Humboldt-Universität zu Berlin - Faculty of Mathematics and Natural Sciences - Cosmos


Pulsars are fast-rotating neutron stars characterized by the emission of electromagnetic radiation pulses with a very regular rate.  Most of the known pulsars were discovered by their radio signals, but pulsed emission can also be seen at other wavelengths (optical, X-rays, gamma-rays).  The pulsed structure of the emission of one of these objects results from the pulsar's fast rotation, (analogue to the light from a lighthouse, see picture on the left), with a rotation period that can vary from source to source from a few milliseconds to several seconds.

Neutron stars are remnants of supernova explosions.  As soon as a the fuel of a massive star (with more than about 10 solar masses) is exhausted, the gravitational pressure cannot be compensated by the thermal pressure and as a consequence, the star collapses into a neutron star or, in the case of the heavier stars (over 20 solar masses) into a black hole.  According to the law of conservation of angular momentum, the angular velocity scales up when the radius scales down, which is the origin of the very fast rotating period of pulsars.

Despite their radius of ca. 10 km neutron stars have a mass of 1.4 to 3 higher than that of the sun. Thus, they have a mass density of up to 2,5·1012 kg/cm³ which is comparable to the mass density within the nucleus, or in other words, a teaspoonful of neutron star material is as massive as a mountain.  In addition to this, neutron stars possess extremely strong magnetic fields up to 108 Tesla which is orders of magnitude stronger than those achievable with current technology (slightly below 100 Tesla).  To put this into perspective: A single cubic meter of the magnetic field in the Crab pulsar contains more energy than the amount generated during the history of mankind.

Pulsed radiation on the high energy gamma-ray scale was detected for the first time only a few years ago by Imaging Atmospheric Cherenkov Telescopes.  But, besides pulsed radiation, pulsars also continuously release huge amounts of energy which 'heat' the pulsar's surroundings and produce so-called pulsar wind nebulae which are detectable at several wavelengths.  By observing the gamma-ray emission of numerous pulsar wind nebulae the H.E.S.S. Experiment in Namibia allows scientists to search for the answer to the question: How is the rotating energy of the pulsar transformed into high-energetic particles and electromagnetic radiation?

Cosmos | Supernovae | Pulsars | Galaxies | Cosmic Rays | γ-Astronomy