New research suggests that hundreds of millions of years ago the Milky Way collided with Antlia 2, a nearby dwarf galaxy.
This collision caused ripples in the edge of the disk of gas around the Milky Way which we still observe today.
Antlia 2 is about one third the size of the Milky Way, and is believed to be the galaxy dominated by dark matter which astronomers predicted to exist back in 2009.
Its location matches the predictions but it was only discovered in 2018 because it has very low density and gives off very little light.
The new data shows that based on Antlia 2’s trajectory, it would have collided with the Milky Way and caused the ripples in its gas disk.
“The discovery could help develop methods to hunt for dark galaxies and ultimately solve the long-standing puzzle of what dark matter is,” astrophysicist Sukanya Chakrabarti, lead author of the study, said in a statement.