Astrophysics: A NICER understanding of black hole evolution

Observations of a black hole system, made by instruments on the International Space Station (ISS), offer novel insights into how these systems behave as material falls into them. The findings, published in Nature this week, suggest that as matter is sucked in, the evolution of X-ray outbursts is controlled by a compact corona region near the black hole.

When material falls into a black hole, it emits a burst of high-energy X-rays, known as a transient event, the detection of which can be used to study the evolution of the system. Whether these bright flares are generated by the corona - a compact region above the accretion disk (a ring of debris falling into the black hole) - or by the disk itself has been a matter of debate.

In March 2018, a new black hole transient, called MAXI J1820+070, was found. Erin Kara and colleagues monitored the evolution of the X-ray emission using the Neutron star Interior Composition Explorer (NICER) instrument on the ISS. By following the event, the researchers found that the corona surrounding the black hole shrinks, whereas there is little change in the size of the accretion disk. These observations indicate that it is the contraction of the corona, not changes in the size of the accretion disk, which causes the changes, the authors conclude.