'Ghost of a Galaxy' May Have Collided with Our Milky Way

A recent study has discovered a galaxy orbiting the Milky Way may have collided with it hundreds of millions of years ago.
Fabienne Lang
Perturbations in the Milky WayESA, CC BY-SA 3.0 IGO / Space in Images

A relatively mysterious and visibly faint galaxy, Antlia 2, discovered just last year, is the focus of a new study that believes it may have collided with our Milky Way hundreds of millions of years ago. 

Ripples to the Milky Way's outer disc could be the cause of this ancient collision.


The research was submitted to The Astrophysical Journal Letters, and has been published on arXiv. It is still under peer review. 

How did the team discover Antlia 2? 

Antlia 2 was discovered during data collection of the second Gaia mission last year. The galaxy hadn't been noticed up until then due to its faintness, and by its placement behind the Milky Way's galactic disc.

The data that assisted in discovering Antlia 2 bases its information on a study that began in 2009, led by astrophysicist Sukanya Chakrabarti of the Univeristy of Rochester Institute of Technology. 

Chakrabarti predicted the existence of a dwarf galaxy dominated by dark matter.

Furthermore, the research team also predicted almost the exact location of this galaxy, which is where Antlia 2 is positioned today. 

Using the Gaia mission data researchers calculated Antlia 2's past movements and ran them through different simulations.

From these calculations the team was not only able to predict the galaxy's position, but also the ripples it left in the Milky Way's disc due to the collisions hundreds of millions of years ago. 

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Dark Matter profile

If the two galaxies did in fact collide, the team will be able to go through Antlia 2's history, which in turn will help offer more information of its dark matter profile.

Chakrabarti said "If Antlia 2 is the dwarf galaxy we predicted, you know what its orbit had to be. You know it had to come close to the galactic disc." 

She continued "That sets stringent constraints, therefore, on not just on the mass, but also its density profile. That means that ultimately you could use Antlia 2 as a unique laboratory to learn about the nature of dark matter."

It is not yet 100 percent confirmed that the ripples on the Milky Way's discs were made by Antlia 2.

We will have to wait another year or two until the next Gaia data is available. This will help confirm if the researchers' predictions are correct.