An intermediate-mass black hole of over 500 solar masses in the galaxy ESO243-49

Abstract

Ultraluminous X-ray sources are extragalactic objects located outside the nucleus of the host galaxy with bolometric luminosities exceeding 10³⁹ergs^-1. These extreme luminosities-if the emission is isotropic and below the theoretical (Eddington) limit, where the radiation pressure is balanced by the gravitational pressure-imply the presence of an accreting black hole with a mass of ~10²-10⁵ solar masses (). The existence of such intermediate-mass black holes is in dispute, and though many candidates have been proposed, none are widely accepted as definitive. Here we report the detection of a variable X-ray source with a maximum 0.2-10keV luminosity of up to 1.1×10⁴²ergs^-1 in the edge-on spiral galaxy ESO243-49, with an implied conservative lower limit for the mass of the black hole of ~500.