Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983apj...266..466g&link_type=abstract
Astrophysical Journal, Part 1, vol. 266, Mar. 15, 1983, p. 466-469. Research supported by the Radcliffe Trust and Royal Society
Astronomy and Astrophysics
Astronomy
79
Astronomical Spectroscopy, Bl Lacertae Objects, Gas Heating, Line Spectra, Seyfert Galaxies, X Ray Astronomy, Compton Effect, Emission Spectra, Gas Cooling
Scientific paper
The flat X-ray spectrum produced by the nucleus of a Seyfert galaxy causes Compton heating in gas accreting onto the central black hole. This heating produces a thermal instability resulting in a two-phase gas at distances about 10 to the 17th - 10 to the 18th cm. The hot phase has a temperature of about 10 to the 8th K and compresses the cold phase (T is about 10,000) into clouds which produce the broad emission lines. BL Lac objects have much steeper X-ray spectra than Seyfert galaxies and consequently do not heat the accreting gas which is stable and cold (T is equal to or less than 10 to the 6th). This cold gas has a low density and emissivity per unit mass, and so no emission lines are seen.
Fabian Andrea C.
Guilbert Paul W.
McCray Richard
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