Magnetic Fields in High-Density Stellar Matter

Abstract

Abstract. I briefly review some aspects of the effect of magnetic fields in the high density regime relevant to neutron stars, focusing mainly on compact star structure and composition, superconductivity, combustion processes, and gamma ray bursts. THE "MAGNETIC FIELD" OF "NEUTRON STARS"A large body of evidence now identifies the presence of strong magnetic fields at (or very near) the surface of neutron stars. Except for a few cases, all the estimations of the magnetic fields of these objects come from the timing measurements of pulsar slowdown. The pulsar is usually modelled as a rapidly rotating neutron star with a dipolar magnetic field configuration in which the rotation axis is not aligned with the dipole axis. Since the period of the pulsed emission is associated with the rotation period P, accurate observations of P and its time derivativesṖ,P, and even the third derivative of P, have been used to shed light on pulsar dynamics. Within this framework the dynamic equation readsΩ = KΩ 3 , with K ≡ (R 6 B 2 p sin 2 α)/(6c 3 I), and Ω = 2π/P. Therefore, some properties of pulsars are plausible of interpretation in terms of timing data, e.g.:• the component of the B-field at the magnetic pole along the rotation axis(1)• the pulsar age t (or alternatively the rotational period at birth P i ),where τ ≡ −P/2Ṗ is the so called characteristic age, I is the moment of inertia of the neutron star, R its radius, and α is the angle between the rotation axis and the dipole axis. Note that, for determining B ⊥ the values of I and R must be assumed based mostly on theoretical arguments. A test of the reliability of these estimates, can be obtained from an independent determination of the age of the pulsar, which is possible for pulsars associated with supernova remnants (SNRs). Assuming that a given pulsar and a given SNR were born together, we can identify t SNR (the SNR age) with the pulsar age t in Eq. (2). Since within the dipole model τ is an upper limit for t, a comparison of t SNR with τ provides a relevant

Dense Quark Matter in a Magnetic Field

“…These compact stars typically have very large magnetic fields. Neutron stars can have magnetic fields as large as B ∼ 10 12 − 10 14 G in their surfaces, while in magnetars they are in the range B ∼ 10 14 − 10 15 G, and perhaps as high as 10 16 G [2] (for a recent review of magnetic fields in dense stars see [3]). Even though we do not know yet of any suitable mechanism to produce more intense fields, the virial theorem [4] allows the field magnitude to reach values as large as 10 18 − 10 19 G. If quark stars are self-bound rather than gravitational-bound objects, the upper limit that has been obtained by comparing the magnetic and gravitational energies, could go even higher.…”