Extreme black holes : new tracers of the accelerated expansion of the universe

The mass of such black holes ranges from about a million to several billion times the mass of the Sun. They can be detected when they accrete large amounts of gas from their surroundings which cause them to release up to a thousand times the energy produced by a galaxy containing some hundred billion stars. The group of scientists studied this class of black holes -the most luminous ones in their mass range- detected in dozens of active galaxies called narrow-line Seyfert 1 galaxies. Theoretical models suggest that in such objects gas accretion onto the black holes goes via a special kind of an inflated gaseous disc called “slim accretion disc”, where the amount of energy emitted in the process is proportional to the black hole mass. Thus measuring the mass using well established methods enables astronomers to derive the amount of released electromagnetic radiation and hence the distance of the black hole and its host galaxy.

The observation of these extreme black holes over a range of distances can be translated into measuring the rate of expansion of the universe, and its variation, at those times. They could be an alternative to the method used so far, based on the few explosions of type Ia supernovae. Unlike these explosions, extreme black holes are not transient and can be observed at all times and distances in the universe. Once identified, these black holes can be studied in detail with follow-up observations. The method has been successfully tested at relatively small distances, and the published paper describes the steps required to enable similar measurements at much larger distances and at times when the universe began its accelerated expansion.

Source

Authors :
Jian-Min Wang (IHEP, Institute of High Energy Physics, Chinese Academy of Sciences), Du Pu (IHEP), David Valls-Gabaud (CNRS UMR 8112, LERMA, Observatoire de Paris), Hagai Netzer (Tel Aviv University, Israel) and Chen Hu (IHEP).