Geneva helps show our galaxy in three dimensions


The third catalog of data from the Gaia satellite has been released, with information on more than 2 billion stars, in which the University of Geneva participated.

The stars are in constant motion. To the human eye, this movement (called proper motion) is imperceptible, but Gaia measures it more and more accurately. Traces in this image show how 40,000 stars, all within 100 parsecs (326 light-years) from the solar system, will move across the sky over the next 400,000 years.

© ESA / Gaia / DPAC, CC BY-SA 3.0 IGO

Mapping our galaxy, the Milky Way, in three dimensions with still unsurpassed precision is the purpose of Gaia mission launched in 2013 by the European Space Agency (ESA), involving around fifty institutions and research centers, including the University of Geneva.

The Gaia satellite, located 1.5 million kilometers from Earth, in the opposite direction of the Sun (Lagrange point L2), collects valuable data about the stars thanks to its two-field telescope and its camera, one billion pixels. These are processed by almost 500 researchers, mainly based in Europe.

1% of the stars in our galaxy identified

“The Gaia mission is unparalleled,” explains Marc Audard, associate professor and researcher in the Department of Astronomy at UNIGE Faculty of Science. Nearly 2 billion sources have been identified (about 1% of the total number of stars in our galaxy), and each of them has been observed an average of 50 times. It’s a real Big Data project ”.

The Gaia satellite continuously lists and observes stars that are sometimes tens of thousands of light-years away, but also asteroids, stars with planets outside the sun, and distant galaxies. Its launch multiplied by 10,000 the number of observed objects and by a factor of 100 the accuracy of the data.

Following the release of two catalogs in 2016 and 2018, the Gaia mission today unveils a new harvest Gaia Data Release 3 (DR3) which pushes the boundaries of our knowledge even further. “Each new release of Gaia data enables exponential growth in the identified sources and type of data. Not only are the positions, distances and motions of the stars much more detailed, but we publish nearly ten million sources whose light intensity is variable, classified and studied in “In addition, we were able to do this for almost 30 types of variable sources (such as eclipsing binary stars or pulsating stars) against only 6 for DR2”, explains Laurent Eyer, teaching and research supervisor at the Department of Astronomy of. The Faculty of Science in UNIGE and coordinator of the unit on the variability of the consortium.

UNIGE measures changes in starlight

At its Ecogia site in Versoix, the University of Geneva in particular measured the variability of the light emitted by the stars. A particularly useful element for determining their characteristics (their mass and their radius for example), but also for calculating the distances in the universe. “Our job at UNIGE is to digest and prepare this data, which is very complex to handle as it is so that the scientific community can use it,” says Laurent Eyer. To process this colossal mass of information (2 billion sources and nearly 400 billion photometric measurements), the UNIGE team used artificial intelligence and more specifically “machine learning”. “).

“We are doing science in order to serve society,” Marc Audard continues. Each Gaia data release has a very significant impact on astronomy and generates the release of several scientific articles. Some research centers even anticipate the development of algorithms to process the data in the catalog. “This data is now available to the scientific community, but also to the general public.

Lots of UNIGE articles

The consortium is already announcing the publication of nearly 50 scientific articles based on DR3, most signed as co-authors or co-authors of the UNIGE team, 17 of which come from the analysis of variability. The publication of the previous catalog had generated a total of 6,000 articles. Papers specifically dealing with Gaia data are regularly among the most cited in the field of astronomy. For the UNIGE team, the challenge will be to further increase the amount of information processed in Geneva. It hopes to reach 100 million variable sources within a few years.

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