. “This is one of the most exciting things that has come out of Gaia,” Price-Whelan says.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Smithsonian magazine and Smithsonian.com place a Smithsonian lens on the world, looking at the topics and subject matters researched, studied and exhibited by the Smithsonian Institution — science, history, art, popular culture and innovation — and chronicling them every day for our diverse readership.

     
  • richardmitnick 10:11 pm on February 15, 2019 Permalink | Reply
    Tags: "Tidal Tails – The Beginning Of The End Of An Open Star Cluster", , , , , ESA/Gaia, The Hyades- the star cluster closest to the Sun,   

    From University of Heidelberg: “Tidal Tails – The Beginning Of The End Of An Open Star Cluster” 

    U Heidelberg bloc

    From University of Heidelberg

    15 February 2019

    Heidelberg researchers verify this phenomenon using Gaia data from the Hyades.

    ESA/GAIA satellite

    1
    Image of the Hyades, the star cluster closest to the Sun. Source: NASA, ESA, and STScI

    NASA/ESA Hubble Telescope

    In the course of their life, open star clusters continuously lose stars to their surroundings. The resulting swath of tidal tails provides a glimpse into the evolution and dissolution of a star cluster. Thus far only tidal tails of massive globular clusters and dwarf galaxies have been discovered in the Milky Way system. In open clusters, this phenomenon existed only in theory. Researchers at Heidelberg University have now finally verified the existence of such a tidal tail in the star cluster closest to the Sun, the Hyades. An analysis of measurements from the Gaia satellite led to the discovery.

    Open star clusters are collections of approximately 100 to a few thousand stars that emerge almost simultaneously from a collapsing gas cloud and move through space at about the same speed. Owing to a number of influences, however, they do begin to disperse after a few hundred million years. Among the factors working against the gravitationally bound stars is the tidal force of a galaxy, which pulls the stars out of the cluster. Tidal tails then form during the movement of the star cluster through the Milky Way. It is the beginning of the end of an open star cluster.

    2
    Position of the Hyades and its now observed tidal tails in the sky. The background shows Gaia’s all-sky view of our Milky Way Galaxy. Source: S. Röser, ESA/Gaia/DPAC

    Together with researchers from the Max Planck Institute for Astronomy in Heidelberg, scientists from the Centre for Astronomy of Heidelberg University (ZAH) have detected this phenomenon for the first time in the Hyades, one of the older and best-studied open star clusters in the Milky Way system. They studied the data published in April 2018 from the Gaia satellite, which has been systematically mapping the heavens for five years. Rather than taking direct photographs, Gaia measures the stars’ motion and position.

    From this data, the Heidelberg astronomers identified two tidal tails of the Hyades with a total of approximately 500 stars extending up to 650 light-years from the cluster. Dr Siegfried Röser of the Königstuhl State Observatory of the ZAH explains that one of the tails precedes the open star cluster and the other follows it. “Our discovery shows that it is possible to trace the trajectories of individual stars of the Milky Way back to their point of origin in a star cluster”, states Dr Röser. The astronomer believes that this marks the beginning of many significant discoveries in galactic astronomy. Apart from the Heidelberg astronomers, a team of researchers from Vienna also discovered the tidal tails of the Hyades.

    The research was conducted under the auspices of The Milky Way System Collaborative Research Centre (CRC 881) at Heidelberg University, which is funded by the German Research Foundation.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Heidelberg Campus

    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 10:34 am on January 10, 2019 Permalink | Reply
    Tags: , , , , Crystallised white dwarf cores, ESA/Gaia, Gaia reveals how Sun-like stars turn solid after their demise, It is estimated that up to 97 per cent of stars in the Milky Way will eventually turn into white dwarfs, The Sun still has about five billion years before it becomes a white dwarf, White dwarfs are the remains of medium-sized stars similar to our Sun   

    From European Space Agency: “Gaia reveals how Sun-like stars turn solid after their demise” 

    ESA Space For Europe Banner

    From European Space Agency

    9 January 2019

    Pier-Emmanuel Tremblay
    University of Warwick
    Coventry, UK
    Tel: +44 24765 28407
    Mob: +44 74647 22697
    Email: P-E.Tremblay@warwick.ac.uk

    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
    Crystallised white dwarf core

    Data captured by ESA’s galaxy-mapping spacecraft Gaia has revealed for the first time how white dwarfs, the dead remnants of stars like our Sun, turn into solid spheres as the hot gas inside them cools down.

