EVIDENCE FOR A BLACK-HOLE FROM HIGH ROTATION VELOCITIES IN A SUB-PARSEC REGION OF NGC4258

MANY galaxies are thought to contain massive black holes-exceeding ten million solar masses-at their centres(1,2), but firm observational ev idence has proved to be surprisingly elusive. The best evidence comes from observing gas or stars rotating rapidly within a small region aro und a central body. If the observed velocities are due solely to the g ravitational force of the central body-as in the Solar System-then the mass of the central body can be readily calculated. Here we present o bservations of rotating gas near the centre of the galaxy NGC4258 (M10 6), which indicate the presence of a mass of 3.6 x 10(7) solar masses in a region less than 0.13 pc in radius. The volume-averaged mass dens ity in this region exceeds by a factor of at least 40 that for any oth er black-hole candidate observed previously. These observations provid e compelling evidence that a massive black hole exists at the centre o f NGC4258.