Pulsars

Intriguing, precisely repeated radio pulses from the plane of our galaxy were discovered in the late 1960's and half-seriously attributed to "little green men" and called LGMs. By a process of elimination and modeling, these periodic sources, called pulsars, are attributed to rotating neutron stars which emit lighthouse type sweeping beams as they rotate. Variations in the normal periodic rate are interpreted as energy loss mechanisms or, in one case, taken as evidence of planets around the pulsar.

Index

Pasachoff
p212

 

HyperPhysics***** Astrophysics

R Nave

Go Back





Neutron Degeneracy

Neutron degeneracy is a stellar application of the Pauli Exclusion Principle, as is electron degeneracy. No two neutrons can occupy identical states, even under the pressure of a collapsing star of several solar masses. For stellar masses less than about 1.44 solar masses (the Chandrasekhar limit), the energy from the gravitational collapse is not sufficient to produce the neutrons of a neutron star, so the collapse is halted by electron degeneracy to form white dwarfs. Above 1.44 solar masses, enough energy is available from the gravitational collapse to force the combination of electrons and protons to form neutrons. As the star contracts further, all the lowest neutron energy levels are filled and the neutrons are forced into higher and higher energy levels, filling the lowest unoccupied energy levels. This creates an effective pressure which prevents further gravitational collapse, forming a neutron star. However, for masses greater than 2 to 3 solar masses, even neutron degeneracy can't prevent further collapse and it continues toward the black hole state.

Index

 

HyperPhysics***** Astrophysics

R Nave

Go Back