NASA's Hubble Space Telescope (HST) has provided a remarkably new detailed view of the core of a galaxy which lies 40 million light-years away, more than half way to the great Virgo Cluster of galaxies. These results promise that astronomers will be able to use the Hubble Space Telescope to probe the mysterious centers of galaxies, in a search for massive black holes.
The image, which was taken with the Wide Field/Planetary Camera on August 17, reveals that stars are much more tightly concentrated at the center of the galaxy than was previously expected. Since the galaxy, cataloged as NCC 7457, is assumed to be a "typical" galaxy, these preliminary findings suggest that the nuclei of normal galaxies may be more densely packed with stars than previously thought.
HST scientists are greatly encouraged by this new observation, and emphasize that it demonstrates intriguing science can be routinely accomplished with the spaceborne observatory. “The images of NGC 7457 show emphatically that research on nuclei of galaxies can still be done", says Dr. Tod Lauer, of the Wide Field/Planetary Camera imaging team, "We've never been able to study any galaxy outside of our Local Group [our "neighborhood" of about two dozen galaxies] at this resolution before."
The centers of galaxies are extremely interesting to astronomers because they are at the heart of violent processes that give rise to cosmic jets, quasars, Seyfert galaxies and other mysterious energetic behavior.
NGC 7457 is a quiescent galaxy that was picked for its "normality" as an early target for assessing the science performance of HST. The resulting images show, to the surprise of astronomers, that an exceptionally bright and compact core is embedded in the diffuse background of the rest of the galaxy. Based on this new image, the stars in the nucleus of NGC 7457 are crowded together at least 30,000 times more densely than those stars we see within our own galactic neighborhood. This extraordinarily high stellar density exceeds earlier estimates from ground-based observation of NGC 7457 by a factor of 400.
It is far from clear whether or not a massive black hole is at the center of NGC 7457, since the images alone do not provide the answer. But these new data suggest that NGC 7457 is an excellent place to use the HST's spectrographs to measure how much mass is concentrated at the center of the galaxy.