Astronomers have discovered a mammoth black hole containing as much mass as 17 billion suns.
The monster object is more than 11 times wider than the orbit of Neptune, the eighth planet in the Solar System.
It lies at the heart of a small lens-shaped galaxy called NGC1277, 220 million light years away in the constellation Perseus.
The black hole makes up an enormous 14% of the galaxy's mass.
Other black holes found at the centres of galaxies only account for around 0.1%.
Black holes are formed from matter collapsing to the point where normal laws of physics break down.
Their gravity is so strong that space and time are distorted, and not even light can escape.
Describing NGC1277, lead scientist Dr Karl Gebhardt, from the University of Texas at Austin, US, said: "This is a really oddball galaxy.
"It's almost all black hole. This could be the first object in a new class of galaxy-black hole systems."
A description of the black hole, found by astronomers using the nine-metre Hobby-Eberly Telescope in Texas, appears in the journal Nature.
The discovery could change theories of how black holes and galaxies form and evolve, say the scientists.