    ESA/GAIA satellite

    This process of solidification, or crystallisation, of the material inside white dwarfs was predicted 50 years ago but it wasn’t until the arrival of Gaia that astronomers were able to observe enough of these objects with such a precision to see the pattern revealing this process.

    “Previously, we had distances for only a few hundreds of white dwarfs and many of them were in clusters, where they all have the same age,” says Pier-Emmanuel Tremblay from the University of Warwick, UK, lead author of the paper describing the results, published today in Nature.

    “With Gaia we now have the distance, brightness and colour of hundreds of thousands of white dwarfs for a sizeable sample in the outer disc of the Milky Way, spanning a range of initial masses and all kinds of ages.”

    It is in the precise estimate of the distance to these stars that Gaia makes a breakthrough, allowing astronomers to gauge their true brightness with unprecedented accuracy.

    2
    Stellar evolution

    White dwarfs are the remains of medium-sized stars similar to our Sun. Once these stars have burnt all the nuclear fuel in their core, they shed their outer layers, leaving behind a hot core that starts cooling down.

    These ultra-dense remnants still emit thermal radiation as they cool, and are visible to astronomers as rather faint objects. It is estimated that up to 97 per cent of stars in the Milky Way will eventually turn into white dwarfs, while the most massive of stars will end up as neutron stars or black holes.

    The cooling of white dwarfs lasts billions of years. Once they reach a certain temperature, the originally hot matter inside the star’s core starts crystallising, becoming solid. The process is similar to liquid water turning into ice on Earth at zero degrees Celsius, except that the temperature at which this solidification happens in white dwarfs is extremely high – about 10 million degrees Celsius.

    In this study, the astronomers analysed more than 15 000 stellar remnant candidates within 300 light years of Earth as observed by Gaia and were able to see these crystallising white dwarfs as a rather distinct group.

    2
    Gaia data

    “We saw a pile-up of white dwarfs of certain colours and luminosities that were otherwise not linked together in terms of their evolution,” says Pier-Emmanuel.

    “We realised that this was not a distinct population of white dwarfs, but the effect of the cooling and crystallisation predicted 50 years ago.”

    The heat released during this crystallisation process, which lasts several billion years, seemingly slows down the evolution of the white dwarfs: the dead stars stop dimming and, as a result, appear up to two billion years younger than they actually are. That, in turn, has an impact on our understanding of the stellar groupings these white dwarfs are a part of.

    “White dwarfs are traditionally used for age-dating of stellar populations such as clusters of stars, the outer disc, and the halo in our Milky Way,” explains Pier-Emmanuel.

    “We will now have to develop better crystallisation models to get more accurate estimates of the ages of these systems.”

    Not all white dwarfs crystallise at the same pace. More massive stars cool down more rapidly and will reach the temperature at which crystallisation happens in about one billion years. White dwarfs with lower masses, closer to the expected end stage of the Sun, cool in a slower fashion, requiring up to six billion years to turn into dead solid spheres.

    The Sun still has about five billion years before it becomes a white dwarf, and the astronomers estimate that it will take another five billion years after that to eventually cool down to a crystal sphere.

    “This result highlights the versatility of Gaia and its numerous applications,” says Timo Prusti, Gaia project scientist at ESA.

    “It’s exciting how scanning stars across the sky and measuring their properties can lead to evidence of plasma phenomena in matter so dense that cannot be tested in the laboratory.”

    Explore the Gaia Data Release 2 archive here

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.

