Journal Article

A supermassive black hole in an ultra-compact dwarf galaxy

van den Bosch, Remco, Strader, Jay, Spitler, Lee, Neumayer, Nadine, Baumgardt, Holger, McDermid, Richard, Mieske, Steffen, Walsh, Jonelle L., Seth, Anil C., Hilker, Michael, Chilingarian, Igor, Frank, Matthias J., Brok, Mark den, Brodie, Jean

2014

Overview

Dynamical modelling of the ultra-compact dwarf galaxy M60-UCD1 reveals the presence of a supermassive black hole; this suggests the object is a stripped galaxy nucleus and implies the existence of supermassive black holes in many other ultra-compact dwarf galaxies. Smallish galaxy hosts supermassive black hole The object M60-UCD1 is the brightest ultracompact dwarf galaxy (UCD) currently known and — at about 200 million solar masses — one of the most massive. Anil Seth et al . have used adaptive optics spectra to resolve the kinematics of M60-UCD1. They detect a supermassive black hole of 21 million solar masses at its centre. M60-UCD1 is thus the lowest-mass system known to host a supermassive black hole. The authors suggest that it may once have been at the centre of a larger galaxy that was later tidally torn apart by a massive neighbour. Their analysis also shows that M60-UCD1's stellar mass is consistent with its luminosity, implying that many other ultra-compact dwarf galaxies may contain previously unrecognized supermassive black holes. Ultra-compact dwarf galaxies are among the densest stellar systems in the Universe. These systems have masses of up to 2 × 10 8 solar masses, but half-light radii of just 3–50 parsecs 1 . Dynamical mass estimates show that many such dwarfs are more massive than expected from their luminosity 2 . It remains unclear whether these high dynamical mass estimates arise because of the presence of supermassive black holes or result from a non-standard stellar initial mass function that causes the average stellar mass to be higher than expected 3 , 4 . Here we report adaptive optics kinematic data of the ultra-compact dwarf galaxy M60-UCD1 that show a central velocity dispersion peak exceeding 100 kilometres per second and modest rotation. Dynamical modelling of these data reveals the presence of a supermassive black hole with a mass of 2.1 × 10 7 solar masses. This is 15 per cent of the object’s total mass. The high black hole mass and mass fraction suggest that M60-UCD1 is the stripped nucleus of a galaxy. Our analysis also shows that M60-UCD1’s stellar mass is consistent with its luminosity, implying a large population of previously unrecognized supermassive black holes in other ultra-compact dwarf galaxies 2 .

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/766/33/34/863 / Black holes / Black holes (Astronomy) / Confidence intervals / Discovery and exploration / Humanities and Social Sciences / letter / Light / multidisciplinary / Observations / Optical properties / Optics / Science / Space telescopes / Star & galaxy formation / Stars & galaxies