A dying star hurtling through space has left a comet-like tail that reveals its history stretching back 30,000 years.
"This is an utterly new phenomenon to us, and we are still in the process of understanding the physics involved," said study team member Mark Seibert of the Carnegie Observatories in Pasadena, Calif.
The red-giant star, called Mira A, is streaming a comet-like tail behind it that is 13 light-years long — thousands of times the breadth of our solar system.
A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion kilometers). The tail is like a glowing bread-crumb trail in the sky showing the star's movements for the past 30 millennia, during which time it has shed large stores of carbon, oxygen and other elements.
"We hope to be able to read Mira's tail like a ticker tape to learn about the star's life," Seibert said.
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Our own sun will one day become a red giant, so the finding, detailed in the Aug. 16 issue of the journal Nature, could provide valuable clues about the fate of our solar system and how stars' cast off remains become seeds for new stars, planets and possibly even life.
A pulsing star
Located about 350 light-years from Earth, Mira is a so-called variable star that pulsates from dim to bright over a period of about 330 days. At its brightest, Mira A is visible to the naked eye.
Traveling alongside Mira A is a smaller star similar to our sun, called Mira B.
The two stars are separated by about 90 astronomical units (AU), with one AU being equal to the distance between the Earth and the sun.
A previous study suggested that dust shed by Mira A is accreting into a ring around Mira B and could one day become the raw material for new planets.
The pair is barreling through space at a swift 291,000 mph (468,000 kilometers per hour).
Scientists think they could be speeded along in their journey by occasional gravity boosts from other passing stars.
Scientists spotted Mira A's tail of streaming gas while using the Galaxy Evolution Explorer, an Earth-orbiting telescope, to survey the sky in ultraviolet light. Nothing of its kind has ever been observed around a star.
Visible only in UV
The streaming tail is only visible in the far ultraviolet, which might explain why it's never been seen before, despite the fact that astronomers have known about Mira A for about 400 years.
"We never have predicted a turbulent wake behind a star that glows only with ultraviolet light," Seibert said.
Mira A was once a star like our sun. As it aged and lost the hydrogen fuel needed to stoke its internal fires, the star swelled into a pulsating red giant.
Eventually, Mira A will eject all of its remaining gas into space, forming a colorful cloud around it called a planetary nebula. This too will fade in time, and Mira A will shrivel into a burnt-out white dwarf.
The Galaxy Evolution Explorer, a NASA project, also spotted a buildup of hot gas, called a bow shock, in front of the star, as well as two thin filaments of material coming out of the star's front and back.
Astronomers think the hot gas in the bow shock is heating up the gas blowing off the star, creating a trailing tail that glows in the ultraviolet.
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