Penrose, 89, told reporters that he had just come out of the shower when he received confirmation of the prize from the Nobel committee.

"I wasn't expecting it at all. It's a huge honour and I'm sure it will be a benefit to promoting ideas which I hope people will look at a little more seriously, ideas about cosmology," he said from his home in Oxford.

Understanding black holes was important to shedding light on the origins of matter and galaxies, the mathematician said, and understanding the "singularities" that lie at their heart was the "greatest puzzle" facing astrophysics today.

"We haven't the faintest idea how to describe the physics that goes on in the middle," he said.

Penrose was jointly awarded the Nobel with two other physicists, in his case for 1964 research that showed Albert Einstein's general theory of relativity leads to the formation of black holes.

Penrose was one of Hawking's PhD examiners in 1966, and they collaborated on work into the origins of the universe.

Martin Rees, Britain's astronomer royal and fellow of Trinity College Cambridge, said they were "the two individuals who have done more than anyone else since Einstein to deepen our knowledge of gravity".

"Sadly, this award was too much delayed to allow Hawking to share the credit with Penrose," he said.

Hawking, who died in March 2018 after a long neurodegenerative illness, dedicated much of his life to explaining the existence of black holes and the Big Bang at the universe's creation.

Penrose said a Nobel prize for Hawking would have been "well-deserved" but was possibly held back by the committee's desire to honour observable, rather than theoretical, science.

Nevertheless, he said evidence to back up Hawking's theories of radiation emitting from the evaporation of older black holes, even from a previously extinct universe, was "extremely strong" and would likely be vindicated in time.

For himself, Penrose said he was happy to have waited until late in life before getting Nobel recognition.

"It's a bad thing to get a Nobel prize too early. I know people who got their prize I would consider too early, and it spoiled their science," he said.

Turning to sci-fi films, Penrose said that he "loved" Stanley Kubrick's "2001: A Space Odyssey". But Christopher Nolan's more recent "Interstellar", featuring a wormhole accessed through a bookcase, was "nonsense".