The animation is based on computer simulations and new Hubble Space Telescope observations of M32. These were reported in the February 13, 1997 issue of Nature Magazine, by Roeland van der Marel (Institute for Advanced Study, Princeton, NJ) and co-investigators Tim de Zeeuw (Leiden University, The Netherlands), Hans-Walter Rix (University of Arizona) and Gerald Quinlan (Rutgers University, NJ). The team further includes Nicolas Cretton (Leiden University, The Netherlands), Steinn Sigurdsson (Cambridge University, UK) and Lars Hernquist (University of California at Santa Cruz). The calculations were done in part on the Cray T3D Parallel Supercomputer of the Pittsburgh Supercomputing Center.
Hubble's Faint Object Spectrograph was able to zoom in to the central light-year of M32, providing five times higher spatial resolving power than the best ground-based observations. The projected velocities of the stars in the galaxy were measured, and their three-dimensional motion was then reconstructed using state-of-the-art computer models. The observed velocities exceed those measured from previous ground-based observations, demonstrating that the stars must be attracted by an invisible black hole. In the absence of a black hole, the stars would move at a much slower rate, as shown in the animation.
M32 is a small companion galaxy of the
great (full extent several times that of the full moon) spiral galaxy
in the constellation of Andromeda. Because of its proximity, only
2.2 million light-years away, M32 has
long been intensively studied with the best ground-based
telescopes. The velocities of the stars near its nucleus suggested the
presence of a black hole as early as 1984. In 1992, Hubble
observations measured a bright peak, or `cusp' of starlight that
independently suggested that the stars were concentrated around a
black hole. The new Hubble measurements of the stellar motions have
further strengthened the evidence for this.