My years in astrophysics

My scientific work in the years 1971-1979 was in the field of high energy astrophysics at the theoretical department headed by academician Ya.B. Zel'dovich. Until 1974 this department (laboratory) was within the Institute of Applied Mathematics of the Academy of Sciences of the USSR (Moscow), and in the year 1974 it was transferred (with the majority of its members) to the Institute for Space Research of the Academy of Sciences of the USSR (Moscow), where it continued to be headed by Ya.B. Zel'dovich until 1979.

The Zel'dovich's laboratory of theoretical astrophysics included about 10 scientists divided into two groups: one headed by Dr. I.D. Novikov (presently a member-correspondent of the Russian Academy of Sciences) and working mostly on the problems of cosmology, and the other headed by Dr. R.A. Sunyaev (presently a full member of the Russian Academy of Sciences) and working mostly on the theory of X-ray stars, black holes, active galactic nuclei. I belonged to the second group, and R.A. Sunyaev was my principal Ph.D. thesis advisor.

In those years most of my work was done under the guidance and together with R.A. Sunyaev. At the same time, all the significant (as well as not so significant) results in our group were always discussed with Ya.B. Zel'dovich, whose general guidance was invaluable to all of us, and without whose approval virtually nothing was published. However, the personal rule of Ya.B. Zel'dovich for becoming a co-author of a publication was always that he must had made a significant direct contribution to calculations and writing of a paper. Unfortunately, I have not had a chance to work so tightly and directly with Ya.B. Zel'dovich personally as to end up with a joint publication.

My work in astrophysics began on the theory of newly discovered fascinating astrophysical objects — binary X-ray pulsars, i.e. X-ray emitting neutron stars with a normal star as a companion in a close binary stellar system. When intense X-rays from the neutron star irradiate the surface of a normal companion star, they induce a strong stellar wind, part of which is captured by the neutron star and accounts for its X-ray luminosity. The theory of X-ray irradiated stellar atmospheres was constructed [3,15], and various observational effects [4,6,10,16,20] both in the X-ray and optical spectral ranges were calculated. This work made up the basis for my Ph.D. thesis defended in 1974 at the Institute for Space Research.

For strongly accreting neutron stars, an important principal question arises as to their limiting luminosity: as is well known, the luminosity by a perfectly spherical mass accretion cannot exceed the so-called Eddington limit because of the outward radiation-pressure gradient due to the Thomson scattering. In Ref. [9] a model was constructed, which demonstrated that by accretion onto strongly magnetized neutron stars the Eddington limit can be significantly surpassed when a super-strong magnetic field channels the accretion flow into the narrow polar regions of such a star.

In the course of these investigations, based to a large extent on sophisticated analysis of various radiation transport problems, several fundamental problems in the theory of radiative transfer have been solved, such as (i) solution of the transport equation and calculation of the directionality of outgoing radiation for strongly magnetized atmospheres with strongly anisotropic scattering and absorption cross-sections [7], (ii) derivation of a formula for the thermalization length by radiation transport in lines in situations where the hypothesis of complete frequency redistribution by resonance scattering becomes non-applicable [18,23], (iii) rigorous analytical solution of the equation of polarized radiation transport for the relict (microwave background) radiation in an anisotropic (3-axial) universe [21].

All reference numbers, like [3,15], are given according to the full list of my publications.

Originally composed: 2007.12.11
Last update: 2007.12.14