Traces of Migration of Stars in the Andromeda Galaxy

Astronomers find evidence of massive stellar migration in Andromeda galaxythe galaxy that will eventually collide with the Milky Way.

The night sky seemed unchanged. But the truth is, the Universe is very dynamic. Similar to the dynamics of human life on Earth, the same thing also happens to stars in various galaxies.

The galaxy is home to billions of stars. But, of course, those billions of stars didn’t just appear out of nowhere. Galaxies also experience growth and evolve by forging stars and through the process of mergers with other galaxies. This latter event is known as galactic immigration. As the name implies, immigration does mean the movement of residents or in this case stars from one galaxy to another.

When two galaxies collide, what happens is not destruction but the merging of the two galaxies, including the stars in them. Large galaxies such as the Milky Way are generally composed of smaller galaxies that have merged throughout cosmic history.

Events like this certainly attract the attention of astronomers.

Star Migration

To uncover the process of star migration, astronomers study the motion of single stars in galaxies including the expansion of stellar halos, and dark matter. But so far, cosmic archaeological investigations like this can only be done in the Milky Way.

What about other galaxies? With the development of technology, of course, astronomers also expand their investigations to other galaxies. The target is certainly a large galaxy neighboring the Milky Way.

Andromeda Galaxy.

The astronomers made the observations with the Dark Energy Spectroscopic Instrument (DESI) attached to the Nicholas U. Mayall 4-meter telescope at Kitt Peak National Observatory. The target of observations and measurements is 7500 stars in the inner halo of the Andromeda Galaxy or Messier 31 aka M31.

As a result, the team of observers found patterns in the position and motion of stars that reveal the life of stars when they are just starting their journey in new galaxies. The existing traces show that these stars migrated when the galaxy merged with M31 two billion years ago.

In theory, migration patterns have been predicted long ago. It’s just that, to find the pattern is not easy. Recent observations of the Andromeda Galaxy have uncovered evidence of galactic immigration in incredible detail.

Andromeda & the Milky Way

The motion patterns of stars in the Andromeda galaxy are evidence of galactic immigration. Credit: KPNO/NOIRLab/AURA/NSF/Local Group Survey Team/TA Rector (University of Alaska Anchorage)/D. de Martin/M. age

For the first time, astronomers can see the motion of stars and the structures that form as a result of galaxy mergers. In fact, these observations not only reveal the history of the Andromeda galaxy but also show the history of the Milky Way.

The inner halos of both galaxies are dominated by a single immigration event.

Not only that.

Most of the stars in the Milky Way’s halo formed in other galaxies and only migrated during the collisions that resulted in the migration of galaxies about 8 – 10 billion years ago. Meanwhile, traces in Andromeda show that the stars “newly” migrated 2 billion years ago. That means events in the Andromeda galaxy are still relatively recent compared to the Milky Way. By studying similar relics in the Andromeda Galaxy, astronomers seem to have found another window into similar events in the Milky Way at more recent times. Although this event in Andromeda occurred 2 billion years ago, it is at least 4-6 billion years younger than the migration patterns found in the Milky Way.

Observation

To trace the history of star migration in M31, the observing team made observations with DESI mounted on the 4-meter Mayall Telescope.

As the name implies, DESI aka Dark Energy Spectroscopic Instrument was built to measure the effects of dark energy on the expansion of the Universe. DESI is a multi-object survey spectrograph capable of measuring the spectra of over 100,000 galaxies every night!

And this DESI capability can also be used to survey nearby galaxies like M31. The survey of stars in the Andromeda galaxy was carried out in just a few hours. Even if the instrument is mounted on the Mayall 4 meter telescope which is 50 years old.

Currently there are many large telescopes in the world. But the presence of the 4-meter Mayall Telescope can still give color to discoveries in the world of astronomy with continuous updating of instruments.

As a result, this telescope can still witness star migration in the Andromeda galaxy.

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