Why Do Black Holes Shine? Transient Objects and Accretion Disks

The universe hosts many transient objects that suddenly brighten. Accretion disks surrounding compact objects such as black holes, neutron stars, and white dwarfs serve as the central engines for all such transients, efficiently converting the gravitational energy of infalling gas into copious radiation and outflows. Accretion disk research has advanced through studies of binary systems pairing a compact object with an ordinary star. In recent years, however, time-domain astronomy has revealed a diversity of transient phenomena that simple theoretical models cannot capture, and a unified description is being sought. This talk explains how gas accretion onto compact objects produces such enormous radiation energy, and introduces the latest research — combining multi-wavelength observations and numerical simulations — aimed at building a unified model.