A collision between the Milky Way and Andromeda is unlikely

Contrary to earlier predictions, it is now thought unlikely that Andromeda, the closest major galaxy to the Milky Way, will collide with our own. Andromeda, also designated Messier 31 (M31), is a spiral galaxy located approximately 2.5 million light-years away.

Slightly larger than the Milky Way, boasting roughly twice the diameter, it was previously believed to be on a collision course with our galaxy based on data, including findings from NASA’s Hubble Space Telescope in 2012. Simulations suggested the merger, potentially creating a new elliptical galaxy nicknamed “Milkomeda,” would occur in about 4 to 5 billion years.

However, a recently published study in Nature Astronomy challenges the certainty of the predicted Milky Way-Andromeda collision. The authors of the paper state that they have used the most recent and precise data from the Gaia and Hubble space telescopes, alongside current mass estimations, tomodel potential future scenarios and pinpoint the primary factors that introduce uncertainty into the Local Group’s evolution over the next 10 billion years.

The Milky Way’s trajectory is affected by the gravitational forces of various objects within our Local Group, including Andromeda, the smaller Triangulum Galaxy (Messier 33, or M33), superclusters, and dwarf galaxies like the Large and Small Magellanic Clouds, the Virgo Supercluster, and the Lakiakea Supercluster. Specifically, the Triangulum Galaxy and the Large Magellanic Cloud significantly influence the potential collision between the Milky Way and Andromeda.

The researchers note that while including M33 raises the likelihood of a merger, the orbit of the Large Magellanic Cloud, being perpendicular to the Milky Way-Andromeda orbit, reduces the probability of their collision.

Milky Way and Andromeda
Three future scenarios for Milky Way & Andromeda encounter. Top left: Galaxies bypass at 1 million light-year separation. Top right: At 500,000 light-years, dark matter provides friction that brings galaxies to a close encounter. Bottom: A 100,000 light-year separation leads to a collision. Credit: NASA / ESA.

Updated simulations reveal a nearly 50% probability that the Milky Way and Andromeda galaxies will not collide within the next 10 billion years. Astronomers acknowledge that their model contains uncertainties and simplifications, such as the assumption of constant mass distributions within galaxies and the Local Group over this timeframe.

Despite these limitations, the latest simulations, incorporating improved physics and observational data, cast significant doubt on the inevitability of a Milky Way-Andromeda collision. The simulations suggest a potential collision between the Milky Way and the Large Magellanic Cloud in approximately 2 billion years, although these events are far beyond our ability to directly observe.