The Nobel Prize for Physics has been awarded to three scientists for their innovative research on black holes.
One of them, Britain's Roger Penrose, won half the prize for using mathematics to prove that black holes are a direct consequence of Einstein's general theory of relativity and the work he did alongside Dr Stephen Hawking in the 1960s.
The other half of the prize went to Professor Andrea Ghez, only the fourth female winner of the prize, who was recognised for her work with Germany's Reinhard Genzel in discovering that an invisible and extremely heavy object, most likely a supermassive black hole, governs the orbits of stars at the centre of our galaxy.
The delight that black holes were honoured by the prestigious Nobel winners was tempered with regret that the accolade came too late for world-renowned Dr Hawking, who died in 2018.
Prof Penrose, from the University of Oxford, worked alongside Dr Hawking for years and the pair studied the origins of the universe together.
"It's a shame that Penrose and Hawking didn't get the Nobel before now," said Luc Blanchet, from the Paris Institute of Astrophysics.
"This prize comes two years after (Prof Hawking's) death yet their work took place in the 1960s and its importance was recognised since the 1980s."
Martin Rees, a British astronomer and fellow of Trinity College Cambridge, said the pair were "the two individuals who have done more than anyone else since Einstein to deepen our knowledge of gravity."
"Sadly, this award was much too delayed to allow Hawking to share the credit with Penrose," he said.
Prof Ghez, of University of California, Los Angeles, is the fourth woman to win the physics prize, after Marie Curie in 1903, Maria Goeppert Mayer in 1963 and Donna Strickland in 2018.
"I hope I can inspire other young women into the field," Prof Ghez said on Tuesday.
Physics is the second of this year's Nobel Prize categories to be awarded, after three scientists won the medicine prize for their breakthrough work on Hepatitis C on Monday.
"The discoveries of this year's laureates have broken new ground in the study of compact and supermassive objects," David Haviland, chairman of the Nobel Committee for Physics, said on awarding the Dh4.04 million ($1.1m) prize.
"But these exotic objects still pose many questions that beg for answers and motivate future research."
Mr Genzel, an astrophysicist at the Max Planck Institute and University of California, Berkeley, and Prof Ghez have led research since the early 1990s focusing on a region called Sagittarius A* in the centre of the Milky Way.
The pair developed methods to see through the huge clouds of interstellar gas and dust, into the heart of the Milky Way, creating new techniques to compensate for the image distortion caused by Earth's atmosphere.
Using the world's largest telescopes, they discovered an extremely heavy, invisible object - around four million times greater than the mass of our Sun - that pulls on surrounding stars, giving our galaxy its characteristic swirl.
