Some of the fastest stars in the Milky Way come from other galaxies

Extreme-velocity stars, which travel through the Milky Way with speeds of hundreds of kilometres per second, may come from dwarf galaxies that our own galaxy gobbled up

Space 8 April 2022

By Leah Crane

Illustration of the Milky Way galaxy as it might appear edge on. The Milky Way is a barred spiral galaxy roughly 100000 light-years in diameter. It is flat, shaped like two fried eggs back-to-back. At the centre is the nucleus, a vast flattened ball of old, red stars orbiting a supermassive black hole. This view imagines our galaxy seen from far from its nucleus, within the galactic plane. A lane of dust bisects the galaxy. Globular clusters (spherical clusters of stars) orbit here. One is seen in close up on the lower right. — Illustration of the Milky Way

Mark Garlick/Science Photo Library/Getty Images

The speediest stars in the galaxy, moving at hundreds or even thousands of kilometres per second, are also some of the least well-studied. A study of 15 of these fast-moving objects has found that most of them probably came from dwarf galaxies devoured by the Milky Way in the distant past.

“Some stars that are travelling fast have been [proposed to have] an extragalactic origin, but this is the first time that a relatively large sample has been analysed and evidence has been shown that they …