Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1973
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1973ap%26ss..25..149o&link_type=abstract
Astrophysics and Space Science, Volume 25, Issue 1, pp.149-194
Astronomy and Astrophysics
Astrophysics
49
Scientific paper
A detailed theory of high-entropy supermassive oblique rotator is developed on the basis of the results of our previous work on the structure and evolution of supermassive rotating magnetic polytropes. Particular attention is paid to the problem of transformation of rotational energy into observable radiation. It is shown that a rather long duration of the quasi-stationary phase in combination with a considerably high value of magnetic dipole radiationL md in comparison with that of thermal radiationL th imposes substantial limitations on the character of the model. This combination is realized in the model of an oblique rotator with a rigid rotation and a poloidal magnetic field. Moreover, the magnetic energy must be comparable, in order of magnitude, with the module of the gravitational energy. The magnitude of the torque acting on the rotator by means of the magnetic field is influenced neither by the external plasma thrown out by the low-frequency radiation pressure, nor by the plasma ejected electrostatically, nor by that flowing out due to rotational instability. For definiteness we assume below that the rotational energy is lost by the rotator in the form of a low-frequency magnetic dipole radiation though many of the conclusions drawn in this paper are also valid for the case when the energy is liberated in some other forms (for example, in magnetohydrodynamic waves). Plasma outflow under rotational instability is considered in detail. This is a pulsating outflow. Near the light cylinder the plasma spreads out and begins to interact intensively with the magnetic dipole radiation. As a result, the particles are accelerated up to relativistic energies. Accelerated electrons radiate by synchrotron mechanism with the radiation maximum in the far infra-red region (Figure 4). Compton scattering of this radiation is in the X-ray and gamma regions. The character of the non-thermal radiation calculated accounts for the essential features of the observable radiation from quasars and active galactic nuclei. A secular variation of the magnetic dipole radiation in the course of evolution of a supermassive oblique rotator (Figure 1) with the account taken of the influence of magnetic dipole losses on the value of the angle between magnetic and rotational axes is discussed in the vacuum approximation substantiated in Section 3. For a wide interval of initial values of this angle the non-thermal (synchrotron and Compton) radiation increases in the course of a quasi-static contraction of the rotator, reaches its maximum at whichL nth≫L th, and then decreases considerably due to rapprochement of the magnetic and rotational axes. Such a behaviour ofL nth corresponds to the expected secular change of the activity of galactic and quasar nuclei as a certain ‘flaring up’, reaching the maximum of their activity and subsequent ‘dying out’. Some essential properties of quasars and quasar-like phenomena in galactic and quasar nuclei are explained on the basis of the theory presented. As an illustration, the parameters of a supermassive rotator modelling the source of activity in quasar 3C 273 are calculated (Table I). The estimate of the frequency of occurrence of rotators withL nth>L th andL nth≲L th is in a reasonable correspondence with the statistics of active phenomena in the nuclei of galaxies of different morphological types. Observational tests for this theory are suggested. The most important one called upon to ascertain the presence in the nuclei of galaxies and quasars of a supermassive body as a source of their activity is the variability of infra-red radiation near its spectral maximum. Similarity and difference between a supermassive oblique rotator and a pulsar, the model of a quasar nucleus as a cluster of pulsars, an axysymmetric rotator and a low-entropy configuration (disk) as stages of the evolution of an oblique rotator as well as the problems of its genesis and fate are discussed at the end of the paper (Section 9). The main results of the paper are listed in Section 10.
Ozernoy Leonid M.
Usov Vladimir V.
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