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Enlarge image | Reconstitution by an artist of high-speed star movements discovered by ESA's Gaia satellite. Image via ESA / Marchetti et al. 2018 / NASA / Hubble.
ESA's Gaia mission is proving to be an excellent provider of fascinating data. Launched in 2013, the mission released its second release of data in April, providing a catalog of accurate positions and movements for 1.3 billion stars. Since then, astronomers around the world have exploited the data for various purposes, for example to track the path of the interstellar object "Umumua to its original solar system. On October 2, 2018, ESA announced that astronomers – who used Gaia's second data publication to search for high-velocity stars chased from the Milky Way – were surprised to find stars rushing to the scene. inside, maybe from another galaxy.
Gaia collects his data via so-called astrometry. His job is to scan the sky several times, observing each of his stars targeted 70 times on average during his five-year mission. We know that our sun and all the stars of the Milky Way are continually moving in large ordered masses around the center of our galaxy. We know it … but before Gaia, we did not have a lot of details about how each star moves. How could we? Data for so many stars would be (are) massive; collecting, storing and analyzing data requires modern space and computer technologies. On the new discovery of 20 high velocity stars, ESA said in a statement:
Gaia measured positions for 1,3 billion stars, parallaxes – an indicator of their distance – and 2D movements in the plane of the sky. For 7 million of the brightest, he also measured the speed with which they move towards us or away from us.
Elena Maria Rossi of the Leiden Observatory, one of the authors of the new study, said:
Of the 7 million Gaia stars with full 3D speed measurements, we found 20 that could travel fast enough to eventually escape the Milky Way.
Moreover, the stars do not seem to escape from the center of our galaxy. This may be expected because stars can be accelerated at high speeds by interacting with a supermassive black hole, like the one in the center of our galaxy. But, instead of moving away from our galaxy, most of the high-velocity stars spotted by these astronomers seem to be rushing towards it.
These could be stars from another galaxy, zooming in the Milky Way.
Astronomers believe that stars could come from the Great Magellanic Cloud, a satellite galaxy of our Milky Way. Or they could have their origin in a galaxy even further. If so, ESA stated:
… They carry the imprint of their original site and study them at much closer distances than their original galaxy could provide unprecedented information on the nature of stars in another galaxy – a similar way to that of studying the Martian material introduced on our planet by meteorites.
Ultimately, Gaia's goal is to provide the very first 3D catalog of positions and star motions in the Milky Way. For the moment, however, astronomers are exploiting the data collected to date and providing many fascinating insights into the behavior of Milky Way stars.
Learn more via ESA
Gaia's vision of our home galaxy, the Milky Way, in a 360-degree interactive view (click on the arrows at the top left) via ESA / Gaia / DPAC; ATG medialab.
Conclusion: Astronomers working with Gaia's second data release discovered 20 other high velocity (or hypervelocity) stars that appear to be from another galaxy and cross our planet.
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