Encountering the first black hole: An interview with black hole co-discoverer Paul Murdin

The Isaac Newton Telescope (INT) made its debut in the astronomical world at the Herstmonceux Observatory in East Sussex, UK, in the late 1960s. Constructed in the 1960s, the INT was inaugurated by Queen Elizabeth II on 1 December 1967.

In its early days, the very first paper that came out of the INT was by Michael Penston, shedding light on the changing nature of a Seyfert galaxy. However, the telescope's tenure at Herstmonceux was not without challenges. Paul Murdin, who supported visitors using the INT, found working with the telescope frustrating due to its difficulty to operate, the constantly changing weather, and the frequent cloud cover.

Despite these challenges, the INT made history during its time at Herstmonceux. It was responsible for the first discovery of a black hole, a groundbreaking discovery that would change the course of astronomical research. The poor observing conditions at Herstmonceux Estate may have contributed to the discovery of the black hole in Cygnus X-1.

Paul Murdin was instrumental in this discovery, working with the INT from about 1962 to 1963 and then again from about 1970. He competed with visitors for access to the telescope for his own programs. If a piece of equipment was being built and needed to be tested, it would be put on the telescope, and Murdin would use the idle time for his own observations.

In 1971, Paul Murdin, along with Louise Webster, made the first ever clear identification of a black hole in Cygnus X-1. This discovery led to Murdin being moved from being a research fellow to a permanent employee.

The INT's stay at Herstmonceux was brief, as it moved to its current home, the Roque de los Muchachos Observatory on the island of La Palma, in 1981 due to unforgiving English weather. Paul Murdin supported the move, although he felt it distanced the facility from his control.

Despite these changes, the INT has continued to make great discoveries and is still in use by astronomers from around the world. It was during his second tenure that Murdin used the INT to study the binary star system Cygnus X-1 and discovered that one of the stellar companions was a black hole.

The INT's journey from Herstmonceux to La Palma marked a significant milestone in astronomical research, paving the way for continued discoveries and advancements in our understanding of the universe. Louise Webster, who passed away on 29 September 1990, and Paul Murdin, who played pivotal roles in the INT's history, will always be remembered for their contributions to the field.