For many years, astronomers have operated under the assumption that the Milky Way is on a path toward a collision with its closest significant neighbor, Andromeda. It appeared nearly guaranteed that the two galaxies would collide in roughly 4 to 5 billion years, combining into a colossal galaxy in the cosmos. In such a case, the merger could spark a whirlwind of star formations and demolitions and might even alter the sun’s orbit. This was presumed to be certain.

Nonetheless, fresh findings from NASA’s Hubble Space Telescope and the Gaia spacecraft, managed by the European Space Agency, indicate that the future of the Milky Way may not be so straightforward. The study, which utilized 100,000 computer simulations forecasting 10 billion years ahead, is featured in the journal Nature Astronomy.

“According to the best existing data, the destiny of our Galaxy remains entirely uncertain,” the researchers noted.

The Milky Way and Andromeda belong to a cluster of around 100 galaxies, bonded by gravity, referred to as the “local group.” For over a hundred years, scientists have understood that Andromeda is moving toward the Milky Way, leading many to think a collision was unavoidable.

It turns out the future is considerably less predictable. Researchers conducted simulations with 22 distinct variables to explore various potential trajectories for the galaxies, attempting to forecast their eventual positions. Their research indicated that the two galaxies would stay in the same plane while orbiting each other.

“But this doesn’t imply they must collide,” stated Till Sawala, the principal author from the University of Helsinki in Finland, in a statement. “They could still glide past one another.”

The researchers discovered that two additional nearby galaxies — the Large Magellanic Cloud and Messier 33 — might greatly affect whether the Milky Way and Andromeda ultimately collide. Although these galaxies are smaller, they possess sufficient mass to influence the outcome.

Incorporating Messier 33, also known as M33 or the Triangulum galaxy, into the simulation increases the likelihood of a galactic merger. Conversely, the Large Magellanic Cloud, whose orbit crosses those of the Milky Way and Andromeda, decreases the probability.

In summary, it’s a genuine “will they, won’t they?” With all the data analyzed, the team arrived at an almost equal, 50-percent chance of the two galaxies colliding within the next 10 billion years. In about half of the potential scenarios tested, the two primary galaxies passed each other, with a distance of 500,000 light-years between them or less: approximately five times the width of the Milky Way.

Sawala recognizes the irony that with more accurate Hubble data, scientists are less confident about the outcome. They’ve merely refined the odds of a cosmic catastrophe to a coin toss.

“That’s due to the more intricate analysis and because we are considering a more comprehensive system,” Sawala stated. “However, the sole path to a new prediction regarding the ultimate fate of the Milky Way will require even better data.”

Galaxy mergers unfold over an inconceivable timescale for humans, on the order of several hundred million years. Prior Hubble research has indicated that such collisions were more frequent in the past when the universe was more compact. Nevertheless, collisions are still occurring as galaxies are thought to be tethered by the gravity of what is described as dark matter — an invisible substance hypothesized to surround them.

There are still numerous unknown variables. Besides dark matter, undiscovered galaxies in the surrounding area could also play a role in whether Andromeda and the Milky Way unite. Future data releases from the Gaia mission, which is charting the locations and movements of stars, may enhance predictions.

“As it stands,” the researchers stated, “claims regarding the imminent downfall of our Galaxy seem greatly overstated.”