We are pleased to welcome Andrew King from the University of Leicester in the United Kingdom as a guest blogger. Andrew is the author of a paper that is the subject of our latest press release. He graduated in Mathematics from the University of Cambridge (UK), and then researched there for his PhD in General Relativity. After postdoctoral positions in London and Hamburg, he moved to the University of Leicester, where he is now Professor of Theoretical Astrophysics. He is a long-term visitor at the Anton Pannekoek Astronomical Institute in the University of Amsterdam, and Visiting Professor at Leiden Observatory. His interests include ultraluminous X-ray sources, accretion and feedback involving supermassive black holes, and how this affects their host galaxies.
A few months ago, Giovanni Miniutti from ESA's Center for Astrobiology in Spain, and collaborators observed that X-ray emission from the low-mass nucleus (that is, a relatively small black hole at its center) of the galaxy GSN 069 brightened by factors of about 100 roughly every 9 hours, staying bright for about an hour each time before returning to the faint state. From the X-ray spectrum — the intensity of X-rays at different wavelengths — they deduced that the X-rays came from an accretion disk around the central black hole of the galaxy, which has the rather low mass of about 400,000 times that of the Sun. I was intrigued by these observations: the eruptions implied that a lot of mass was being fed into the accretion disc every 9 hours, and the reasonably stable period suggested there was something in a very close orbit around the black hole.