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  • richardmitnick 5:05 pm on July 26, 2020 Permalink | Reply
    Tags: "How old are the stars?", Accurately measuring the ages of the stars is the missing piece in the puzzle of Galactic archaeology that would help us understand how the Milky Way formed and evolved., , , , Chemical clocks, , ESA Gaia, , , Giada Casali, HARPS instrument on the ESO 3.6-metre telescope, Isochrone fitting method, , Laura Magrini, , The Gaia-ESO survey is the largest public spectroscopic survey (it used the Very Large Telescope (VLT) for over 300 nights!) carried out on an eight-metre-diameter telescope.   

    From ESOblog: “How old are the stars?” 

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    From ESOblog

    24 July 2020

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    Science Snapshots

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    Giada Casali and Laura Magrini

    It’s one of the biggest challenges in astrophysics: accurately measuring the ages of the stars is the missing piece in the puzzle of Galactic archaeology that would help us understand how the Milky Way formed and evolved. Scientists have started using the novel “chemical clocks” method to measure the ages of stars close to the Sun, but a team of astronomers recently used data from ESO telescopes to discover that the situation becomes much more complicated when we move outside our solar neighbourhood. We find out more from the scientists who led the research.

    Q. Firstly, what exactly do you mean when you talk about “chemical clocks”?

    Giada Casali (GC): When we talk about chemical clocks, we are referring to the ratios between particular pairs of elements — called chemical abundance ratios — in a star, that display a strong dependence on age. Every star is made up of lots of different elements that are produced in different processes and at different time scales, which is why we can use them as an innovative way to measure a star’s age.

    Laura Magrini (LM): For example, massive stars produce some elements quickly, whereas smaller stars produce them more slowly. So in theory, by looking at the spectrum of light from a star and measuring the abundance ratio between an element produced very quickly (when the Galaxy was very young) and an element produced much more slowly (and therefore only produced recently), we have a sort of track of when a star formed, and can therefore predict its age. Using stars located very close to the Sun, astronomers have discovered relations between age and some specific age-dependent abundance ratios. But we wanted to know: Are these relations universal? Can they be applied to all the stars in our Galaxy?

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    In April 2015 the HARPS laser frequency comb was installed on the HARPS planet-finding instrument on the ESO 3.6-metre telescope at the La Silla Observatory in Chile after completion of an intense first commissioning phase. The increase in accuracy made possible by this new installation should in future allow HARPS to be able to detect Earth-mass planets in Earth-like orbits around other stars for the first time. Credit ESO.

    ESO/HARPS at La Silla


    ESO 3.6m telescope & HARPS at Cerro LaSilla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    This picture shows a HARPS spectrum of the light from the two laser frequency combs that that were tested. Credit: ESO.

    Q. Could you summarise what you found in this research [Astronomy and Astrophysics] ?

    LM: Our idea, matured with Lorenzo Spina at Monash University in Australia, was to use archival data from the HARPS instrument on the ESO 3.6-metre telescope to measure specific chemical clocks in stars similar to the Sun, but with different abundances of elements heavier than helium and hydrogen. When we say “similar to the Sun”, we mean stars with very similar surface temperature and surface gravity and we call them solar-like stars; selecting such stars means that any variation in their spectrum of light is due to differences in chemical abundances, which we can presume are related only to their age.

    GC: We compared the ages of the solar-like stars, calculated due to their very well-known properties, with the ratios of specific elements, for example yttrium to magnesium, which is particularly strongly dependent on age. We were expecting to be able to apply our relation everywhere, but when we looked at the yttrium to magnesium ratio in stars further away from the Sun, in the direction of the Galactic centre, we found less yttrium than we would expect to find in stars of the same age close to the Sun. This means that this specific chemical clock relationship doesn’t apply in the same way everywhere in the Milky Way!

    Q. Were you surprised by this discovery?

    LM: Absolutely! Previous studies gave us hope that there may be a universal relationship between chemical clocks and age for solar-like stars throughout the Milky Way, but we found that this relationship can’t be applied everywhere. We think the difference arises because the stars didn’t all form at the same time, rather the Galaxy formed “inside out”, with the inner parts forming the quickest. This means that the star formation process varies throughout the Galaxy and the contribution of low and high mass stars with varying amounts of heavy elements is different in different places and at different epochs.

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    A Hertzsprung-Russell diagram for open clusters observed with the European Space Agency’s Gaia mission, plotted over an image of open cluster NGC 3293. Credit: Gaia data – ESA/Gaia/DPAC, Carine Babusiaux and co-authors of the paper Gaia Data Release 2: Observational Hertzsprung-Russell diagrams; Credit NGC 3293 – ESO/G. Beccari; Credit graphic design – R. Spiga (INAF)

    ESA/GAIA satellite

    The x axis shows the colour of stars in open clusters, and the y axis shows their apparent brightness as seen from Earth.

