The massive galaxies present within the current Universe weren’t always so big. Evidence signifies that they have been constructed up over time, mostly by collisions with different galaxies. These collisions have left marks that scientists will still detect: streams of stars that were drawn in from the victims of the collisions, and faint dwarf galaxies that always orbit the more significant object that devoured many of their stars. With sufficient data, it is possible to turn into a galactic historian and reconstruct the events that brought the modern-day giants to their present form.
Uncovering a few of that history was the goal of a significant, multinational collaboration, spelled out clearly in its name: the Pan-Andromeda Archaeological Survey. In a paper revealed in Nature, the team describes uncovering some of our nearest galactic neighbor’s violent previous. The article exhibits that Andromeda was built in part by two first collisions that have left clusters of stars occupying two perpendicular orbits. In the means of writing their paper, the researchers also uncovered a little bit of a mystery about an unexpected alignment between a few of these clusters and Andromeda’s satellite galaxies.
The brand new work focuses on what are known as globular clusters, which are large groups of stars held together by gravity. Unlike different stars—which shift place relative to each other as they orbit a galaxy’s center—the stars of a globular cluster stick together and orbit as a gaggle. As a result, these gravitationally bound clusters of stars can survive the collisions between galaxies. Meaning they can be utilized as markers to retrace those collisions.