Historical Introduction. Star Formation: the Early History

Abstract

As evident from its colloquial style, this essay was never intended for publication; it was prepared for a seminar on star formation given at the If A in March 2000. Others who participated in the early development of the subject may have seen it otherwise, but this is how it looked to me. — G.H.

It is not easy to reconstruct what the astronomical community thought of star formation prior to about 1930. In 1854–1863 Helmholtz and Kelvin (the original references are given by [6] p. 484) had considered the possibility that the Sun’s luminosity was derived from slow contraction, but the time scale was very short: contraction from infinite radius to the present value, at the current luminosity, could have sufficed for only 10 to 30 Myr. The reigning idea thereafter seemed to be that stars lose mass by radiating it away, and hence that a star’s mass decreases systematically with age. Stars were supposed to begin their lives as massive red giants, evolve up the giant branch to the main sequence at type B, and then ever more slowly down the main sequence toward the M dwarfs. I can find no explanation of where those massive red giants came from. One senses the attitude that the origin of stars was something unknown and unknowable: it happened in the remote past under circumstances that we were unlikely to fathom.