    Q. So why did you decide to carry out this research in the first place?

    GC: We wanted to investigate another method to date stars. Determining stellar ages is really important for astronomers to understand how the Milky Way formed and evolved, but it’s actually one of the most difficult parts of astrophysics. The most common technique used at the moment is called isochrone fitting; this technique compares the observed colours and brightnesses of stars with the expected ones from theoretical predictions, and from that comparison it infers the ages of the stars.

    The technique works very well for groups of stars all of the same age, for example members of star clusters. However, it is very difficult to use it to date individual stars, unless their properties are particularly well known. For solar-like stars, we do know their properties, so we can calibrate the new chemical clock method with the isochrone fitting method to find a new way to date stars with unknown properties.

    LM: Our idea was to find a universal relation, valid across the entire Milky Way, that would allow us to measure stellar ages simply by measuring their chemical composition…but life is always more complicated! In the past, we looked specifically at the abundance between carbon and nitrogen, which is a very effective method of figuring out the ages of giant stars. We found that since this abundance ratio essentially depends on stellar evolution, it is effectively valid across the entire Galactic disc, while it can vary, for instance, in the Galactic halo.

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

    Our ultimate aim is to collect different chemical relations for many stars that we know the ages of. The Gaia-ESO survey — which we used for both pieces of research — is the largest public spectroscopic survey (it used the Very Large Telescope (VLT) for over 300 nights!) carried out on an eight-metre-diameter telescope. It provides the most accurate database of detailed chemical abundances in stars across all the components of the Galaxy, and is also the only one focusing on star clusters, sampling all stars from young to old. The Gaia-ESO survey, therefore, is a fundamental tool for our research.

    Q. What are the implications of this discovery?

    LM: The result means that astronomers need to be more careful when they are trying to work out the ages of stars, as it is not as simple as we had previously assumed. We applied the relationships we found for different pairs of chemical elements in the HARPS data for nearby stars to open star clusters observed in the Gaia-ESO survey, and found that our relationship, built for the solar neighbourhood, does not correctly calculate the ages of stars in clusters in the Milky Way’s inner disc, where star formation and evolution happens much faster.

    We know that the Milky Way is made up of two discs of stars — one thin and one thick. Recent results from the European Space Agency’s Gaia satellite show that the thick disc probably formed through the interaction of the Milky Way with another galaxy several billion years ago, and that the stars in each disc have different ages. It is known that the stars in the thick disc contain much more magnesium than iron, for example, suggesting a different star formation history. Using our chemical clock relations, we were able to confirm the difference in ages of the two discs for stars located close to the Sun.

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    The anatomy of the Milky Way.
    Left: NASA/JPL Caltech, R Hurt; Right: ESA, Layout: ESA/ATG Medialab

    Q. Why do you think is it important to measure the ages of stars and understand the formation and the evolution of the Milky Way?

    LM: The only place that we can measure the ages of individual stars so precisely is the Milky Way. So by investigating these stars in more detail, we can better understand spiral galaxies, which are among the most common — and for me the most beautiful — type of galaxies in the Universe. As the luminous part of the Universe, galaxies are our “window” to understanding the Universe’s evolution; they are vital for understanding how it formed and evolved, and what its future could hold.

    Q. Do you plan to follow up this research in any way?

    GC: We want to dig deeper into the relationship between various chemical abundance ratios and distance from the centre of the Milky Way using open star clusters as a calibrator. In particular we will continue to use data from the Gaia-ESO survey and APOGEE.

    LM: In just a few years, the Extremely Large Telescope (ELT) will be up and running, and will allow us to resolve stars — and obtain their individual light spectra — in other galaxies with a similar detail to what we can now achieve only in the Milky Way. The ELT will be able to look at individual stars in other galaxies in our Local Group, and in the Virgo cluster of galaxies, so that we can measure their chemical composition and extend our studies to different environments.

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    Seen from the southern skies, the Large and Small Magellanic Clouds (the LMC and SMC, respectively) are bright patches in the sky. These two irregular dwarf galaxies, together with our Milky Way Galaxy, belong to the so-called Local Group of galaxies.

    Local Group. Andrew Z. Colvin 3 March 2011

    Astronomers once thought that the two Magellanic Clouds orbited the Milky Way, but recent research suggests this is not the case, and that they are in fact on their first pass by the Milky Way.

    The LMC, lying at a distance of 160 000 light-years, and its neighbour the SMC, some 200,000 light-years away, are among the largest distant objects we can observe with the unaided eye. Both galaxies have notable bar features across their central discs, although the very strong tidal forces exerted by the Milky Way have distorted the galaxies considerably. The mutual gravitational pull of the three interacting galaxies has drawn out long streams of neutral hydrogen that interlink the three galaxies.

