Here’s some good news: Our galaxy may not be destined to end in a fiery collision with the Andromeda galaxy as soon as previously thought. While earlier research regarded the collision as a virtual certainty within five or six billion years, new research questions that.
The Andromeda Galaxy, a spiral galaxy also known as Messier 31 or simply M31, is one of several galaxies, including the Milky Way, that comprise what is known as the Local Group. Astronomers have long known that Andromeda is on a collision course with the Milky Way. In 2012, data from NASA’s Hubble Space Telescope got more specific when it confirmed suspicions that the two galaxies are destined to collide in about four or five billion years.
But an analysis of new data from Hubble and the European Space Agency’s Gaia Space Telescope has caused researchers to question that time frame. According to Till Sawala, an astrophysicist at the University of Helsinki, the likelihood of that event occurring within the next 10 billion years is approximately 50/50. Sawala and colleagues published the results of their analysis in Nature Astronomy.
Read More: Some Stars In Our Galaxy Came From Andromeda
Galactic Simulations
Previous simulations had taken into account the gravitational effects of Andromeda and the Milky Way, and a few considered the effects of M33, the third major player in the Local Group, explains Cameron Hummels, a computational astrophysicist at Caltech.
Sawala and his team, however, ran about 100,000 simulations using different combinations of possibilities that included the influence of another galaxy in the Local Group, the Large Magellanic Cloud (LMC).
“Gaia, the European Space telescope that's been operating for the last 10 years or so, really was able to home in very well on the motion of Andromeda and the Large Magellanic Cloud, and M33 for that matter, across the sky in a way that's much more precise and much more accurate than what we had when these previous iterations of simulations were being done,” says Hummels.
“It is perhaps somewhat ironic that, despite access to more accurate measurements, we now find less certainty about the outcome,” says Sawala.
What If They Do Collide?
What happens when galaxies collide? Both not much and a whole lot. The thing to keep in mind is that there’s a lot of empty space between the stars. If the two galaxies do collide, the chances of individual stars crashing into one another are extremely low, less than one percent, says Hummels.
“The bulk of the volume in these galaxies is just empty space, and the individual stars themselves are tiny relative to the overall volume in which they're sitting,” he says.
But that doesn’t mean there won’t be some fireworks. Galaxies contain not only stars, but also a significant amount of gas, which fuels the creation of new stars. And these gases will crash into each other, and when they do, those collisions will likely produce new generations of stars.
Some of them will be very massive and turn into supernovae very quickly, says Hummels. So even though stars won’t collide, the merger of the two galaxies won’t be completely passive.
“It will still have the fireworks display, even if not for the reasons people might think,” he says.
More Data to Come
Humans will be long gone before this happens, even if it happens on the original timeline of four to five billion years. (For one thing, our Sun will be running out of fuel by then.) But that doesn’t mean scientists shouldn’t think about it. Research like this helps us better understand our galaxy and our universe.
The next data release from the Gaia telescope is expected in 2026, which should provide even more accurate measurements of the motion and mass of galaxies in the Local Group. But making accurate predictions requires not only more and better data, says Sawala, but more realistic models.
“The calculations that underpin our work and similar work in this field are ultimately still quite simplistic,” he says. “In my view, to take advantage of new and upcoming measurements and to understand both the past and the future evolution of the Local Group in its full cosmological context requires more advanced simulations.”
And that is exactly what Sawala and his collaborators are working on. Stay tuned.
Read More: Meet the Milky Way's Neighbor: The Andromeda Galaxy
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
NASA. NASA’s Hubble Shows Milky Way is Destined for Head-On Collision
Nature Astronomy. No certainty of a Milky Way–Andromeda collision
Avery Hurt is a freelance science journalist. In addition to writing for Discover, she writes regularly for a variety of outlets, both print and online, including National Geographic, Science News Explores, Medscape, and WebMD. She’s the author of Bullet With Your Name on It: What You Will Probably Die From and What You Can Do About It, Clerisy Press 2007, as well as several books for young readers. Avery got her start in journalism while attending university, writing for the school newspaper and editing the student non-fiction magazine. Though she writes about all areas of science, she is particularly interested in neuroscience, the science of consciousness, and AI–interests she developed while earning a degree in philosophy.
