Olbers's Paradox and the Spectral Intensity of the Extragalactic Background Light
Abstract
There is still confusion in some quarters as to why the intensity of the intergalactic radiation field is low and why Olbers's paradox is resolved. To remedy this in a fashion which is simple but different from previous bolometric work, the intensity as a function of wavelength is calculated, first in expanding uniform cosmological models and then in equivalent static ones. This separates the influence of the expansion of the universe from that of the age of the galaxies. In realistic expanding models, results are given for the spectral intensity of the extragalactic background light at 5100 A for a range of cosmological parameters and for galaxies which form at different redshifts and either have constant luminosities or a reasonable degree of evolution. The theoretical intensities in expanding models are mostly within observational limits. In hypothetical static models the intensities are higher, but only by modest factors. For most combinations of cosmological model, galaxy formation redshift and galaxy evolution, the expansion only reduces the intensity by a factor of about 3-4. (To reduce it by an order of magnitude from what it would be in a static model would require that the universe be close to de Sitter dynamically.) This confirms the conclusion drawn from earlier bolometric calculations of the extragalactic background light by Wesson, Valle, and Stabell, and shows Harrison is right about Olbers's paradox. Contrary to what is implied in some books, the latter is not resolved mainly by the cosmological redshift. The darkness of intergalactic space is a result primarily of the finite age of the galaxies, in conjunction with other factors including the finite speed of light, and only secondarily of the expansion of the universe.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 1991
- DOI:
- 10.1086/169638
- Bibcode:
- 1991ApJ...367..399W
- Keywords:
-
- Background Radiation;
- Cosmology;
- Extraterrestrial Radiation;
- Relic Radiation;
- Astronomical Models;
- Galactic Evolution;
- Luminosity;
- Red Shift;
- Universe;
- Astrophysics;
- COSMIC BACKGROUND RADIATION;
- COSMOLOGY;
- GALAXIES: PHOTOMETRY;
- RELATIVITY