The Andromeda Galaxy Is Getting Closer and Closer. But Will It Actually Collide with Our Milky Way?

The Andromeda galaxy is hurtling toward us at a speed of 110 kilometers (68 miles) per second. That may sound fast, but don't panic just yet

The Andromeda Galaxy is the closest large galaxy to our Milky Way, and it’s getting closer and closer. In fact, astronomers believe the two galaxies are destined to collide.

But a new study suggests that fate is not necessarily written in the stars.

The Andromeda galaxy is hurtling toward us at a speed of 110 kilometers (68 miles) per second. That may sound fast, but don’t panic just yet — the galaxy is still about 2.5 million light-years away from Earth, so it’s expected to take a few billion years to reach us.

Previous studies were absolutely certain that a collision was almost inevitable, but a deeper analysis in a recent study by researchers from the University of Helsinki and Durham University in England suggests the chances of a collision occurring in the next 10 billion years are 50/50.

Using the latest and most accurate motion and mass data from Gaia and the Hubble Space Telescope, the team simulated the motions of not only the Milky Way and Andromeda, but also other major players in our solar system's Local Group – the Large Magellanic Cloud and Triangulum Galaxy.

When the Milky Way and Andromeda were considered individually, a collision occurred within the next 10 billion years in about half of the simulations, the team says.

Adding the Triangulum to the mix increased the probability to two-thirds, while simulations using the Milky Way, Andromeda, and the Large Magellanic Galaxy reduced the odds to just one-third. Combining the four galaxies into a single simulation resulted in the Milky Way and Andromeda merging just over 50 percent of the time.

In cases where collisions do occur, we appear to have more time than previously thought. The study found that the average time for a merger is more than 7.6 billion years in the future, much longer than previously estimated at 4 to 5 billion years.

“Even using the latest and most accurate observational data, the future evolution of the Local Group is uncertain,” the team concludes.

“Interestingly, we find roughly equal probability for the widely announced merger scenario (albeit with an average merger time later than previously reported) and one where [Milky Way and Andromeda] survive without merging.”

Galaxies colliding with each other sounds like an apocalypse of epic proportions, but there’s really nothing to worry about. The first point, of course, is the time frame – the Sun is only expected to live for another 5 billion years or so. This means that life on Earth will witness several Local Armageddon-esque events long before the galaxies merge.

Even if other life forms were to find themselves in the crossfire, they would be unlikely to really notice the cosmic buildup happening around them. Galaxies look very dense from a distance, but up close they are mostly empty space. There is only so much room for stars to fit around each other, so they would be very unlikely to notice anything happening around them, and it is highly unlikely that any two stars will actually collide.

However, their gravitational interactions would push each other into new orbits: for example, our Sun, which is probably in its red giant phase by then, is thought to bounce farther out to the edge of the galaxy.

In its place, new stars will form more quickly, as the compressed hydrogen increases star formation. The two galaxies will lose their current spiral shape, forming instead a giant elliptical galaxy. Astronomers have already dubbed the end result a “Milcomeda”.

Or, of course, the Milky Way and Andromeda could just swing by each other and continue to evolve as separate galaxies for eons to come. The point is, we don’t know for sure what their timelines look like, and while other studies have been confident enough to claim that the collision was the result of the two galaxies evolving, that doesn’t necessarily mean the two galaxies could be almost certainly merging. The new work poses the issue in the form of a lottery.

Further research, including upcoming Gaia data releases, could help paint a clearer picture.

“At present, claims about the imminent demise of our galaxy appear to be greatly exaggerated,” the paper states.

The research was published as a preliminary version on Arxiv.

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