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Andrei Gruzinov

Publications and source records attributed to Andrei Gruzinov.

At least 55 records · Page 3Linked to original sources
arXiv2012

Electrodynamics of Massless Charges with Application to Pulsars

Electromagnetic field together with zero-mass charges moving in this field form a well-behaved semi-dissipative dynamical system -- Electrodynamics of Massless Charges (EMC). We give equations of EMC, argue that EMC is an adequate theory for calculating pulsar magnetospheres, give an illustrative numerical calculation (showing that bolometric luminosity of an aligned rotator is approximately equal to half the spin-down power). EMC looks like a portion of the full pulsar theory that will resolve the already calculated bolometric luminosity into light curves and spectra.

astro-ph.HE↗
arXiv2011

New Electrodynamics of Pulsars

We have recently proposed that Force-Free Electrodynamics (FFE) does not apply to pulsars -- pulsars should be described by the high-conductivity limit of Strong-Field Electrodynamics (SFE), which predicts an order-unity damping of the Poynting flux, while FFE postulates zero damping. The strong damping result has not been accepted by several pulsar experts, who claim that FFE basically works and the Poynting flux damping can be arbitrarily small. Here we consider a thought experiment -- cylindrical periodic pulsar. We show that FFE is incapable of describing this object, while SFE predictions are physically plausible. The intrinsic breakdown of FFE should mean that the FFE description of the singular current layer (the only region of magnetosphere where FFE and the high-conductivity SFE differ) is incorrect. Then the high-conductivity SFE should be the right theory for real pulsars too, and the pure-FFE description of pulsars should be discarded.

astro-ph.HE↗
arXiv2011

Stars and Black Holes in Massive Gravity

Generically, massive gravity gives a non-unique gravitational field around a star. For a special family of massive gravity theories, we show that the stellar gravitational field is unique and observationally acceptable, that is close to Einsteinian. The black hole solutions in this family of theories are also studied and shown to be peculiar. Black holes have a near-horizon throat and the curvature diverging at the horizon. We show that there exists a sub-family of these massive gravity theories with non-singular at horizon black holes.

hep-th↗
arXiv2011

Ohmic Power of Ideal Pulsars

Ideal axisymmetric pulsar magnetosphere is calculated from the standard stationary force-free equation but with a new boundary condition at the equator. The new solution predicts Ohmic heating. About 50% of the Poynting power is dissipated in the equatorial current layer outside the light cylinder, with about 10% dissipated between 1 and 1.5 light cylinder radii. The Ohmic heat presumably goes into radiation, pair production, and acceleration of charges -- in an unknown proportion.

astro-ph.HE↗
arXiv2011

Pulsar Magnetosphere

We argue that existing models of the ideal pulsar magnetosphere are incorrect because of the improper treatment of the singular current layer outside the light cylinder. We simulated the axisymmetric pulsar magnetosphere in the Force-Free limit of Strong-Field Electrodynamics. It turns out that even in the Force-Free limit, some field lines enter the singular current layer which lies beyond the light cylinder in the equatorial plane. As a result: (i) about 10% of the Poynting flux is dissipated between 1 and 1.5 light cylinder radii, (ii) there is no singular current layer within the light cylinder.

astro-ph.HE↗
arXiv2010

Solitary Magnetic Bubbles

Stability and attractor property of free-floating axisymmetric magnetic bubbles in high-conductivity plasmas is (tentatively, numerically) demonstrated. The existence of compact non-singular axisymmetric magnetic equilibria is proved. Being attractors, the solitary magnetic bubbles should exist in nature.

physics.plasm-ph↗
arXiv2009

Magnetic Equilibrium

We propose that generic magnetic equilibrium of an ideally conducting fluid contains a volume-filling set of singular current layers. Singular current layers should exist inside neutron stars. Residual dissipation in the singular current layers might be the main mechanism for the magnetic field decay. The slow decay of the field might be the clock responsible for triggering the magnetar flares.

astro-ph.HE↗
arXiv2009

The first magnetic fields in the universe

We show that the first structures that form in the universe should spontaneously generate magnetic fields. No primordial seed field is required for this "first dynamo". Although the first dynamo starts with kinetic plasma instabilities, we argue that an adequate magnetohydrodynamic description might be possible via a simple trick. This should allow a numerical study of the effect of the first magnetic fields on the first baryonic objects.

