Representative Image courtesy: @NASA Photograph:( Twitter )
The answer is hidden in collision of two supermassive black holes and gravitational force this exerts
Andromeda galaxy is the nearest large galaxy to the Milky Way. Naturally, we have our scientific eyes in its direction. the galaxy is 2.5 million lightyears away from us.
There is a strange elongated cluster of stars near the centre of the Andromeda galaxy. Astronomers now know the reason behind it.
Galaxies have supermassive black holes at the centre. It is common for two galaxies to collide in space. In such a case, the supermassive black holes at the centre of these galaxies collide as well. The black holes are first locked in a gravitational dance in which they revolve around each other. They merge afterwards to form a single supermassive black hole.
This merger causes a gravitational 'kick' in the form of gravitational waves. This 'kick' is somewhat like a recoil of a gun when bullet is fired.
A latest study says that this gravitational kick on a cosmic scale is powerful enough to form an elongated disc near the centre of a galaxy. This disc is a mass made up of millions of stars. And this is what is visible at the centre of the Andromeda galaxy.
To arrive at the conclusion, a team of researchers at University of Colorado Boulder ran simulation of collision of supermassive black holes. The team found that resulting force of the collision was enough to stretch disc of nearby stars in an elongated shape rather than a symmetrical one.