Interstellar Origin of Cosmic Radiation at Radio-Frequencies

Abstract

RECENT publications of measurements of radiation from interstellar space¹ and from the sun^2,3 have important astronomical consequences. In the measurement of cosmic radiations at 5 metres wave-length, the maximum value of 13.2 × 10²¹ Î" v watts/sq. metre was obtained. This is equivalent to a radiation intensity of 4 × 10¹⁸ ergs/sec./kilocycle band-width/sq. cm./sq. degree. We have previously investigated⁴ the theory of interstellar radiation arising from free-free transitions by electrons in the field of protons. From astronomical observations the numbers of protons and electrons in interstellar space, in the neighbourhood of the sun, are known to be of the order of 1 per cubic centimetre. On this basis we computed the expected intensity of radiation at the earth; the maximum predicted value is found to be 5 × 10¹⁸ ergs/sec./kc./sq.cm./sq. degree, at about 1 metre wave-length. The accompanying graph shows the predicted free-free radiation from interstellar space as well as the presently available high-frequency measures. The plotted observations are the observed maximum intensities, in the region of Sagittarius. Data at the slightly longer wave-length bands, near 10 metres, would be of critical importance. The new and accurate observations by Hey, Phillips, and Parsons¹ lie remarkably close to our predicted curve. Their observations show relatively low concentration of the radio-frequency radiation to the galactic plane, compared to both interstellar matter and stars. Possibly a slight under-estimation of background noise might explain this effect.