Mass Loss from Pulsating Neutron Stars

Abstract

DESPITE the trend of recent evidence, both observational and theoretical¹, that radial pulsations may not be the source of variation in pulsars, the pulsational hypothesis has still not been disproved. In particular, the expected pulsational damping times of degenerate stars may be sufficiently long (for small oscillations) that observable variations could occur over a period of millions of years (J. M. Cohen and L. C. Rosen, private communication), in spite of some earlier theoretical evidence to the contrary². One of the chief difficulties with the pulsational hypothesis, however, is that the calculated fundamental periods are longer than 1.5 s for white dwarfs^3,4 and shorter than 1 ms for most neutron-star models⁵, whereas most pulsars have periods lying between these extremes. Overtone pulsations in white dwarfs have been suggested as a mechanism³, but this possibility seems rather unlikely, and neither it nor the suggestion that pulsations are occurring in the non-degenerate envelope⁶ or atmosphere⁷ of a white dwarf can explain the 33 ms variations of the Crab Nebula pulsar in Taurus. In this article, a new possibility involving radial pulsations of a neutron star which is undergoing mass loss will be pointed out, with a view to interpreting the observed period^8,9 and secular increase of period^10,11 of the Crab Nebula pulsar.