Saturday , June 19 2021

Thanks to Gaia, we now know exactly when we will face Andromeda



Astronomers have known for some time that Andromeda's Milky Way and Galaxies will collide at some future date. The best assumption for this meeting is about 3.75 billion years. But now a new study based on ESA's Data Release 2 from Gaus's mission brings some clarity about this future clash.

The overall picture of the collision is greater than just the Milky Way and Andromeda (M31). The two galaxies are part of a group of galaxies called the Local Group, and the Local Group has a third large member – the triangular galaxy (M33). Although the Local Group contains other galaxies, the above-mentioned three make up the bulk of the mass. Of the three, Andromeda is the most massive, the Milky Way is the second most massive, and the Triangle is the third.

Local group of galaxies, including the massive members M31 (Galaxy Andromeda) and the Milky Way, as well as other nearby galaxies. Sincerely: Wikipedia Commons / Antonio Ciccolella
Local group of galaxies, including the massive members M31 (Galaxy Andromeda) and the Milky Way, as well as other nearby galaxies. Full Image at https://en.wikipedia.org/wiki/Local_Group#/media/File:Local_Group_and_nearest_galaxies.jpg Credit: Wikipedia Commons / Antonio Ciccolella

The local group consists of more than 54 different galaxies, although most of them are dwarfs gravitationally attached to the big three. The gravitational center of the band is somewhere between the Milky Way and Andromeda.

Although the collision is foreseen for some time, there is still much uncertainty. The Hubble Space Telescope and other ground bands such as the very long bases (VLBA) provided the evidence of this collision. With this data astronomers have learned a bit about how Andromeda and Triangle's orbits have changed over time.

Andromeda and the Triangle are the two spiral galaxies, like the Milky Way, and are somewhere between 2.5 and 3 million light-years from us. They are also close enough to interact gravitationally, which blurs the collision predictions.

This is where the mission of Georgi Evangeliev comes from.

"We had to investigate the movements of galaxies in 3D to reveal how they evolved and evolved, and what created and influenced their characteristics and behavior."


Researcher Leading Author Roland van der Marel, Space Telescope Science Institute (STScI) Baltimore, USA.

"We had to investigate the movements of the galaxies in 3D to discover how they evolved and evolved and what created and influenced their characteristics and behavior,"Says lead author Roland van der Marel of the Space Telescope Science Institute (STScI) in Baltimore, USA."We managed to do this by using the second set of high-quality data released by Gaia."

Gaia's mission is to make a 3D map of our Milky Way galaxy and so does the same for parts of the local group. While es bands like Hubble give us sharp opinions to other members of the Local Group, they do not give us accurate measurements of the positions and movements of the individual stars. This is Gaia's mission.

Two Images of the Triangle Galaxy. To the left is the image of Hubble, and to the right – Gaia's image. Image Credit: ESA / Gaia / DPAC Hubble, NIT

"We crossed Gaea's data to identify thousands of separate stars in the two galaxies, and we explored how these stars move in their galactic homes,"Adds co-author Marc Fardal, also from STScI. "While Gaia seeks to study the Milky Way above all, she is powerful enough to see particularly massive and bright stars in the nearby star forming areas – even in galaxies outside of ours."

In the past, when astronomers use Hubble and other observatories to explore the movements of the three largest members of the local group, they find two possibilities. Or, the Triangle Galaxy has an incredibly long orbit around Andromeda, but has already fallen into it in the past or is in its first autumn. Each scenario reflects a different orbital path and thus a different history of formation and future for each galaxy.

But now Gaea has given astronomers much more data to work with. It not only reveals how galaxies move in space, but also shows their spin speed. Spin speed data has long been desirable since astronomers began studying the formation and development of galaxies a hundred years ago, and Gaia has finally delivered.

"Finally, an observatory had to make Gaia make it."

Roeland van der Marel, STScI.

"Finally, one observatory advanced as Gaia,"says Roland. "For the first time, we measured the M31 and M33 rotation in the sky. Astronomers saw galaxies as clustered worlds that could not be separate "islands," but now we know otherwise. It took 100 years and Gaia finally measured the real, slow speed of rotation of the nearest large galactic neighbor, M31. This will help us understand more about the nature of galaxies."

Researchers behind the study combine existing data with new Gaia Release 2 data to create a more accurate picture of how Andromeda and Triangulum move in space. They have been able to design this in the past and in the future for billions of years.

"The speeds we have found show that M33 can not be in a long orbit around M31, "says co-author Ekta Patel from the University of Arizona, USA. – Our models unanimously suggest that M33 should be on its first phase in M31."

The trajectories of the Milky Way, Andromeda, and the triangular galaxies. Photo author: E. Patel, G. Besla (University of Arizona), R. van der Marel (STScI)
The trajectories of the Milky Way, Andromeda, and the triangular galaxies. Photo author: E. Patel, G. Besla (University of Arizona), R. van der Marel (STScI)

The study also reveals what is expected of the Milky Way and Andromeda. Instead of a collision (which is called a tidal interaction, since no star or planet is likely to collide), there will be a bigger blow. And instead of happening for about 3.75 billion years, it will be about 4.5 billion years. Phu!

"This finding is critical to our understanding of how galaxies evolve and interact. "

Timo Finges, ESA Gaia Research Associate

The new book and new Gaia data also shed light on how galaxies like Andromeda and Triangle are shaping and developing.

"This finding is critical to our understanding of how galaxies evolve and interact, – says Timo Frost, a scientist from the ESA Gaia project. "We see unusual traits in both M31 and M33, such as twisted streams and tails of gas and stars. If galaxies have not gathered before, they can not be created by the forces felt during the merger. Maybe they are formed by interactions with other galaxies or by gas dynamics in the galaxies themselves.

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