We Have Detected Indicators of Our Milky Approach Colliding With One other Galaxy

Antlia 2, the “ghost of a galaxy” orbiting the Milky Approach, is a darkish horse in additional methods than one. Not solely is it so faint it was solely simply found final yr, it could now be liable for curious ripples within the hydrogen fuel that makes up the Milky Approach’s outer disc.

In response to new analysis, Antlia 2’s present place is per a collision with the Milky Approach lots of of thousands and thousands of years in the past that would have produced the perturbations we see in the present day. The paper has been submitted for publication and is present process peer evaluate. 

Antlia 2 was a little bit of a shock when it confirmed up within the second Gaia mission information launch final yr. It is actually near the Milky Approach – considered one of our satellite tv for pc galaxies – and completely monumental, in regards to the dimension of the Massive Magellanic Cloud.

However it’s extremely diffuse and faint, and hidden from view by the galactic disc, so it managed to evade detection.

That information launch additionally confirmed in better element ripples within the Milky Approach’s disc. However astronomers had identified about perturbations in that area of the disc for a number of years by that time, even when the information wasn’t as clear as that supplied by Gaia.

It was primarily based on this earlier info that, in 2009, astrophysicist Sukanya Chakrabarti of the Rochester Institute of Know-how and colleagues predicted the existence of a dwarf galaxy dominated by darkish matter in just about the precise location Antlia 2 was discovered almost a decade later.

Utilizing the brand new Gaia information, the staff calculated Antlia 2’s previous trajectory, and ran a collection of simulations. These produced not simply the dwarf galaxy’s present place, however the ripples within the Milky Approach’s disc by means of a collision lower than a billion years in the past.

Simulation of the collision: The fuel distribution is on the left, stars on the best. (RIT)

Beforehand, a special staff of researchers had attributed these perturbations to an interplay with the Sagittarius Dwarf Spheroidal Galaxy, one other of the Milky Approach’s satellites.

Chakrabarti and her staff additionally ran simulations of this situation, and located that the Sagittarius galaxy’s gravity in all probability is not robust sufficient to provide the consequences noticed by Gaia.

“Thus,” the researchers wrote of their paper, “we argue that Antlia 2 is the possible driver of the noticed giant perturbations within the outer fuel disk of the Galaxy.”

Earlier simulations run by the staff that found Antlia 2 prompt that a lot of the dwarf galaxy’s materials has, over time, been absorbed by way of tidal interactions with the Milky Approach. If the 2 collided, that is one doable approach a minimum of some materials was transferred.

And, if the 2 collided, this can enable astronomers to hint the dwarf galaxy’s historical past, which may shed some mild on its darkish matter profile. Whereas more often than not darkish matter tends to clump collectively in galactic centres, Antlia 2’s extraordinary diffuseness may imply it is residence to a special distribution.

And Chakrabarti’s earlier prediction was closely reliant on the presence of darkish matter.

“If Antlia 2 is the dwarf galaxy we predicted, you realize what its orbit needed to be. You understand it needed to come near the galactic disc,” she stated.

“That units stringent constraints, subsequently, on not simply on the mass, but in addition its density profile. That signifies that in the end you could possibly use Antlia 2 as a singular laboratory to study in regards to the nature of darkish matter.”

There’s nonetheless a chance that one thing else created the ripples, however the staff has considered that, too. Based mostly on their reconstruction of previous occasions, they predicted the long run positions of the celebs in Antlia 2.

The subsequent Gaia information launch is due in a yr or two. If the information matches the staff’s predictions, it’ll add vital weight to the idea.

The analysis has been submitted to The Astrophysical Journal Letters, and has been printed on arXiv.