Astron. Astrophys. 355, 1009-1014 (2000)

3. Conclusion

In this work we have studied the effect of magnetic field on the existence of nuclear crust for a non-rotating strange star. We find that the electrostatic potential, electron degenerate pressure and the amount of nuclear crust decrease with the magnetic field for a certain range of values. This range, however, depends on the value of the electron chemical potential at the neutron drip point. For we find that the surface magnetic field, Gauss can reduce the nuclear crust mass. The magnetic field with intensity lying outside this range does not have any effect on the crust mass. However, if rotation is included, it will contribute to the crust by adding a centrifugal force to the electric intensity and the crust may contain larger amount of nuclear mass (Glendenning and Weber 1992). Therefore, under the joint influence of these two effects the crust thickness may not be as thick as obtained by Glendenning and Weber (1992). In such a case, arguments against the strange star pulsar exhibiting glitches may be stronger (Alpar 1987).

The dipolar magnetic field strengths of isolated pulsars are calculated from the magnetic dipole radiation breaking in the standard way. The recent ROSAT data collected for a few radio pulsars have shown that the diploar magnetic field strength, Gauss (Tsuruta 1998). Should evidence of very high surface magnetic field become available, our model may be useful for at least observational grounds.

If a rotating strange star with very strong surface magnetic field contains thin nuclear crust, it will be very difficult to supply charged particles sufficiently to form a rotating, charged magnetosphere, as first described by Goldreich and Julian (1969). This is due to the fact that the pulsar emission mechanism which depends on the stellar surface as a source of plasma will not work for a very thin surface.

Strong magnetic fields may influence strange star's cooling rates: a thinner crust is less insulating and gives faster cooling of strange star surface during the first few years. This fact can be important for future observations of young compact objects. The results for the reaction rates as a function of magnetic fields are available (Cheng et al. 1994), but the application to strange star's cooling with thin or thick nuclear crust is yet to be done. A model for the X-ray burst phenomenon involving unstable helium burning on the surface of an accreting strange star with nuclear crust may be an interesting problem because its consequences are observable in the form of well separated flashes. A model for X-ray burster involving unstable helium burning on an accreting neutron star have already worked out (Wallace et al. 1982). Strong magnetic fields may influence the reaction rates and the consequences of this alteration for the helium flashes have not been explored yet.

© European Southern Observatory (ESO) 2000

Online publication: March 21, 2000
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