Astronomers Spot Galaxy Hurling a Star Cluster into Intergalactic Space

Astronomers have made a surprising find. They've discovered that a galaxy has hurled an entire star cluster toward Earth at more than two million miles per hour. The newly found cluster is now doomed to drive through the void between galaxies.

The cluster was first spotted after researchers spent years studying the area around a galaxy nearby. They sorted targets by color to separate stars and galaxies from globular clusters, and then used a telescope to examine the clusters in detail.

"Astronomers have found runaway stars before, but this is the first time we've found a runaway star cluster," said Nelson Caldwell, one of the researchers, in a news release.

The star cluster in this case is called HVGC-1, which stands for hypervelocity globular cluster. Globular clusters are relics of the early universe, and usually contain thousands of stars crammed into a ball that's only a few dozen light-years across. The Milky Way galaxy is home to about 150 globular clusters.

HVGC-1 was hurled from M87, a galaxy that holds thousands of globular clusters. The cluster has a high velocity that surprised the researchers. Currently, they're unsure exactly how HVGC-1 managed to attain this high velocity, but they do have theories.

One of the theories depends on the idea that M87 has a pair of supermassive black holes at its core. It's possible that the star cluster moved too closely to these black holes, and that many of its outer stars were plucked off; while the outer stars were taken away, though, the main cluster remained intact. The two black holes then could have acted like a slingshot and flung the cluster away.

Currently, HVGC-1 is moving fast enough that it's doomed to escape M87 altogether. In fact, scientists estimate that it may have already left the galaxy and is floating into intergalactic space.

The findings are published in The Astrophysical Journal Letters.