Roy Kerr

Roy Patrick Kerr was born on 16 May 1934 in Kurow, New Zealand, and grew up through difficult childhood circumstances before his mathematical talent carried him to the University of Canterbury and then to St John's College, Cambridge, where he completed his PhD in 1959. His early work was in the general theory of relativity at a time when the field was considered a mathematical backwater with few testable predictions and almost no astrophysical relevance.

In 1963, working at the University of Texas at Austin, Kerr solved a problem that had defeated relativists for nearly half a century: finding the exact vacuum solution of Einstein's field equations for a rotating mass. Rather than attacking the equations directly, he restricted attention to spacetimes that were algebraically special in the Petrov classification of the curvature, and stationary and axially symmetric. Within that family he found a clean two-parameter solution — fixed by mass and angular momentum — and verified it satisfied the vacuum equations. The resulting paper was barely longer than a page.

The significance of the Kerr metric grew enormously over the following decade. The discovery of quasars in 1963, pulsars in 1967, and the realization that astrophysical collapse generically produces rotating remnants made Kerr's solution the description of essentially every real black hole. The no-hair theorem later established that any isolated, uncharged, stationary black hole must be exactly a Kerr black hole — making his solution not one example among many but the unique answer.

Kerr spent much of his career back in New Zealand at the University of Canterbury, where he led the mathematics department. He was awarded the Hughes Medal of the Royal Society in 1984, the Albert Einstein Medal in 2013, the Crafoord Prize in 2016 (shared), and was made a Companion of the New Zealand Order of Merit. He remains a vocal participant in debates about black-hole interiors and the validity of the singularity theorems.