From COSMOS Magazine: “10 billion years ago, the Milky Way ate a smaller galaxy dubbed Gaia-Enceladus”

Cosmos Magazine bloc

From COSMOS Magazine

23 July 2019
Barry Keily

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Artist’s impression of the merger between the Gaia-Enceladus galaxy and the Milky Way. NASA/ESA/Hubble, CC BY-SA 3.0 IGO

NASA/ESA Hubble Telescope

The Milky Way achieved its present form about 10 billion years ago when it merged with a smaller, neighbouring galaxy, new observations and modelling show.

Researchers led by astrophysicist Carme Gallar of the Universidad de La Laguna in Spain took advantage of measurements taken by the European Space Agency’s Gaia space observatory, which was launched in 2013 for the dedicated purpose of mapping the positions of stars with unprecedented accuracy.

ESA/GAIA satellite

They took the new data and subjected it to the two most commonly used techniques for estimating the age of stars – comparison with existing stellar models and what is known as colour-magnitude diagram fitting.

The approach was applied to Gaia measurements for the galaxy’s two outer rings of stars – known as the blue and red haloes – and what astronomers call its thick central disc.

The results showed that the stars in the haloes were all more ancient than those in the disc, with those in the former category all exceeding 10 billion years old.

MIlky Way Galaxy NASA/JPL-Caltech /ESO R. Hurt

The sharp age difference, the researchers say, confirms and, for the first time, accurately dates a titanic encounter between the progenitor of the Milky Way and a neighbouring, smaller galaxy, dubbed Gaia-Enceladus.

The different colours of the two haloes are an indication of the iron content of their respective stars. Red stars contain more of it than blue ones. Colour also often indicates great age. Until now, thus, astronomers assumed that the Milky Way’s blue halo was younger than its red one.

Gallar and colleagues used Gaia data to show that this is not the case. Their modelling reveals that the red and blue haloes contain stars of identical age, and that each region started and ceased star production at about the same time.

The difference in iron content, the researchers say, is a function of a galaxy size – more massive galaxies contain larger amounts of metal than smaller ones. Thus, they write, the result “means that the stars in the red sequence of the halo, being more metal-rich, must have formed in a galaxy that was more massive than the one where the stars in the blue sequence were formed.”

The blue halo, they say, represents the remnants of Gaia-Enceladus – a galaxy they estimate to have been around a quarter of the size of the proto Milky Way.

The research is published in the journal Nature Astronomy.

See the full article here .


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From European Space Agency: “Gaia starts mapping our galaxy’s bar”

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From European Space Agency

16 July 2019

Friedrich Anders
Institut de Ciències del Cosmos
Universitat de Barcelona, Spain
Email: fanders@fqa.ub.edu

Cristina Chiappini
Leibniz-Institut für Astrophysik Potsdam (AIP)
Germany
Email: cristina.chiappini@aip.de

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

ESA/GAIA satellite

The first direct measurement of the bar-shaped collection of stars at the centre of our Milky Way galaxy has been made by combining data from ESA’s Gaia mission with complementary observations from ground- and space-based telescopes.

Milky Way NASA/JPL-Caltech /ESO R. Hurt. The bar is visible in this image

The second release of data from ESA’s Gaia star-mapping satellite, published in 2018, has been revolutionising many fields of astronomy. The unprecedented catalogue contains the brightnesses, positions, distance indicators and motions across the sky for more than one billion stars in our Milky Way galaxy, along with information about other celestial bodies.

As impressive as this dataset sounds, this is really just the beginning. While the second release is based on the first 22 months of Gaia’s surveys, the satellite has been scanning the sky for five years and has many years ahead. New data releases planned in coming years will steadily improve measurements as well as provide extra information that will enable us to chart our home galaxy and delve into its history like never before.

Meanwhile, a team of astronomers have combined the latest Gaia data with infrared and optical observations performed from ground and space to provide a preview of what future releases of ESA’s stellar surveyor will reveal.