    ESA50 Logo large

     
  • richardmitnick 8:32 am on December 14, 2018 Permalink | Reply
    Tags: , , , , ESA/Gaia   

    From European Space Agency: “The Universe of Gaia” 


    ESA / CNES / Arianespace; ESA / Gaia / DPAC; Gaia Sky / S. Jordan / T. Sagristà; Koppelman, Villalobos and Helmi; Marchetti et al. 2018; NASA / ESA / Hubble; ESO, M. Kornmesser, L. Calçada

    ESA Space For Europe Banner

    From European Space Agency

    13/12/2018

    Launched in December 2013, ESA’s Gaia satellite has been scanning the sky to perform the most precise stellar census of our Milky Way galaxy, observing more than one billion stars and measuring their positions, distances and motions to unprecedented accuracy.

    ESA/GAIA satellite

    The second Gaia data release, published in April, has provided scientists with extraordinary data to investigate the formation and evolution of stars in the Galaxy and beyond, giving rise to hundreds of scientific studies that are revolutionising our view of the cosmos.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.

    ESA50 Logo large

     
  • richardmitnick 9:55 am on November 1, 2018 Permalink | Reply
    Tags: , , , , ESA/Gaia, Galactic Ghosts-Gaia Uncovers Major Event in the Formation of the Milky Way   

    From European Space Agency: “Galactic Ghosts-Gaia Uncovers Major Event in the Formation of the Milky Way” 

    ESA Space For Europe Banner

    From European Space Agency

    31 October 2018

    Amina Helmi
    Kapteyn Astronomical Institute
    University of Groningen
    The Netherlands
    Email: ahelmi@rug.astro.nl

    Carine Babusiaux
    Université Grenoble Alpes, CNRS, IPAG
    Grenoble, France
    GEPI, Observatoire de Paris, Université PSL, CNRS
    Meudon, France
    Email: carine.babusiaux@univ-grenoble-alpes.fr

    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
    Galactic merger

    ESA’s Gaia mission has made a major breakthrough in unravelling the formation history of the Milky Way.

    ESA/GAIA satellite

    Instead of forming alone, our Galaxy merged with another large galaxy early in its life, around 10 billion years ago. The evidence is littered across the sky all around us, but it has taken Gaia and its extraordinary precision to show us what has been hiding in plain sight all along.

    Gaia measures the position, movement and brightness of stars to unprecedented levels of accuracy.

    Using the first 22 months of observations, a team of astronomers led by Amina Helmi, University of Groningen, The Netherlands, looked at seven million stars – those for which the full 3D positions and velocities are available – and found that some 30,000 of them were part of an ‘odd collection’ moving through the Milky Way. The observed stars in particular are currently passing by our solar neighbourhood.

    We are so deeply embedded in this collection that its stars surround us almost completely, and so can be seen across most of the sky.

    2
    Debris of galactic merger

    Even though they are interspersed with other stars, the stars in the collection stood out in the Gaia data because they all move along elongated trajectories in the opposite direction to the majority of the Galaxy’s other hundred billion stars, including the Sun.

    They also stood out in the so-called Hertzprung-Russell diagram – which is used to compare the colour and brightness of stars – indicating that they belong to a clearly distinct stellar population.

    The sheer number of odd-moving stars involved intrigued Amina and her colleagues, who suspected they might have something to do with the Milky Way’s formation history and set to work to understand their origins.

    In the past, Amina and her research group had used computer simulations to study what happens to stars when two large galaxies merge. When she compared those to the Gaia data, the simulated results matched the observations.

    “The collection of stars we found with Gaia has all the properties of what you would expect from the debris of a galactic merger,” says Amina, lead author of the paper published today in Nature.

    In other words, the collection is what they expected from stars that were once part of another galaxy and have been consumed by the Milky Way. The stars now form most of our Galaxy’s inner halo – a diffuse component of old stars that were born at early times and now surround the main bulk of the Milky Way known as the central bulge and disc.

    3
    The components of the Milky Way

    The Galactic disc itself is composed of two parts. There is the thin disc, which is a few hundred light years deep and contains the pattern of spiral arms made by bright stars. And there is the thick disc, which is a few thousand light years deep. It contains about 10–20 percent of the Galaxy’s stars yet its origins have been difficult to determine.

