brightest galaxies in the vicinity of ours, only surpassed by the Andromeda Galaxy and the Sombrero Galaxy) and the companion galaxies NGC 247, PGC 2881, PGC 2933, Sculptor-dE1, and UGCA 15 form a gravitationally-bound core near the center of the group. Most other galaxies associated with the Sculptor Group are only weakly gravitationally bound to this core. Starburst NGC 253's starburst has created several super star clusters on NGC 253's center (discovered with the aid of the Hubble Space Telescope): one with a mass of 1.5*106 solar masses, and absolute magnitude of at least −15, and two others with solar masses and absolute magnitudes around −11; later studies have discovered an even more massive cluster heavily obscured by NGC 253's interstellar dust with a mass of solar masses, an age of around years, and rich in Wolf-Rayet stars. The super star clusters are arranged in an ellipse around the center of NGC 253, which from the Earth's perspective appears as a flat line. Star formation is also high in the northeast of NGC 253's disk, where a number of red supergiant stars can be found, and in its halo there are young stars as well as some amounts of neutral hydrogen. This, along with other peculiarities found in NGC 253, suggest that a gas-rich dwarf galaxy collided with it 200 million years ago, disturbing its disk and starting the present starburst. As happens in other galaxies suffering strong star formation such as Messier 82, NGC 4631, or NGC 4666, the stellar winds of the massive stars produced in the starburst as well as their deaths as supernovae have blown out material to NGC 253's halo in the form of a superwind that seems to be inhibiting star formation in the galaxy. Although supernovae are generally associated with starburst galaxies, only one supernova has been detected within the Sculptor Galaxy. The supernova, named SN 1940E, is located approximately 54″ southwest of the galaxy's nucleus. It was discovered in November 1940. Central black hole Research suggests the presence of a supermassive black hole in the center of this galaxy with a mass estimated to be 5 million times that of the Sun, which is slightly heavier than Sagittarius A*. Distance estimates At least two techniques have been used to measure distances to Sculptor in the past ten years. Using the planetary nebula luminosity function method, an estimate of 10.89 million light years