According to new research, Antlia 2’s current position is consistent with a collision with the Milky Way hundreds of millions of years ago that could have produced the perturbations we see today. The paper has been submitted for publication and is undergoing peer review.
Antlia 2 was a bit of a surprise when it showed up in the second Gaia mission data release last year. It’s really close to the Milky Way – one of our satellite galaxies – and absolutely enormous, about the size of the Large Magellanic Cloud.
But it’s incredibly diffuse and faint, and hidden from view by the galactic disc, so it managed to evade detection.
That data release also showed in greater detail ripples in the Milky Way’s disc. But astronomers had known about perturbations in that region of the disc for several years by that point, even if the data wasn’t as clear as that provided by Gaia.
It was based on this earlier information that, in 2009, astrophysicist Sukanya Chakrabarti of the Rochester Institute of Technology and colleagues predicted the existence of a dwarf galaxy dominated by dark matter in pretty much the exact location Antlia 2 was found nearly a decade later.
Using the new Gaia data, the team calculated Antlia 2’s past trajectory, and ran a series of simulations. These produced not just the dwarf galaxy’s current position, but the ripples in the Milky Way’s disc by way of a collision less than a billion years ago.
Previously, a different team of researchers had attributed these perturbations to an interaction with the Sagittarius Dwarf Spheroidal Galaxy, another of the Milky Way’s satellites.
Chakrabarti and her team also ran simulations of this scenario, and found that the Sagittarius galaxy’s gravity probably isn’t strong enough to produce the effects observed by Gaia.
“Thus,” the researchers wrote in their paper, “we argue that Antlia 2 is the likely driver of the observed large perturbations in the outer gas disk of the Galaxy.”