Comet-like tail discovered behind star

A star which has been observed for over 400 years shocked the scientific world when a tail was discovered trailing behind the star, writes Leo Enright


Astronomers have astonished themselves by discovering something totally unexpected. Just when they thought there was nothing new to be learned about a star that has been observed for more than four centuries by professionals and amateurs alike,  Mira – a common-or-garden variable star – has gone and flummoxed everyone.

  It is a dramatic reminder that Hamlet was right when he declared: “There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy”.

Mira is one of the best studied stars in the sky. Discovered in 1596 by the great Italian physician Fabricius, it was the first variable star ever recorded, with an 11 month cycle that sees it grow in brightness and then fade away. For this reason it was named

“Mira”, meaning “marvelous”, by the 17th Century Polish astronomer Hevelius. It eventually became the model for an entire class of stars known as the “Mira variables”.

But despite centuries of accumulated observations nobody had ever noticed that there was an enormous comet-like tail trailing behind the star. This is probably because Mira's brilliant tail does not register at all in visible light, only in the ultraviolet range of the spectrum, which is how it was spotted by the American astronomy satellite Galex,  the Galaxy Evolution Explorer.

“I was shocked when I first saw this completely unexpected humongous tail trailing behind a well-known star” said Galex's chief scientist, Dr Christopher Martin of the California Institute of Technology.
Our picture shows Mira racing through space very many times faster than a speeding bullet (Mira is clocking 130 kilometers per second, whereas a rifle bullet might reach one kilometer per second). As it hurls along, it is shedding material that will be recycled into new stars, planets and possibly even into life itself.

Mira is moving from left to right, and is visible as the pinkish dot in the bulb shape to the right of the image; it is traveling so fast that it is creating a “bow shock” (as in the bow of a ship), a build-up of hot gas forming ahead of the star in the direction of its motion.

This heated hydrogen gas then flows around behind the star, forming a complicated wake with streams and loops that are still being analysed.

In some ways, this picture is a vision of our own future, because Mira is a highly evolved “Red Giant” star near the end of its life. 

Five billion years from now, our own Sun will become a Red Giant which will engulf the Earth and everything out to the orbit of Mars.

But Mira is different from our Sun in one important respect. While our star travels serenely around the disk of our Milky Way galaxy, Mira is charging through it, like a
fairground horse on a merry-go-round, periodically plunging through the main disk.

Because Mira is not moving with the “pack” it is travelling much faster and has released enough material over the past 30,000 years to seed at least 3,000
Earth-sized planets or nine Jupiter-sized ones. It is scattering the stuff of creation like snuff at a wake.