Milky Way's Oldest Stars Came from Other Galaxies

An international collaboration of researchers determined that the most ancient stars observable in the Milky Way were not in fact produced within our galaxy. These objects are what remains of old galaxies that once collided with our own, helping it grow to its current size.

Though not particularly large, the Milky Way is still an impressive 120,000 light-years across, and astronomers believe that it grew to its current size by cannibalizing on a large number of dwarf galaxies that used to orbit around it.

Past investigation manged to uncover traces of such events, with one paper proposing that the latest one occurred only a few hundred million years ago. During galactic collisions, the colliding space structures can merge their black holes, and stir gas clouds that promote stellar formation.

According to the new study, it would appear that such events are the reason why old, red stars are visible at our galaxy's core. These objects were in fact formed in other, dwarf galaxies, and only made their way into ours following collisions.

The research was carried out by experts at the Durham University's Institute for Computational Cosmology, who worked together with colleagues at the Max Planck Institute for Astrophysics, in Germany, and the Groningen University, in Holland.

The collaboration itself is part of the larger Aquarius Project, whose main goal is to use massive supercomputer simulations to understand how large galaxies such as our own came to be.

When two galaxies collide, the gravitational forces they exert on each other are impressive. They are able to rip entire sections of the smaller galaxy apart, causing it to deform until it finally merges with the larger one.

Some computer models of the early Universe say that the Cosmos was filled with dwarf galaxies a couple of billions after the Big Bang. Most of these objects led very short and violent lives, colliding with each other to form the large behemoth galaxies we see today.

“Effectively we became galactic archaeologists, hunting out the likely sites where ancient stars could be scattered around the galaxy,” says ICC investigator Andrew Cooper, quoted by Daily Galaxy.

“Our simulations show how different relics in the galaxy today, like these ancient stars, are related to events in the distant past,” the expert goes on to say.

“Like ancient rock strata that reveal the history of Earth, the stellar halo preserves a record of a dramatic primeval period in the life of the Milky Way which ended long before the Sun was born,” he concludes.