Britain’s Roger Penrose, Germany’s Reinhard Genzel and American Andrea Ghez won the 2020 Nobel Prize for Physics for their discoveries about one of the most exotic phenomena in the universe — the black hole.

Penrose, professor at the University of Oxford, won half of this year’s prize of 10 million Swedish crowns ($1.1 million) for his work using mathematics to prove that black holes are a direct consequence of Albert Einstein’s general theory of relativity.

Genzel — of the Max Planck Institute and University of California, Berkeley — and Ghez at the University of California shared the other half for discovering that an invisible and extremely heavy object governs the orbits of stars at the centre of our galaxy.

Ghez is the fourth woman to be awarded the Nobel Prize for Physics, after Marie Curie in 1903, Maria Goeppert-Mayer in 1963 and Donna Strickland in 2018.

What is a black hole?

A black hole is born when a large star collapses in on itself. Far from being a “hole”, they are instead incredibly dense objects with a gravitational pull so strong that nothing, not even light, may escape them. As they suck in matter such as gas, dust and space debris, they form an accretion disk — a churning mass of super-accelerated particles that are among the brightest objects in the Universe — around them.

Scientists generally believe that there are two types of black holes. The more common stellar black holes — up to 20 times more massive than the Sun — form when the centre of a very big star collapses in on itself.

Supermassive black holes are at least a million times bigger than the Sun and their origins are uncertain.

Einstein predicted in 1915, in his general theory of relativity, that space and time could be warped by the force of gravity. Yet he did not actually believe in black holes, and finding a way to prove their existence baffled scientists for another 50 years.

What are the main contributions of the trio?

Roger Penrose used ingenious mathematical methods in his proof that black holes are a direct consequence of Einstein’s general theory of relativity. 

In January 1965, ten years after Einstein’s death, Penrose proved that black holes really can form and described them in detail. At their heart, black holes hide a singularity in which all the known laws of nature cease. His groundbreaking article is still regarded as the most important contribution to the general theory of relativity since Einstein.

Reinhard Genzel and Andrea Ghez each lead a group of astronomers that, since the early 1990s, has focused on a region called Sagittarius A* at the centre of our galaxy. 

The orbits of the brightest stars closest to the middle of the Milky Way have been mapped with increasing precision. The measurements of these two groups agree, with both finding an extremely heavy, invisible object that pulls on the jumble of stars, causing them to rush around at dizzying speeds. Around four million solar masses are packed together in a region no larger than our solar system.

Using the world’s largest telescopes, Genzel and Ghez developed methods to see through the huge clouds of interstellar gas and dust to the centre of the Milky Way. Stretching the limits of technology, they refined new techniques to compensate for distortions caused by the Earth’s atmosphere, building unique instruments and committing themselves to long-term research. Their pioneering work has given us the most convincing evidence yet of a supermassive black hole at the centre of the Milky Way.

The discoveries of this year’s laureates have broken new ground in the study of compact and supermassive objects. But these exotic objects still pose many questions that beg for answers and motivate future research. Not only questions about their inner structure, but also questions about how to test our theory of gravity under the extreme conditions in the immediate vicinity of a black hole.

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