The Hubble Space Telescope, peering deep into the heart of a distant galaxy, has astonished astronomers by revealing a scattering of dense clusters of young blue stars that appear to be clues to the cataclysmic collisions of galaxies eons ago.
Astronomers were surprised by the discovery of such young examples of the celestial structures known as globular clusters, long supposed to be among the oldest features in any galaxy.
A globular cluster is a dense spherical collection of stars, as many as 10 million, crowded closer together than anywhere else in a galaxy.
Previous studies found such clusters to be so ancient -- often as much as 10 billion years old -- that they have been used as benchmarks for estimating the age of the universe.
But at a meeting of the American Astronomical Society in Atlanta last week, Dr. Jon R. Holtzman, an astronomer at the Lowell Observatory in Flagstaff, Ariz., reported that the 50 clusters of blue stars photographed by the orbiting telescope appear to be no older than a few hundred million years.
They were observed in NGC1275, an especially bright galaxy near the constellation Cassiopeia approximately 200 million light-years away.
"Such objects have never before been seen," Dr. Holtzman said.
Scientists said the relatively young globular clusters were one of the most important discoveries yet made by the Hubble telescope.
The telescope has been orbiting Earth since April 1990, and has been sending back an increasing flow of data despite flaws in its primary mirror.
Not only were the star clusters a surprise, experts said, but they promised to yield insights into how many galaxies evolve.
Dr. James E. Hesser, director of the Dominion Astrophysical Observatory in Victoria, British Columbia, said, "I'm blown away by these observations."
In the Hubble images, the globular cluster appears as bright blue dots near the galaxy's nucleus. When young and blazing at high temperatures, stars are blue.
As they age, stars grow cooler and redder. A few relatively young clusters have been seen in other galaxies, but none as massive and compact as these.
Dr. Holtzman said the stars in NGC1275 all appear to be about the same age, which suggests that they all formed at about the same time in response to the same phenomenon.
That could have been the collision of two galaxies.
Because of its peculiar shape, some astronomers have suspected that NGC1275 actually may be two galaxies -- a giant elliptical galaxy and a smaller spiral galaxy -- passing through one another. It is believed that elliptical galaxies may form from the mergers of several spiral galaxies.
Dr. Holtzman suggested that such a merger or collision could have triggered the creation of new stars in the dense concentrations reported, though it is not clear how this could have occurred.
The fact that elliptical galaxies can contain a hundred times as many globular clusters as spiral galaxies lends further support to the idea that galaxy collisions somehow create globular clusters.
Scientists said other clues to the birth of globular clusters may stem from the fact that NGC1275 lies at the heart of the Perseus cluster of galaxies.
The galaxy is surrounded by a luminous halo of hot gas, observed in X-rays. Since gravity pulls this superheated gas into the galaxy, the condensing gas also might produce the newborn stars that are tied by gravity into globular clusters.
The discovery of the young star clusters will be reported soon in greater detail in the Astronomical Journal.
Dr. Holtzman's colleagues in the research were Dr. Sandra M. Faber of the University of California at Santa Cruz; Dr. Edward Shaya of the University of Maryland; Dr. Tod R. Lauer of the National Optical Astronomy Observatories in Tucson, Ariz.; Dr. Edward Groth of the Institute for Advanced Study in Princeton, N.J., and Dr. Deidre Hunter of the Lowell Observatory.