With the help of data gathered by ESA’s Gaia mission, astronomers have discovered that a series of stars traveled into the Milky Way, perhaps from a different galaxy.
As noted by experts in a study published in the journal Monthly Notices of the Royal Astronomical Society, the stars navigate in the Milky Way at hundreds of kilometers per second, and their movements say experts, contain huge amounts of information about the galaxy’s past.
The fastest stars are the so-called “hypervelocity stars”.
It is believed that they are born near the galactic center, from which they escape towards the limits of the Milky Way by their interaction with a supermassive black hole, at the center of the galaxy.
The discovery is somewhat surprising as experts note that so far, only a small number of hypervelocity stars have been discovered, so the second Gaia data catalog offers a unique opportunity to search for more stars of this type.
Gaia has measured the positions, parallaxes (indicating their distance) and two-dimensional movements in the plane of the sky of 1,300 million stars. And for a subset of seven million of the brightest stars, Gaia has also measured how fast they are moving away from Earth.
“Of the seven million Gaia stars with full 3D velocity measurements, we found twenty that could be traveling fast enough to eventually escape from the Milky Way,” explains Elena Maria Rossi, one of the authors of the new study.
Rossi and her colleagues, who had discovered several hypervelocity stars last year in an exploratory study based on Gaia’s first data catalog, were “pleasantly surprised” as they expected to find, at best, ONE star that escaped from the Galaxy among the seven million.
But there is more: “Instead of moving away from the galactic center, most of the hypervelocity stars detected seem to approach it,” adds Tommaso Marchetti, co-author of the study.
“It could be stars from another galaxy, which are crossing the Milky Way,” he says.
According to experts, these traveling stars could be our first alien visitors.
An article published by the European Space Agency indicates that it is possible that these intergalactic ‘intruders’ originally arrived from 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 site of origin, and studying them at much closer distances than their parent galaxy could provide unprecedented information on the nature of stars in another galaxy – similar in a way to studying martian material brought to our planet by meteorites,” explains the European space agency.
“Stars can be accelerated to high velocities when they interact with a supermassive black hole,” Elena explains.
“So the presence of these stars might be a sign of such black holes in nearby galaxies. But the stars may also have once been part of a binary system, flung towards the Milky Way when their companion star exploded as a supernova. Either way, studying them could tell us more about these kinds of processes in nearby galaxies.”