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

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

    ESA/GAIA satellite

    From ESA GAIA Mission

    via

    EarthSky

    August 30, 2018
    Paul Scott Anderson

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

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    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.

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

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

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

    Parallax method ESA

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

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

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

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

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

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

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

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

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

    Radial Velociity Method. ESO


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


    Radial Velocity Method-Las Cumbres Observatory

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    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.”

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    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.

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  • 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

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

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

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    What do we do?

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

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

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

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

    ESO 50 Large

    From ESOblog

    25 May 2018

    1
    From ESA/GAIA

    ESA/GAIA satellite

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    See the full article here .


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    Astrobites bloc

    From astrobites

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

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

    ESA/GAIA satellite

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

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

    See the full article here .


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

    What do we do?

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

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

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

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

    NASA NExSS bloc

    NASA NExSS

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    From Many Worlds

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

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

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

    ESA/GAIA satellite

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

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

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

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

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

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

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

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

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

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

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

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


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

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

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

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

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

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

    3
    Parallax is the apparent shift in the position of stars as the Earth orbits the sun. It can be used to determine distances between stars. (ESA/ATG medialab)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    NASA/TESS

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

    See the full article here .

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    About Many Worlds

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

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

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

    About NExSS

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

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

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

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

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

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

    Astrobites bloc

    From astrobites

    May 7, 2018
    Matthew Green

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

    Status: Submitted to MNRAS, open access

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

    ESA/GAIA satellite

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

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

    See the full article here .

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    What do we do?

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

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

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

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

    AASNOVA

    AAS NOVA

    4 May 2018
    Kerry Hensley

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

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


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

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

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

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

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

    ESA/GAIA satellite


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

    A Classic Technique

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

    ESA/Hipparcos satellite

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

    New Measurement to an Old Cluster

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

    NASA/ESA Hubble Telescope

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

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

    Unprecedented Precision

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

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

    Citation

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

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

    See the full article here .

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    1

    AAS Mission and Vision Statement

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

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

    Adopted June 7, 2009

     
  • richardmitnick 11:39 am on May 2, 2018 Permalink | Reply
    Tags: A Hyper Quick Return to Hypervelocity Stars, , , , , , ESA Gaia   

    From astrobites: “A Hyper Quick Return to Hypervelocity Stars” 

    Astrobites bloc

    astrobites

    Title: Revisiting Hypervelocity Stars after Gaia DR2
    Authors: D. Boubert, James Guillochon, Keith Hawkins, Idan Ginsburg, N. Wyn Evans
    First Author’s Institution: Institute of Astronomy, University of Cambridge
    1
    Status: Open access on arxiv

    Hypervelocity stars appear to be in a tearing hurry. While the sun moseys around the Milky Way with no intent of leaving, hypervelocity stars are raring to leave home with speeds greater than the escape velocity of our galaxy. While the existence of hypervelocity stars was predicted in 1988, the first one was discovered in 2005 traveling at about 3 million km/hr (for comparison, the sun has an orbital velocity of about 828,000 km/hr).

    The Gaia mission aims to provide the most precise measurements of position and radial velocity for over a billion stars throughout and just beyond the Milky Way. The second Gaia data release (DR2) was on April 25, 2018. With measurements of 1.3 billion stars, it was a large step up from the first data release that covered about 2 million stars.

    ESA/GAIA satellite

    2
    Figure 1. The difference between a candidate’s velocity in the galaxy-centered frame and the escape velocity as a function of the probability of being gravitationally bound, Pbound. The authors compare the differenced velocity for the hypervelocity candidates before (a) and after DR2 (b) [Figure 2 in the paper].

    See the full article here .

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    What do we do?

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

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

     
  • richardmitnick 9:34 am on April 21, 2018 Permalink | Reply
    Tags: , , , , ESA Gaia, ,   

    From University of Heidelberg: “Stars Are Born in Loose Groupings” 

    U Heidelberg bloc

    University of Heidelberg

    20 April 2018

    Analysis of Gaia satellite data points to a new view of star formation.

    ESA/GAIA satellite

    Based on previously published data from the Gaia Mission, researchers at Heidelberg University have derived the conditions under which stars form. The Gaia satellite is measuring the three-dimensional positions and motions of stars in the Milky Way with unprecedented accuracy.

