In 2013, the European Space Agency launched the Gaia satellite with the ambitious goal of mapping every star in our galaxy. Recently, scientists have used the data collected by Gaia to try and find stars in our galaxy that were on their way out of it. Instead, they’ve discovered more than a dozen stars that appear to have originated in galaxies other than our own.
Gaia is a unique satellite because it’s designed to not only watch other stars, but also measure the distances to all of them and determine which direction and how fast they’re moving. The goal of Gaia is to create a 3D map of our galaxy capable of telling us where those stars are located now and at any point in the past or future.
A group of researchers at Leiden Observatory in the Netherlands decided to use that information to find stars that were headed out of our galaxy for good. Sometimes, when stars get too close to the galaxy’s center, they can get caught up in the gravitational fields and ejected with so much force they end up leaving the galaxy completely. The Leiden researchers looked through Gaia’s data to try and find stars with high speeds to identify those kinds of stars.
However, when they looked through the data, they realized that most of the high-speed stars they found were heading toward the center of the galaxy, rather than away from it. The researchers believe this is because those stars were the ones ejected from other galaxies, and they’ve managed to make their way to ours.
Of 20 high-speed stars the researchers found, 13 appear to have come from other galaxies. In particular, most of those stars seem to have come from the Large Magellanic Cloud, a small nearby galaxy that orbits our own Milky Way. And while they may ultimately be destined to depart, we should get to enjoy their company for a good, long while.