The Large Magellanic Cloud, a dwarf galaxy located approximately 163,000 light-years away, is on a collision course with the Milky Way with which it will merge in about 2.4 billion years, according to new research. This catastrophic event could wake up our Galaxy’s dormant supermassive black hole, which would begin devouring surrounding gas and increase in size by up to 8 times; the Milky Way’s stellar halo will undergo an equally impressive transformation, becoming 5 times more massive; the merger will also gravitationally eject central disk stars into the halo.
The Milky Way Galaxy and the Large and Small Magellanic Clouds. Image credit: Nina McCurdy / Nick
Risinger / NASA.
Galaxies like our own Milky Way are surrounded by a group of smaller satellite galaxies that orbit around them, in a similar way to how bees move around a hive.
Typically, these satellite galaxies have a quiet life and orbit around their hosts for many billions of years. However, from time to time, they sink to the center, collide and are devoured by their host galaxy.
The Large Magellanic Cloud is the brightest satellite galaxy of the Milky Way and only entered our neighborhood about 1.5 billion years ago.
Until recently astronomers thought that it would either orbit our Galaxy for many billions of years, or, since it moves so fast, escape from our Galaxy’s gravitational pull.
However, recent measurements indicate that the Large Magellanic Cloud has nearly twice as much dark matter than previously thought.
“Since it has a larger than expected mass, the Large Magellanic Cloud is rapidly losing energy and is doomed to collide with our Galaxy,” said Durham University astronomer Marius Cautun and co-authors.
The researchers used the EAGLE galaxy formation supercomputer simulation to predict the collision.
“While two billion years is an extremely long time compared to a human lifetime, it is a very short time on cosmic timescales,” Dr. Cautun said.
“The destruction of the Large Magellanic Cloud, as it is devoured by the Milky Way, will wreak havoc with our Galaxy, waking up the black hole that lives at its center and turning our Galaxy into an active galactic nucleus or quasar.”
“This phenomenon will generate powerful jets of high energy radiation emanating from just outside the black hole. While this will not affect our Solar System, there is a small chance that we might not escape unscathed from the collision between the two galaxies which could knock us out of the Milky Way and into interstellar space.”
“Beautiful as it is, our Universe is constantly evolving, often through violent events like the forthcoming collision with the Large Magellanic Cloud,” said Professor Carlos Frenk, also from Durham University.
“Barring any disasters, like a major disturbance to the Solar System, our descendants, if any, are in for a treat: a spectacular display of cosmic fireworks as the newly awakened supermassive black hole at the center of our Galaxy reacts by emitting jets of extremely bright energetic radiation.”
The study appears in the Monthly Notices of the Royal Astronomical Society.
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Marius Cautun et al. 2019. The aftermath of the Great Collision between our Galaxy and the Large Magellanic Cloud. MNRAS 483 (2): 2185-2196; doi: 10.1093/mnras/sty3084
