Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userGeneration of strong magnetic fields in a nascent neutron star accounting for the chiral magnetic effect
111
0
0.0
(
0
)
Authors
Maxim Dvornikov
Ask ChatGPT about the research
No Arabic abstract
We propose the mean field dynamo model for the generation of strongest magnetic fields, $Bsim 10^{15},{rm G}$, in a neutron star (NS) accounting for the chiral magnetic effect (CME) driven by the shock in a supernova (SN) progenitor of that NS. The temperature jump at a narrow shock front, where an initial magnetic field existing in inflowing matter rises sharply, is the source of the CME that prevails significantly the erasure of the CME due to the spin-flip through Coulomb collisions in plasma. The growth of the magnetic field just behind the shock given by the instability term $ ablatimes (alpha {bf B})$ in induction equation, stops after a successful SN explosion that throws out the mantle of a protoneutron star. As a result, such an explosion interrupts the transfer of strongly magnetized plasma from the shock onto NS surface and leads to the saturation of the magnetic field. Assuming the rigid protostar rotation, we employ the mean field dynamo, which is similar to the $alpha^2$-dynamo known in the standard magnetohydrodynamics (MHD). The novelty of our model is that $alpha^2$-dynamo is based on concepts of particle physics, applied in MHD, rather than by a mirror asymmetry of convective vortices in the rotating convection.
rate research
Read More
We suggest a new mean field dynamo model in anomalous MagnetoHydroDynamics (AMHD) accounting for the mean spin (polarization) of the magnetized chiral (ultrarelativistic) plasma of a neutron star (NS). For simplicity we consider a non-superfluid NS with its rigid rotation neglecting also any matter turbulence (convection) within a star. On this way, we recover the Chiral Magnetic Effect (CME) as a possible source for the amplification of a seed, sufficiently strong magnetic field, $Bsim 10^{13},text{G}$, up to values $Bgtrsim 10^{18},text{G}$ in old NSs, having ages $tgtrsim 10^6,text{yr}$. The important issue in AMHD model suggested is the continuous evolution of the chiral imbalance providing the CME for these ages, $partial_tmu_5 (t) eq 0$, in spite of the fast spin-flip in Coulomb collisions in the dense NS plasma that leads to vanishing $mu_5to 0$ at an earlier epoch in the corresponding protoneutron star. In contrast to the conventional mean-field dynamos, the dynamo drivers in the model are produced due to magnetic field generated at the previous stages of stellar evolution. It makes our model basically nonlinear.
Neutron stars are natural physical laboratories allowing us to study a plethora of phenomena in extreme conditions. In particular, these compact objects can have very strong magnetic fields with non-trivial origin and evolution. In many respects its magnetic field determines the appearance of a neutron star. Thus, understanding the field properties is important for interpretation of observational data. Complementing this, observations of diverse kinds of neutron stars enable us to probe parameters of electro-dynamical processes at scales unavailable in terrestrial laboratories. In this review we first briefly describe theoretical models of formation and evolution of magnetic field of neutron stars, paying special attention to field decay processes. Then we present important observational results related to field properties of different types of compact objects: magnetars, cooling neutron stars, radio pulsars, sources in binary systems. After that, we discuss which observations can shed light on obscure characteristics of neutron star magnetic fields and their behaviour. We end the review with a subjective list of open problems.
We study the effects of isovector-scalar meson $delta$ on the equation of state (EOS) of neutron star matter in strong magnetic fields. The EOS of neutron-star matter and nucleon effective masses are calculated in the framework of Lagrangian field theory, which is solved within the mean-field approximation. From the numerical results one can find that the $delta$-field leads to a remarkable splitting of proton and neutron effective masses. The strength of $delta$-field decreases with the increasing of the magnetic field and is little at ultrastrong field. The proton effective mass is highly influenced by magnetic fields, while the effect of magnetic fields on the neutron effective mass is negligible. The EOS turns out to be stiffer at $B < 10^{15}$G but becomes softer at stronger magnetic field after including the $delta$-field. The AMM terms can affect the system merely at ultrastrong magnetic field($B > 10^{19}$G). In the range of $10^{15}$ G -- $10^{18}$ G the properties of neutron-star matter are found to be similar with those without magnetic fields.
We investigate, by numerical lattice simulations, the static quark-antiquark potential, the flux tube properties and the chiral condensate for $N_f = 2+1$ QCD with physical quark masses in the presence of strong magnetic fields, going up to $eB = 9$ GeV$^2$, with continuum extrapolated results. The string tension for quark-antiquark separations longitudinal to the magnetic field is suppressed by one order of magnitude at the largest explored magnetic field with respect to its value at zero magnetic background, but is still non-vanishing; in the transverse direction, instead, the string tension is enhanced but seems to reach a saturation at around 50 % of its value at $B = 0$. The flux tube shows a consistent suppression/enhancement of the overall amplitude, with mild modifications of its profile. Finally, we observe magnetic catalysis in the whole range of explored fields with a behavior compatible with a lowest Landau level approximation, in particular with a linear dependence of the chiral condensate on $B$ which is in agreement, within errors, with that already observed for $eB sim 1$ GeV$^2$.
Young neutron stars (NSs) have magnetic fields $B$ in the range $10^{12}-10^{15}$ G, believed to be generated by dynamo action at birth. We argue that such a dynamo is actually too inefficient to explain the strongest of these fields. Dynamo action in the mature star is also unlikely. Instead we propose a promising new precession-driven dynamo and examine its basic properties, as well as arguing for a revised mean-field approach to NS dynamos. The precession-driven dynamo could also play a role in field generation in main-sequence stars.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
