Paul Geoffrey Murdin OBE FRAS (born 5 January 1942) is a British astronomer. He identified the first clear candidate for a black hole, Cygnus X-1, with his colleague Louise Webster.

Prof Paul Murdin OBE FRAS
Paul Murdin and Roger Davies, NAM (2012)
2nd President of the European Astronomical Society
In office 21 August 1993 – 5 July 1997
Preceded by	Lodewijk Woltjer
Succeeded by	Jean-Paul Zahn [fr]
Personal details
Born	(1942-01-05) 5 January 1942 (age 82)
Citizenship	British
Spouse	Lesley Murdin
Children	3
Alma mater	University of Oxford (MA) University of Rochester (PhD)

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.

With Louise Webster, he submitted a paper with "modest" language to Nature, only mentioning the term “black hole” in the final sentence.^[1] Woolley was quite conservative in his views on astronomy, regarding black holes as "fanciful" (also famously dismissing worthwhile space exploration as "utter bilge"). Astronomer Charles Thomas Bolton then published a paper with a similar conclusion and more astronomers followed suit. The discovery helped Murdin to secure his future employment.^[2][3]

He and Webster were amongst the first staff astronomers at the Anglo-Australian Telescope and he continued in his vein of discovery using similar techniques. He returned to the Royal Greenwich Observatory and worked on developing the UK-Netherlands observatory at La Palma, which became the Isaac Newton Group of Telescopes. He was its first head of operations until 1987. He was the director of the Royal Observatory, Edinburgh from 1991–93. Then he joined the Particle Physics and Astronomy Research Council, planning and developing the UK's space research policy. He was President of the European Astronomical Society and Treasurer of the Royal Astronomical Society (to which he'd first been elected as a Junior Member at the age of 17 in 1959, moving to Fellow in April 1963), during which time membership increased, its public outreach programme was established and its journal became the most prominent worldwide. He presided over or chaired various committees of the International Astronomical Union (IAU).^[4][5][6]

He has authored and edited academic and popular books on astronomy and has written for many journals and newspapers, and well as having appeared regularly on television and radio programmes. In 2023 he was a guest on the BBC Radio 4 programme The Life Scientific.^[7] Now retired and living in Cambridge, he is a visiting professor at Liverpool John Moores University, Senior Fellow Emeritus at the Institute of Astronomy, Cambridge and Senior Member at Wolfson College.^[4][8]