Hubble Space Telescope Discovers Young Star Clusters in Giant Galaxy
16 January 1992NASA's Hubble Space Telescope has provided intriguing new clues to cataclysmic events in the history of the peculiar galaxy NGC 1275, located approximately 200 million light-years from Earth.Astronomers have discovered about 50 bright objects at the center of the galaxy which appear to be young massive globular star clusters. This is a surprising discovery because most globular clusters are among the oldest objects in the universe; in fact, they are used as a bench mark for estimating the age of the universe.
"Such objects have never before been seen," says Dr. Jon Holtzman, of Lowell Observatory, Flagstaff, AZ, who led the observing team that made the finding.
These results are being reported in a press conference at the 179th meeting of the American Astronomical Society in Atlanta, Georgia. The paper is being presented by Dr. Jon Holtzman; Dr. Sandra M. Faber, of the University of California, Santa Cruz; Dr. Edward Shaya, of the University of Maryland; Dr. Tod R. Lauer, of the National Optical Astronomy Observatories, Tuscon, AZ; Dr. Edward Groth, of the Institute for Advanced Studies, Princeton, NJ; Dr. Deidre Hunter, of Lowell Observatory and other members of the Wide Field/Planetary Camera Instrument Definition Team. Their results will be published in a paper to appear in an upcoming issue of the Astronomical Journal.
Holtzman's team did not expect to find young star clusters in NGC 1275 when it began observing with the Hubble Space Telescope's Wide Field/Planetary Camera. "We were looking for information to help us understand all the peculiarities in the galaxy, but instead we discovered yet another strange feature," says Holtzman. This result may lead to a better understanding of how galaxies evolve and interact through the process of collisions and mergers.
Globular clusters are dense spherical collections of stars, containing 100,000 to 10 million stars packed in a region only about 100 light-years in diameter. More than 100 globular clusters orbit the Milky Way in a diffuse swarm. The brighter of these appear as "fuzzy" stars to the naked eye.
Stars within these clusters are very old, believed to have formed early in the history of the universe. Surprisingly, the clusters in NGC 1275 appear to contain young, hot stars. "Although young star clusters are observed in other galaxies, none have been as massive and compact as those seen in NGC 1275," says Holtzman.
NGC 1275 has such a peculiar shape, some astronomers previously have suspected that it may actually be two galaxies - a giant elliptical galaxy and a smaller spiral galaxy - passing through one another. In fact, elliptical galaxies in general may result from the merger of several spiral galaxies. Holtzman suggests that the clusters may have formed as a result of just such a merger or collision. The fact that elliptical galaxies can contain a hundred times more globular clusters than spiral galaxies lends further support to the notion that galaxy collisions also create new globular clusters.
Other clues to the birth of globular clusters may come from the fact that NGC 1275 lies at the heart of the Perseus cluster of galaxies, a rich collection of more than 500 galaxies. Because NGC 1275 is located at the center of this cluster, the galaxy is surrounded by a luminous halo of hot gas, which glows in X-rays. Gravity pulls this superheated gas into the galaxy as a cooling flow," which produces filaments. This cooling, condensing gas might also produce newborn stars.
Holtzman and his colleagues plan to take longer exposures with HST to see if there are many more fainter clusters. He also plans to take pictures in ultraviolet light to help pin down the age of the clusters better.