Last summer, researchers identified a handful of stars that had been kicked out of the center of our Galaxy, one of which seemed destined to escape the Milky Way. Now, the same team has found more runaway stars that might actually be escapees from a galaxy besides our own.
High velocity stars are of interest to astronomers for two primary reasons: the stars can indicate extreme interactions with supernovae and black holes, and they can help probe the gravitational field of the Galaxy by mapping the distribution of dark matter.
However, identifying fast-moving stars with respect to the billions of background stars is quite difficult. Stars in the Milky Way travel at a range of speeds depending on their location and any interactions with nearby massive objects. The majority of stars live in a thin disc or in a bulge around our Galaxy’s central supermassive black hole. Stars in the disc all rotate in the same direction while the orbits of stars in the bulge and halo can be randomly distributed.