Black hole bullseye sheds light on interstellar dust
What looks like a shooting target (right) is actually an image of nested rings of X-ray light centred on an erupting black hole. On June 15, NASA's Swift satellite detected the start of a new outburst from V404 Cygni, where a black hole and a sun-like star orbit each other.
A team led by Andrew Beardmore from our Department of Physics and Astronomy imaged the system using the X-ray Telescope aboard Swift, revealing a series concentric rings extending about one-third the apparent size of a full moon.
The black hole's erupting flares emit X-rays in all directions, some of which is reflected back back to us by interstellar dust layers that lie between the Earth and the black hole, while some of the light travels a longer distance and reaches us slightly later. The time delay creates a light echo, forming rings that expand with time. There are multiple rings because there are multiple reflecting dust layers between 4,000 and 7,000 light-years away from us.
A movie made by combining the observations shows the expansion and gradual fading of the rings:
Dr Beardmore said: "With these observations we can make a detailed study of the normally invisible interstellar dust in the direction of this black hole."