UH Hilo Astronomer Helps Discover "Orphan" Star Clusters

University of Hawaiʻi at Hilo
Posted: Jul 21, 2003

A University of Hawaiʻi at Hilo astronomer is among a group of scientists from the United States and the United Kingdom who have discovered a population of previously unknown star clusters in what was thought to be empty space.

UH Hilo astronomer Dr. Michael West was among investigators who presented the research July 17, 2003 at the International Astronomical Union's 25th General Assembly in Sydney, Australia.

"The new data confirm our discovery, and are providing new insights to the origin of these objects," said West.

The objects West refers to are actually "globular clusters," systems of up to a million stars compacted together by gravity into dense sphere-shaped groupings. Studies of globular clusters have provided many important insights over the years into the formation of their parent galaxies.

The discovery of this new type of star cluster was made using images obtained last year with the Hubble Space Telescope and the giant 10-meter Keck Telescope atop Mauna Kea on the Big Island of Hawaiʻi.

"We found hundreds of 'orphaned' globular clusters," West said.

According to West, these intergalactic globular star clusters probably once resided in galaxies just like most of the normal globular clusters that we see in nearby galaxies today. However, the pull of gravity from a passing galaxy can rip stars and star clusters loose. In some cases entire galaxies can be damaged or destroyed by violent collisions or by the collective gravitational pull from their galactic neighbors. It is thought that the partial or complete destruction of their parent galaxies spilled these globular star clusters into intergalactic space.

Finding these globular clusters hasn't been easy, West added.

"With only one exception, all of the intergalactic globular clusters detected are so many millions of light-years away that they just look like tiny points of light in a vast sea of blackness," he explained. "Because they're so far away these objects are very faint, almost a billion times fainter than the unaided human eye can see. Detecting such faint objects pushes the limits of even what the Hubble Space Telescope can do."

West said that the discovery of orphaned globular clusters can help scientists with their understanding of both the origin and nature of the universe.

"By studying these intergalactic vagabonds in greater detail we hope to learn more about the numbers and types of galaxies that may have been destroyed so far during the life of the universe," West said. "Some of these orphaned star clusters might also eventually be adopted by other galaxies if they stray close enough to be captured by their gravity."

In addition to West, collaborators on this research, which involves two separate but complementary teams, are: Drs. Patrick Cote and Andres Jordan, Rutgers University; Dr. Ronald Marzke, San Francisco State University; Dr. Michael Gregg, University of California at Davis; Dr. Henry Ferguson, Space Telescope Science Institute; Dr. Ted von Hippel, University of Texas; and Dr. Nial Tanvir, University of Hertfordshire, England.