Upper mass limit for neutron stars including differential rotation
We show that any significant amount of differential rotation initially present in a neutron star will be damped out within a few days. Consequently, differential rotation need not be considered in determining the upper mass limit for neutron stars. We determine this limit with the fewest possible assumptions. Without rotation the mass may not exceed 8 M/sub sun/Rigid body rotation may increase the mass by no more than 30% according to calculations by others. Thus we find the upper mass limit including rotation to be 11 M/sub sun/Our limit requires no assumptions about the equation of state above a density of 2 x 10/sup 14/ g cm/sup -3/. We can think of no plausible way in which this limit would be violated other than the breakdown of general relativity. If one is willing to accept dP/drho< or =1 as a constraint imposed by causality on static equations of state, the upper mass limit would be reduced to 7 M/sub sun)/s)/sup -3/(B/10/sup 12/ gauss)/sup 3/2/ (R/sub asterisk6/ cm)/sup 9/2/(m/Zm/sub e/)/sup 1/2/ ergs s/sup -1/. This luminosity is sufficient to explain radio pulsars if the beam energy can be converted to radio radiation with reasonably high efficiency, but is insufficient to explain pulsed ..gamma..-ray emission from the Crab and other pulsars. In these numerical estimates, we assume that the closed magnetosphere extends to the light cylinder. We also investigate the rotation rate of the plasma, and show that on the open-field lines of the aligned rotator, the beam current induces a twist to the field lines such that an observer at infinity sees the plasma as nonrotating. We apply these results and point out the necessity of including the effects of field-line curvature in a realistic model.
- Research Organization:
- Harrison M.,Randall Laboratory, Department of Physics, University of Michigan
- OSTI ID:
- 7082913
- Journal Information:
- Astrophys. J.; (United States), Vol. 217:1
- Country of Publication:
- United States
- Language:
- English
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