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Key takeaways

  • The Milky Way and Andromeda galaxies are slowly converging at 85 km/s and will merge in a few billion years.
  • New data from the Gaia observatory shows that these galaxies are already exchanging stars as part of this process.
  • Stars traveling at speeds over 700 km/s can escape their home galaxies; many such “runaway stars” have been detected.
  • These high speeds often result from interactions with supermassive black holes or supernova events in their galaxies of origin.
  • Some stars from Andromeda have entered the Milky Way and could become permanent residents after multiple gravitational encounters.

The Andromeda Nebula (M31) is the biggest component of the Local Group and the nearest spiral galaxy to Earth. According to spectral research, its tremendous gravity draws the Milky Way. The two star systems are currently converging at a sluggish rate of 85 km/s, and in a few billion years they will combine into a single grand elliptical galaxy. However, an examination of data from the European Gaia astrometric observatory revealed that the initial stage of this merger has already occurred, with the systems actively swapping stars.

The vast majority of stars in the Milky Way orbit its center in more or less elliptical orbits. The Sun completes one revolution every 220 million years, traveling at an average speed of 250 km/s. Despite its fast speed, it is unable to escape our solar system because to the enormous collective gravity.

In 2005, astronomers at the Harvard-Smithsonian Center for Astrophysics detected a strange object traveling virtually directly from the galactic center at speeds exceeding 700 km/s. This is sufficient to break away from the “galactic embrace” and depart the Milky Way forever. Later, similar items were unearthed on a regular basis. They were given the term “high-velocity stars” (HVS).

It is thought that these “runaway stars” get their super-fast speeds from the collision of stellar pairings with a supermassive black hole in the center of the Milky Way. In this situation, it absorbs one of the components of the double system while accelerating the other’s departure. A satellite of a big star can also get a tremendous “push” when the star explodes as a supernova at the conclusion of its active life.

However, speedy stars can also arise from distant galaxies. To investigate this hypothesis, a team from the Institute of Astrophysics in Karlsruhe, Germany, led by Lukas Gulzow, examined data from the Gaia project, which estimates distances to numerous galactic objects as well as their radial and apparent velocities. The scientists detected about 18 million HVSs. The second part of the investigation involved computer modeling with a map of the gravitational potential inside the Local Group. It demonstrated that the trajectories and velocities of a tiny subset of the particles accurately match to those that left the Andromeda Nebula hundreds of millions of years ago and “moved” to our galaxy. Obviously, there is also a reverse migration.

As they approach the Milky Way, the “runaway stars” accelerate under its gravity and attain a hyperbolic excess of speed that will prevent them from remaining in our “starry home”; one day, they will depart and go on another intergalactic trip. Some of them, however, may possibly become our “permanent residents” if they slow down enough during several gravitational encounters with its stars. Thus, despite their amazing distance of 2.5 million light-years, the Local Group’s biggest galaxies have already began an active star exchange.

According to Universe Today

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