Antlia 2, the "galaxy's ghost" that circles around the Milky Way, is a dark horse in more than one way. Not only is it so bad that it was just discovered last year, it can now be responsible for the curious waves of hydrogen gas that make the outer disk of the Milky Way.
According to a new study, the current position of Antlia 2 is in line with the Milky Way collisions hundreds of millions of years ago that could produce the disturbances that we see today. The paper is submitted for publication and goes through a review.
Antlia 2 was a bit of a surprise when it appeared in the second release of the Gaia mission last year. It's really close to the Milky Way – one of our satellite galaxies – and an absolutely huge size around the Great Magellanic Cloud.
But it is incredibly diffuse and weak, and hidden from the view of the galactic disk, so it has managed to avoid detection.
Read more: Scientists have calculated the mass of the Milky Way and are much more massive than previously thought
This release of data also showed in more detail the waves on the disk of the Milky Way. But astronomers knew of perturbations in that region of the disk for several years until that moment, even if the data were not as clear as those given by Gaia.
Based on these earlier information, astronomist Sukanya Chakrabarti of Rochester Institute of Technology and Colleagues in 2009 predicted the existence of a dwarf galaxy in which dark matter prevails in an almost exact location Antlia 2 was found almost ten years later.
Using the new Gaia data, the team calculated the last Antlia 2 path and spent a series of simulations. They produced not only the current position of the dwarf galaxy, but also the waves of the Milky Way disc through a collision of less than a billion years.
Earlier, a different team of researchers of this perturbation attributed interaction with the dwarf spherical Sagittarius galaxy, another one of the Milky Way satellites.
Chakrabarti and her team also conducted simulations of this scenario and found that the gravity of the Sagittarius galaxy was probably not strong enough to produce the effects Gaia observed.
"Therefore," the researchers wrote in their paper, "we claim that Antlia 2 is probably the driver of perceived large perturbations in the external gas galaxy of the Galaxy."
Previous simulations performed by the team that discovered Antley 2 suggest that a large part of the material of the dwarf galaxy, over time, is absorbed through tidal interactions with the Milky Way. If the two crashed, this is one of the possible ways of transferring at least some material.
And, if two collide, it will allow astronomers to track the history of a dwarf galaxy that could illuminate the dark matter profile. While most of the darkness tends to accumulate in galactic centers, the extraordinary diffusion of Antlia 2 could mean that it is the home of a different distribution.
Chakrabarti's previous predictions were heavily reliant on the presence of dark matter.
Read more: Perhaps we all are made of vanagalactic matter from distant stars, reveals a new study
"If Antlia 2 is the galaxy of the dwarfs we predicted, you know how its orbit was. You know that we had to come closer to the galactic disk," she said.
"It sets strict limits, therefore, not only on the mass, but also on its density profile. This means that in the end you can use Antlia 2 as a unique laboratory to learn about the nature of the dark matter."
There is still the possibility that something else has created waves, but the team also thought about it. Based on the reconstruction of past events, predicted future positions of the stars in Antlia 2.
The next Gaia data release is scheduled for a year or two. If the data matches the team's predictions, this will add a significant weight to the theory.
The research was delivered Astrophysical Journal Letters, and was published on arXiv.