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

    On 23 February 1987 the LMC hosted a dramatic cosmic explosion when a supernova (SN 1987A) ignited near the Tarantula Nebula. SN 1987A ranks among the brightest and closest events of this kind ever observed in recorded history.

    SN 1987A remnant, imaged by ALMA. The inner region is contrasted with the outer shell, lacy white and blue circles, where the blast wave from the supernova is colliding with the envelope of gas ejected from the star prior to its powerful detonation. Image credit: ALMA / ESO / NAOJ / NRAO / Alexandra Angelich, NRAO / AUI / NSF.

    Al Sufi, the Persian astronomer, described the LMC for the first time in his Book of Fixed Stars in AD 964. He called it Al Bakr, describing it as the White Ox of southern Arabia. Referred to in some older books as Nubecula Major and Minor, the Clouds take their modern name from the explorer Ferdinand Magellan, who first recorded their existence on his voyage of circumnavigation in 1519–22, and brought news of them to Europe; although a letter written by Amerigo Vespucci during his third voyage about 1503–4 may refer to them indirectly. Credit: ESO/S. Brunier

    Biography Giada Casali and Laura Magrini

    Giada Casali is a PhD student in her final year at the University of Florence/INAF-Astrophysical Observatory of Arcetri (Italy). She obtained her bachelor’s and master’s degrees at the University of Pisa (Italy). Giada has been working in the field of galactic archaeology, combining data collected by the European Space Agency’s Gaia satellite and ground-based large spectroscopic surveys. Her expertise mainly focuses on stellar spectroscopy and the determination of stellar ages.

    Laura Magrini obtained her PhD in 2003 at the University of Florence (Italy), in collaboration with the Instituto de Astronomía de Canarias (Spain). After several postdoctoral positions in the field of galactic archaeology, since 2012 she has worked as a researcher at the INAF-Astrophysical Observatory of Arcetri. She works on galaxy formation and evolution, using spectroscopic data of stellar populations in the Milky Way and nearby galaxies.

    See the full article here .


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

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
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    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo,

    Glistening against the awesome backdrop of the night sky above ESO_s Paranal Observatory, four laser beams project out into the darkness from Unit Telescope 4 UT4 of the VLT, a major asset of the Adaptive Optics system


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

    ESO VLT 4 lasers on Yepun


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

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

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

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

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    ESO APEXESO/MPIfR APEX high on the Chajnantor plateau in Chile’s Atacama region, at an altitude of over 4,800 m (15,700 ft)at the Llano de Chajnantor Observatory in the Atacama desert.

    A novel gamma ray telescope under construction on Mount Hopkins, Arizona. a large project known as the Cherenkov Telescope Array, composed of hundreds of similar telescopes to be situated in the Canary Islands and Chile. The telescope on Mount Hopkins will be fitted with a prototype high-speed camera, assembled at the University of Wisconsin–Madison, and capable of taking pictures at a billion frames per second. Credit: Vladimir Vassiliev

     
  • richardmitnick 7:00 am on May 26, 2020 Permalink | Reply
    Tags: "Galactic crash may have triggered Solar System formation", , , , , ESA Gaia, , Sagittarius galaxy   

    From European Space Agency – United Space in Europe: “Galactic crash may have triggered Solar System formation” 

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    From European Space Agency – United Space in Europe

    5.25.20

    Tomás Ruiz-Lara
    Instituto de Astrofísica de Canarias
    San Cristóbal de La Laguna, Tenerife, Spain
    Email: tomasruizlara@gmail.com

    Carme Gallart
    Instituto de Astrofísica de Canarias
    San Cristóbal de La Laguna, Tenerife, Spain
    Email: carme.gallart@iac.es

    ESA Media Relations
    Email: media@esa.int

    The formation of the Sun, the Solar System and the subsequent emergence of life on Earth may be a consequence of a collision between our galaxy, the Milky Way, and a smaller galaxy called Sagittarius, discovered in the 1990s to be orbiting our galactic home.

    Astronomers have known that Sagittarius repeatedly smashes through the Milky Way’s disc, as its orbit around the galaxy’s core tightens as a result of gravitational forces. Previous studies suggested that Sagittarius, a so called dwarf galaxy, had had a profound effect on how stars move in the Milky Way. Some even claim [Nature] that the 10 000 times more massive Milky Way’s trademark spiral structure might be a result of the at least three known crashes with Sagittarius over the past six billion years.

    A new study, based on data gathered by ESA’s galaxy mapping powerhouse Gaia, revealed for the first time that the influence of Sagittarius on the Milky Way may be even more substantial.

    ESA/GAIA satellite

    The ripples caused by the collisions seem to have triggered major star formation episodes, one of which roughly coincided with the time of the formation of the Sun some 4.7 billion years ago.

