Astronomers: Star collisions are rampant, catastrophic

Three frames from an animation showing a computer-modeled collision between stars

June 2, 2000
Web posted at: 11:08 p.m. EDT (0308 GMT)

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By RIchard Stenger
CNN Interactive Staff Writer

NEW YORK (CNN) -- Astronomers once thought stellar collisions never or rarely happened. But new research has convinced many that stellar mergers are commonplace and perhaps capable of producing the most violent and energetic events observable in the universe.

"Most people a few years ago though that collisions didn't happen," said physicist Mike Shara of the American Museum of Natural History in New York, which organized the first international conference on the topic this week.

But in the center of many galaxies, including our own, dense swarms of stars make such events inevitable, he said.

"Suddenly we're starting to get lots of collisions. There's probably one about every ten seconds," said Shara, curator of the museum's astrophysics department.

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Using space telescopes like the Hubble and Chandra and powerful computer calculations, astronomers have focused on globular clusters to study what they consider offspring of such mergers: blue stragglers, which are bluer, hotter and younger than their neighbors.

"They have no business being there. There's no other way to make them, other than to collide stars," Shara said.

Dozens of scientists from around the world presented the latest research on star collisions at the conference.

A team of Villanova University researchers reported the discovery of an object that most likely formed from the merger of three stars, a binary pair and a solitary one.

Such a collision has been predicted in the past, but now the astronomy team has "the smoking gun," Shara said: measurements of the giant star's mass.

Stellar collisions produce a variety of results, astronomers said. Slowly merging pairs can form giant superstars. Two violently colliding stars may eject all their material, destroying both.

Some may only draw each other into orbit. Their cores never touch, and the result is a binary star. Others may pass by neighbors quickly, disrupting the outer envelopes or atmospheres of both stars.

Super-dense neutron stars emit powerful bursts of energy when they crash into one another. Some of the conference astronomers speculated that such collisions are responsible for intense explosions of gamma rays, observed in the distant reaches of space.

"They are the most violent energetic events in the universe," Shara said. "Some release a thousand times as much energy in a few seconds as the sun would in its lifetime."

Even black hole mergers "almost certainly happen" in some cases when galaxies run into each other, Shara said.

Scientists think such collisions cause gravitational waves that travel through space. New instruments may allow them to measure those ripples in the near future.

"We'll be learning about how gravity works in a very intense environment that we could never approach on Earth," said Vickie Kalogera of the Harvard Smithsonian Center for Astrophysics.

Current research indicates that stellar collisions are quite common in dense star clusters, where millions of stars can be found within a space spanning less than 100 light years.

But terrestrial dwellers take heart. Such catastrophes are infinitesimally rare in cosmic backwaters far removed from the centers of galaxies, like a spiral arm of the Milky Way where the sun resides. Our neighborhood star will burn out long before another crashes into it.

"It you waited ten million times the age of the universe, only then would you have a 50-50 chance of a collision," Shara said.

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American Museum of Natural History
Hubble Heritage Project
The Chandra X-ray Observatory Center
Villanova University
Harvard-Smithsonian Center for Astrophysics

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