Paul Murdin
Paul Geoffrey Murdin born 5 January 1942. He is a British astronomer who, together with his colleague Louise Webster, identified the first clear black hole candidate, Cygnus X-1. He studied Mathematics and Physics at the universities of Oxford and Rochester. In 1962, he took an eight-week summer residential course supporting researchers at the Royal Greenwich Observatory in Herstmonceux and at the end was offered a post by the Astronomer Royal, Richard Woolley. He left to study a PhD at Rochester and returned to the RGO in 1970 as a research fellow. During his three-year contract there, he wondered what he could contribute to find out about the provenance of powerful cosmic x-ray sources that had recently been detected, particularly Cygnus X-1. After he had made unsuccessful searches for light variations and unusual spectra among the hundreds of stars within the area of positional uncertainty of the X-ray source, a radio star was found that was coincident with a star HDE226868. He decided, with the Australian Louise Webster, to investigate whether the star was a binary star, possibly with one of the pair being the X-ray source as well as a radio source, but not being visible. They measured the Doppler shift to find that HDE226868 was a binary star with an orbit of 5.6 days orbiting an invisible partner, presumably the source of the X-rays, and which they calculated to be certainly more than 2.5 and probably more than six solar masses. Such a star cannot be a white dwarf or neutron star and they assumed this body to be a black hole.
