Europeans crack Crab Nebula energy emission mystery
A British-Italian group of scientists has shed light on the story behind the origin of high energy emission from the Crab Nebula, a supernova remnant and pulsar wind nebula. First discovered in the 18th century, the Crab Nebula is, for many, one of space's most spectacular sights. This latest study detected neutron stars from the area of the Crab Nebula and the findings were recently published in the journal Science. The scientists from the University of Southampton in the UK, the Italian National Institute for Astrophysics (INAF) and the Italian Institute for Space Astrophysics and Cosmic Physics (IASF) said they detected the neutron stars, also known as rotation-powered pulsars, by using spectroscopic imaging and measuring the polarisation or alignment of the high energy radiation waves in the gamma-ray band. Thanks to their investigation, the energetic photons were found to develop near the pulsar. Past research has shown that pulsar systems containing neutron stars accelerate particles to huge energies, on average about 100 times more than the strongest accelerators on Earth. Questions, however, remained as to the exact workings of these systems. But scientists also wondered about the location of the accelerated particles. Aboard the European Space Agency's INTEGRAL spacecraft, the research team used a gamma-ray telescope to measure the polarisation of the high energy radiation in detail. 'The majority of the gamma-rays are derived directly from the jet,' the researchers said. Headed by University of Southampton's Professor Tony Dean, the team evaluated data that was collected from more than 600 individual observations of the Crab Nebula. The data was then compared with the output generated from a sophisticated computer model. Polarisation emerges thanks to the alignment of an electric vector with the spin axis of the neutron star, according to the researchers. The outcome is a highly ordered structure located near the pulsar. 'The remarkable alignment of the electric vector with the rotational axis of the pulsar, together with its similarity to the optical polarisation angle, suggests that both fluxes originate at the same site close to the neutron star,' explained Professor Dean. 'The findings have clear implications on many aspects of high energy accelerators such as the Crab (Nebula).' Experts say a supernova explosion generated the Crab Nebula, which was initially observed in 1054 by Chinese astronomers as a new star in the constellation of Taurus. The Crab was then later discovered in 1731 by John Bevis, a British amateur astronomer. The explosion, say the experts, left behind a pulsar or rotating neutron star surrounded by a nebula of radiating particles. Some 6,300 light years away from the Sun, it consists of a mass of filaments measuring about 6 arcminutes (i.e. a unit of angular distance equal to a 60th of a degree) long and 4 arcminutes wide. The filaments are made up of ionised helium and hydrogen, as well as carbon, iron, neon, nitrogen and sulphur. The Crab Nebular is shaped like a prolate spheroid, the experts say.
Countries
Italy, United Kingdom