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It is estimated that there are 108 neutron stars in our galaxy. About 1000 of these have actually been observed by astronomers so far. Neutron stars typically have masses of around 1-2 solar masses and diameters of approximately 10 km. Thus, they have enormous densities that are similar to those encountered in the nucleus of the atom. In fact, in certain ways, neutron stars are similar to giant atomic nuclei the size of a city.
The first clear detection of neutron stars (but their existence had been forecasted theoretically) was in the discovery of radio pulsars in the 1960s. Although most neutron stars have been discovered as radio pulsars, the vast majority of the energy emitted by neutron stars is in very high energy photons (X-rays and Gamma-rays, with the highest energies exceeding 100 MeV) rather than radio waves. Typically only about 1/100,000 of their radiated energy is in the form of radio waves.
History of the idea of neutron stars and their discovery.
Baade and Zwicky predict the possible existence of a neutron star.
Oppenheimer works out the theory of neutron stars.
Virtual trips to black holes & neutron stars
Java Applet: Orbits in Strongly Curved Spacetime
C-ship: Relativistic ray traced images (special relativity illustrations)
gravitational field of a neutron star is much stronger than that of a white dwarf,
leads to much higher temperatures than in the nova outburst.
This in turn
tends to produce X-rays rather than visible light in the thermonuclear runaway on
the surface of the neutron star.
By tracking the motion of the knots of material in the nebula and extrapolating the motion back it is possible to infer the place and time of the explosion. This can in turn be used to estimate how far the neutron star has traveled since the explosion and therefore its average velocity. By these means, the neutron star is found to have a space velocity of about 1000 km/s, suggesting that it was kicked out of the supernova explosion at high speed. Such high-velocity neutron stars are of particular interest for understanding supernova explosions. If the neutron star gets such a high kick velocity, this suggests that there is something unsymmetric in the explosion itself that sends the crushed core of the star in a particular direction with high velocity.
This purported neutron star is also
of interest because analysis of the atomic
composition of the supernova remnant (using optical spectra) in comparison with stellar
evolution models suggests that the mass of the progenitor star that produced the supernova was 25
solar masses. If this indirect inference is correct, this is the most massive supernova progenitor
known to have produced a neutron star (rather than a black hole).