Black Holes Take Centre Stage

The stories behind the 2020 Nobel Prize for Physics

For years, early October has shone a global spotlight on Sweden with the annual announcement of the Nobel Prizes. The Peace and Economic Sciences prize-winners are yet to be revealed, while the Physiology or Medicine, Chemistry, Literature, and Physics names have already been released to the public. The latter announcement especially was a poignant one, recognising Roger Penrose for his discoveries about black holes; much of his work was in collaboration with Stephen Hawking, who is now ineligible for the prize on account of his death only a little over two years ago. The two other Physics awardees, Andrea Ghez and Reinhard Genzel, independently carried out crucial experimental work on black holes. This year’s cosmic theme is pertinent, coming after the 2019 release of the first ever black hole image from the Event Horizon Telescope Collaboration.

The first theoretical predictions of black holes arose from Albert Einstein’s revolutionary theory of general relativity, which suggested that accumulating mass could form a point in space so dense that the curvature of space-time would be infinite – a singularity, where the laws of physics would not hold. Einstein, who found this outcome extremely undesirable, and other theorists initially assumed that this was a mathematical peculiarity with no actual, physical counterpart. It took Penrose and Hawking’s work in 1965 to prove that for sufficiently large stars of the right type – stars whose existence in the observable universe was well documented – their ultimate collapse would almost unavoidably lead to the formation of black holes. The result of their studies was an incredible catalogue of profound discoveries about physics and the appearance of our universe. The extreme conditions of black hole interiors provide space for exploring the most fundamental and mysterious questions about nature. These ideas include what the existence of black holes means for our ability to predict the future based on information about the present, which Penrose also investigated, and whether black holes can destroy information, violating one of science’s most vital conservation principles.

Ghez, who follows in the footsteps of Marie Curie, Maria Goeppert-Mayer, and Donna Strickland as only the fourth woman to win a Nobel Physics Prize, and Genzel are leaders in the field of black hole detection. The achievement that earned them the Nobel was their separate discovery of a supermassive black hole at the centre of the Milky Way, our home galaxy. Their respective teams used interferometry (merging observations from several telescopes) to track the motion of flares and nearby stars orbiting the black hole, enabling them to determine more about its properties, such as mass, and its location. This information is critical for understanding how our entire galaxy changes and has changed over time.

While Penrose’s work in particular is from several decades ago, all the discoveries acknowledged in this year’s Nobel Physics prize are key to the questions and puzzles that continue to motivate physicists today and into the future. With their astonishing and impenetrable nature, black holes are sure to shape scientists’ way forward.

Francesca VII