THE SUDDEN DEATH OF THE NEAREST QUASAR

Abstract

Galaxy formation is significantly modulated by energy output from\nsupermassive black holes at the centers of galaxies which grow in highly\nefficient luminous quasar phases. The timescale on which black holes transition\ninto and out of such phases is, however, unknown. We present the first\nmeasurement of the shutdown timescale for an individual quasar using X-ray\nobservations of the nearby galaxy IC 2497, which hosted a luminous quasar no\nmore than 70,000 years ago that is still seen as a light echo in `Hanny's\nVoorwerp', but whose present-day radiative output is lower by at least 2 and\nmore likely by over 4 orders of magnitude. This extremely rapid shutdown\nprovides new insights into the physics of accretion in supermassive black\nholes, and may signal a transition of the accretion disk to a radiatively\ninefficient state.\n