Free electron density in H I regions as an indicator of ionizing dark matter

• Published in: Nature (London) 1990-07, Vol.346 (6279), p.40-42
• Main Author: Sciama, D. W
• Format: Article
• Language: English
• Subjects: Astronomy; Astrophysics; Atoms & subatomic particles; Earth, ocean, space; Elementary particle and nuclear processes; Exact sciences and technology; Fundamental aspects of astrophysics; Fundamental astronomy and astrophysics. Instrumentation, techniques, and astronomical observations; Humanities and Social Sciences; letter; multidisciplinary; Pulsars; Science; Science (multidisciplinary); Stars & galaxies
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/346040a0

IT has recently been proposed 1 that the free electrons giving rise to the observed dispersion of pulsar signals result mainly from photoionization induced by the decay of dark matter particles in the Galaxy. For reasons related to conservation of energy and momentum the decay photons would have a unique energy in the rest frame of the decaying particles, and in the proposed theory this energy is close to 14 eV. A crucial prediction of the theory is that in regions where the dark matter density is approximately constant, the free electron density n e in opaque H I regions should also be approximately constant, when averaged over several mean free paths for the ionizing photons. The determination of an accurate distance for the pulsar PSR1451-68 (ref. 2), in combination with its known dispersion measure and with previous observations of two other pulsars with accurate distances, leads to a successful test of this prediction.