Smallest black hole ever found

By Space.com Staff

Scientists may have found the smallest black hole yet by listening to its X-ray "heartbeat."

The black hole, if it truly exists, would weigh less than three times the mass of the sun, putting it near the theoretical minimum mass required for a black hole to be stable.
The researchers can't directly observe the black hole, but they measured a rise and fall in X-ray light coming from a binary star system in our Milky Way galaxy that they think signals the presence of a black hole.
Until now, this X-ray pattern, which is similar to a heartbeat registered on an electrocardiogram, has been seen in only one other black hole system.

NASA's Rossi X-ray Timing Explorer (RXTE) spacecraft measured this X-ray heartbeat in a star system in the direction of the constellation Scorpius, at a distance between 16,000 and 65,000 light-years away (a light-year is the distance light travels in a single year, about 6 trillion miles (10 trillion kilometers).
Researchers think the system, officially called IGR J17091-3624, includes one normal star with a companion black hole. Mass would stream off this normal star and fall toward the black hole, forming a flattened disk around it. As friction in the disk heats the gas to millions of degrees, the disk would emit high-energy X-rays that can be seen across the galaxy.
As changes occur inside the disk, cyclical variations can be seen in the X-rays streaming from it, which pulse in varied intensity like a heartbeat.
The astronomers recognized the signal from this system because of its similarity to another black hole system called GRS 1915+105 that pulses in much the same way. This other system contains a black hole that weighs about 14 times the sun's mass, which sends out X-rays in highly structured patterns that last between seconds and hours.