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Web address:
http://www.sciencedaily.com/releases/2008/08/
080828172835.htm
Origin Of High Energy Emission From Crab Nebula Identified
enlarge
The Crab Nebula from the Hubble Space Telescope. (Credit: NASA, ESA, J. Hester,
A. Loll (ASU); Acknowledgement: Davide De Martin (Skyfactory))
ScienceDaily (Aug. 29, 2008) — Another piece of the jigsaw in understanding how
neutron stars work has been put in place following the discovery by scientists
of the origin of the high energy emission from rotation-powered pulsars.
Pulsar systems containing neutron stars accelerate particles to immense
energies, typically one hundred times more than the most powerful accelerators
on Earth. Scientists are still uncertain exactly how these systems work and
where the particles are accelerated.
Now a team of researchers from the UK and Italy, led by Professor Tony Dean of
the University of Southampton, has detected polarized gamma-ray emission from
the vicinity of the Crab Nebula - one of the most dramatic sights in deep
space. By using spectroscopic imaging and measuring the polarization - or the
alignment - of the waves of high energy radiation in the gamma-ray band, they
have shown that these energetic photons originate close to the pulsar.
The Crab Nebula is the result of a supernova explosion which was seen from
Earth on 4 July 1054. The explosion left behind a pulsar or rotating neutron
star with a nebula of radiating particles around it.
The neutron star contains the mass of the Sun squeezed into a volume of about
10 km radius, rotating very fast - about 30 times a second - thereby generating
magnetic fields and accelerating particles. A highly collimated jet, aligned
with the spin axis of the pulsar and a bright radiating torus around the
pulsar, are also seen. The Crab is known to accelerate electrons, and possibly
other particles, to extremely high energies, both along the jet and around the
torus, where they can be traced in the gamma-ray domain.
Looking into the heart of the neutron star with a gamma-ray telescope on the
European Space Agency's INTEGRAL spacecraft orbiting Earth, the researchers
made a detailed study of the high energy radiation to assess their
polarization. They deduced that the majority of the gamma-rays are derived
directly from the jet.
They analysed data from over 600 individual observations of the Crab by the
INTEGRAL spectrometer to assess the polarization of the gamma-rays and compared
this data to the output from a sophisticated computer model.
The results show polarization with an electric vector aligned with the spin
axis of the neutron star, demonstrating that a significant fraction of the high
energy electrons responsible for the polarized photons are produced in a highly
ordered structure close to the pulsar.
Professor Tony Dean of the University's School of Physics and Astronomy
comments: "The remarkable alignment of the electric vector with the rotational
axis of the pulsar, together with its similarity to the optical polarization
angle, suggests that both fluxes originate at the same site close to the
neutron star. The findings have clear implications on many aspects of high
energy accelerators such as the Crab."
The result also may have profound implications for fundamental physics. Some
theories of quantum gravity have predicted that at very short distances a
particular direction in space would be picked out, breaking Lorentz invariance.
A consequence of this would be that the polarization vector of light would
slowly rotate as it propagated through space. The Crab Nebula has a well known
rotational axis and now the first measurements of the polarization of
gamma-rays have been shown to be aligned with it and not rotated away from it.
This very strictly limits non-Lorentz invariance.
Adapted from materials provided by University of Southampton, via AlphaGalileo.
Need to cite this story in your essay, paper, or report? Use one of the
following formats:
APA
MLA
University of Southampton (2008, August 29). Origin Of High Energy Emission
From Crab Nebula Identified. ScienceDaily. Retrieved August 29, 2008, from
http://www.sciencedaily.com /releases/2008/08/080828172835.htm
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