Magnetic 'bubble' in distant galaxy

The white dotted line shows how a magnetic bubble cocoons the galaxy

By BBC News Online science editor Dr David Whitehouse

A giant magnetic "bubble" measuring 3,000 light-years across has been discovered in a nearby galaxy. Astronomers say that nothing similar has ever been seen before.

The astronomers, from the Joint Astronomy Centre in Hawaii, were mapping the magnetic structure of galaxy M82 in order to see stars being born in smouldering gas clouds.

M82: An energetic galaxy

"We were really surprised to see the huge bubble," said British astronomer Jane Greaves.

"This is a new feature of galaxies that we didn't know about before and could show how magnetic fields help shape the evolution of starburst regions."

Strange galaxy

The most likely explanation for the bubble is that enormously energetic winds are forcing the magnetic field into the outer halo of the galaxy. The winds are outflows of interstellar gas, powered by stars.

Galaxy M82 makes up to fifty times more stars than other galaxies, but the reason for this remains unexplained.

Astronomer Wayne Holland said: "One of the most exciting things is that we see some magnetic field lines pointing right into the nucleus of the galaxy.

"Since the particles in gas clouds tend to flow along the lines of magnetic force, then we may have a clue as to why this galaxy has such a predominance of star-forming activity at its centre."

To obtain the observations, the team used the James Clerk Maxwell Telescope equipped with a revolutionary new camera called Scuba.

The scientists used a new technique that detects tiny differences in emission from interstellar dust. They discovered that the dust grains are lined up around local magnetic fields, just like iron filings around an ordinary magnet.

The next step will be to use the same technique to look at other galaxies, to see if M82 is a freak or if other nearby starburst galaxies show the same thing.

The research is published in the journal Nature.