The huge interstellar objects grow up to masses billions of times that of our sun - and, while growing, can outshine the entire galaxy that surrounds them.
But how and why they form is a mystery. Now scientists believe that collisions with smaller galaxies may explain why such enormous objects develop.
The growth of supermassive black holes has been mysterious because the glaring light of a growing supermassive black hole can outshine the entire host galaxy, making it difficult to observe.
It's been known for some time that supermassive black holes are usually found in the most massive galaxies, and that their size is proportional to the 'bulge' in the centre of the galaxy - ie the mass of the stars in the middle.
A new survey by an international team headed by Dr John Silverman of the University of Kashiwa, Japan, hints that the holes grow when two galaxies 'collide'. Read More