[ad_1]
Antlia 2, the "ghost of a galaxy" orbiting the Milky Way, is a black horse in more ways than one. Not only is it so weak that it was discovered only last year, but it is perhaps now at the origin of curious undulations of hydrogen which constitutes the outer disk of the Milky Way.
According to new research, the current position of Antlia 2 is consistent with a collision with the Milky Way hundreds of millions of years ago that could have produced the disturbances we see today. The document has been submitted for publication and is under peer review.
Antlia 2 was a bit of a surprise when it appeared in the second publication of the Gaia mission data last year. It's very close to the Milky Way – one of our satellite galaxies – and absolutely huge, the size of the Great Magellanic Cloud.
But he is incredibly diffuse and weak, and hidden from view by the galactic disk, so he managed to escape detection.
This data publication also showed more detailed ripples in the Milky Way disk. But astronomers were aware of the disturbances in this region of the record for several years, even though the data was not as clear as that provided by Gaia.
Based on this information, in 2009, astrophysicist Sukanya Chakrabarti of the Rochester Institute of Technology and his colleagues predicted the existence of a dwarf galaxy dominated by dark matter at approximately the exact location of Antlia 2, discovered almost ten years later.
Using the new Gaia data, the team calculated the past trajectory of Antlia 2 and ran a series of simulations. These did not only produce the current position of the dwarf galaxy, but also the undulations of the Milky Way disk causing a collision less than a billion years ago.
Simulation of the collision: The gas distribution is on the left, the stars on the right. (RIT)
Previously, another team of researchers attributed these disturbances to an interaction with the spheroidal galaxy of the Sagittarius Dwarf, another satellite of the Milky Way.
Chakrabarti and his team also conducted simulations of this scenario and discovered that the gravity of the Sagittarius galaxy probably was not powerful enough to produce the effects observed by Gaia.
"So," the researchers wrote in their article, "we affirm that Antlia 2 is probably the engine of the major disturbances observed in the outer gas disk of the galaxy".
Previous simulations performed by the team that discovered Antlia 2 suggested that much of the material in the dwarf galaxy had, over time, been absorbed by tidal interactions with the Milky Way. If both collide, this is a possible way to transfer at least some of the material.
And, if the two meet, this will allow astronomers to trace the history of the dwarf galaxy, which could enlighten us on its dark matter profile. Most of the time, dark matter tends to clump in the galactic centers, but the extraordinary spread of Antlia 2 could mean that its distribution is different.
And the previous prediction of Chakrabarti relied heavily on the presence of dark matter.
"If Antlia 2 is the dwarf galaxy we predicted, you know what its orbit should be, you know it had to get close to the galactic disk," she said.
"This imposes strict constraints not only on the mass, but also on its density profile, which means that you can use Antlia 2 as a unique laboratory to learn more about the nature of dark matter."
It is always possible that something else has created the ripples, but the team has also thought about that. Based on their reconstruction of past events, they predicted the future positions of the stars in Antlia 2.
The next Gaia data release is scheduled in a year or two. If the data matches the team's forecast, this will add significant weight to the theory.
The search was submitted to The letters of the astrophysical journal, and was published on arXiv.
[ad_2]
Source link