    According to the team’s simulations, as well as supplying the halo stars, the accreted galaxy could also have disturbed the Milky Way’s pre-existing stars to help form the thick disc.

    “We became only certain about our interpretation after complementing the Gaia data with additional information about the chemical composition of stars, supplied by the ground-based APOGEE survey,” says Carine Babusiaux, Université Grenoble Alpes, France, and second author of the paper.

    Stars that form in different galaxies have unique chemical compositions that match the conditions of the home galaxy. If this star collection was indeed the remains of a galaxy that merged with our own, the stars should show an imprint of this in their composition. And they did.

    The astronomers called this galaxy Gaia-Enceladus after one of the Giants in ancient Greek mythology, who was the offspring of Gaia, the Earth, and Uranus, the Sky.

    “According to the legend, Enceladus was buried under Mount Etna, in Sicily, and responsible for local earthquakes. Similarly, the stars of Gaia-Enceladus were deeply buried in the Gaia data, and they have shaken the Milky Way, leading to the formation of its thick disc,” explains Amina.

    4

    Even though no more evidence was really needed, the team also found hundreds of variable stars and 13 globular clusters in the Milky Way that follow similar trajectories as the stars from Gaia-Enceladus, indicating that they were originally part of that system.

    Globular clusters are groups of up to millions of stars, held together by their mutual gravity and orbiting the centre of a galaxy. The fact that so many clusters could be linked to Gaia-Enceladus is another indication that this must have once been a big galaxy in its own right, with its own entourage of globular clusters.

    Further analysis revealed that this galaxy was about the size of one of the Magellanic Clouds – two satellite galaxies roughly ten times smaller than the current size of the Milky Way.

    Ten billion years ago, however, when the merger with Gaia-Enceladus took place, the Milky Way itself was much smaller, so the ratio between the two was more like four to one. It was therefore clearly a major blow to our Galaxy.

    “Seeing that we are now starting to unravel the formation history of the Milky Way is very exciting,” says Anthony Brown, Leiden University, The Netherlands, who is a co-author of the paper and also chair of the Gaia Data Processing and Analysis Consortium Executive.

    Since the very first discussions about building Gaia 25 years ago, one of the mission’s key objectives was to examine the various stellar streams in the Milky Way, and reconstruct its early history. That vision is paying off.

    “Gaia was built to answer such questions,” says Amina. “We can now say this is the way the Galaxy formed in those early epochs. It’s fantastic. It’s just so beautiful and makes you feel so big and so small at the same time.”

    “By reading the motions of stars scattered across the sky, we are now able to rewind the history of the Milky Way and discover a major milestone in its formation, and this is possible thanks to Gaia,” concludes Timo Prusti, Gaia project scientist at ESA.

    The merger that led to the formation of the Milky Way’s inner stellar halo and thick disk by A. Helmi et al is published in Nature.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.

    ESA50 Logo large

     
  • richardmitnick 10:30 am on October 22, 2018 Permalink | Reply
    Tags: , , , , , ESA/Gaia, Gaia’s 2nd data release: 1.7 billion stars!   

    From EarthSky: “Gaia’s 2nd data release: 1.7 billion stars!” 

    1

    From EarthSky

    April 26, 2018 [Missed on first go round. Better late than never.]
    Deborah Byrd


    Gaia’s view of our home galaxy, the Milky Way, in a 360 degree interactive view (click arrows in upper left) via ESA/Gaia/DPAC; ATG medialab.

    Why did ESA’s director of science say Gaia’s observations are “redefining the foundations” of astronomy? Also, links to virtual reality resources made possible by Gaia, available for you to explore.

    It was less than a century ago, in 1920, that astronomers were famously debating the nature of so-called spiral nebulae. Some believed they lay inside our own Milky Way galaxy and were, perhaps, forming solar systems. Others thought they were large and distant separate galaxies. Thus the wisest astronomers of yesteryear couldn’t be sure of the true nature of our home galaxy, the Milky Way.

