the consequences of a future merger

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According to new simulations, Andromeda and the Milky Way will completely merge in about ten billion years. Less than seventeen million years after this definitive alliance, their supermassive black holes will then come together to become one.

The Milky Way evolves within a set of galaxies known as the Local Group, just like Andromeda (thirty-three times as massive). We have known since the early 1900s that these two galaxies are moving closer to each other. A merger is therefore inevitable. According to the latest data from ESA’s Gaia satellite, currently orbiting the Earth, this encounter will not happen in 3.9 billion years as it was supposed, but in 4.3 to 4.5 billion years. However, not everything will happen overnight.

As part of a recent study, a team led by astronomer Riccardo Schiavi relied on N-body computer simulations to estimate the consequences of this cosmic encounter.

A definitive merger in ten billion years

For this work, the researchers first estimated the number of massive objects involved in the two galaxies. We also know that Andromeda (or M31) is tilted slightly towards the Earth and that it is approaching 110 km / s. Finally, the distance between the two galaxies is about 2.55 million light years. Once this information is in hand, you can start the simulations.

Based on these analyzes, the first groups of stars will begin to intersect in about 4.3 billion years as expected. However, the two galaxies will then merge completely. about six billion years later. They will then form a giant elliptical galaxy that the researchers baptized “Milkomeda” (fusion of Milky Way and Andromeda). The video below illustrates this accelerated merging process.

Two black holes to become one

These new simulations also give us new insight into what will happen to the two supermassive black holes positioned at the center of these two galaxies. According to the team, they will merge about 16.6 billion years ago after the definitive formation of Milkomeda.

Just before these two black holes crash against each other, gravitational waves will be generated before propagating into the Universe. According to the researchers, any civilization evolving within 3.25 million light years of the Earth, which will have detection technology comparable to our current capacities, will be able to detect the “echoes” of this collision.

As predicted by NASA, it is unlikely that the stars will collide during this fusion as the distances between them are enormous.

Details of the study are published in the journal Astronomy and astrophysics.

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