Scientists warn of Milky Way's collision with another galaxy

The Milky Way galaxy is rushing through space towards the Andromeda galaxy at high speed and will eventually collide with it. Scientists are already modeling the consequences of this cosmic event, although this is a very distant prospect.

Thus, the researchers point out that galaxies seem to have already begun the process of star exchange, Universe Today writes. They detect high-velocity stars (HVS) that have been pushed out of the Andromeda galaxy and are moving towards the Milky Way.

From the point of view of an Earth observer, stars are static objects in space. We can only observe their movement across the sky from east to west due to the daily rotation of the Earth. However, in reality, space objects move relative to each other at speeds that are incredible by Earth's standards. It's just that due to the vast distances involved, this movement seems imperceptible.

At the same time, some of the fastest objects in the galaxy are HVSs. These include stars that move through space at a speed of about 1000 km per second. For comparison, the Earth travels about 30 km in space per second.

Scientists discovered the first HVS in 2005. Since then, they have discovered several more such objects and suggest that some of them may leave the Milky Way.

Usually, the movement of stars is the result of their rotation around the center of the galaxy. For example, the Sun, which is the center of our planetary system, takes 220 million Earth years to complete a full revolution around the Milky Way.

It is believed that the reason for the high speed of the HVS is due to the gravitational interaction between binary stars and black holes. This idea was proposed by the American stellar dynamics theorist Jack Gilbert Hills. According to his assumption, a black hole (a stellar or supermassive black hole in the center of a galaxy) captures one star from a binary star system, and the other is thrown out and starts moving at a tremendous speed. Other reasons for this are the transformation of one of the stars into a supernova or the result of galactic interactions.

To understand the interaction between the Milky Way and the Andromeda Galaxy, the team led by Lukas Gulzow from the Institute of Astrophysics in Germany had to conduct a rather in-depth analysis. First, they had to understand the relative motion of the two galaxies, and then model the gravitational potential of the entire system, which is the total acceleration acting on an object anywhere in any galaxy at any given time. Finally, the team was able to create a stellar motion simulation to model the HVS trajectories.

The study calculated the trajectories of 18 million HVSs for two different scenarios. In one, two galaxies with the same mass were calculated, and in the other, the Milky Way, which has about half the mass of the Andromeda galaxy. The initial HVS positions in the simulation were randomly generated around the center of Andromeda. The ejection directions were random, and the results showed that 0.013% and 0.011% of the HVS are now within a 50 kiloparsec radius around the center of the Milky Way.

The modeling showed that some HVSs will slow down enough as they travel through space to be captured by the Milky Way. The team mapped the modeled positions of the stars against the sky and compared the data with the positions of high-speed stars from the Gaia catalog (release 3) and found that the modeled distribution of positions corresponds to the Gaia data.

Thus, the researchers concluded that HVSs from Andromeda may indeed migrate to the Milky Way. Scientists do not expect that there will be thousands of such stars, but they will be evenly distributed in the center of the Milky Way. Even though they may even be able to be detected based on the speed and trajectories of the stars, further research is needed.

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