Pulsar pair gives scientists magneto-pause for thought

A study of the first double-pulsar binary system to be discovered shows that magnetic interactions between the pulsars are strikingly similar to those between the Sun and the Earth.

Radiation and particles emitted from one pulsar appear to have a similar warping effect on the magnetic bubble surrounding its companion star as the solar wind has on the Earth's magnetosphere.

The pulsar pair was discovered in 2003 by an international team of scientists, including astronomers from Jodrell Bank Observatory, working at the Parkes Radio Telescope in Australia. Several other binary systems containing a pulsar and a neutron star have been identified but the pair of pulsars, PSRs J0737-3039A and B, is the only example where both co-orbiting objects show the regular flash of a pulsar signal. Since the discovery, astronomers have been observing the pulsars as they orbit one another separated by less than a million kilometres, a distance smaller than the diameter of the Sun. Writing in February's Astronomy & Geophysics Magazine, Francis Graham-Smith and Maura Ann McLaughlin show how studies of the pulsar pair have dramatically improved our understanding of pulsars and neutron stars, as well as interactions between charged particles and magnetic fields.

The two pulsars have different rotational periods: pulsar A rotates 44 times each second whereas pulsar B takes 2.8 seconds to spin once on its axis. Each pulsar's signature flash-rate allows astronomers to track them both during their orbit and deduce information about their magnetic environment. Each pulsar is only about ten kilometres across but is surrounded by a magnetosphere that is thousands of kilometres in diameter. Because we view the orbit nearly edge-on, once per orbit pulsar A is eclipsed as it passes behind pulsar B. Pulsar B's magnetosphere is over 100 times larger than that of pulsar A and this should mean that it blocks sight of pulsar A's radiation flashes for several minutes during each orbit. However, initial observations showed that the eclipse lasted for just 30 seconds, indicating that B's magnetosphere has a much smaller diameter than expected.

Observations show that there is a distinct boundary, or magnetopause, surrounding pulsar B's magnetosphere. Just as the solar wind warps the Earth's magnetosphere as it sweeps past, a wind emitted from pulsar A appears to be constricting the magnetosphere of pulsar B, compressing it into a comet-like tail that streams radially outwards.

By contrast, pulsar A's magnetosphere is much smaller and appears to be unaffected by its proximity to pulsar B. Previous observations of single pulsars have shown the existence of pulsar winds, but the double-pulsar binary system gives the first opportunity to study a stream close to its source. Contrasting the interactions of the wind in the pulsar system with those of the solar wind in the terrestrial system, where the magnetic fields are more than three orders of magnitude smaller, should assist plasma physicists in understanding large and small-scale processes.

The pulsar pair has already been used to demonstrate the effects of Einstein's theory of General Relativity and was ranked by the journal "Science" as the sixth most important scientific breakthrough in 2004.

Further Information

The full text of the article and accompanying images can be found at: http://www.ras.org.uk/html/press/pn0502ras_information.html

More details of the remarkable interactions between the two pulsars can be found in McLaughlin et al. (Astrophysical Journal, 2004, 613, L57) and McLaughlin et al. (Astrophysical Journal, 2004, 616, L131).

Jodrell Bank Observatory's press pages: http://www.jb.man.ac.uk/news/doublepulsar2/