Supersonic star has tail like a comet


A favourite star for amateur astronomers is Mira, in the constellation of Cetus the Whale. Its name literally means “the wonderful” because it varies hugely in brightness in a little under a year.

Now astronomers have just discovered that this red giant, star is even more wonderful than they realised. Observations from an observatory in space reveal that Mira is trailing an incredibly long tail, rather like the con-trail from a jet, as it travels faster than a bullet through space.

The discovery was made using Nasa’s Galaxy Evolution Explorer, which scans the universe in ultraviolet light. When it viewed Mira – also known as Omicron Ceti – it recorded what looked more like a comet to astronomers.

They measured a tail 13 light-years long, or around 20,000 the distance of distant dwarf planet Pluto from the Sun. It is the first time any such tail has been observed flowing from a star.

Mark Seibert, of the Carnegie Observatories in Pasadena and co-author of a paper in the journal Nature, said: “This is an utterly new phenomenon to us, and we are still in the process of understanding the physics involved. We hope to be able to read Mira’s tail like a ticker tape to learn about the star’s life.”

Mira is travelling unusually fast for a red giant star, at 130 kilometers per second, or 291,000 miles per hour. Astronomers believe it may have been given a gravitational boost by other passing stars.

They believe its amazing tail – formed of carbon, oxygen and other important elements – will also offer a unique opportunity to study how stars like our sun die and ultimately seed new solar systems.

As well as a tail, Galaxy Evolution Explorer also discovered a bow shock – a build-up of hot gas – in front of the star, plus two thin streams of material coming out of the star’s front and rear.

Mira, which lies 350 light-years from Earth and has a white dwarf star companion, undergoes vast changes in brightness. At some times it can be seen easily with the unaided eye while at others you will need binoculars or a telescope to spot it. Earlier this year, as Skymania recorded, it was particularly bright.

One day, far in the future, our own Sun is expected to swell up into a red giant like Mira. It could then become big enough even to swallow up the orbit of the Earth.

Photo: NASA/JPL-Caltech.

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Paul Sutherland

Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.
Paul Sutherland

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Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.

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