The three winners led the decades-long effort to understand these dark cosmic secrets
October 6, 2020
BLACK HOLES are some of the most exotic objects in the universe. They are so dense that nothing, not even light, can escape their immense attraction. It is believed that at the center of a black hole is a point of infinite density called the singularity, where the known laws of physics collapse.
Understanding these dark cosmic objects took decades of effort. On October 6, the Nobel Prize Committee of the Royal Academy of Sciences of Sweden bestowed the most famous award in physics on three of those who led this effort.
Half the price of SKr 10 million (US $ 1.1 million) went to Sir Roger Penrose of Oxford University, who used Albert Einstein’s general theory of relativity to predict how black holes might form in the universe. Andrea Ghez and Reinhard Genzel from the Universities of Los Angeles and Berkeley at the University of California shared the other half for their decades of work mapping the movements of stars around the center of the Milky Way. Their studies have shown that there is a huge cosmic object here that is believed to be a supermassive black hole.
Although black holes were predicted about a century ago as a result of general relativity (which is actually a theory of how gravity shapes the structure and contents of the universe), early work suggested that they could only become perfectly symmetrical from collapse Stars or clouds of gas. This is hardly realistic, and Einstein himself doubted that they actually existed.
They therefore remained a theoretical curiosity until 1965, when Dr. Penrose, as he was then, worked out the details of how real matter could collapse into a black hole. Using a mathematical concept that he called an enclosed surface, he showed that even asymmetrical, lumpy stars and clouds of dust can form black holes. This work provided the tools observational astronomers needed to go on the hunt for them.
By definition, it is impossible to see black holes directly. Instead, physicists gain knowledge by studying how their gravity affects the movements of their star neighbors. Dr. Ghez and Dr. Genzel used this idea to gather evidence that Sagittarius A * – a bright source of radio waves in the center of the Milky Way, Earth’s home galaxy – is actually a supermassive black hole around which all the stars in the galaxy, including the sun, orbit .
Dr. Ghez and her team used the Keck Observatory Telescope in Hawaii with its ten meter wide primary mirror to conduct their observations. Dr. Genzel’s group used a series of eight-meter-wide telescopes high in the mountains of the Atacama Desert in Chile. These instruments were sensitive enough to peek through the clouds of dust that otherwise obscure the heart of the Milky Way to observers from Earth.
In three decades of observation, both research groups independently tracked around 30 of the brightest stars in the galactic center (see graphic). They found that the closer a star was to Sagittarius A *, the faster it moved. While the Sun, which is about 26,000 light years from center, takes about 200 m years to complete an orbit of Sagittarius A *, a star named S2, approaching 17 light hours, completes a single orbit in a dizzy 16 years. These measurements have enabled astronomers to compose an image of Sagittarius A * as a black hole about 4 m solar mass packed into a region of space as large as the solar system.
In April 2019, the first image of a black hole (the local equivalent of Sagittarius A * at the center of a galaxy called M87, 53 m light-years from Earth) was released. This was recorded with the Event Horizon Telescope, a collaboration that connects eight existing radio telescopes around the world and enables a far higher resolution than any individual instrument can handle. If technology improves, the Event Horizon Telescope could one day also provide a more detailed image of the region around Sagittarius A *.
Sir Roger, who had to step out of the shower to answer the call from the Academy telling him of his victory just before it was announced to the world, said the award was “an extreme honor and a great pleasure”. Later, speaking from his Oxford home, he remembered that it had taken astronomers a long time to take his ideas about black holes seriously. “There was a lot of skepticism in the early days,” he said. Eventually, however, observational studies began to gather evidence of their existence. “It was remarkable and gratifying to see that [my] It has been shown that work in the universe is something real. “
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