    Milky Way Galaxy Credits: NASA/JPL-Caltech/R. Hurt

    They couldn’t know it is indeed one galaxy of billions in the universe. And they couldn’t have imagined that now, just 100 years later, we’d have a space observatory like Gaia, whose goal is nothing less than to provide a 3D map of our galaxy. This mission had its second data release this week, along with a host of virtual reality resources for scientists and the public. The European Space Agency (ESA) said Gaia’s data makes possible:

    “… the richest star catalog to date, including high-precision measurements of nearly 1.7 billion stars and revealing previously unseen details of our home galaxy.”

    The new data, which ESA called phenomenal, is based on 22 months of Gaia’s charting of the sky. Günther Hasinger, ESA’s director of science, said:

    “The observations collected by Gaia are redefining the foundations of astronomy.”

    Why all the superlatives? What’s so amazing about Gaia’s data?

    Gaia gathers its phenomenal data in the most unglamorous of ways, via what’s called astrometry. Okay, now, hang in there with me. Think about this. Gaia’s job is to scan the sky repeatedly, observing each of its targeted billion stars an average of 70 times over its five-year mission. So, for example, we know our sun and all the stars in the Milky Way are moving continuously in great orderly masses around the center of our galaxy. We know that … but we didn’t have many details about how each star moves. How could we? The data for so many stars would be (are) massive; collecting the data, storing it and analyzing it requires today’s spacecraft and computer technologies.

    Over its five years, again and again and again, Gaia will acquire data points on the positions of Milky Way stars. Thus astronomers have already been able to produce an illustration like the very wonderful one below, which shows median velocities (the distances and directions traveled by each star per unit of time) of stars in our Milky Way.

    And so we begin to see – not just see in our minds, but actually see via Gaia’s actual data – that, due to the movements of its stars, our Milky Way galaxy is rotating, with us in its midst. You can see that in one illustration of Gaia’s data, below:

    2
    All-sky map of median velocities of about a billion stars toward or away from our sun, made possible by the Gaia mission. When you look at this map, you’re seeing a large-scale pattern caused by rotation of our Milky Way galaxy. Image via DPAC/ESA/STFC.

    And that’s just one example of the type of insight Gaia’s data can provide. ESA said:

    “Gaia was launched in December 2013 and started science operations the following year. The first data release, based on just over one year of observations, was published in 2016; it contained distances and motions of two million stars.

    The new data release, which covers the period between July 25, 2014, and May 23, 2016, pins down the positions of nearly 1.7 billion stars, and with a much greater precision. For some of the brightest stars in the survey, the level of precision equates to Earth-bound observers being able to spot a Euro coin lying on the surface of the moon.”

    Gaia is also gathering other types of data. The illustration below shows some of the ways in which Gaia sees our Milky Way:

    3
    Gaia’s all-sky view of our Milky Way galaxy and neighboring galaxies. The maps show the total brightness and color of stars (top), the total density of stars (middle) and the interstellar dust that fills the galaxy (bottom). These images are based on observations performed by the ESA satellite in each portion of the sky between July 2014 and May 2016, which were published as part of the Gaia second data release on April 25, 2018. Image via ESA.

    Virtual Reality Resources. Also, along with this second data release by Gaia, ESA has released several virtual reality resources to help visualize Gaia’s extraordinary data set, both for public outreach and for scientific purposes.

    One of the public offerings is Gaia Sky, a real-time, 3D astronomy visualisation software that runs on Windows, Linux and MacOS, developed in the framework of ESA’s Gaia mission by the Gaia group at the Astronomisches Rechen-Institut (Zentrum für Astronomie Heidelberg, University of Heidelberg, Germany). It contains a simulation of our solar system, a view of the second Gaia data release (with different selections based on parallax relative errors, ranging from a few million to hundreds of millions of stars), and additional astronomical and cosmological data to visualize star clusters, nearby galaxies, distant galaxies and quasars, and the Cosmic Microwave Background. The data are extensive, and you’ll want to explore them yourself here. ESA also offered this fun trailer for Gaia Sky:

    4
    Screen shot from Gaia Sky, a real-time, 3D astronomy visualization software that runs on Windows, Linux and MacOS.

    So you can see … there’s really a lot here to think about and explore, both for the public and for scientists. And maybe you can begin to see that – to those astronomers debating the nature of spiral nebulae in 1920 – Gaia’s data might have seemed nothing short of miraculous!

