Are Andromeda and the Milky Way doomed to collide? Maybe not

Scientists found the Andromeda galaxy, referred to as M31, a whole lot of years in the past, and round a century in the past, we realized that it had unfavourable radial velocity towards the Milky Way. In different phrases, ultimately, the 2 galaxies would merge spectacularly. That has been frequent information for astronomers since then, however is it actually true?

A new paper from researchers on the College of Helsinki posted to the arXiv preprint server appears to be like at a number of confounding elements, together with the gravitational affect of different galaxies in our local group, and finds solely a 50% probability that the Milky Way will merge with the Andromeda galaxy within the subsequent 10 billion years.

That looks as if a fairly large factor to get the physics incorrect on. So, how did the authors come to that conclusion? They accounted for an issue that has been popularized in media as of late—the three-body—or on this case, four-body—drawback. And with that drawback comes plenty of uncertainty, which is why there’s nonetheless a 50% probability that this big occasion may nonetheless occur.

Considering of Andromeda and the Milky Way in isolation would not account for the opposite galaxies in what we all know because the “Native Group.” This includes roughly 100 smaller galaxies at numerous orientations, distances, and speeds.

The biggest of the remaining galaxies is the Triangulum galaxy, M33, which is about 2.7 million light-years away and consists of upwards of a mere 40 billion stars. That is about 40% of the roughly 100 billion stars within the Milky Way however a mere 4% of the practically 1 trillion stars estimated to exist in Andromeda. Nonetheless, they might have their very own gravitational pull, contorting the simplistic dynamic between Andromeda and the Milky Way.

Additional confounding that dynamic is the Massive Magellanic Cloud, which is both the second or third closest galaxy to our personal at a distance of solely 163,000 mild years. That is barely bigger than the Milky Way’s diameter, at 105,700. It additionally homes round 20 billion stars, so whereas it is even much less large than M33, it nonetheless exerts a hefty gravitational pull.

The authors accounted for the gravitational pull of each of these different galaxies of their calculations of the paths of the Milky Way and Andromeda over the subsequent few billion years. They discovered that the difficult dance of astronomical giants may doubtlessly end in a situation the place the 2 galaxies do not merge. Nevertheless, there was one other important issue of their calculations: uncertainty.

Scientists by no means like uncertainty. In reality, a lot of their analysis tries to put bounds on sure parameters, just like the rotational pace of galaxies or the distances between them. Sadly, regardless of their proximity, there are a lot of uncertainties surrounding the 4 galaxies used within the examine, and people uncertainties make exact calculations of the consequences of their gravitational and rotational pull tough.

Creating estimates reasonably than concrete numbers is a technique scientists typically take care of uncertainty, and on this case, that estimate fell proper on the 50% mark by way of whether or not or not the 2 galaxies would collide. Nevertheless, there’s nonetheless plenty of uncertainty in that estimate, and many extra confounding elements, together with the opposite galaxies within the local group, will affect the ultimate end result.

In the end, time will assist remedy the thriller, however that could be a very very long time on the size of galaxy mergers. If it occurs in any respect, a merger between the Milky Way and Andromeda will occur lengthy after our personal sun has burned out, and people will both die out with it or discover a method to increase to new stars. And if, at that time, we get easy accessibility to a further galaxy’s value of sources, it could be all the higher for us.