Although black holes are invisible, they can be found by watching their effect on nearby gas and stars. For stellar-mass black hole IGR J17091, this is exactly what is happening. Its gravity is pulling gas away from a companion star and this gas has formed into a disk around the black hole, which is driving off wind.
However, there's something special about IGR J17091--the wind it's creating is the fastest wind ever discovered blowing off a disk surrounding a stellar-mass black hole.
In most other ways IGR J17091 is pretty much a ho-hum black hole: it's located in the Milky Way galaxy and is orbited by a sun-like star; its average weight--between five and 10 times the mass of our sun; and, was born like all other stellar-mass black holes--when an extremely massive star collapsed. But its wind speed equals some of the fastest winds generated by, which are millions or billions of times bigger.
"This is like the cosmic equivalent of winds from a category five hurricane," Ashley King, lead author of a study published on IGR J17091, said in a statement. "We weren't expecting to see such powerful winds from a black hole like this."
The wind speed was recorded by astronomers using NASA's Chandra X-ray Observatory, which clocked it around 20 million mph, or about 3 percent of the speed of light. This is nearly 10 times faster than had ever been seen from a stellar-mass black hole and may help scientists better understand how these types of black holes behave."It's a surprise this small black hole is able to muster the wind speeds we typically only see in the giant black holes," Jon M. Miller, co-author of the study, said in a statement. "In other words, this black hole is performing well above its weight class."
Typical theory on black holes is that their gravitational pull is so strong that everything near it gets sucked in; supposedly even the speed of light is not fast enough to escape. However, scientists believe this isn't the case with IGR J17091. With such strong wind, they believe that possibly more material is being swept away than being captured.
"Contrary to the popular perception of black holes pulling in all of the material that gets close," King said, "we estimate up to 95 percent of the matter in the disk around IGR J17091 is expelled by the wind."
Another interesting aspect of IGR J17091 is that two months before the winds were recorded, astronomers at the Chandra X-ray Observatory saw no evidence of high-speed wind. They say that this means the wind is likely to turn on and off over time.