Black holes are so dense and their gravitational pull is so strong that no form of radiation can escape them – not even light.
They act as intense sources of gravity which hoover up dust and gas around them.
Their intense gravitational pull is thought to be what stars in galaxies orbit around.
How they are formed is still poorly understood.
Supermassive black holes are incredibly dense areas in the centre of galaxies with masses that can be billions of times that of the sun. They cause dips in space-time (artist’s impression) and even light cannot escape their gravitational pull
Astronomers believe they may form when a large cloud of gas up to 100,000 times bigger than the sun, collapses into a black hole.
Many of these black hole seeds then merge to form much larger supermassive black holes, which are found at the centre of every known massive galaxy.
Alternatively, a supermassive black hole seed could come from a giant star, about 100 times the sun’s mass, that ultimately forms into a black hole after it runs out of fuel and collapses.
When these giant stars die, they also go ‘supernova’, a huge explosion that expels the matter from the outer layers of the star into deep space.