The Promiscuous Life of Stars

19 February 2002 (All day)

Hanky panky. Stars inside globular clusters like this one may have more interesting social lives than astronomers knew.

Stars in globular clusters--the cosmic nurseries where all stars are born--have far more, and far more varied liaisons than astronomers thought. A new computer simulation of globular clusters finds that stars consort in a variety of short-term arrangements--from simple collisions between two stars to "ménage-a-trois" systems with three stars orbiting one another. The study sheds light on how exotic stars called blue stragglers form.

Most stars lead a relatively predictable life: How they age and evolve is determined by their initial mass, and eventually they burn up all their hydrogen fuel and end up as feeble white dwarfs. But a few somehow get an extra lease on life. Blue stragglers, for example, are bright, blue and heavy stars that, given their mass, should have aged and become white dwarfs a long time ago. To get a better idea of how these unusual objects form, astronomers Jarrod Hurley and Michael Shara of the American Museum of Natural History in New York City simulated the entire life of 20,000 stars in a globular cluster. The simulation--one of the largest of its type to date--was made possible by new, purpose-built computer chips called GRAPE-6, each of which performs 30 billion arithmetic operations per second.

The simulation produced 500 curious encounters, including a short-lived stellar three-way and more complex systems involving up to five stars. And the component stars of one particularly "flirtatious" double star repeatedly swapped partners, Hurley and Shara will report in an upcoming issue of the Astrophysical Journal. They found that blue stragglers were far more likely to be born from collisions or mergers resulting from these types of interactions than they were from random collisions.

Astronomer Christian Knigge from the University of Southampton says that the simulation provides the best understanding yet of the behavior of stars in clusters. The simulations could explain the frequency of particular types of blue straggler stars formed in different interactions, Knigge says, and should help observers hone their strategy for finding them.

Related links
Astrophysics department at the American Museum of Natural History
Hubble Space Telescope image of blue straggler stars at home in a globular cluster

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