Updated A space-based observatory has captured images of a 13 light-year long tail stretching out behind a well known red-giant star, Mira.
The pictures have come as a complete shock to astronomers: Mira has been gazed upon from Earth for almost half a millennium, but nothing like this tail has ever been seen before.
A new ultraviolet mosaic from NASA's Galaxy Evolution Explorer shows a speeding star that is
leaving an enormous trail of "seeds" for new solar systems. Image credit: NASA/JPL-Caltech
Astronomers say the images have provided a unique insight into the way stars like our sun die. Mira was once a humble yellow dwarf like our own sun. Over the aeons it ran out of hydrogen and started burning helium, swelling up to become a much larger and cooler red giant. It pulsates, periodically becoming large enough to see with the naked eye.
It was NASA's Galaxy Evolution Observer that saw the tail. It was conducting a routine survey of the sky, in ultraviolet, when astronomers noticed what looked like a huge comet streaking across the sky at nearly 300,000 miles per hour*.
Christopher Martin, pricipal investigator on the GEE project, based at the California Institute of Technology, professed himself completely shocked when he saw "this completely unexpected, humongous tail trailing behind a well-known star".
"It was amazing how Mira's tail echoed on vast, interstellar scales the familiar phenomena of a jet's contrail or a speedboat's turbulent wake," he added.
The scientists say the trail of matter the star leaves behind will eventually seed the birth of other suns.
Download the full, high-res version of the picture from NASA here. ®
*In its press announcement, NASA describes this as supersonic. Tch tch. Space is a vacuum in which there is no sonus to be superior to. Might as well compare it to the speed of the average sheep (roughly 150,000 times as fast, we reckon).
Update: We'd like to thank reader Sergio Gelato for the following comment, but would stress that the presence of sheep in the footnote should have tipped you all off to the fact that it was supposed to be read with your humour detectors switched to on.
Sergio, over to you:
The article says Mira has a speed of 130 km/s relative to the local ISM, and that's the sound speed for a medium at a temperature of about 10^6 K, which is perfectly reasonable for the "hot" phase of the Galactic ISM.
Even without directly measuring the local ISM temperature, the presence of a bow shock in front of the star is indicative of a supersonic motion of the stellar ejecta, at the very least.
And who are we to argue with that? ®