A monster galaxy’s violent meal times

Andromeda is a monster of a galaxy. And given it will one day collide with our own, a global team of Australian-led researchers has been looking into its violent past. Andromeda has been swallowing other galaxies for billions of years. The researchers were able to identify two periods of galactic feasting by studying clusters of stars, deposited when these galaxies were shredded. And that’s revealed something unexpected. The first population of clusters have orbits around Andromeda that share a distinct rotational axis. And so does the second population but with an axis that is at right angles to the first. Andromeda is likely to collide with the Milky Way in about four billion years.