Antlia 2, the "spirit of a galaxy" orbiting the Milky Way, is in many ways a dark horse. Not only is it so weak that it was just discovered last year, it may also be responsible for strange waves in the hydrogen gas that make up the outer disk of the Milky Way.
Recent research suggests that the current position of Antlia 2 coincides with a collision with the Milky Way hundreds of millions of years ago, which could have created the disruption we see today. The paper has been submitted for publication and is subject to peer review.
Antlia 2 was a small surprise when it appeared in the second release of the Gaia missionary data last year. It's very close to the Milky Way ̵
But it is incredibly diffuse and weak and is not seen by the galactic disk, so it escapes the discovery.
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This data release also showed more detailed waves on the Milky Way disc. But astronomers had known about this region of the disk for several years, even though the data was not as clear as Gaia's.
Based on this earlier information, astrophysicist Sukanya Chakrabarti of the Rochester Institute of Technology and colleagues predicted the existence of a dark matter dominated dwarf galaxy in 2009. For almost a decade, Antlia 2 was found right there.
Using the new Gaia data, the team calculated the previous trajectory of Antlia 2 and performed a series of simulations. These created not only the current position of the dwarf galaxy, but also the waves in the disk of the Milky Way through a collision less than a billion years ago.
Previously, another research team had attributed these disturbances to an interaction with the Sagittarius Dwarf Spheroidal Galaxy, another satellite of the Milky Way.
Chakrabarti and her team also performed simulations of this scenario and found that the gravity of the Sagittarius galaxy is probably not strong enough to evoke the effects Gaia observes.
"As the researchers argue in their work," Antlia 2 is the likely driver of the observed large perturbations in the galaxy's outer gas disk. "
Previous simulations of the team that discovered Antlia 2 suggested that much of the dwarf galaxy's material was absorbed by tidal interactions with the Milky Way over time, and that if the two collide, it's a possible pathway
And when the two collide, astronomers can understand the history of the dwarf galaxy, which could shed some light on their dark matter profile, while dark matter tends to clump together in galactic centers most of the time , the extraordinary diffusivity of Antlia 2 could mean that there is a different distribution.
And Chakrabarti's earlier prediction was heavily dependent on the presence of dark matter.
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"When Antlia 2 di e of our predicted dwarf galaxy is, you know, what your orbit must have you know it had to get close to the galactic disk, "she said.
"This not only severely restricts the mass, but also the density profile, which means that you can ultimately use Antlia 2 as a unique laboratory to explore the nature of dark matter."
There is still the possibility that something else is causing the waves, but the team has also thought about it. Based on their reconstruction of past events, they predicted the future positions of the stars in Antlia 2.
The next release of Gaia data is due in a year or two. If the data matches the team's predictions, the theory is weighted heavily.
The study was submitted to The Astrophysical Journal Letters and published on arXiv.