Mathematics – Logic
Scientific paper
Feb 1970
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1970natur.225..836k&link_type=abstract
Nature, Volume 225, Issue 5235, pp. 836-837 (1970).
Mathematics
Logic
4
Scientific paper
IT is now established that there is a universal X-ray background with an energy flux of about 10-7 erg cm-2 sr-1 s-1 (M. Oda, at the thirty-seventh IAU symposium, Rome, 1969). One possibility is that the background is a superposition of X-ray emission by all the galaxies in the universe, but the value obtained by taking the average X-ray emission per galaxy as that estimated for our galaxy is not enough1. Silk2 has taken the evolution of the universe into account using observations on radio sources as a guide to raise the intensity to the required level. The second explanation is the Compton scattering of the universal microwave background photons by intergalactic electrons3. This seems to be inadequate using earlier estimates of the intensity of intergalactic electrons, and an appeal to cosmological evolution did not help4. Recently, however, Brecher and Morrison5 using shorter lifetimes for escape of electrons from galaxies, and also the observations on radio sources, find the Compton process capable of explaining the X-ray background. Both explanations involve important assumptions, however. Silk estimates the average galactic emission by assuming that the galaxy contains a hundred sources like the strongest observed source Sco X-1. Brecher and Morrison assume that the lifetime of electrons in all galaxies is less than a million years and that the electrons escape into intergalactic space without being trapped in galactic haloes.
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