Minimum torque and minimum dissipation black hole-driven winds

Authors
Citation
B. Punsly, Minimum torque and minimum dissipation black hole-driven winds, ASTROPHYS J, 506(2), 1998, pp. 790-804
Citations number
27
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Space Sciences
Journal title
ASTROPHYSICAL JOURNAL
ISSN journal
0004-637X → ACNP
Volume
506
Issue
2
Year of publication
1998
Part
1
Pages
790 - 804
Database
ISI
SICI code
0004-637X(19981020)506:2<790:MTAMDB>2.0.ZU;2-F
Abstract
This article is an investigation of paired winds of magnetized plasma on th e magnetic flux tubes that thread a rotating black hole. The paired wind sy stem includes an ingoing accretion wind and an outgoing magnetically and ce ntrifugally slung wind. We consider wind systems in which the field-line an gular velocity, Omega(F), is established by the causal physics of plasma in jection into the azimuthally symmetric magnetic flux tubes, Omega(F)much le ss than Omega(H), where Omega(H) is the angular velocity of the black hole. There is another school of thought that holds that Omega(F) approximate to Omega(H)/2 is the proper choice of held-line angular velocity. However, it has been argued previously by this author that there is no known microphys ics associated with the gravitational held of a rotating black hole that ca n produce the predominantly field-aligned poloidal current flows associated with Omega(F) approximate to Omega(H)/2. Furthermore, the detailed structu re of MHD waves in the background of the geometry of the hole argues agains t the causal structure implicit in assuming Omega(F) approximate to Omega(H )/2. Consequently, for the purposes of this paper we assume that the relati vely low angular velocity of the injected plasma sets Omega(F) much less th an Omega(H) throughout the following. Two families of solutions are analyze d. A "minimum dissipation solution," which obeys the perfect MI-ID approxim ation everywhere, is shown to be the analog of the Blandford-Znajek solutio n for an imposed value of Omega(F) much less than Omega(H). A second paired -wind system is studied in which the outgoing wind is the perfect MHD "mini mum torque solution." The paired ingoing wind in the perfect MHD limit cann ot reach the event horizon. It is shown that the ingoing perfect MHD wind j oins onto a de deflagration wind. It is argued that the second paired-wind system is physically more reasonable on the basis of causality, minimum ene rgy, and minimum dissipation principles. The minimum dissipation aspect of the discussion requires a general relativistic understanding of entropy gen eration in the event horizon.