    “It is known from existing models that Sagittarius fell into the Milky Way three times – first about five or six billion years ago, then about two billion years ago, and finally one billion year ago,” says Tomás Ruiz-Lara, a researcher in Astrophysics at the Instituto de Astrofísica de Canarias (IAC) in Tenerife, Spain, and lead author of the new study.

    “When we looked into the Gaia data about the Milky Way, we found three periods of increased star formation that peaked 5.7 billion years ago, 1.9 billion years ago and 1 billion years ago, corresponding with the time when Sagittarius is believed to have passed through the disc of the Milky Way.”

    Ripples on the water

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    Sagittarius collisions trigger star formation in Milky Way

    The researchers looked at luminosities, distances and colours of stars within a sphere of about 6500 light years around the Sun and compared the data with existing stellar evolution models. According to Tomás, the notion that the dwarf galaxy may have had such an effect makes a lot of sense.

    “At the beginning you have a galaxy, the Milky Way, which is relatively quiet,” Tomás says. “After an initial violent epoch of star formation, partly triggered by an earlier merger as we described in a previous study [Nature], the Milky Way had reached a balanced state in which stars were forming steadily. Suddenly, you have Sagittarius fall in and disrupt the equilibrium, causing all the previously still gas and dust inside the larger galaxy to slosh around like ripples on the water.”

    In some areas of the Milky Way, these ripples would lead to higher concentrations of dust and gas, while emptying others. The high density of material in those areas would then trigger the formation of new stars.

    “It seems that not only did Sagittarius shape the structure and influenced the dynamics of how stars are moving in the Milky Way, it has also led to a build-up of the Milky Way,” says Carme Gallart, a co-author of the paper, also of the IAC. “It seems that an important part of the Milky Way’s stellar mass was formed due to the interactions with Sagittarius and wouldn’t exist otherwise.”

    The birth of the Sun


    Dwarf galaxy collisions make stars form in Milky Way
    The Sagittarius dwarf galaxy has smashed through the galactic disc of the 10 000 times more massive Milky Way for the first time about six billion years ago. The collision caused ripples in the interstellar dust and gas of the at that time relatively quiet Milky Way. Two further collisions followed 2 billion and 1 billion years ago. According to findings of a paper published in the journal Nature Astronomy in May 2020, in the aftermath of each of these collisions the galaxy experienced a period of intense star formation.
    The effects of Sagittarius on the structure and movement of stars in the Milky Way have been described previously, but the new findings for the first time show that the dwarf galaxy was likely directly responsible for the build-up of the stellar mass in the Milky Way. In fact, our parent star, the Sun, formed during the period in the wake of the first known collision. The scientists admit that it cannot be proven whether the particular cloud of dust and gas that gave rise to our parent star collapsed as a result of the collision with Sagittarius. It, however, seems possible that without the dwarf galaxy crossing paths with the Milky Way, Earth and life on it may not have been born.

    In fact, it seems possible that even the Sun and its planets would not have existed if the Sagittarius dwarf had not gotten trapped by the gravitational pull of the Milky Way and eventually smashed through its disc.

    “The Sun formed at the time when stars were forming in the Milky Way because of the first passage of Sagittarius,” says Carme. “We don’t know if the particular cloud of gas and dust that turned into the Sun collapsed because of the effects of Sagittarius or not. But it is a possible scenario because the age of the Sun is consistent with a star formed as a result of the Sagittarius effect.”

    Every collision stripped Sagittarius of some of its gas and dust, leaving the galaxy smaller after each passage. Existing data suggest that Sagittarius might have passed through the Milky Way’s disc again quite recently, in the last few hundred million years, and is currently very close to it. In fact, the new study found of a recent burst of star formation, suggesting a possible new and ongoing wave of stellar birth.

    According to ESA Gaia project scientist Timo Prusti, such detailed insights into the Milky Way’s star formation history wouldn’t be possible before Gaia, the star-mapping telescope launched in late 2013, whose two data releases in 2016 and 2018 revolutionised the study of the Milky Way.

    http://www.esa.int/Science_Exploration/Space_Science/Gaia/Gaia_s_billion-star_map_hints_at_treasures_to_come
    http://www.esa.int/Science_Exploration/Space_Science/Gaia/Gaia_creates_richest_star_map_of_our_Galaxy_and_beyond

    “Some determinations of star formation history in the Milky Way existed before based on data from ESA’s early 1990s Hipparcos mission,” says Timo.

    ESA/Hipparcos satellite

    “But these observations were focused on the immediate neighbourhood of the Sun. It wasn’t really representative and so it couldn’t uncover those bursts in star formation that we see now.

    “This is really the first time that we see a detailed star formation history of the Milky Way. It’s a testament to the scientific power of Gaia that we have seen manifest again and again in countless ground-breaking studies in a period of only a couple of years.”

