Andromeda galaxy ate several dwarf galaxies in two-course lunch

By Ruby Prosser Scully

Robert Gendler/NASA

Andromeda, our nearest major galaxy, has feasted on plenty of galaxies for the duration of its lifetime, gobbling them up and incorporating their stars into itself. Now we know the feast went down in two clear phases.

We know Andromeda ate quite a pair of galaxies on account of it has a large halo of stars dotted around its periphery. These appear to had been caught in the galaxy’s orbit for the duration of collisions with smaller, dwarf galaxies. Nonetheless untangling how and when these collisions took space includes prognosis of the leftover huge name particles, which isn’t easy.

Geraint Lewis at the College of Sydney, Australia, and a world crew of researchers studied the halo utilizing info from the Pan-Andromeda Archaeological Uncover. They centered on groups of thousands and thousands of stars that are packed together in spheres identified as globular clusters. “We are cosmic archaeologists, excluding we’re digging via the fossils of lengthy-ineffective galaxies in desire to human history,” says Lewis.

These clusters would have retained a level of structure from their parent dwarf galaxy for a whereas after they had been captured by Andromeda. Nonetheless this would have gradually disappeared because the galaxy broke down. Lewis and his colleagues traced what stays of these structures.

They discovered that half of the clusters had been orbiting a system around Andromeda’s core and the quite a pair of half had been orbiting in a perpendicular orientation. The principal neighborhood composed have some of their substructure intact, suggesting the collision that created them took space barely no longer too lengthy in the past – doubtlessly excellent a pair of billion years in the past. The second neighborhood of clusters retain much less of their common structure, suggesting they had been swallowed around 7 to 10 billion years in the past.

Lewis says he used to be anticipating to get some trends in the cluster distribution, but seeing two clear binges on quite a pair of galaxies by Andromeda caught him with out be conscious.

Even stranger, the older of the two groups of clusters looks to line up with the orbit of a series of dwarf galaxies that are composed orbiting Andromeda this day. These galaxies are identified to be barely young, and yet they seem in the identical orbit because the older neighborhood of galaxies that Andromeda dined on.

Journal reference: Nature, DOI: 10.1038/s41586-019-1597-1