How some black holes gobble up cosmic mass
Black holes (BHs) are the remnants of former stars that have collapsed upon themselves, becoming so dense and compact that not even light can escape their gravitational pull. BHs have a voracious appetite for other material in the Universe for the same reason and accrete it on a regular basis. SMBHs include those in active galactic nuclei (AGN) at the centres of many galaxies, among them the Milky Way. They were full-grown very early on and their rapid accretion exceeds the classical limit (Eddington limit) imposed by the balance between gravity and liberated radiation. SMBHs in AGN accrete over decades to millennia, making their study impractical. EU-funded scientists launched the project 'Timing and spectroscopy in the Eddington regime' (TASER) to conduct a comprehensive study of suitable analogues on faster time scales close to home. Black-hole binaries (BHBs) are systems where a normal star orbits a black hole, feeding it material, which the black hole accretes. The black holes in these systems are only ten times more massive than our sun and these smaller BHs that accrete at or near the Eddington limit undergo changes on much smaller timescales than the supermassive black holes. The team set out to identify and study many of these and their joint time and energy (spectral) properties Just prior to project initiation, the fellow discovered the first extragalactic microquasar in our nearest galaxy Andromeda. Microquasars are BHBs that spew out a powerful jet of plasma when accretion rates spike. Work showing that the microquasar accreted at close to Eddington rates led to a publication in the prestigious peer-reviewed journal Nature. Subsequent studies investigated how the jet and inflow might couple together, a key component of Eddington accretion. The seminal work established that the phenomenon can in fact be studied with extragalactic microquasars in nearby galaxies, providing a larger sample population than found in the Milky Way. This has opened the door to a comprehensive search for more extragalactic microquasars. In the meantime, researchers developed algorithms for analysis of the spectral and timing characteristics of those sources. The spectral-timing codes are expected to provide important insight into the nature of 'super-Eddington' accretion in BHs and thus shed light on the origins and evolution of the Universe.
Keywords
Black holes, accretion, spectroscopy, Eddington regime, black-hole binaries
