The Hubble Space Telescope - peering into the heart of a distant galaxy - has confirmed the existence of black holes, astronomers say.
"Even though I've been a black hole skeptic in the past, I believe this is definitive," says NASA's Daniel Weedman.
But if the super-massive phenomenon found isn't a black hole, says scientist Richard Harms, "it must be something even harder to understand with our present theories."
Scientists say the finding supports a key part of Einstein's 79-year-old theory of relativity - that very massive objects would actually warp time and space.
A black hole is thought to be a collapsed star whose mass is so dense not even light can escape its gravitational pull.
Hubble's discovery is based on measuring the velocity of a disk of hot gas whirling around the center of a galaxy 50 million light years away.
Light travels about 6 trillion miles in one year.
Astronomers say the black hole is the mass of 2.3 billion suns squeezed into an area no larger than our solar system.
Astronomers have had tantalizing glimpses of what may be much smaller black holes several times the mass of the sun, but nothing as immense - or located in a galactic core - as this one appears to be.
This latest data from the repaired Hubble is "at the top or near the top" of its achievements, says Weedman.
