A team of scientists from UK and Germany used a 42-ft telescope at the Jodrell Bank Observatory in Cheshire, England, to determine how the magnetic field structure and rotation of a powerful pulsar in the center of the famous Crab Nebula evolves with time.
This composite image shows the Crab Nebula. The Crab pulsar is in the center of the image. Image credit: X-ray – NASA / CXC / ASU / J. Hester et al.; optical – NASA / HST / ASU / J. Hester et al.
The Crab pulsar, also known as PSR B0531+21, is the central star in the Crab Nebula. It is a young neutron star which formed in a massive cosmic explosion seen on Earth in 1054 CE as a bright star in the daytime sky. The star itself is only about 15.5 miles across but contains the mass of nearly 1 million Earths.
Now rotating 30 times a second, the pulsar emits beams of radio waves that, like a lighthouse, produce flashes each time it rotates.
The new results, published in the journal Science, reveal a steady change in these flashes during a 22-year experiment watching the star, telling astronomers about its very strong magnetic field and helping them learn about the otherwise-inaccessible interior of the star.
The Crab pulsar in ‘on’ and ‘off ‘ state.
The flashes, or pulses, come in pairs. The new observations show that the spacing of these pairs of pulses is increasing by 0.6 degrees per century, an unexpectedly large rate of evolution. The team has shown that this means that the magnetic pole is moving towards the equator.
“The most surprising aspect of is that this change is happening so rapidly, when the interior of the star is superconducting, and the magnetic field should be frozen in position,” said study lead author Prof Andrew Lyne from the University of Manchester.
“This pulsar is just 960 years old, so while 22 years gives only a small sample of its lifetime, it is a much larger fraction of a stellar lifetime than astronomers usually get to study,” added co-author Professor Sir Francis Graham Smith, also from the University of Manchester.
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Bibliographic information: Andrew Lyne et al. 2013. Evolution of the Magnetic Field Structure of the Crab Pulsar. Science, vol. 342, no. 6158, pp. 598-601; doi: 10.1126/science.1243254
