STELLAR MOTIONS AROUND A NEARBY BLACK HOLE

This animation shows the motions of stars caught in the gravitational
field of a three-million solar mass black hole in the core of the
nearby galaxy M32. Stars swarm around the black hole like angry bees
around a hive.

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.