'Great Collision' Could Wake Up the Supermassive Black Hole at the Milky Way's Center

A "great collision" between the Milky Way and another nearby galaxy could result in the awakening of a suppermassive black hole, causing it to swell up to eight times its current mass, devouring surrounding gas and throwing out huge amounts of high-energy radiation.

Galaxies are not stagnant. They are moving around space all the time and often collide and merge. It is thought that in around eight billion years, the Milky Way will collide with Andromeda, our closest neighbouring galaxy.

However, about six billion years before this, there could be another cosmic car crash, when our home galaxy is hit by the Large Magellanic Cloud (LMC), a satellite galaxy that is around 14,000 light years in diameter and orbits the Milky Way.

In a study published in the Monthly Notices of the Royal Astronomical Society, scientists from the U.K.'s Durham University have said the collision could take place in two million years and that if and when this happens, it could wake up the supermassive black hole that sits at the center of the Milky Way.

The LMC is around 163,000 light years from the Milky Way and while it could continue to orbit our home galaxy, it may be caught by the gravitation pull and come hurtling towards us. Measurements currently suggest that its mass is bigger than initially thought, placing the second scenario as the more likely of the two.

If the collision takes place, models suggest the dormant supermassive black hole Sagittarius A* could wake up and swell by a factor of around eight. Its mass would increase as it starts feeding on the surrounding gas.

"While two billion years is an extremely long time compared to a human lifetime, it is a very short time on cosmic timescales," Marius Cautun, a postdoctoral fellow in Durham University, said in a statement: "While two billion years is an extremely long time compared to a human lifetime, it is a very short time on cosmic timescales.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 centre 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."

Should the collision increase the mass of Sagittarius A* as predicted, it would make the Milky Way more typical of similar sized galaxies astronomers observe—simply put, our supermassive black hole is too small.

Daniel Brown, an astronomer at the U.K.'s Nottingham Trent University, who was not involved in the study, said the findings help model future collisions and help address some of the "oddities" observed in the Milky Way. "We have a not so massive black hole that seems to be very quiet at the centre of our galaxy, and odd chemical composition issues with stars surrounding our Galaxy," he told Newsweek. "This is where [the researchers] with their models show how a merger in two to three billion years with our largest satellite galaxy will make us average again: larger more active central black hole and more stars of typical chemical composition in the surrounding of the Milky Way."

This collision is not expected to affect our own solar system in any way, although Cautun notes there is a "small chance" it could be knocked out of the Milky Way and interstellar space. Should mankind still exist in two million years, the collision would produce a "spectacular dispay of cosmic fireworks," study co-author Carlos Frenk added.

9_27_Andromeda Milky Way
This illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. In this image, representing Earth’s night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull. NASA/ESA/Z Levay/R van der Marel/STScI/T Hallas/A Mellinger