Disclaimer: machine translated by DeepL which may contain errors.
A black hole is a celestial body whose gravity is so strong that not even light can escape, and it is one of the most mysterious objects in the universe. Although predicted 100 years ago based on Einstein's general theory of relativity, it was initially thought to be a hypothetical theoretical object because its properties were so out of the ordinary. Later, however, it was shown that when a heavy star burns out, it becomes a black hole, and quasars, the brightest objects in the universe, were thought to be giant black holes that shine brightly while sucking in gas. Furthermore, at the end of the 20th century, the motion of a star at the center of the Milky Way Galaxy indicated the existence of a black hole with a mass of 4 million solar masses (subject of the 2020 Nobel Prize in Physics), and research over the past 100 years has made black holes unquestionable.
However, despite years of research, "visual" evidence of black holes remained elusive until recently. As the saying goes, "Seeing is believing" and "seeing is believing," human beings are creatures who value sight among their various senses, and scientists are no different in thinking, "If there is a black hole, I want to see it! Scientists are no different.
Even so, a black hole is a celestial body that absorbs even light, so it is impossible to see it directly. The only way is to see the black hole as a "shadow picture" against the background of ambient light. Moreover, since the apparent size of a black hole is small, extremely high vision is required. For this reason, we have synthesized the Earth-sized telescope EHT (Event Horizon Telescope), which combines radio telescopes from around the world. Hundreds of scientists from around the world worked for more than 10 years to achieve a value of 3 million with human eyesight by observing radio waves of 1.3 mm wavelength with a telescope of 11,000 km in diameter. The result is a photograph of the shadow of a black hole (Figure). On the left is a giant black hole at the center of the Milky Way (announced in 2022), and on the right is a giant black hole at the center of the elliptical galaxy M87 (announced in 2019). Both images show a doughnut-like ring and a black hole at the center. The ring is a structure created by light orbiting the black hole, and the black hole in the center is the shadow of the black hole. These photographs provide visual confirmation of the existence of a black hole, a celestial body from which not even light can escape.
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| A giant black hole photographed by the international project EHT. On the left is Sagittarius A, the center of the Milky Way Galaxy, and on the right is the black hole at the center of the elliptical galaxy M87. In both cases, the black hole is captured as a shadow against the background of radio waves around the black hole. The lower panel shows a larger-scale image taken by the East Asian VLBI Network (EAVN), where the presence or absence of a jet is a prominent difference between the two objects. | ||
While the existence of black holes has been confirmed over the past 100 years, there are still many mysteries that need to be solved. For example, the two black holes in the figure have very different properties in terms of whether they have jets or not. This is thought to be due to the difference in the amount of gas sucked into the black holes, but the detailed radiation mechanism of the jets is unknown and is a subject for future research. In particular, there is a theory that the jet is accelerated by extracting energy from the spinning black hole, and further verification is awaited. The motion of matter around a black hole is expected to provide a new test of the general theory of relativity, and if any fraying of the theory is found, it will lead to a breakthrough in physics. In this field, it is expected that we will be able to see moving images of the area around a black hole in the future, and I have great expectations that some of the young people who will lead the next generation of researchers will take up the challenge of solving the mysteries of black holes.
Published in the September 2022 issue of Faculty of Science News