    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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  • richardmitnick 10:15 am on August 28, 2019 Permalink | Reply
    Tags: , , , , ESA Gaia,   

    From European Space Agency: “Gaia untangles the starry strings of the Milky Way” 

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    From European Space Agency

    28 August 2019

    Marina Kounkel
    Western Washington University, USA
    Email: marina.kounkel@wwu.edu

    Kevin Covey
    Western Washington University, USA
    Email: kevin.covey@wwu.edu

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


    Gaia tracing starry strings in the Milky Way.

    Rather than leaving home young, as expected, stellar ‘siblings’ prefer to stick together in long-lasting, string-like groups, finds a new study of data from ESA’s Gaia spacecraft.

    ESA/GAIA satellite

    Exploring the distribution and past history of the starry residents of our galaxy is especially challenging as it requires astronomers to determine the ages of stars. This is not at all trivial, as ‘average’ stars of a similar mass but different ages look very much alike.

    To figure out when a star formed, astronomers must instead look at populations of stars thought to have formed at the same time – but knowing which stars are siblings poses a further challenge, since stars do not necessarily hang out long in the stellar cradles where they formed.

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    This diagram shows a face-on view of stellar ‘families’ – clusters (dots) and co-moving groups (thick lines) of stars – within about 3000 light-years from the Sun, which is located at the centre of the image. The diagram is based on data from the second data release of ESA’s Gaia mission. Each family is identified with a different colour and comprises a population of stars that formed at the same time. Purple hues represent the oldest stellar populations, which formed around 1 billion years ago; blue and green hues represent intermediate ages, with stars that formed hundreds of millions of years ago; orange and red hues show the youngest stellar populations, which formed less than a hundred million years ago. Thin lines show the predicted velocities of each group of stars over the next 5 million years, based on Gaia’s measurements. The lack of structures at the centre is an artefact of the method used to trace individual populations, not due to a physical bubble. A recent study using data from Gaia’s second data release uncovered nearly 2000 previously unidentified clusters and co-moving groups of stars and determined the ages for hundreds of thousands of stars, making it possible to track stellar ‘siblings’ and uncover their surprising arrangements. The study revealed that the most massive among these familial groups of stars may keep moving together through the galaxy in long, string-like configurations for billions of years after their birth.

    “To identify which stars formed together, we look for stars moving similarly, as all of the stars that formed within the same cloud or cluster would move in a similar way,” says Marina Kounkel of Western Washington University, USA, and lead author of the new study [The Astronomical Journal].

    “We knew of a few such ‘co-moving’ star groups near the Solar System, but Gaia enabled us to explore the Milky Way in great detail out to far greater distances, revealing many more of these groups.”

    Marina used data from Gaia’s second release to trace the structure and star formation activity of a large patch of space surrounding the Solar System, and to explore how this changed over time. This data release, provided in April 2018, lists the motions and positions of over one billion stars with unprecedented precision.

    The analysis of the Gaia data, relying on a machine learning algorithm, uncovered nearly 2000 previously unidentified clusters and co-moving groups of stars up to about 3000 light years from us – roughly 750 times the distance to Proxima Centauri, the nearest star to the Sun. The study also determined the ages for hundreds of thousands of stars, making it possible to track stellar ‘families’ and uncover their surprising arrangements.

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    Stellar families in Gaia’s sky

    “Around half of these stars are found in long, string-like configurations that mirror features present within their giant birth clouds,” adds Marina.

    “We generally thought young stars would leave their birth sites just a few million years after they form, completely losing ties with their original family – but it seems that stars can stay close to their siblings for as long as a few billion years.”

    The strings also appear to be oriented in particular ways with respect to our galaxy’s spiral arms – something that depends upon the ages of the stars within a string. This is especially evident for the youngest strings, comprising stars younger than 100 million years, which tend to be oriented at right angles to the spiral arm nearest to our Solar System.

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    Stellar groups and strings in the Milky Way – edge-on view

    The astronomers suspect that the older strings of stars must have been perpendicular to the spiral arms that existed when these stars formed, which have now been reshuffled over the past billion years.

    “The proximity and orientation of the youngest strings to the Milky Way’s present-day spiral arms shows that older strings are an important ‘fossil record’ of our galaxy’s spiral structure,” says co-author Kevin Covey, also of Western Washington University, USA.

    “The nature of spiral arms is still debated, with the verdict on them being stable or dynamic structures not settled yet. Studying these older strings will help us understand if the arms are mostly static, or if they move or dissipate and re-form over the course of a few hundred million years – roughly the time it takes for the Sun to orbit around the galactic centre a couple of times.”

    Gaia was launched in 2013, and is on a mission to chart a three-dimensional map of our galaxy, pinpointing the locations, motions, and dynamics of roughly one percent of the stars within the Milky Way, along with additional information about many of these stars. Further Gaia releases, including more and increasingly precise data, are planned for the coming decade, providing astronomers with the information they need to unfold the star-formation history of our galaxy.

