January 26, 2005
Pulsar Pair Gives Magneto-pause for Thought
RAS -- 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.
Animation of the pulsar binary system. Click to download the full animation (1MB).
The Royal Astronomical Society is the UK's leading professional body for astronomy & astrophysics, geophysics, solar and solar-terrestrial physics, and planetary sciences. The Society publishes two specialist scientific publications, Monthly Notices of the RAS and Geophysical Journal International, together with a full-colour journal of news and reviews, Astronomy & Geophysics.
Pulsars are spinning neutron stars - the dense remnants of large stars that have run out of fuel and blown off their outer layers in supernova explosions. Jets of charged particles stream from their poles, generating bright beams of electromagnetic radiation. The rotational axis and magnetic field axis of pulsars are not aligned, so the radiation beams emitted from the poles appear to sweep round like a lighthouse's flash.
Double Pulsar Binary System PSRs J0737-3039A and B
Pulsars J0737-3039A and B were discovered by an international team of scientists, including astronomers from Jodrell Bank Observatory UK. Pulsar A was discovered in April 2003 using the Parkes radiotelescope in Australia (Burgay et al. Nature, 2003, 426, 531). Pulsar B was discovered in October 2003 during a test of a new technique to search for fast binary pulsars (Lyne et al. Science, 2004, 303, 1153).
The Solar Wind
The solar wind is a stream of electrically charged particles that is emitted in all directions from the Sun's outermost layers. The solar wind distorts the shape of the Earth's magnetic field, compressing it on the sunward side and pushing it into a long tail on the far side. Earth's magnetic field shields the planet from the bulk of the solar wind, which would otherwise strip away our atmosphere.
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