Black holes have always been some of the most enigmatic objects in the universe since their first mention in modern physics in the early days of General Relativity.
The models of Black Holes all predict that when it is ‘feeding’ – that is absorbing matter from the surrounding space – material will spiral round its equator in an accretion disk.
The Hubble Space Telescope has recently collected precise data on the accretion disk of a black hole at the centre of an extremely energetic galaxy far across the universe – a Quasar (QSO).
HE 1104-1805 Credit: NASA, ESA and J.A. Muñoz (University of Valencia)
The faint smudge in the centre of the image is a galaxy that sits between Earth and the QSO. The light from the QSO is primarily produced by material in the accretion disk of its central supermassive black hole – such black holes can be several million times the mass of the sun but could fit inside our Solar System. The mass of this foreground galaxy causes the light from the QSO behind to lens – magnifying and distorting the image. Such gravitational lensing can produce multiple images as in this case two bright images of the QSO have been generated some distance apart – the two bright starlike objects in the image.
It is by carefully observing how these images vary overtime and comparing the data from each image, that fine detail of the central accretion disk has been collected.
The variation is due to the lensing of the QSO altering slightly as the foreground galaxy moves relative to Earth and the QSO. Specifically a star in the foreground galaxy can move across the accretion disk image and alter the light that is beamed towards Hubble over the course of several days. This manifests itself in the data as slight colour changes in the light from the QSO being detected. As colour is related to temperature, and the star crosses the entire accretion disk astronomers have been able to study the temperature, colour and scale of the accretion disk to an accuracy comparable to studying individual grains of sand on the moon from the surface of the Earth.
The measurements show that the disk is between 4 and 11 light days across – that is a range of between 100 billion and 300 billion kilometres – whilst in normal everyday measurements this uncertainty seems ridiculously large we must remember that the QSO is billions of light years away and so the accuracy is phenomenally high. What’s more the technique shows lots of room for refinements in the future and so it is inevitable that the accuracy of such measurements will improve as well.
You can see a video and explanation of how the data was collected here
and can read more about the discovery here
Sigma Orionis 