It has been centuries since astronomers discovered the existence of the Andromeda Galaxy; it has been almost a century since the scientific community noticed that this celestial body was approaching us. In other words, the two galaxies, Andromeda and our own, the Milky Way, will have a spectacular collision. But is this really true?
A new study by researchers at the University of Helsinki casts doubt on this idea, considering several important factors, such as the gravitational influence of other galaxies, and finding that the chances of this intervening galaxy were only 50%, over the next 10 billion years.
Have astronomers been wrong all along? To find out, scientists in Helsinki tackled the so-called “four-body problem.” With that problem comes a huge dose of uncertainty, which explains why there’s only a one-in-two chance of this interstellar event happening.
The “four-body” problem, formally called the four-body problem N Body, is “a problem in celestial mechanics consisting in determining the trajectories of a set of bodies N “Objects attract each other,” we can read on the Wikipedia page dedicated to this question.
What we must understand above all is that this is a particularly complex problem that requires long and tedious calculations, as well as in-depth knowledge of the factors taken into account.
According to the authors of the new study, looking at Andromeda and the Milky Way separately does not take into account other galaxies in what we call the “Local Group,” which includes about 100 smaller galaxies, each with its own direction, distance from the others, and speed.
The largest of these other galaxies is the Triangulum Galaxy, located 2.7 million light-years from our own, and containing approximately 40 billion stars. This represents about 40% of the approximately 100 billion stars contained in the Milky Way, but only 4% of the 1,000 billion stars can be found in the Andromeda Galaxy. After all, this “few” number of stars has its own gravity, complicating the “simpler” dynamics between the Andromeda Galaxy and the Milky Way.
However, according to the researchers, we must also take into account the Large Magellanic Cloud, the second or third closest galaxy to our own, which is only 163,000 light-years away. With 20 billion stars in it, it also has a gravitational influence on our galactic neighborhood.
The study authors say they took into account the gravitational influence of these two other galaxies as part of their calculations of the paths of the Milky Way and Andromeda over the next billion years.
According to them, the complex dance of these space giants could lead to a scenario in which the two galaxies do not merge. However, there is another factor to consider: uncertainty.
To avoid this dilemma, the researchers resort to estimates, rather than hard numbers. In this case, the study authors estimate that there is a 50 percent chance that the two galaxies will collide and merge.
However, the researchers caution that several factors contribute to this enormous mystery, including the influence of other galaxies in the Local Group.
Ultimately, they write again, time will solve this mystery, but we are talking about very, very large time periods. If such a collision were to occur, it would in any case occur long after our sun has produced its last rays. Humanity would either die with our star – if it had not disappeared long before then – or it would learn to travel between solar systems in the meantime, accessing an almost infinite amount of resources in the process.