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

    Milky Way by GAIA ESA

    Using these data, Dr Jacob Ward and Dr Diederik Kruijssen determined the positions, distances and speeds of a large number of young massive stars within 18 nearby loose stellar groupings. The researchers were able to demonstrate that there is no evidence whatsoever that these associations are expanding. They therefore could not have originated as a dense cluster and then expanded to their current size.

    The long-standing model of star formation maintains that most, if not all stars originate in relatively densely packed star clusters. Experts refer to this as the “monolithic” model of star formation. Based on that model, every grouping of young stars observable today must have had its origin in one or more much denser clusters. After the stars formed, these clusters expelled the remaining molecular gas and were able to expand due to the loss of the gravitationally bound mass. Today’s less dense clusters would have formed in this way and hence now, millions of years later, would evidence clear signs of strong expansion.

    For Dr Ward and Dr Kruijssen, the results of their research clearly indicate that the “monolithic” model of star formation is simply not viable. Both researchers favour another explanation, namely that only a small fraction of stars are born within dense clusters. Instead, stars form across wide-spread molecular gas clouds across a broad range of densities. This “hierarchical” model of star formation explains today’s star clusters and associations with a variety of densities showing no signs of further expansion.

    The next publication of data from the Gaia Mission is scheduled for April 25 this year. By then, data on over a billion stars will have been collected – at least five hundred times that of the two million stars that were included in this initial study. Jacob Ward and Diederik Kruijssen hope that this new data will enable them to expand their study to potentially hundreds of loose stellar groupings, known as OB Associations, and to delve much further into the question of how stars originate. Dr Ward and Dr Kruijssen conduct research at the Institute of Astronomical Computing at Heidelberg University’s Centre for Astronomy (ZAH). Their research is part of the work being done in the Collaborative Research Center (CRC 881) “The Milky Way System”.

    1
    Hubble Space Telescope image of the OB association Cepheus OB4, one of the loose groupings of young stars studied by Dr Ward and Dr Kruijssen. The young stars are visible in bright blue; the gas and dust left after their formation is shown in red colours and dark shades. The results of the Gaia satellite show that Cepheus OB4 undergo no expansion, indicating that the stars formed in their current spatial configuration.
    Source: Davide De Martin & the ESA/ESO/NASA Photoshop FITS Liberator.

    See the full article here .

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    U Heidelberg Campus

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

     
  • richardmitnick 4:44 pm on January 4, 2018 Permalink | Reply
    Tags: , , , , ESA Gaia, , ultra-low frequency gravitational waves produced by supermassive black hole binaries   

    From The Kavli Foundation Kavli Institute for Cosmology, Cambridge: “Using GAIA to detect low frequency gravitational waves “ 

    KavliFoundation

    The Kavli Foundation

    Kavli Institute for Cosmology, Cambridge

    Jan 04, 2018
    No writer credit

    1
    ESA/GAIA

    A group of Cambridge astronomers, including Anthony Lasenby from the Cavendish Astrophysics Group and Kavli Institute for Cosmology, have made the first investigation of the sensitivity of the GAIA satellite to ultra-low frequency gravitational waves produced by supermassive black hole binaries [Physical Reviw Letters].

    The method is similar to that used in Pulsar Timing Arrays, except that instead of the gravitational wave modifying the apparent frequency of a pulsar, it modifies the apparent positions of stars observed by GAIA, making them oscillate with a characteristic pattern on the sky, An example of this is shown in the figure in which a gravitational wave is travelling from one pole of the celestial sphere, and the black and red lines indicate the induced apparent motions of the stars within a hemisphere (exaggerated by a large factor to make them visible), corresponding to the two possible polarisations of the wave. Using a method which allows the information in the star motions to be compressed by a factor of 10^6, the study shows that it will be possible to search for individually resolvable waves within the full GAIA data set of many billions of stars, and that the sensitivity of GAIA could be comparable to that of current or near-future pulsar timing arrays over a slightly wider frequency band.

    2
    No image caption or credit.

    The paper was selected as the cover article for a recent issue of Physical Review Letters, and is accompanied by an Editor’s Choice Focus article.

    See the full article here .

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    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

     
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