Colossal tail trails dying star


Aug 15, 2007

The tail measures a massive 13 light years in length

A distant star that hurtles through space at extraordinary speeds has a huge, comet-like tail trailing in its wake, astronomers say.

The appendage, which measures a colossal 13 light years in length, was spotted by Nasa's Galaxy Evolution Explorer (Galex) space telescope.

The researchers said that nothing like it had ever been spotted around a star.

They believe the star, known as Mira, will help them to study what happens as stars meet their demise.

Mark Seibert, a co-author of the paper, which was published in the journal Nature, and a scientist at the Carnegie Observatories in Pasadena, said: "This is an utterly new phenomenon to us, and we are still in the process of understanding the physics involved."

Racing through space

Mira (also called Mira A) has captivated astronomers for more than 400 years.

It sits about 350 light-years from Earth in a constellation known as Cetus, and is accompanied in orbit by a smaller secondary star, called Mira B, forming a binary system.

Billions of years ago, Mira would have been much like our Sun, but as it now enters its death-throes it has swollen into a type of star known as a red giant.

As it races through space at 130km/s (80 miles per second) it sheds vast amounts of material.

Yet despite centuries of study, its spectacular tail had remained undetected.

Now, ultraviolet images taken by the Galex space telescope have uncovered Mira's unusual feature.

Barry Madore, a co-author of the paper and senior research astronomer at the Carnegie Observatories, said: "Galex is so exquisitely sensitive to ultraviolet light and it has such a wide field of view that it is uniquely poised to scan the sky for previously undiscovered ultraviolet activity.

"The fact that Mira's tail only glows with ultraviolet light might explain why other telescopes have missed it."

The ultraviolet images also revealed a "bow shock" - a region, in front of the star, where hot gas builds up as Mira's stellar wind meets clouds of interstellar gas and dust.

The team believes that the hot gas in the bow shock is heating up gas that the star is shedding to create a turbulent tail trailing in its wake.

The scientists said that the tail was made up of the material that Mira has been ejecting over a period of 30,000 years.

Mark Seibert said: "We hope to be able to read Mira's tail like a ticker tape to learn about the star's life."

Studying the carbon, oxygen and other elements that make up the tail, the team said, could also provide an insight into how new solar systems and possibly even life are formed.

"After 400 years of study, Mira continues to astound," the team concluded.