“We looked in particular at two of the stellar parameters contained in the Gaia data: the surface temperature of stars and the ‘extinction’, which is basically a measure of how much dust there is between us and the stars, obscuring their light and making it appear redder,” says Friedrich Anders from University of Barcelona, Spain, lead author of the new study.

“With this study [Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G=18, Astronomy & Astrophysics], we can enjoy a taster of the improvements in our knowledge of the Milky Way that can be expected from Gaia measurements in the third data release,” explains co-author Anthony Brown of Leiden University, The Netherlands, and chair of the Gaia Data Processing and Analysis Consortium Executive.

“These two parameters are interconnected, but we can estimate them independently by adding extra information obtained by peering through the dust with infrared observations.”

The team combined the second Gaia data release with several infrared surveys using a computer code called StarHorse, developed by co-author Anna Queiroz and collaborators. The code compares the observations with stellar models to determine the surface temperature of stars, the extinction and an improved estimate of the distance to the stars.

As a result, the astronomers obtained much better determination of the distances to about 150 million stars – in some cases, the improvement is up to 20% or more. This enabled them to trace the distribution of stars across the Milky Way to much greater distances than possible with the original Gaia data alone.

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Revealing the galactic bar

“With the second Gaia data release, we could probe a radius around the Sun of about 6500 light years, but with our new catalogue, we can extend this ‘Gaia sphere’ by three or four times, reaching out to the centre of the Milky Way,” explains co-author Cristina Chiappini from Leibniz Institute for Astrophysics Potsdam, Germany, where the project was coordinated.

There, at the centre of our galaxy, the data clearly reveals a large, elongated feature in the three-dimensional distribution of stars: the galactic bar.

“We know the Milky Way has a bar, like other barred spiral galaxies, but so far we only had indirect indications from the motions of stars and gas, or from star counts in infrared surveys. This is the first time that we see the galactic bar in 3D space, based on geometric measurements of stellar distances,” says Friedrich.

“Ultimately, we are interested in galactic archaeology: we want to reconstruct how the Milky Way formed and evolved, and to do so we have to understand the history of each and every one of its components,” adds Cristina.

“It is still unclear how the bar – a large amount of stars and gas rotating rigidly around the centre of the galaxy – formed, but with Gaia and other upcoming surveys in the next years we are certainly on the right path to figure it out.”

The team is looking forward to the next data release from the Apache Point Observatory Galaxy Evolution Experiment (APOGEE-2), as well as upcoming facilities such as the 4-metre Multi-Object Survey Telescope (4MOST) at the European Southern Observatory in Chile and the WEAVE (WHT Enhanced Area Velocity Explorer) survey at the William Herschel Telescope (WHT) in La Palma, Canary Islands.

SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude2,788 meters (9,147 ft)


SDSS Apache Point Observatory Galactic Evolution Experiment – Apogee

4MOST 4-metre Multi-Object Spectroscopic Telescope, on ESO’s VISTA, telescope, at Cerro Paranal,


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, with an elevation of 2,635 metres (8,645 ft) above sea level

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WEAVE (WHT Enhanced Area Velocity Explorer)

ING 4.2 meter William Herschel Telescope at Roque de los Muchachos Observatory on La Palma in the Canary Islands, 2,396 m (7,861 ft)

The third Gaia data release, currently planned for 2021, will include greatly improved distance determinations for a much larger number of stars, and is expected to enable progress in our understanding of the complex region at the centre of the Milky Way.

“We are revealing features in the Milky Way that we could not see otherwise: this is the power of Gaia, which is enhanced even further in combination with complementary surveys,” concludes Timo Prusti, Gaia project scientist at ESA.

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

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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

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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.

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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.

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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 .


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Please help promote STEM in your local schools.

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

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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.

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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 .

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

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From University of Heidelberg

15 February 2019

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

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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.

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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 .

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

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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

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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 .


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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.

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#astronomy, #astrophysics, #basic-research, #cosmology, #crystallised-white-dwarf-cores, #esagaia, #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: “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

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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.

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#astronomy, #astrophysics, #basic-research, #cosmology, #esagaia