Astronomy Photo of the Day
This is an illustration, not a photo, but quite nifty. It's credited to April Hobart of the Chandra X-ray Observatory.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgbGjVlbJ3HOk1Y2HnQM9TIMnFRK2u4XtUqRqt89I8JrX6K8ekomJNW97Tzh-4fB_TG81A2rX7Zhl7vH-EfiX4KZLGr-gFVZKVmIpOlIGu4iXWBIcni8jwe4bb4b4-lWqkWp0esmg/s400/blackhole_hobart.jpg)
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgbGjVlbJ3HOk1Y2HnQM9TIMnFRK2u4XtUqRqt89I8JrX6K8ekomJNW97Tzh-4fB_TG81A2rX7Zhl7vH-EfiX4KZLGr-gFVZKVmIpOlIGu4iXWBIcni8jwe4bb4b4-lWqkWp0esmg/s400/blackhole_hobart.jpg)
In the center of a swirling whirlpool of hot gas is likely a beast that has never been seen directly: a black hole. Studies of the bright light emitted by the swirling gas frequently indicate not only that a black hole is present, but also likely attributes. The gas surrounding GRO J1655-40, for example, has been found to display an unusual flickering at a rate of 450 times a second. Given a previous mass estimate for the central object of seven times the mass of our Sun, the rate of the fast flickering can be explained by a black hole that is rotating very rapidly. What physical mechanisms actually cause the flickering -- and a slower quasi-periodic oscillation (QPO) -- in accretion disks surrounding black holes and neutron stars remains a topic of much research.
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