    “Gaia is a truly ground-breaking mission that is revealing the history of the Milky Way – and its constituent stars – like never before,” adds Timo Prusti, Gaia project scientist at ESA.

    “As we will determine the ages for a larger number of stars distributed throughout our galaxy, not just those residing in compact clusters, we’ll be in an even better position to analyse how these stars have evolved over time.”

    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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  • richardmitnick 8:05 am on April 30, 2019 Permalink | Reply
    Tags: , , , , , ESA Gaia   

    From European Space Agency: “Gaia’s first asteroid discoveries” 

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    From European Space Agency

    29/04/2019

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    While scanning the sky to chart a billion stars in our Milky Way galaxy, ESA’s Gaia satellite is also sensitive to celestial bodies closer to home, and regularly observes asteroids in our Solar System.

    ESA/GAIA satellite

    This view shows the orbits of more than 14 000 known asteroids (with the Sun at the centre of the image) based on information from Gaia’s second data release, which was made public in 2018.

    The majority of asteroids depicted in this image, shown in bright red and orange hues, are main-belt asteroids, located between the orbits of Mars and Jupiter; Trojan asteroids, found around the orbit of Jupiter, are shown in dark red.

    In yellow, towards the image centre, are the orbits of several tens of near-Earth asteroids observed by Gaia: these are asteroids that come to within 1.3 astronomical units (AU) to the Sun at the closest approach along their orbit. The Earth circles the Sun at a distance of 1 AU (around 150 million km) so near-Earth asteroids have the potential to come into proximity with our planet.

    Most asteroids that Gaia detects are already known, but every now and then, the asteroids seen by ESA’s Milky Way surveyor do not match any existing observations. This is the case for the three orbits shown in grey in this view: these are Gaia’s first asteroid discoveries.

    The three new asteroids were first spotted by Gaia in December 2018, and later confirmed by follow-up observations performed with the Haute-Provence Observatory in France, which enabled scientists to determine their orbits.

    Haute-Provence Observatory 1.93 meter telescope interior

    L’Observatoire de Haute-Provence, in the southeast of France,, about 90 km east of Avignon and 100 km north of Marseille Altitude 650 m (2,130 ft)

    Comparing these informations with existing observations indicated the objects had not been detected earlier.

    While they are part of the main belt of asteroids, all three move around the Sun on orbits that have a greater tilt (15 degrees or more) with respect to the orbital plane of planets than most main-belt asteroids.

    The population of such high-inclination asteroids is not as well studied as those with less tilted orbits, since most surveys tend to focus on the plane where the majority of asteroids reside. But Gaia can readily observe them as it scans the entire sky from its vantage point in space, so it is possible that the satellite will find more such objects in the future and contribute new information to study their properties.

    Alongside the extensive processing and analysis of Gaia’s data in preparation for subsequent data releases, preliminary information about Gaia’s asteroid detections are regularly shared via an online alert system so that astronomers across the world can perform follow-up observations. To observe these asteroids, a 1-m or larger telescope is needed.

    Once an asteroid detected by Gaia has been identified also in ground-based observations, the scientists in charge of the alert system analyse the data to determine the object’s orbit. In case the ground observations match the orbit based on Gaia’s data, they provide the information to the Minor Planet Center, which is the official worldwide organization collecting observational data for small Solar System bodies like asteroids and comets.

    This process may lead to new discoveries, like the three asteroids with orbits depicted in this image, or to improvements in the determination of the orbits of known asteroids, which are sometimes very poorly known. So far, several tens of asteroids detected by Gaia have been observed from the ground in response to the alert system, all of them belonging to the main belt, but it is possible that also near-Earth asteroids will be spotted in the future.

    A number of observatories across the world are already involved in these activities, including the Haute-Provence Observatory, Kyiv Comet station, Odessa-Mayaki, Terskol, C2PU at Observatoire de la Côte d’Azur and Las Cumbres Observatory Global Telescope Network. The more that join, the more we will learn about asteroids – known and new ones alike.

    C2PU (Centre Pédagogique Planète et Univers),at Observatoire de la Côte d’Azur

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

    Acknowledgement: Gaia Data Processing and Analysis Consortium (DPAC); Gaia Coordinating Unit 4; B. Carry, F. Spoto, P. Tanga (Observatoire de la Côte d’Azur, France) & W. Thuillot (IMCCE, Observatoire de Paris, France); Gaia Data Processing Center at CNES, Toulouse, France

    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.

