Ultraluminous X-ray sources are extragalactic objects located outside the nucleus of the host galaxy with bolometric luminosities1 exceeding 1039 erg s-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 0.2–10 keV luminosity of up to 1.1 × 1042 erg s-1 in the edge-on spiral galaxy ESO 243-49, with an implied conservative lower limit for the mass of the black hole of ∼500.
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We thank N. Schartel for granting an observation under the XMM-Newton project scientist discretionary time programme. We thank R. Belmont, A. King, J.-P. Lasota, K. Mukai, T. Roberts, S. Rosen, S. Sembay and M. Watson for discussions. S.A.F. acknowledges funding from the CNES. S.A.F. and O.G. acknowledge STFC funding. This work made use of the 2XMM Serendipitous Source Catalogue constructed by the XMM-Newton Survey Science Centre on behalf of ESA. We thank the Swift team for performing a TOO observation that provided justification for an additional observation with XMM-Newton. This work was based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.
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Farrell, S., Webb, N., Barret, D. et al. An intermediate-mass black hole of over 500 solar masses in the galaxy ESO 243-49. Nature 460, 73–75 (2009). https://doi.org/10.1038/nature08083
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