The 2020 Nobel Prize in Physics has been awarded to Roger Penrose, Reinhard Genzel, and Andrea Ghez for their groundbreaking theoretical and observational work on black holes.
Half of the 10 million kronor (about $1.12 million) prize goes to Penrose for "the discovery that black hole formation is a robust prediction of the general theory of relativity." The other half is shared between Genzel and Ghez for "the discovery of a supermassive compact object at the center of our galaxy." The scientists and their team discovered Sagittarius A*, the supermassive black hole at the center of the Milky Way.
Roger Penrose’s work was crucial to our understanding of black holes. Einstein’s theory of general relativity provided the mathematical tools to describe an object so dense that nothing, including light, could escape it. But Einstein did not believe they existed. It was Penrose who came up with a model that described how such an extreme object could form. His revolutionary 1965 paper is the basis for most of the field today.
The other half of the prize is observational. Reinhard Genzel and Andrea Ghez are both leaders of groups of astronomers that over the last three decades have studied the stars at the very center of the Milky Way. The orbits of these stars suggest the presence of an incredibly dense object; one packing over 4 million times the mass of the Sun into an object that would fit comfortably within the orbit of Mercury.
Both teams have continued monitoring the center of the galaxy, providing crucial tests for general relativity. They showed that gravitational redshift really does happen and that stars do follow orbits that cannot be explained with Newton’s law of gravity.
When asked what a black hole is, Professor Ghez answered frankly about the mysterious objects that seem to lead to more questions the more they are studied. “We don’t know," Ghez, a professor at UCLA, said. "We have no idea what’s inside the black hole. And that’s what makes these things such exotic objects that really represent the breakdown of our physical understanding, of the laws of physics.”
Professor Ghez is the fourth woman to receive the Physics Prize (tying female Nobel prize winners with male Nobel winners named James, if you're keeping score) out of more than 200 laureates since the Prizes started in 1901.
“I’m thrilled to receive the prize," Ghez said. "I take very seriously the responsibility associated with being the fourth woman to receive the prize. I hope I can inspire other young women into the field. It is a field that has so many pleasures, and if you are passionate about the science there is so much that can be done.”