Mathematics – Logic
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...19111901b&link_type=abstract
American Astronomical Society, 191st AAS Meeting, #119.01; Bulletin of the American Astronomical Society, Vol. 29, p.1400
Mathematics
Logic
Scientific paper
Gamma-ray bursts now appear to be primarily of extragalactic origin. Statistically, assuming isotropic emission, the observed event rates and fluxes imply that one event occurs per 10(4) \ - 10(6) \ years per galaxy, with about 10(51) \ - 10(53) \ ergs in gamma-rays emitted per event. Unless the Milky Way is unusual, a gamma-ray burst should occur within 10(2) \ - 10(3) \ pc of the Sun in a time span of order 10(8) \ years. Independent of the underlying cause of the event, it would irradiate the solar system with a brief flash of MeV gamma-rays with a fluence as large as 10(9) - 10(11) \ erg cm(-2) . What is the effect of such an event on the Earth and objects nearby? Ruderman (\underbar{Science}, 184, 1079, 1974) and subsequent authors have considered a number of effects of a flash of gamma-rays from a nearby supernova explosion on the Earth's atmosphere, and on its biota. However, with regard to the demise of the dinosaurs, it appears that there was a marked increase in the deposition rate of the rare earth iridium coincident with their extinction. For this reason, an asteroid-Earth impact has been considered the leading contender for the death of the dinosaurs. Here we consider a new mechanism for mass biological extinctions, caused by small comets nudged into the inner solar system by nearby gamma-ray bursts. If comets populate the Oort cloud with a wide distribution of masses, radii and orbital eccentricities, we find that small (< 1 km), low density (10(-2) \ gm cm(-3) ) objects in highly eccentric orbits can be injected into the inner solar system by a nearby gamma-ray burst. For a relatively brief period of time, the near Earth comet population would increase dramatically. The consequent increased probability of comet-Earth impacts of appropriate energy and material content could account for many of the characteristics of the Cretaceous-Tertiary or other terrestrial mass biological extinctions.
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