NASA’s Chandra X-ray space telescope recently observed the disk of gas around a black hole and found it to be orbiting orbiting at the record-breaking speed of 30 million kilometers per hour. This speed is three percent of the speed of light, and is some ten times faster than any other accretion disk observed so far. The gas is spinning so fast that it is throwing out a lot of material, possibly even more than the black hole manages to attract in the first place.
The black hole in question lies in the constellation Scorpius. Unlike the supermassive black hole at the centre of our galaxy, this is a more ordinary stellar mass black hole, weighing in at between five and ten times the mass of our own Sun and measuring only a few kilometers across. Black holes of this size are formed when the very largest stars burn their fuel rapidly in a blaze of glory before exploding as a supernova in one of the most violent events in the universe.
Chandra is able to determine the speed at which a gas disk rotates by looking at the spectrum of X-ray light which it emits. As with visible light, photons of specific energies interact with different atoms, molecules and ions. If we split light into a high enough resolution spectrum, we often see lines appearing corresponding to the different colours which correlate with those specific energies. This is often used to identify the gas which emitted the light, or a gas through which light has passed, but sometimes we see the distinctive patterns of lines in the wrong place. Depending on which way the pattern has been displaced, we say that the spectrum has been either redshifted or blueshifted. These shifts happen when the source of the lines is moving towards or away from us, leading to a doppler effect which causes the wavelengths to change. When we see both blueshifting and redshifting in the spectrum, we know that parts of the object are moving towards us, and that parts are movnig away. From this, Chandra’s project scientists were able to infer that the object was rotating, and by measuring the amount of red- and blueshift, they could measure its speed.
Read more on Chandra’s official website here: http://chandra.harvard.edu/photo/2012/igr/