BEIJING - Astronomers have discovered a black hole in the Milky Way so huge that it challenges existing models of how stars evolve, researchers said Thursday.

The Milky Way is estimated to contain 100 million stellar black holes but LB-1 is twice as massive as anything scientists thought possible, said Liu Jifeng, a National Astronomical Observatory of China professor who led the research.

"Black holes of such mass should not even exist in our galaxy, according to most of the current models of stellar evolution," he added.

Scientists generally believe that there are two types of black holes.

The more common stellar black holes -- up to 20 times more massive than the Sun -- form when the centre of a very big star collapses in on itself.

Supermassive black holes are at least a million times bigger than the Sun and their origins are uncertain.

LB-1 was discovered by an international team of scientists using China's sophisticated telescope.