    The video at the full article shows a comparison between Gaia’s first and second data releases.

    Bottom line: The Gaia space observatory’s mission is to create a 3D map of our Milky Way galaxy. This week was its 2nd data release, consisting of high-precision measurements of some 1.7 billion stars. ESA also released a host of virtual reality resources, based on Gaia data.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.

     
  • richardmitnick 9:51 am on October 22, 2018 Permalink | Reply
    Tags: , , , , , ESA/Gaia, Our Milky Way almost collided with another galaxy   

    From EarthSky: “Our Milky Way almost collided with another galaxy” 

    1

    From EarthSky

    October 22, 2018
    Deborah Byrd

    Astronomers found a snail-shaped substructure of stars in our larger Milky Way galaxy.

    Milky Way Galaxy Credits: NASA/JPL-Caltech/R. Hurt

    It indicates the Milky Way is still enduring the effects of a near-collision that set millions of stars moving like ripples on a pond.

    1

    How do we know our own Milky Way galaxy’s history? One way is to observe the current motions of Milky Way stars (or as current as we can get them, given the finite speed of light). A revolution in our ability to track Milky Way star motions began in late 2013, with the launch of the European Space Agency’s Gaia mission.

    ESA/GAIA satellite

    Its job is to scan the sky repeatedly, observing each of its targeted billion stars an average of 70 times over the five-year mission. In this way, Gaia will see exactly how these stars are moving; ultimately, the scientists want to use this data to construct a 3-D map of our galaxy. In the meantime, with each new release of Gaia’s data, astronomers are uncovering new insights about our galaxy. Now Gaia data have revealed a near-collision between our Milky Way and a small galaxy hundreds of millions of years ago.

    The new work is based on Gaia’s second data release. It shows that some stars in our Milky Way galaxy are moving “like ripples on a pond,” these astronomers said, due to that long-ago collision.

    The timeframe for the close encounter is about 300 to 900 million years ago. That’s relatively recent history, astronomically speaking.

    The culprit could be the Sagittarius dwarf galaxy, one of several dozen small galaxies known to accompany our larger galaxy in space. The Milky Way is in the process of cannibalizing this little galaxy, which contains only a few tens of millions of stars, in contrast to our galaxy’s 100 billion stars.

    Teresa Antoja from Universitat de Barcelona, Spain, led the research. She said:

    “At the beginning the features were very weird to us. I was a bit shocked and I thought there could be a problem with the data because the shapes are so clear.”


    Gaia’s view of our home galaxy, the Milky Way, in a 360 degree interactive view (click arrows in upper left) via ESA/Gaia/DPAC; ATG medialab.

    3
    In this all-sky map of the density of stars in our Milky Way galaxy – observed by the Gaia mission between July 2014 and May 2016 – the Sagittarius dwarf galaxy, a small satellite of the Milky Way, is leaving a stream of stars behind as an effect of our larger galaxy’s gravitational tug. This star stream from the Sagittarius dwarf is visible as an elongated feature below our galaxy’s center (pointing in the downwards direction). Image via Gaia mission/ESA.

    A statement from the Gaia mission explained:

    “The pattern was revealed because Gaia not only accurately measures the positions of more than a billion stars but also precisely measures their velocities on the plane of the sky. For a subset of a few million stars, Gaia provided an estimate of the full three-dimensional velocities, allowing a study of stellar motion using the combination of position and velocity, which is known as ‘phase space.’

    In phase space, the stellar motions revealed an interesting and totally unexpected pattern when the star’s positions were plotted against their velocities. [Antoja] couldn’t quite believe her eyes when she first saw it on her computer screen.