    ESA50 Logo large

     
  • richardmitnick 12:09 pm on January 31, 2019 Permalink | Reply
    Tags: , , , , ESA Gaia, , , NASA’s NICER Mission Maps ‘Light Echoes’ of New Black Hole   

    From NASA: “NASA’s NICER Mission Maps ‘Light Echoes’ of New Black Hole” 

    NASA image
    From NASA

    Jan. 30, 2019

    Jeanette Kazmierczak
    jeanette.a.kazmierczak@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    NASA NICER on the ISS


    NASA/NICER on the ISS

    1
    In this illustration of a newly discovered black hole named MAXI J1820+070, a black hole pulls material off a neighboring star and into an accretion disk. Above the disk is a region of subatomic particles called the corona. Credit: Aurore Simonnet and NASA’s Goddard Space Flight Center

    Scientists have charted the environment surrounding a stellar-mass black hole that is 10 times the mass of the Sun using NASA’s Neutron star Interior Composition Explorer (NICER) payload aboard the International Space Station. NICER detected X-ray light from the recently discovered black hole, called MAXI J1820+070 (J1820 for short), as it consumed material from a companion star. Waves of X-rays formed “light echoes” that reflected off the swirling gas near the black hole and revealed changes in the environment’s size and shape.

    “NICER has allowed us to measure light echoes closer to a stellar-mass black hole than ever before,” said Erin Kara, an astrophysicist at the University of Maryland, College Park and NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who presented the findings at the 233rd American Astronomical Society meeting in Seattle. “Previously, these light echoes off the inner accretion disk were only seen in supermassive black holes, which are millions to billions of solar masses and undergo changes slowly. Stellar black holes like J1820 have much lower masses and evolve much faster, so we can see changes play out on human time scales.”

    A paper describing the findings, led by Kara, appeared in the Jan. 10 issue of Nature and is available online from [Nature].


    Watch how X-ray echoes, mapped by NASA’s Neutron star Interior Composition Explorer (NICER) revealed changes to the corona of black hole MAXI J1820+070.
    Credits: NASA’s Goddard Space Flight Center

    J1820 is located about 10,000 light-years away toward the constellation Leo. The companion star in the system was identified in a survey by ESA’s (European Space Agency) Gaia mission, which allowed researchers to estimate its distance.

    ESA/GAIA satellite

    Astronomers were unaware of the black hole’s presence until March 11, 2018, when an outburst was spotted by the Japan Aerospace Exploration Agency’s Monitor of All-sky X-ray Image (MAXI), also aboard the space station.

    JAXA MAXI on the ISS

    J1820 went from a totally unknown black hole to one of the brightest sources in the X-ray sky over a few days. NICER moved quickly to capture this dramatic transition and continues to follow the fading tail of the eruption.

    “NICER was designed to be sensitive enough to study faint, incredibly dense objects called neutron stars,” said Zaven Arzoumanian, the NICER science lead at Goddard and a co-author of the paper. “We’re pleased at how useful it’s also proven in studying these very X-ray-bright stellar-mass black holes.”

    A black hole can siphon gas from a nearby companion star into a ring of material called an accretion disk. Gravitational and magnetic forces heat the disk to millions of degrees, making it hot enough to produce X-rays at the inner parts of the disk, near the black hole. Outbursts occur when an instability in the disk causes a flood of gas to move inward, toward the black hole, like an avalanche. The causes of disk instabilities are poorly understood.

    Above the disk is the corona, a region of subatomic particles around 1 billion degrees Celsius (1.8 billion degrees Fahrenheit) that glows in higher-energy X-rays. Many mysteries remain about the origin and evolution of the corona. Some theories suggest the structure could represent an early form of the high-speed particle jets these types of systems often emit.

    Astrophysicists want to better understand how the inner edge of the accretion disk and the corona above it change in size and shape as a black hole accretes material from its companion star. If they can understand how and why these changes occur in stellar-mass black holes over a period of weeks, scientists could shed light on how supermassive black holes evolve over millions of years and how they affect the galaxies in which they reside.

    One method used to chart those changes is called X-ray reverberation mapping, which uses X-ray reflections in much the same way sonar uses sound waves to map undersea terrain. Some X-rays from the corona travel straight toward us, while others light up the disk and reflect back at different energies and angles.

    X-ray reverberation mapping of supermassive black holes has shown that the inner edge of the accretion disk is very close to the event horizon, the point of no return. The corona is also compact, lying closer to the black hole rather than over much of the accretion disk. Previous observations of X-ray echoes from stellar black holes, however, suggested the inner edge of the accretion disk could be quite distant, up to hundreds of times the size of the event horizon. The stellar-mass J1820, however, behaved more like its supermassive cousins.

    As they examined NICER’s observations of J1820, Kara’s team saw a decrease in the delay, or lag time, between the initial flare of X-rays coming directly from the corona and the flare’s echo off the disk, indicating that the X-rays traveled shorter and shorter distances before they were reflected. From 10,000 light-years away, they estimated that the corona contracted vertically from roughly 100 to 10 miles — that’s like seeing something the size of a blueberry shrink to something the size of a poppy seed at the distance of Pluto.

