Tagged: RAdial Velocity Experiment (RAVE) survey Toggle Comment Threads | Keyboard Shortcuts

  • 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, , RAdial Velocity Experiment (RAVE) survey, , 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 .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    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 5:33 pm on February 14, 2017 Permalink | Reply
    Tags: , , , , , , , RAdial Velocity Experiment (RAVE) survey   

    From Dunlap: “Missing Stars in the Solar Neighbourhood Reveal the Sun’s Speed and Distance to the Centre of the Milky Way Galaxy” 

    Dunlap Institute bloc
    Dunlap Institute for Astronomy and Astrophysics

    Feb 13 2017
    Dr. Jason Hunt
    Dunlap Fellow
    Dunlap Institute for Astronomy & Astrophysics
    University of Toronto
    p: 416-978-3147
    e: jason.hunt@dunlap.utoronto.ca

    Chris Sasaki
    Communications Co-ordinator
    Dunlap Institute for Astronomy & Astrophysics
    University of Toronto
    p: 416-978-6613
    e: csasaki@dunlap.utoronto.ca
    w: dunlap.utoronto.ca

    1
    A composite image shows the Gaia spacecraft against a backdrop of the Milky Way Galaxy. Image: ESA/ATG medialab; background image: ESO/S. Brunier

    Using a novel method and data from the Gaia space telescope, astronomers from the University of Toronto have estimated that the speed of the Sun as it orbits the centre of the Milky Way Galaxy is approximately 240 kilometres per second.

    In turn, they have used that result to calculate that the Sun is approximately 7.9 kiloparsecs from the Galaxy’s centre—or almost twenty-six thousand light-years.

    Using data from the Gaia space telescope and the RAdial Velocity Experiment (RAVE) survey, Jason Hunt and his colleagues determined the velocities of over 200,000 stars relative to the Sun. Hunt is a Dunlap Fellow at the Dunlap Institute for Astronomy & Astrophysics, University of Toronto.

    The collaborators found an unsurprising distribution of relative velocities: there were stars moving slower, faster and at the same rate as the Sun.

    But they also found a shortage of stars with a Galactic orbital velocity of approximately 240 kilometres per second slower than the Sun’s. The astronomers concluded that the missing stars had been stars with zero angular momentum; i.e. they had not been circling the Galaxy like the Sun and the other stars in the Milky Way Galaxy;

    “Stars with very close to zero angular momentum would have plunged towards the Galactic centre where they would be strongly affected by the extreme gravitational forces present there,” says Hunt. “This would scatter them into chaotic orbits taking them far above the Galactic plane and away from the Solar neighbourhood.”

    “By measuring the velocity with which nearby stars rotate around our Galaxy with respect to the Sun,” says Hunt, “we can observe a lack of stars with a specific negative relative velocity. And because we know this dip corresponds to 0 km/sec, it tells us, in turn, how fast we are moving.”

    Hunt and his colleagues then combined this finding with the proper motion of the supermassive blackhole known as Sagittarius A* (“A-star”) that lies at the centre of the Galaxy to calculate the 7.9 kiloparsec distance.

    Proper motion is the motion of an object across the sky relative to distant background objects. They calculated the distance in the same way a cartographer triangulates the distance to a terrestrial landmark by observing it from two different positions a known distance apart.

    The result was published in Astrophysical Journal Letters in December 2017.

    The method was first used by Hunt’s co-author, current chair of the Department of Astronomy & Astrophysics at the University of Toronto, Prof. Ray Calberg, and Carlberg’s collaborator, Prof. Kimmo Innanen. But the result Carlberg and Innanen arrived at was based on less than 400 stars.

    Gaia is creating a dynamic, three-dimensional map of the Milky Way Galaxy by measuring the distances, positions and proper motion of stars. Hunt and his colleagues based their work on the initial data release from Gaia which included hundreds of thousands of stars. By the end of its 5 year mission, the space mission will have mapped well over 1 billion stars.

    The velocity and distance results are not significantly more accurate than other measurements. But according to Hunt, “Gaia’s final release in late 2017 should enable us to increase the precision of our measurement of the Sun’s velocity to within approximately one km/sec, which in turn will significantly increase the accuracy of our measurement of our distance from the Galactic centre.”

    Additional notes:

    1) The RAdial Velocity Experiment, or RAVE, is a survey of stars conducted at the Australian Astronomical Observatory (AAO) between 2003 and 2013. It measured the positions, distances, radial velocities and spectra of half-a-million stars—over two hundred thousand of which are included in Gaia data.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Dunlap Institute campus

    The Dunlap Institute is committed to sharing astronomical discovery with the public. Through lectures, the web, social and new media, an interactive planetarium, and major events like the Toronto Science Festival, we are helping to answer the public’s questions about the Universe.
    Our work is greatly enhanced through collaborations with the Department of Astronomy & Astrophysics, Canadian Institute for Theoretical Astrophysics, David Dunlap Observatory, Ontario Science Centre, Royal Astronomical Society of Canada, the Toronto Public Library, and many other partners.

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