The 2020 Nobel Prize in Physics has been awarded to three researchers who were successful in proving the presence of black holes by theory and observation. They have made giant strides in the quest to understand the mysterious celestial bodies, paving the way for the first-ever images of black holes captured by a team of scientists from around the world, including Japan. Hopes are rising that the photography team may also receive the Nobel Prize in the near future.
Black holes are extremely high-density celestial regions with gravitational pull so strong that any object in their surroundings that gets close enough is “swallowed.” Even light that travels at 300,000 kilometers (186,000 miles) per second — the fastest in the universe — cannot escape, causing them to appear as “black holes” in outer space.
The existence of black holes is said to have been predicted toward the end of the 18th century by British and other scientists. Albert Einstein’s completion of the Theory of General Relativity in 1916 demonstrated gravity’s deformation of space-time, affirming the likelihood of black holes. However, there was no evidence other than mathematical equations, and it is said that Einstein himself was skeptical about whether black holes truly existed.
It was Sir Roger Penrose, 89, professor emeritus of Oxford University (U.K.), who established the theoretical presence of black holes. In his paper published in 1965 based on the theory of general relativity, he proved that “singularities” with infinite density exist at the center of black holes, mathematically demonstrating they can actually be formed in space.
It is extremely difficult, however, to capture an image of black holes, which are small, coal-black celestial bodies.
Trying various approaches amid rapid strides in observation technology, researchers such as Professor Reinhard Genzel, 68, the director of the Max Planck Institute for Extraterrestrial Physics of Germany, and Professor Andrea Ghez, 55, at the University of California of the United States, came out with indirect evidence strongly supporting the existence of black holes.
The two have closely observed of a small, mysterious celestial body called “Sagittarius A*” since the 1990s. The entity, which is situated at the center of the Milky Way galaxy where the solar system is located, emits high-intensity radio waves. Nearby stars have been found revolving around it at hyper-speed, as if being drawn in by its strong gravitation. Since the speed of the stars accelerates as they approach the mass, researchers have concluded that it must be a supermassive black hole with a mass equal to about four million suns.
In the wake of the discovery, the momentum for directly capturing images of black holes grew. In 2017, a consortium was formed by about 200 scientists from around the world including Japan, with the aim of using radio telescopes to collaborate in a bid to capture images of the monster lurking at the heart of the distant galaxy M87. In a world’s first, the team announced its success in capturing an image of the supermassive black hole and its shadow last year.
Talking about the achievement, Professor Mareki Homma of the National Astronomical Observatory of Japan, who heads the Japanese participants in the international team, paid respect to this year’s three Nobel laureates: “It is thanks to the pioneering studies by these accomplished scholars that we have been able to attain success.”
It is somewhat customary for the Nobel Prize in Physics to be awarded alternately among the two major fields of space and elementary particles and physical properties. Given that the prize in 2019 was awarded for the discovery of an exoplanet outside the solar system, the selection of the prize winners from the space field for two straight years is considered extraordinary.
Given the decision to award the Nobel Prize for the indirect establishment of the existence of black holes, it is increasingly thought that the team that first provided photographic evidence also deserves recognition. As Professor Homma put it: “The most probable focus of attention will be the U.S. project leader of the black hole photography team, and it will be no surprise for us to see the award made, say, five or 10 years from now. The Nobel Prize this time recognizes the significance of black hole studies as one of the key research fields in physics, which provides great encouragement to us as junior researchers [in the field].”
The era of directly seeing black holes has arrived, and from now on our research will tackle such tasks as clarifying their structure and physical properties. There are a pile of mysteries yet, however, including the unsettled hypothesis by Professor Penrose’s late colleague, British physicist Dr. Stephen Hawking, that black holes will eventually shrink and evaporate.
Where will the study of black holes end? Professor Homma noted: “By viewing things on a cosmic scale, we will eventually become able to understand truths about nature. We may even discover new laws of physics that could topple the theory of relativity. As we study the origin of galaxies, new discoveries might have indirect links to the origins of humans. It’s possible. In fact, what makes black hole research so fascinating is that you don’t know what you may find.”
(Find access to the story in its original Japanese here.)
Author: Yukiko Une, Staff Writer of the Science News Department, The Sankei Shimbun