Our galaxy, ‘The Milky Way’ had a sibling. 2 billion years ago, our galaxy’s biggest neighbour Andromeda had devoured it. But now, scientists have found proof of its existence and have named it as M 32p.

Isn’t it astounding? ‘A whole galaxy’ was invisible till date!

The bigger question is how did scientists find an eaten up galaxy? The answer is inside Andromeda’s stomach. A huge halo(spherical population of stars surrounding disk galaxies), bigger than Andromeda, was found which was unusual when compared to the halo of other galaxies. This led to the conclusion that Andromeda has remnants of M 32p. 

Further details and evidence can be found in the press release of Richard D'Souza and Eric Bell of the University of Michigan's Department of Astronomy on Nature Astronomy.

https://www.eurekalert.org/pub_releases/2018-07/uom-tmw071818.php