Scientists have found the biggest black holes known to exist – each one 10 billion times the size of our sun.
The two gigantic black holes in clusters of elliptical galaxies more than 300 million light years away, have been discovered by astronomers at the University of California, Berkeley. That is relatively close on the galactic scale.
The previous black hole record was as large as six billion suns.
The scientists suggest these black holes may be the leftovers of quasars that crammed the early universe, says the journal Nature.
They are similar in mass to young quasars, they said, and have been well hidden until now.
Researchers used ground-based telescopes and the Hubble Space probe for the job, as well as supercomputers in Texas.
A black hole is formed by the collapse of a super-size star. It’s a region where nothing, not even light, can escape.
That is why they are so difficult to find in space. They cannot be viewed directly because there is no light.
But matter swirling around a black hole heats up and emits radiation that can be detected by Hubble.
The telescope can then observe the effect of the black hole on stars and gas around it.
Astronomers have sometimes likened black holes to watching women in white dresses dancing with men in black tuxedos in a dimly-lit ballroom. You only see the women, but you can predict the existence of their invisible partners because they spin and whirl around a central axis.
Searching for stars whose motions are influenced by invisible partners is one way black holes are discovered.
Most, if not all galaxies, are believed to have black holes at their centre. The bigger the galaxy, it seems, the bigger the black hole.
Quasars are some of the most energised and distant of galactic centres.
The researchers said their findings suggest differences in the way black holes grow, depending on the size of the galaxy.
Astrophysicist Chung-Pei Ma, part of the Berkeley team, speculates that the black holes remained hidden for so long because they are living in quiet retirement.
“For an astronomer, finding these insatiable black holes is like finally encountering people nine feet tall whose great height had only been inferred from fossilised bones. How did they grow so large?” asked Ms Ma.
“This rare find will help us understand whether these black holes had very tall parents or ate a lot of spinach.”
Oxford University astrophysicist Michele Cappellari agreed that the two newly-discovered black holes “probably represent the missing dormant relics of the giant black holes that powered the brightest quasars in the early universe”.
One of the newly detected black holes is 9.7 billion times the size of the sun. The second, slightly further from earth, is as big or even bigger.