Astronomers Find Comet-Like Tail Trailing Mira, a Red Giant Star

Comets have long been known to have trails tailing behind them as they approach our planet. The appearance of the tail and the proximity of our planet are coincidental. What causes comets to have tails is that ice particles start to melt as the core of the comet gets closer to the sun. Astronomers were surprised to find a comet like tail trailing behind a star called Mira, something that has not been seen on any star previously.

Chris Martin, an astronomer at the California Institute of technology, described the phenomenon as "completely new and unexpected."

The star had been a favorite target of astronomers because it is one of the few variable red giants. It is known to expand and contract over a period of 322 days.

"It's compressing the interstellar medium like a boat moving through the water ... and the gas in this bow shock is actually very hot," said Mark Siebert, who works at the Observatories of the Carnegie Institution of Washington in Pasadena.

Mira, which is about 350 light years from earth, has been studied for almost four centuries. It is currently a red dwarf, the final life stage of a star before it goes nova and collapses into a white dwarf. (A supernova is from a massive start that throws off enough of its fuel to avoid becoming a black hole.) Astronomers have working on the Galex space telescope have an uncovered a usual feature of the store. Much like the comets mentioned earlier, the star leaves a trail behind it as it travels through the galaxy. The trail measures some 13 light years from the star to its end.

The likely reason that other telescopes aimed on the distant star may have missed the trail has to do with the light frequencies they detect. The visible light spectrum and radio waves are the most common wavelengths used by astronomers to study celestial bodies. The Galex space telescope, however, is more sensitive to ultraviolet light.

The scientists studying Mira believe that the tail is caused by a "bow shock." A bow shock is a region of hat gas that builds up in front of the star. The research team speculates that the hot gases in the "bow shock" causes the gases shedded by the star to be heat up, thus leaving the long trail behind the red giant.

The Galex astronomers speculate that the star may have been shedding these gases and creating its tail for over 30,000 years. The scientists hope that by studying the star further insight can be gained into the processes that go on in a dying star.

Sources:

http://news.bbc.co.uk/2/hi/science/nature/6947607.stm

http://news.nationalgeographic.com/news/2007/08/070815-cometlike-tail.html