Matter-Antimatter Annihilation as an Energy Source in Seyfert Galaxies

Abstract

The extreme infrared luminosities of some Seyfert galaxies place severe requirements on the efficiency of the energy source. It is attractive to suggest that matter-antimatter annihilation supplies the necessary energy source; efficiencies of up to ∼50% are, in principle, obtainable. However, there is a price to pay for such an explanation: gamma rays and neutrinos.

In a typical nucleon-antinucleon annihilation roughly ⅓ Mc² is released in electron-positron pairs, ∼⅔ Mc² in ∼3 gamma rays and ∼Mc² in ∼3 electron-neutrinos and ∼6 muon-neutrinos. As a result, if the observed infra-red power is to be derived from the energy in electron-positron pairs, then the flux of gamma rays would be 10²-10³ times the upper limits to the gamma ray flux. It is, of course, possible to account for the absence of the gamma rays by insisting that they be absorbed in the source. The neutrinos, however, will not be stopped and hence provide the possibility of testing the annihilation hypothesis.

We have computed the spectrum of neutrinos produced in annihilation. Assuming the product of the space density and infrared luminosity of Seyfert galaxies varies with redshift (z) as: L (z) n (z) = L₀n₀ (1 + z)^m we have computed the flux of μ-neutrinos contributed by all Seyfert galaxies out to a given red-shift for m = 3 and m = 6.5 (strong evolution). Further, assuming the “3K” and “0.3 mm” background radiation fields to be caused by a burst of “Seyfert type” objects at appropriate redshifts, we have again computed the expected μ-neutrino flux. When these results are compared with present limits on the flux of μ-neutrinos at the Earth, as determined from experiments performed by several groups deep underground, it emerges that the predicted flux is comparable to or greater than present upper limits. Thus, annihilation probably does not supply the infrared sources in Seyfert galaxies with the energy they require.