February 22, 2012 by staff
Black Hole, Black hole IGR J17091-3624 might be the smallest known black hole, but it has the “cosmic equivalent of winds from a category five hurricane.”
That’s the conclusion of Dr. Ashley King, who led group of astronomers working with NASA’s Chandra X-Ray Observatory and National Radio Astronomy Observatory’s Expanded Very Large Array to observe the black hole, which I shall refer to as “Lenny” for the remainder of this article so I don’t inadvertently type the wrong numeric sequence.
(Why Lenny? That’s my way of honoring Leonard Susskind, who’s done quite a bit of work on Black Holes and was one of the originators of String Theory.)
Lenny is part of a binary system and is orbited by a star that’s similar to our own sun. It’s known as a stellar-mass black hole, meaning that its mass is similar to that of a large star. In this case, it’s about three times the mass of the Sun – at least, that’s the best mass estimate right now, though Dr. Peter Edmonds at the Chandra Observatory indicated to me that that estimate is “highly uncertain.”
What is clear about Lenny, though, is that despite its small size, it produces fearsome winds of ionic gasses near its disk. Winds that astronomers have clocked at 20 million miles per hour – or about 3% of the speed of light. Those types of speeds are usually only seen near supermassive black holes that are hundreds of thousands of times more massive than Lenny.
“It’s a surprise this small black hole is able to muster the wind speeds we typically only see in the giant black holes,” said researcher Jon M. Miller in a press release. “In other words, this black hole is performing well above its weight class.”
The winds are generated by the magnetic field of black holes, which interact with the high-temperature ions to cause rapid movements. Those movements either take the form of winds or jets. In the latter, the ionic gasses fire in a focused stream in a direction perpendicular to the accretion disk surrounding a black hole.
The winds observed around Lenny aren’t constant, and depending on the movement of the gasses and the magnetic field, both jets and winds are seen. In fact, it’s likely that jets are a fairly regular occurrence around Lenny, as the Rossi X-Ray Timing Explorer has observed a regular “heartbeat” of X-ray expulsions that would be consistent with a jet firing from the black hole.
What’s particularly interesting about the winds produced by Lenny is that they’re not only unusually fast for a black hole of its size, but it’s also causing more matter to fly away from the black hole than to be attracted to it. A lot more.
“Contrary to the popular perception of black holes pulling in all of the material that gets close, we estimate up to 95 percent of the matter in the disk around IGR J17091 is expelled by the wind,” said King.
It seems that the past year has really provided a wealth of new information about black holes and how they work, often to the surprise of the astronomers and physicists observing them. Hopefully, a lot of these surprises and information will go a long way towards gaining a greater understanding of how black holes work. And by doing so, hopefully physicists will understand more about the fundamental laws of nature.
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