Mira's comet-like tail
Ultraviolet images from NASA's Galaxy Evolution Explorer show a speeding star that is leaving an enormous trail of "seeds" for new solar systems. The star, named Mira after the Latin word for "wonderful," is shedding material that will be recycled into new stars, planets and possibly even life as it hurls through our galaxy.
The Galaxy Evolution Explorer discovered the strange tail during part of its routine survey of the entire sky at ultraviolet wavelengths. When astronomers first saw the picture, they were shocked because Mira has been studied for over 400 years yet nothing like this has ever been documented before.
Mira's comet-like tail stretches a startling 13 light-years across the sky. For comparison, the nearest star to our Sun, Proxima Centauri, is only about 4 light-years away. Mira's tail also tells a tale of its history — the material making it up has been slowly blown off over time, with the oldest material at the end of the tail being released about 30,000 years ago.
While most stars travel along together around the disk of our Milky Way, Mira is charging through it. Because Mira is not moving with the "pack," it is moving much faster relative to the ambient gas in our section of the Milky Way. It is zipping along at 291,000 mph (130 km/s) relative to this gas.
Mira's breakneck speed together with its outflow of material are responsible for its unique glowing tail. Images from the Galaxy Evolution Explorer show a large build-up of gas, or bow shock, in front of the star, similar to water piling up in front of a speeding boat. Scientists now know that hot gas in this bow shock mixes with the cooler, hydrogen gas being shed from Mira, causing it to heat up as it swirls back into a turbulent wake. As the hydrogen gas loses energy, it fluoresces with ultraviolet light, which the Galaxy Evolution Explorer can detect.