    One shape in particular caught her attention. It was a snail shell-like pattern in the graph that plotted the stars’ altitude above or below the plane of the galaxy against their velocity in the same direction.”

    It had never been seen before.”

    But, these astronomers said, the Gaia data had undergone multiple validation tests. They said the only conclusion they could draw was that these features do exist in the vast space of our Milky Way. And they believe the structures they see come from a near-collision. Antoja explained:

    “It is a bit like throwing a stone in a pond, which displaces the water as ripples and waves.”

    Unlike the water molecules, which settle again, the stars retain a “memory” that they were perturbed, these astronomers said:

    “This memory is found in their motions. After some time, although the ripples may no longer be easily visible in the distribution of stars, they are still there when you look in their velocities.”

    Why didn’t astronomers see them before? The technology had not advanced far enough to enable that to happen. Antoja said:

    “It looks like suddenly you have put the right glasses on and you see all the things that were not possible to see before.”

    5
    Artist’s concept of perturbations in star velocities – like ripples in a pond – newly discovered in our Milky Way galaxy by the Gaia mission. These ripples suggest a smaller galaxy nearly collided with our Milky Way, 300 to 900 million years ago. Image via ESA.

    Bottom line: A snail-shaped substructure of stars in our larger Milky Way galaxy indicates the Milky Way is still enduring the effects of a near-collision that set millions of stars moving, like ripples on a pond.

    Source: A dynamically young and perturbed Milky Way disk [Nature]

    Via ESA

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.

     
  • richardmitnick 11:06 am on September 26, 2018 Permalink | Reply
    Tags: , , , , , ESA/Gaia   

    From European Space Agency: “Gaia finds candidates for interstellar ‘Oumuamua’s home” 

    ESA Space For Europe Banner

    From European Space Agency

    25 September 2018

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

    Coryn Bailer-Jones
    Max Planck Institute for Astronomy
    Heidelberg, Germany
    Tel: +49 6221 528224
    Email: calj@mpia.de

    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

    1
    Artist’s impression of ‘Oumuamua. Credit: ESO / M. Kornmesser. Phys.org

    Using data from ESA’s Gaia stellar surveyor, astronomers have identified four stars that are possible places of origin of ‘Oumuamua, an interstellar object spotted during a brief visit to our Solar System in 2017.

    ESA/GAIA satellite

    The discovery last year sparked a large observational campaign: originally identified as the first known interstellar asteroid, the small body was later revealed to be a comet, as further observations showed it was not slowing down as fast as it should have under gravity alone. The most likely explanation of the tiny variations recorded in its trajectory was that they are caused by gasses emanating from its surface, making it more akin to a comet.

    But where in the Milky Way did this cosmic traveller come from?

    Comets are leftovers of the formation of planetary systems, and it is possible that ‘Oumuamua was ejected from its home star’s realm while planets were still taking shape there. To look for its home, astronomers had to trace back in time not only the trajectory of the interstellar comet, but also of a selection of stars that might have crossed paths with this object in the past few million years.

    “Gaia is a powerful time machine for these types of studies, as it provides not only star positions but also their motions,” explains Timo Prusti, Gaia project scientist at ESA.

    To this aim, a team of astronomers led by Coryn Bailer-Jones at the Max Planck Institute for Astronomy in Heidelberg, Germany, dived into the data from Gaia’s second release, which was made public in April.


    The Gaia data contain positions, distance indicators and motions on the sky for more than a billion stars in our Galaxy; most importantly, the data set includes radial velocities – how fast they are moving towards or away from us – for a subset of seven million, enabling a full reconstruction of their trajectories. The team looked at these seven million stars, complemented with an extra 220 000 for which radial velocities are available from the astronomical literature.

    As a result, Coryn and colleagues identified four stars whose orbits had come within a couple of light years of ‘Oumuamua in the near past, and with relative velocities low enough to be compatible with likely ejection mechanisms.

