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Search for the Pulsar On
Less than three years after the explosion of the supernova 1987A In the Large Magellanic cloud in the Southern llcmlsphcr, It appears that astronomers of the European Southern Observatory ESO in Chile have made an exciting discovery. They have found evidence for the existence of a neutron star.
The "classical" theory of star development assumes that. In the interior of stars rich in mass - the star which exploded as supernova 1987A probably contained about twelve times as much mass as the sun -- the nuclear convcr-sion processes which provide energy take place up to the formation of iron nuclei. The energy released in this manner is normally used to heat up the star; a process necessary to maintain its inner stability.
Without this "pressure" from the interior, the star would colapsc under its own gravitation. However, during the last phase of a star's life, an ever increasing amount of energy is dissipated almost without effect in the form of neutrinos. These ghostly particles leave the star interior unhindered and can cause the giant gas ball to lose Its equilibrium: the iron core collapses in unrestrained fashion and the exterior of the star follows suit like a house of cards.
This devastating collapse destroys the material forming processes taking place in the sar core; where previously nuclei and electrons could coexist. the electrons are. now so lo speak, pressed into the nuclei, whereby the protons change into neutrons by emitting additional neutrinos. These nuclei can be so densely packed together that a cubic centimeter of such "degenerated" material would weigh several hundred million tonnes on earth -- approx, as much as a million locomotives. Such a compact ball of neutrons has an exceptionally hard surface, on which the collapsing gas material of the original star is sharply braked and extremely heated up. In such a situation the star material accumulates to such an extent that even the neutrinos, temporarily, find it difficult lo escape from the collapsing core and lose part of their energy. This cvergy component is. however, enough to force the gas material outwards and so start the explosion of the outer star remains; the supernova phenomenon runs Its course.
The Identification of the Crab Nebula in the constellation Taurus with a star explosion at the same place, recorded by Chinese Astronomers in July 1054 played a singiftcant roll in the development of this model. Walter Baade, a native of Germany had already pointed lo a possible connection between the two phenomena in the mid forties, and shortly following the discovery of the pulsars at the end of the sixties by British Radfoastronomers, Just such an object was also located in the crab Nebula. It rotates around Its own axis 30 times per second and thereby propagates pulses of radiation from a point on its surface, like a rotating navigation light. However, this crab Nebula pulsar is now loo old to draw conclusions about its original conditions
While up to now. scientists could not be certain if a neutron star really was left behind at the position of supernova 1987 A. the ESO astronomers on the Chilean mountain l.a Sllla appear lo have found ck-ar evidence of the existence of Jusl such an object. Using a 3.60 meter telescope, they were able lo observe that the Infrared radiation from the expanding material cloud had not further decreased in intensity, the temperature of the material Hying away had, mcn-whilc, settled at approx, minus 110 degrees Celsius. Obviously, the energy emitted from the radioactive nuchlcar disintegration in Ihe supernova phase, which has continually decreased in intensity, has meanwhile fallen below the Intensity of that of the nculorn star created at the same lime which has remained constant. Nonetheless. Il remains unclear how long the center of the star explosion will remain obscured and If ihe neutron star will then be revealed as a
- Hermann Michael Hahn