Black hole image proves Canterbury University professor Roy Kerr's solution

Thursday, 11 April 2019

Not only have astronomers captured an image of a supermassive black hole 55 million light years away, they've also proven a solution that Canterbury University Professor Roy Kerr came up with more than 50 years ago.

Back in 1963, Canterbury Distinguished Professor Kerr achieved what had eluded others for nearly half a century, solving some of the most difficult equations of physics by hand, Canterbury University said. He found the exact solution of Albert Einstein's equations that describe rotating black holes.

Kerr's discovery sparked a revolution in physics. At that time there was no consensus that such objects even existed; the term black hole was only coined in 1967.

The 2016 discovery of gravitational waves - caused by colliding black holes - was also made possible by Kerr's solution.

READ MORE: The first image of a black hole has been revealed by scientists

Kerr said he set his alarm for 1am Thursday to see the unveiling of the image - which turned out to be the supermassive black hole at the heart of giant elliptical galaxy Messier 87. The black hole contains the same mass as 6.5 billion suns.

'The EHT photo is just the beginning of a new phase in the understanding of our universe. The visual evidence will continue to get more and more sophisticated,' Kerr said.

The Royal Society of London described Kerr's work as of particular importance to general relativistic astrophysics, and all subsequent detailed work on black holes had depended fundamentally on it.

Canterbury University Physics Professor David Wiltshire said the creation of the close image was a red letter day for Kerr.

'More is coming in the next decade as technology finally catches up with general relativity just over 100 years after Albert Einstein conceived it, and over 50 years since Roy Kerr discovered its most important solution.'

Kerr is also mentioned in the abstract to a research paper, published on Thursday (NZ time) in The Astrophysical Journal Letters, about the work that resulted in the image of the M87 black hole.

'Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity,' the paper said.

Kerr's discovery was also discussed by Stephen Hawking in his book A Brief History of Time. Kerr black holes rotated at a constant rate, with their size and shape depending only on their mass and rate of rotation, Hawking wrote.

'If the rotation is zero, the black hole is perfectly round and the solution is identical to the Schwarzschild solution. If the rotation is non-zero, the black hole bulges outward near its equator (just as the Earth or the Sun bulge due to their rotation), and the faster it rotates, the more it bulges. So … it was conjectured that any rotating body that collapsed to form a black hole would eventually settle down to a stationary state described by the Kerr solution.'

Kerr gained a Bachelor of Science from Canterbury in 1954 and his Masters the following year. He then went to Cambridge and was awarded his doctorate in 1959. It was Austin University in Texas that he discovered the solution to Einstein's equations that defined the space outside a rotating star or black hole. 

Kerr returned to Canterbury University where he was a mathematics professor for 22 years until his retirement in 1993.

He was awarded the British Royal Society's Hughes Medal in 1984 and the Rutherford Medal from the New Zealand Royal Society in 1993. He was made a Companion of the New Zealand Order of Merit in 2011, and was awarded the 2013 Albert Einstein medal by the Albert Einstein Society in Switzerland.

The University of Canterbury awarded the rare honour of the title Canterbury Distinguished Professor to Emeritus Professor Kerr who also received the prestigious Crafoord Prize in Sweden in 2016. Canterbury Distinguished Professor is the highest academic title that can be awarded by the university and has been conferred only twice before. Title recipients are Nobel Prize winners or equivalent, such as the Crafoord Prize, which is worth over $1 million