30 Marzo 2017 15:52
Supermassive black holes are the great destroyers of outer space. They usually reside at the centres of large galaxies, where they devour any planets, stars or celestial bodies that stray too close.
However, as if that wasn't scary enough, astronomers have now observed something even more ominous than a stationary black hole. Eight billion light years away, the black hole in galaxy 3C 186 seems to have been set loose and has gone rogue, hurtling through space like a massive vacuum cleaner, sucking up whatever gets in its way. Astronomers estimate that the black hole is cruising along at 4.7 million miles per hour. To put that in perspective, it would take it less than three minutes to reach the moon from Earth.
Although it is heading towards the Milky Way, astronomers say we shouldn't be too worried yet. It would take millions of years to reach us. However, experts are interested in finding out just how this black hole – which weighs billions of times more than the sun – was set loose. In other words, what force could have been strong enough to get it moving?
The primary hypothesis is that it was set on it's course by gravitational waves. Around 100 years ago, Albert Einstein defined these as ripples caused by catastrophic events that take place in the universe. They are powerful waves, like the concentric circles you see after throwing a hefty stone into a pond.
The catastrophic event could have been the merging of two galaxies. Through the telescope, a series of elongated arcs, called 'tidal tails' have been observed. These are produced by the gravitational pull resulting from the violent fusion of two galaxies into one. Experts believe that galaxy 3C 186 must have fused with another galaxy, causing the two black holes to do the same.
The two black holes from the merging galaxies must have fused into one, which shot out like a projectile
If two black holes approaching each other have the same mass and velocity, they don't emit gravitational waves of equal strength in all directions, but rather one very strong wave in a particular direction. When the black holes collide and fuse, the new massive black hole shoots out like a projectile in the opposite direction to the waves.
'When I first saw this, I thought we were seeing something very peculiar,' said team leader Marco Chiaberge, of the Space Telescope Science Institute (STScl) and John Hopkins University.
What he saw was a quasar – the bright rings of gas that surround a black hole and enable them to be seen – 35,000 light years away from the centre of the galaxy where the hole should have been located. Information collected subsequently, including X-rays and ultraviolet light, revealed that this was indeed a supermassive black hole that had been set loose and was flying through space.