    All four are dwarf stars – with masses similar to or smaller than our Sun’s – and had their ‘close’ encounter with the interstellar comet between one and seven million years ago. However, none of them is known to either harbour planets or to be part of a binary stellar system; a giant planet or companion star would be the preferred mechanism to have ejected the small body.

    While future observations of these four stars might shed new light on their properties and potential to be the home system of ‘Oumuamua, the astronomers are also looking forward to future releases of Gaia data. At least two are planned in the 2020s, which will include a much larger sample of radial velocities, enabling them to reconstruct and investigate the trajectories of many more stars.

    “While it’s still early to pinpoint ‘Oumuamua’s home star, this result illustrates the power of Gaia to delve into the history of our Milky Way galaxy,” concludes Timo.

    Science paper:
    Plausible home stars of the interstellar object ‘Oumuamua found in GaiaDR2 by C.A.L. Bailer-Jones et al is accepted in The Astronomical Journal.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.

    ESA50 Logo large

     
  • richardmitnick 12:55 pm on September 24, 2018 Permalink | Reply
    Tags: , , , , , ESA/Gaia, ,   

    From COSMOS Magazine: “A galactic near-miss set stars on an unexpected path around the Milky Way” 

    Cosmos Magazine bloc

    From COSMOS Magazine

    24 September 2018
    Ben Lewis

    A close pass from the Sagittarius dwarf galaxy sent ripples through the Milky Way that are still visible today.

    1
    Image Credit: R. Ibata (UBC), R. Wyse (JHU), R. Sword (IoA)

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

    1
    Tiny galaxy; big trouble. Gaia imaging shows the Sagittarius galaxy, circled in red. ESA/Gaia/DPAC

    ESA/GAIA satellite

    Between 300 and 900-million years ago the Sagittarius dwarf galaxy made a close pass by the Milky Way, setting millions of stars in motion, like ripples on a pond. The after-effects of that galactic near miss are still visible today, according to newly published findings.

    The unique pattern of stars left over from the event was detected by the European Space Agency’s star mapping mission, Gaia. The details are contained in a paper written by Teresa Antoja and colleagues from the Universitat de Barcelona in Spain, and published in the journal Nature.

    The movements of over six million stars in the Milky Way were tracked by Gaia to reveal that groups of them follow different courses as they orbit the galactic centre.

    In particular, the researchers found a pattern that resembled a snail shell in a graph that plotted star altitudes above or below the plane of the galaxy, measured against their velocity in the same direction. This is not to say that the stars themselves are moving in a spiral, but rather that the roughly circular orbits correlate with up-and-down motion in a pattern that has never been seen before.

    While some perturbations in densities and velocities had been seen previously, it was generally assumed that the movement of the disk’s stars is largely in dynamic equilibrium and symmetry about the galactic plane. Instead, Antoja’s team discovered something had knocked the disk askew.

    “It is a bit like throwing a stone in a pond, which displaces the water as ripples and waves,” she explains.

    Whereas water will eventually settle out after being disturbed, a star’s motion carries signatures from the change in movement. While the ripples in the distribution caused by Sagittarius passing by has evened out, the motion of the stars themselves still carry the pattern.

    “At the beginning the features were very weird to us,” says Antoja. “I was a bit shocked and I thought there could be a problem with the data because the shapes are so clear.”

    The new revelations came about because of a huge increase in quality of the Gaia data, compared to what had been captured previously. The new information provided, for the first time, a measurement of three-dimensional speeds for the stars. This allowed the study of stellar motion using the combination of position and velocity, known as “phase space”.

    “It looks like suddenly you have put the right glasses on and you see all the things that were not possible to see before,” says Antoja.

    Computer models suggest the disturbance occurred between 300 and 900 million years ago – a point in time when it’s known the Sagittarius galaxy came near ours.

    In cosmic terms, that’s not very long ago, which also came as a surprise. It was known that the Milky Way had endured some much earlier collisions – smashing into a dwarf galaxy some 10 billion years ago, for instance – but until now more recent events had not been suspected. The Gaia results have changed that view.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: