In the past, the Andromeda galaxy discovered traces of an ancient disaster
Two billion years ago, the Andromeda galaxy closest to the Milky Way (apart from dwarf satellite galaxies) tore into small pieces and swallowed another galaxy, astrophysicists from the University of Michigan established.
The galaxy, which collided with Andromeda two billion years ago, ceased to exist as a galaxy; its stars and dust were scattered in different directions, but some evidence of this ancient catastrophe was preserved in the form of a barely noticeable star halo larger than Andromeda itself, and a small galaxy - the Andromeda satellite M32. Studying M32 will help scientists understand how spiral galaxies - such as Andromeda and the Milky Way - evolve and what happens when they collide with other large clusters of stars.
In the Local group of galaxies, Andromeda is the largest; The Milky Way is 2.5–5 times smaller, and the third in size is M32, a dwarf galaxy and Andromeda’s satellite. Astrophysicists Eric Bell and Richard D'Souza simulated the events that led to the formation of the M32; simulation results published this week in Nature Astronomy .
Huge halos, consisting of far-spaced stars, often surround large galaxies; it is assumed that the halo is the remnants of smaller clusters of stars absorbed by large galaxies. The super-giant Andromeda galaxy, consisting of a trillion stars, has absorbed hundreds of smaller galaxies during its existence, so it is quite difficult to establish the fate of individual galaxies who died in a collision with Andromeda. However, the Bell and D'Sauza model shows that most of the stellar halo surrounding Andromeda comes from one large galaxy that collided with Andromeda for a very long time; she was named M32p.
M32p was at least 20 times larger than all the galaxies colliding with the Milky Way in its 12 billion years of existence. Before the clash, she was the third largest in the Local Group. Some of its stars (from the densest central part) survived a collision with Andromeda and now makes up the M32 galaxy. “M32 is a strange galaxy: it looks like very ancient, compact elliptical galaxies, but it is full of young stars; it’s one of the most compact galaxies in the Universe, we don’t know others like that, ”Bell explains.
The results of Bell and D'Sauza are confirmed by previously obtained data that two billion years ago in the Andromeda galaxy there was a stellar “baby boom” - an unexpected surge in the intensity of star formation.
The Milky Way, too, sooner or later will collide with the Andromeda galaxy and, given the difference in size, will be absorbed by a larger neighbor; this will happen, according to recent estimates, in five billion years. Perhaps the Bell and D'Sauza model will predict the outcome of this collision. Until now, it was believed that a collision of comparable-sized galaxies destroys the central disks of both, however, Andromeda survived the collision with M32p, preserving the structure of its central disk; scientists have to clarify their ideas about how such clashes occur.