the magnetic field of a star has been mapped for the first time by a team of researchers at the National Radio Astronomy Observatory, usa . The team led by Kemball and P Diamond has mapped the magnetic field of tx Camelopardalis ( tx Cam), a red giant star about 100 light years away. A giant star is one with a relatively large radius. The brightness of such stars is high as the radiating area is correspondingly large ( Astrophysical Journal Letters , Vol 487 No 2).

As the magnetic field of a star cannot be observed directly, the researchers used radio waves, which are polarised by magnetic fields, to map it. Radio waves from the stars that are at a great distance from the Earth are too faint to be seen.However, in this case, the radio waves could be detected because of the presence of clouds of silicon monoxide near the star, which amplified the signals.

The researchers used a network of 10 radio telescopes stretching across the us . This network, known as Very Long Baseline Array, achieves unprecedented resolution because it operates like a single telescope with a dish size equal to the size of continental usa. By observing the polarisation of the radio waves, the scientists have been able to get a two-dimensional map of the magnetic field of the star.

They claim that the field is very much like that of the Earth with lines going around the star. Nevertheless, there are also some areas where the field lines are twisted. The first detailed map of the magnetic field of a star could provide important insights into the behaviour of stars and also throw light on stellar formation. Kemball and his team plan to observe the star perio-dically to ascertain if there is any temporal cycle associated with the magnetic field.