How big is the event horizon of a black hole?
ScienceDaily — The point of no return: In astronomy, it's known as a black hole -- a region in space where the pull of gravity is so strong that nothing, not even light, can escape. Black holes that can be billions of times more massive than our sun may reside at the heart of most galaxies.
Such supermassive black holes are so powerful that activity at their boundaries can ripple throughout their host galaxies. Now, an international team, led by researchers at MIT's Haystack Observatory, has for the first time measured the radius of a black hole at the center of a distant galaxy -- the closest distance at which matter can approach before being irretrievably pulled into the black hole.
The scientists linked together radio dishes in Hawaii, Arizona and California to create a telescope array called the "Event Horizon Telescope" (EHT) that can see details 2,000 times finer than what's visible to the Hubble Space Telescope. These radio dishes were trained on M87, a galaxy some 50 million light years from the Milky Way. M87 harbors a black hole 6 billion times more massive than our sun; using this array, the team observed the glow of matter near the edge of this black hole -- a region known as the "event horizon."
"Once objects fall through the event horizon, they're lost forever," says Shep Doeleman, assistant director at the MIT Haystack Observatory and research associate at the Smithsonian Astrophysical Observatory. "
It's an exit door from our universe. You walk through that door, you're not coming back." Doeleman and his colleagues have published the results of their study this week in the journal Science....
Using the technique, Doeleman and his team measured the innermost orbit of the accretion disk to be only 5.5 times the size of the black hole event horizon. According to the laws of physics, this size suggests that the accretion disk is spinning in the same direction as the black hole -- the first direct observation to confirm theories of how black holes power jets from the centers of galaxies. Keep on reading...