Gaia does it again

The Milky Way is apparently a hotspot for stars immigrating from other galaxies.In a new study published in Monthly Notices of the Royal Astronomical Society, a trio of astronomers set out to find hypervelocity stars fleeing our galaxy, but surprisingly discovered most of the rapidly moving stars are actually barreling into the Milky Way from galaxies beyond."Rather than flying away from the [Milky Way's] Galactic Center, most of the high velocity stars we spotted seem to be racing toward it," said lead author Tommaso Marchetti , a PhD candidate at Leiden Observatory, in a press release . "These could be stars from another galaxy, zooming right through the Milky Way."In order to carry out the study, the team — like so many others — relied on data collected by the European Space Agency's Gaia satellite . In April of this year, Gaia published its much-anticipated second data release , which measured the precise positions, parallaxes, and 2D motions (up-down, left-right) of over 1.3 billion stars in the Milky Way.For 7 million of the brightest stars in the set, Gaia managed to obtain 3D motions by also measuring how quickly the stars were moving toward or away from the Earth. These stars with accurate 3D motions are the ones that authors of the new study wanted to investigate further.In particularly, the researchers were hoping to find, at most, one hypervelocity star fleeing our galaxy out of the 7 million they compiled; however, they were pleasantly surprised to find more than just one. "Of the 7 million Gaia stars with full 3D velocity measurements, we found 20 that could be traveling fast enough to eventually escape from the Milky Way," explains co-author Elena Maria Rossi Out of the 20 excessively speeding stars they found, the researchers pinpointed seven so-called "hyper-runaway star candidates," which are escaping stars that seem to originate from the Milky Way's galactic disk. Meanwhile, none of stars appear to come from the Milky Way's core, and the remaining 13 unbound stars (including the two fastest, which zip through our galaxy at about 1.5 million miles per hour) cannot be traced back to the Milky Way at all.According to the study, if the results are confirmed, these 13 curious stars could very well be the "tip of the iceberg" for a large extragalactic population of stars whizzing through the Milky Way.