astro-ph.CO↗
arXiv2008

Dissipative Pulsar Magnetosphere

Dissipative axisymmetric pulsar magnetosphere is calculated by a direct numerical simulation of the Strong-Field Electrodynamics equations. The magnetic separatrix disappears, it is replaced by a region of enhanced dissipation. With a better numerical scheme, one should be able to calculate the bolometric lightcurves for a given conductivity.

astro-ph↗
arXiv2008

Giant AGN Flares and Cosmic Ray Bursts

We predict a new class of very intense, short-duration AGN flares capable of accelerating the highest energy cosmic rays, resulting from the tidal disruption of a star or from a disk instability. The rate and power of these flares readily explains the observed flux and density statistics of UHECRs. The photon bursts produced by the predicted AGN flares are discussed; they may soon be detectable. Observations are shown to exclude that continuous jets of powerful Active Galactic Nuclei are the sole source of ultrahigh energy cosmic rays; the stringent requirements for Gamma Ray Bursts to be the source are delineated.

astro-ph↗
arXiv2008

GRB: magnetic fields, cosmic rays, and emission from first principles?

We describe a scenario for large-scale magnetic field generation and particle acceleration in a collisionless collision of cold plasma clouds. A first-principle (i.e. using particles) numerical simulation of this process might be possible. Our scenario is essentially 3D. We argue that {\it large-scale} magnetic fields are not generated in 2D, even in collisionless plasma. We calculate and numerically simulate magnetic field generation by relativistic collisionless Kelvin-Helmholtz instability in 2D. Collisionless tangential discontinuity might be more important than collisionless shock, because tangential discontinuity remains unstable even in the hydro limit, when the shock stabilizes.

astro-ph↗
arXiv2008

Strong-Field Electrodynamics

Strong-Field Electrodynamics (SFE) is Maxwell theory with a certain Lorentz-covariant Ohm's law which uses only the electromagnetic degrees of freedom. We show that SFE is {\it semi-dissipative}: while the dissipation rate of the electromagnetic energy is non-negative, it can be exactly zero for non-trivial electromagnetic fields. It appears that SFE is well-defined for arbitrary electromagnetic fields. It should be possible to calculate the dissipative pulsar magnetosphere and resolve the magnetic separatrix using SFE. We show that SFE reduces to Force-Free Electrodynamics (FFE) in the large conductivity limit. In the regions where the ideal FFE 4-current is space-like, SFE predicts small dissipative corrections. In the regions where the ideal FFE 4-current is time-like, SFE predicts a zero correction. This indicates that bright pulsars radiate primarily from the magnetic separatrix.

astro-ph↗
arXiv2007

Dissipative Strong-Field Electrodynamics

A dissipative Lorentz-covariant Ohm's law which uses only the electromagnetic degrees of freedom is proposed. For large conductivity, Maxwell equations equipped with this Ohm's law reduce to the equations of Force-Free Electrodynamics (FFE) with small dissipative corrections, but only in the regions where the ideal FFE 4-current is space-like. This might indicate that the pulsar emission comes primarily from the magnetic separartrix.

astro-ph↗
arXiv2007

Directed Relativistic Blast Wave

A spherically symmetrical ultra-relativistic blast wave is not an attractor of a generic asymmetric explosion. Spherical symmetry is reached only by the time the blast wave slows down to non-relativistic velocities, when the Sedov-Taylor-von Neumann attractor solution sets in. We show however, that a directed relativistic explosion, with the explosion momentum close to the explosion energy, produces a blast wave with a universal intermediate asymptotic -- a selfsimilar directed ultra-relativistic blast wave. This universality might be of interest for the astrophysics of gamma-ray burst afterglows.

astro-ph↗
arXiv2006

Neutrino signatures of supernova turbulence

Convection that develops behind the shock front during the first second of a core-collapse supernova explosion is believed to play a crucial role in the explosion mechanism. We demonstrate that the resulting turbulent density fluctuations may be directly observable in the neutrino signal starting at t>~ 3-4 s after the onset of the explosion. The effect comes from the modulation of the MSW flavor transformations by the turbulent density fluctuations. We derive a simple and general criterion for neutrino flavor depolarization in a Kolmogorov-type turbulence and apply it to the turbulence seen in modern numerical simulations. The turbulence casts a "shadow", by making other features, such as the shock front, unobservable in the density range covered by the turbulence.

astro-ph↗