Researchers have suspected that ripples in the outer disk of the Milky Way may have been created by a violent interaction in the past between our galaxy and one of its smaller companions hundreds of millions of years ago. Now, researchers think they have found that companion: Antlia 2. The study is published in arXiv.
The dwarf galaxy was only recently discovered thanks to the European Space Agency’s Gaia satellite. Antlia 2 has been described as a “ghost of a galaxy” because it is extremely diffuse. It is dim for its size and has the lowest surface brightness of any galaxy discovered so far. It is almost as large as the biggest companion of the Milky Way, the Large Magellanic Cloud, but 10,000 times fainter.
Lead author Sukanya Chakrabarti performed dynamical simulations of our galaxy in 2009 and predicted the location of a small galaxy dominated by dark matter that could have disrupted the Milky Way. Antlia 2 is close to that location, so Chakrabarti and her team consider it a prime suspect.
“We don’t understand what the nature of the dark matter particle is, but if you believe you know how much dark matter there is, then what’s left undetermined is the variation of density with radius,” Chakrabarti, an assistant professor from Rochester Institute of Technology, said in a statement. “If Antlia 2 is the dwarf galaxy we predicted, you know what its orbit had to be. You know it had to come close to the galactic disc. That sets stringent constraints, therefore, on not just on the mass, but also its density profile. That means that ultimately you could use Antlia 2 as a unique laboratory to learn about the nature of dark matter.”
The Gaia space observatory is currently creating a comprehensive 3D map of billions of stars in the Milky Way and its neighboring galaxies. The researchers hope to gain more information about the motion of stars within Antlia 2 in upcoming data released by Gaia in order to work out its distribution of matter (both visible and dark) and whether or not the small galaxy really did smash through the Milky Way.