    “This is the first time that we’ve seen this kind of evidence that it’s the corona shrinking during this particular phase of outburst evolution,” said co-author Jack Steiner, an astrophysicist at the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research in Cambridge. “The corona is still pretty mysterious, and we still have a loose understanding of what it is. But we now have evidence that the thing that’s evolving in the system is the structure of the corona itself.”

    To confirm the decreased lag time was due to a change in the corona and not the disk, the researchers used a signal called the iron K line created when X-rays from the corona collide with iron atoms in the disk, causing them to fluoresce. Time runs slower in stronger gravitational fields and at higher velocities, as stated in Einstein’s theory of relativity. When the iron atoms closest to the black hole are bombarded by light from the core of the corona, the X-ray wavelengths they emit get stretched because time is moving slower for them than for the observer (in this case, NICER).

    Kara’s team discovered that J1820’s stretched iron K line remained constant, which means the inner edge of the disk remained close to the black hole — similar to a supermassive black hole. If the decreased lag time was caused by the inner edge of the disk moving even further inward, then the iron K line would have stretched even more.

    These observations give scientists new insights into how material funnels in to the black hole and how energy is released in this process.

    “NICER’s observations of J1820 have taught us something new about stellar-mass black holes and about how we might use them as analogs for studying supermassive black holes and their effects on galaxy formation,” said co-author Philip Uttley, an astrophysicist at the University of Amsterdam. “We’ve seen four similar events in NICER’s first year, and it’s remarkable. It feels like we’re on the edge of a huge breakthrough in X-ray astronomy.”

    NICER is an Astrophysics Mission of Opportunity within NASA’s Explorer program, which provides frequent flight opportunities for world-class scientific investigations from space utilizing innovative, streamlined and efficient management approaches within the heliophysics and astrophysics science areas. NASA’s Space Technology Mission Directorate supports the SEXTANT component of the mission, demonstrating pulsar-based spacecraft navigation.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

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

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

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

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

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

    Caltech Logo

    From Caltech

    12/18/2018

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

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

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

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

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

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

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

    ESA/GAIA satellite

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

    NASA Wise Telescope

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

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

    NASA/Spitzer Infrared Telescope

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

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

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

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

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


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


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

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

    See the full article here .


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


    Stem Education Coalition

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

    Caltech campus


    Caltech campus

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

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

    DiscoverMag

    From Discover Magazine

    November 2, 2018
    Stephen Ornes

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

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

    ESA GAIA Release 2 map

    ESA/GAIA satellite

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

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

    MIlky Way Halo NASA ESA STScI

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

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

    Sgr A* from ESO VLT


    SgrA* NASA/Chandra


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

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

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

    Large Magellanic Cloud. Adrian Pingstone December 2003

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

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

    Milky Way Dark Matter Halo Credit ESO L. Calçada

    This conversation has been edited for clarity and length.

    Where do hypervelocity stars come from?

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

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

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

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

    It’s a conservation of energy problem.

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

    How do you find a hypervelocity star?

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

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

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

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

    How does Gaia look at stars?

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

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

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

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

    Why do you want better measures on unbound stars?

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

    How can a star be useful?

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

    How can hypervelocity stars map the gravitational potential?

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

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

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

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

    How is dark matter distributed in the galaxy?

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

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

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

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

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

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

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

    See the full article here .

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

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


    Manu Garcia, a friend from IAC.

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

    ESA Space For Europe Banner

    From European Space Agency

    2.10.18

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

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

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

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

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

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

    ESA/GAIA satellite


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

    NASA/ESA Hubble Telescope

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    See the full article in Englsh here .


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

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

    ESA/GAIA satellite

    From ESA GAIA Mission

    via

    EarthSky

    August 30, 2018
    Paul Scott Anderson

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

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

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

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

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

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

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

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

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

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

    Parallax method ESA

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

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

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

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

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

    3
    Graph showing distribution of covering fractions for all stars in the Gaia-RAVE database overlap (left) and just those stars with less than 10 percent error in their Gaia parallax distance and less than 20 percent error in their RAVE spectrophotometric distance (right). If the parallax distance is smaller than the spectrophotometric distance, that is interpreted this as a negative covering fraction, and could be an indication of a Dyson sphere surrounding that star. Image via Zackrisson et al. 2018.

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

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

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

    Radial Velociity Method. ESO


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


    Radial Velocity Method-Las Cumbres Observatory

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

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

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

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

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

    5

    See the full article here .


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

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

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

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

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

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

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

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

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

    From astrobites: ” Clearing Up Stellar Streams with Gaia” 

    Astrobites bloc

    From astrobites

    26 June 2018
    Nora Shipp

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

    Status: Submitted to ApJL

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

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

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    What do we do?

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

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

     
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