Odd Star Sheds Cometlike Tail

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In fact, Mira is speeding through the galaxy at 291,000 miles (468,000 kilometers) an hour—an unusually fast clip that may be the result of gravitational boosts from other passing stars.

Mira's supersonic speed causes a type of shock wave known as a bow shock to form in front of the star, study co-author Mark Seibert, from the Observatories of the Carnegie Institution of Washington in Pasadena, explained at the briefing.

"It's compressing the interstellar medium like a boat moving through the water ... and the gas in this bow shock is actually very hot," he said.

Cool wind blowing off the star mixes with this hot bow-shock gas, and the mixture flows around and behind Mira, creating the long wake, he added.

Eventually, Mira will eject all of its remaining gas into space, forming a shell called a planetary nebula.

The nebula will fade with time, leaving only the burnt-out core of the original star, an extremely dense object called a white dwarf. (Related: "Solar System's Fate Predicted by Nearby White Dwarf?" [December 21, 2006].)

Common Process?

The material in Mira's tail was shed over the past 30,000 years. Studying the tail will allow scientists to understand how stars like the sun die and seed new solar systems in the process, Caltech's Martin said.

Mira is a common type of star, Carnegie's Seibert added, and even though the cometlike tail phenomenon has never been seen before, the behavior is likely widespread.

Michael Shara is a curator at the American Museum of Natural History in New York and a professor of astronomy at Columbia University.

He was not involved in the study but participated in the briefing to offer perspective on the discovery.

"It's giving us this fantastic insight, I think, into the death processes of stars and their renewals—their phoenix-like revivals as their ashes get cycled back into the next generation of stars," Shara said.

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