Andromeda galaxy once merged with another

Scientists analyzed the movement of stars in the Andromeda galaxy and came to the conclusion that some of them were once part of another star system. Our neighbor merged with it about 2 billion years ago.

Andromeda Galaxy. Source:

Andromeda galaxy swallowed up another star system

A group of scientists from the UK and the USA studied the stars in the Andromeda galaxy and came to the conclusion that about 2 billion years ago this star system experienced a merger. The researchers talked about their discovery in a publication in the Astrophysical Journal.

In their work, the scientists relied on the Nicholas U. Mayall 4-meter telescope at the Kitt Peak National Observatory and the US Department of Energy’s Dark Energy Spectroscopic Instrument (DESI). The first of them is a telescope that has been observing the sky for 50 years, and the second is the most powerful device on Earth for analyzing the radiation of astronomical objects.

It was the ability of the latter to simultaneously isolate hundreds of thousands of point energy sources and analyze their spectra that allowed scientists to accurately determine the velocity vectors of approximately 7,500 stars in the neighboring Andromeda Galaxy, or M31. And some of them clearly did not belong to this star system.

Scientists concluded that about 2 billion years ago, the Andromeda galaxy merged with another star system. Perhaps this was not the first such event in its history, but we can observe the traces of this merger as clearly as possible.

How often do galaxies merge

The discovery was made possible thanks to a theory that was developed quite a long time ago based on the observation of the Milky Way. It has also experienced mergers with other systems more than once. The last of them happened about 8-10 billion years ago, and most of the luminaries in the halo, the spherical component of the Milky Way, inherited it after this event.

Visualization of the movement of stars in the Andromeda galaxy. Source: KPNO/NOIRLab/AURA/NSF/E. Slawik/D. Martin/M. Zamani

Given this, scientists have put forward the theory that mergers may be the main mechanism for the growth of galaxies. And even provided patterns of movement of stars in them, evidence of these events. But so far they have not been observed anywhere.

The discovery of such stars in M31 is interesting not only because it is the first to prove this theory. It was also interesting that it happened much later than what happened to the Milky Way. That is, we can observe the consequences of what has happened relatively recently.

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