The illusion of neutron star magnetic field estimates

Abstract

Neutron stars radiate in a broad band spectrum from radio wavelengths up to very high energies. They have been sorted into several classes depending on their respective place in the P − P diagram and depending on spectral/temporal properties. Fundamental physical parameters such as their characteristic age and magnetic field strength are deduced from these primary observables. However this deduction relies mostly on interpretations based on simple vacuum or force-free rotating dipole models that are unrealistic. In this paper, we show that the computation of the stellar surface magnetic field is poorly estimated or even erroneous if multipolar components and particle loading are neglected. We show how quadrupolar magnetic field and monopolar winds alter field estimates and characteristic ages in the P − P diagram. Corrections brought by general relativity are also discussed. We derive some important parameters of pulsar physics such as the wind Lorentz factor (γ) times the pair multiplicity (κ) to be around γ κ ≈ 10 8 − 10 10 . Therefore, the standard magnetodipole radiation losses formula must be used with caution to reckon neutron star surface magnetic fields and related secular evolution parameters. Depending on models we found that all field strengths, both for magnetars and for pulsars lie below the quantum critical value of B c ≈ 4,4 · 10 9 T.

A two-fluid analysis of waves in a warm ion–electron plasma

“…Estimates of the magnetic field B w in Ref. 20 were used alongside Goldreich-Julian density estimates 21 for the pulsar (J1734-3333) and magnetar (Swift J1834) cases in Fig. 5b.…”

“…A selection of physical environments are represented by a dot. 5,[18][19][20][21] The dashed blue line indicates the record artificial magnetic field strength, B = 1200 T. 22 In this formulan andb are unit vectors defined asn = k/k andb = B/B, v ph indicates the phase speed as before, and P ω , P k , and P λ are polynomials defined as…”

“…(b) The magnetic field strength for which the critical value Ecr would be attained for a proton-electron plasma (solid line) and a carbon-electron plasma (dashed line) as functions of the (electron) density. A selection of physical environments are represented by a dot 5,[18][19][20][21]. The dashed blue line indicates the record artificial magnetic field strength, B = 1200 T 22.…”

Does elasticity stabilize a magnetic neutron star?

“…It suggests a star with a uniform shear modulus equal to a typical crustal value (∼ 10 29 Joule • m −3 ) can sustain a magnetic field of strength up to about 10 11 T (Figure 7). This field strength is higher than the inferred maximum magnetic field values (∼ 10 8−10 T) at the surface of neutron stars (Konar 2017;Pétri 2019). We can therefore say that a star with a non-zero shear modulus throughout its entire volume, equal to the typically estimated crustal value, would be capable of stabilising a neutron star with a realistic magnetic field strength.…”

Spheroidal magnetic stars rotating in vacuum

“…The spheroidal corrections to the spin down can be of the same order of magnitude as those arising from the force-free corrections which reach up to a factor 3 for the orthogonal rotator. This leads to a weaker magnetic field estimate compared to the standard vacuum magneto-dipole losses as shown by (Pétri 2019). We infer that the combination of spheroidal geometry and force-free magnetosphere will lower even more the dipole magnetic field strength expectation.…”