When will Andromeda collide with our galaxy?


Astronomers have long suspected that the Milky Wayour galaxy, and its nearest neighbour, Andromeda, They will inevitably collide. A brutal collision that will forever change the appearance of the sky.

But maybe it’s different from what we thought so far. Using data from the European Space Agency’s (ESA) Gaia satellite, researchers have concluded that our neighbor it will hit us sideways instead of hitting us head-on.

Moreover, this will not happen in 3.9 billion years, as assumed, but in 4.5 billion: about 600 million years later provided that. The Universe grants us a little more time.

The Local Group is a large collection of galaxies, including our Milky Way, Andromeda (M31) and the Triangle (M33), which make up most of the mass of the group. The two disc-shaped spiral galaxies lie between 2.5 and 3 million light-years away from us and are close enough to each other to interact.

As the researchers explain in the journal “The Astrophysical Journal”the orbits of these two neighboring galaxies have changed over time.

There were two possibilities: either the Triangle galaxy is in an incredibly long 6 billion year orbit around Andromeda but has fallen there in the past, or this is the first time it has. Each scenario reflects a different orbital trajectory, which would imply a different formation history and future for each galaxy.

the movement of the stars

While the Hubble Space Telescope has obtained the sharpest view ever of Andromeda and the Triangle, Gaia has another mission: to measure the individual position and movement of many of its stars with unprecedented precision.

“We scoured data from Gaia and identified thousands of stars in both galaxies, then studied their motion within them,” says Mark Farda, of the Space Telescope Science Institute (STScI) in Baltimore (USA) and co-author of the study.

“Although Gaia’s main purpose is to study the Milky Way, it is powerful enough to detect particularly bright and massive stars in nearby star-forming regions, even in galaxies beyond our own.” , he added. To add.

The stellar motions measured by Gaia show not only how these galaxies move through space, but also how each of them rotates on its own axis. A century ago, when astronomers began to understand the nature of galaxies, measuring their rotation was impossible with the telescopes available at the time.

Now for the first time the researchers were able to measure the rotation of M31 and M33 in the sky. “Astronomers saw galaxies as aggregated worlds that could not form independent ‘islands’, but we now know that is not the case. It took us 100 years and Gaia to be able to measure the tiny actual rotational speed of our galactic neighbor, M31. This will help us better understand the nature of galaxies.”explains Roeland van der Marel, of the Space Telescope Science Institute (STScI) in Baltimore (USA), and lead author of the study from which this information emerges.

the path of the orbit

By combining existing observations with the new release of Gaia data, the researchers were able to determine the movement of Andromeda and the Triangle in spaceas well as calculate the orbital path of each galaxy both backward and forward in time for billions of years.

“The velocities found show that M33 cannot be in a long orbit around M31,” says study co-author Ekta Patel from the University of Arizona. All of our models imply that M33 must start falling into M31.”

For this reason, even if the Milky Way and Andromeda are always destined to collide and merge, it is likely that the timing and the degree of destruction of this interaction is different from that expected.


The movement of Andromeda differs somewhat from previous estimates, so according to the conclusions of the study, it is quite possible that this galaxy looking at the Milky Way, instead of colliding head-on. This will happen in 4.5 billion years, about 600 million years later than expected.

ESA’s Gaia project scientist Timo Prusti believes the discovery is crucial to our understanding of how galaxies evolve and interact.

“We have observed unusual phenomena in M31 and M33, such as irregular shapes in the streams and tails of stars and gas. If the galaxies have not yet merged, these phenomena cannot be due to the unleashed forces during a merger. Perhaps they were formed by interaction with other galaxies, or by gas dynamics within the galaxies themselves.” points out.

Researchers hope that observations from Gaia will help make increasingly precise measurements of the structure and dynamics of galaxies beyond our own.

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Reference article: https://www.abc.es/ciencia/abci-sabemos-donde-andromeda-cocara-nuestra-galaxia-201902180211_noticia.html

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