There’s a 50% Chance That Our Galaxy Will Collide With Andromeda, But We're Dead No Matter What

Collisions between two galaxies are common in the universe. It’s the end that experts have been predicting for the Milky Way for over a century when they discovered that our neighbor, Andromeda, was on a collision course toward us. Now, a new study has cast doubt on the idea that astronomers have accepted for 112 years.

Andromeda and its journey to the Milky Way. These are the two largest galaxies in the Local Group, a collection of more than 50 galaxies that make up our neighborhood in the cosmos. And they’re relatively close, astronomically speaking: just 2.5 million light-years away.

In 1912, astronomer Vesto Slipher observed Andromeda with his spectrograph and detected a blue shift, indicating that the galaxy was moving toward Earth.

The collision that may never happen. It’s widely believed that Andromeda (M31) will collide with the Milky Way in 4 or 5 billion years. The two spiral galaxies will merge to form a new giant elliptical galaxy.

Our galaxy would have no chance against the much larger size of its rival. Andromeda has a diameter of 220,000 light-years, while the Milky Way’s disk is estimated to measure 100,000 light-years. However, the latest research leaves all possibilities open.

It’s like flipping a coin. A new study published on arXiv, which has not yet been peer-reviewed, states that the Andromeda–Milky Way collision has a 50% chance of happening. It's the same as flipping a coin and betting on whether it'll come up come up heads or tails.

This is the conclusion reached by an international team of astronomers after reviewing the latest observations from the Gaia and Hubble space telescopes and the latest mass estimates for all the objects involved, including nearby Local Group galaxies that could deflect the course of the protagonists.

The four-body problem. In their analysis, scientists considered the gravitational interactions of the Triangulum Galaxy (also known as M33, the third largest galaxy in the Local Group) and the Large Magellanic Cloud (a dwarf galaxy close to the Milky Way that has already swallowed other galaxies on its way to ours).

The authors calculated possible future scenarios and identified the primary sources of uncertainty in the Local Group for the next 10 billion years. The result is so complex that, they state, the best estimate of the probability of an Andromeda-Milky Way collision is 50%.

There will be no one left on Earth. When the collision happens, the solar system could be ejected from the galaxy or pulled away from its core. The good news is that in 5 billion years, we probably won’t be here. The Sun will have exhausted the hydrogen in its core and begun to fuse helium, expanding into a red giant until it loses its outer layers.

If Andromeda collides with our galaxy, it will do so when there’s no more life on Earth because the planet’s surface will have become too hot for liquid water to exist. Our only chance will be to have conquered other stars if we haven’t gone extinct or killed each other first.

This article was written by Matías S. Zavia and originally published in Spanish on Xataka.

Images | NASA/JPL-Caltech

Related | The End of the Universe: What Science Tells Us About the Inevitable Fate of the Cosmos