Seongcheol Yoon, Professor, Department of Physics and Astronomy, Seoul National UniversityReal images of the black hole at the center of our galaxy have recently been captured. This is an achievement achieved by the ‘Event Horizon Telescope (EHT)’ international joint research team, in which domestic astronomers from the Korea Astronomy and Space Science Institute, Kyungpook National University, Seoul National University, and Yonsei University are also participating.
A black hole, which means ‘black hole’, is a phenomenon created by matter with a very strong gravitational force. This phenomenon occurs because the gravity at the center is so strong that even light cannot escape. If a black hole was alone in a remote place, it would not be possible to directly confirm its existence through light. But if the light-emitting material surrounds the black hole, the story is different.
For example, what would it look like if you pierce a hole in the middle of a piece of white paper with an awl? The surface of the paper looks white to our eyes due to the reflected light, but the hole in it will appear as a black dot because light only passes through it and does not reflect it.
The process by which the EHT research team obtained images of the supermassive black hole at the center of our galaxy is similar. This black hole is surrounded by gases such as hydrogen and helium. However, this disk-shaped gas emits bright light in the propagation region. This made it possible to directly identify the black hole, the central region where no light is emitted.
The mass of the black hole captured this time is 4.3 million times that of the Sun. However, the radius of this black hole is only 22 million km, which is smaller than the distance between the Sun and Mercury of 36 million km. Previously, the EHT research team captured an image of a giant black hole at the center of the galaxy ‘M87’, which is 53 million light-years away from our galaxy in 2019. This black hole has a mass of 6.5 billion times that of the Sun and a radius of 2,000 times that of the central black hole of our galaxy. However, compared to the total size of the M87 galaxy, it is only a dot smaller than a particle.
In fact, you need a high-resolution telescope to see these ‘small’ black holes. The resolution increases as the size of the telescope increases. A radio telescope as large as the diameter of the Earth could achieve such a precise resolution that an orange on the moon’s surface could be discerned from the ground. To this end, the EHT research team built a radio interferometer system equivalent to the size of the Earth by connecting several radio telescopes spread around the world. This virtual giant radio telescope was finally able to obtain an image of a black hole.
The existence of black holes was already predicted 100 years ago in 1915 by German mathematician Karl Schwarzschild in the process of solving the equations of the general theory of relativity. Since then, numerous scholars have been studying how the physical environment around the black hole changes depending on the black hole mass and angular momentum.
This observation paved the way for a deep understanding of the characteristics of the giant black hole at the center of our galaxy and precise verification of various predictions of the general theory of relativity. This will give us a clearer understanding of how giant black holes formed and how they influenced the formation and evolution of our galaxy.
Black holes are the most popular topic of public lectures by scientists. This is probably because it is a bizarre phenomenon that cannot be seen in everyday life. Black holes have brought new experiences to mankind. It also makes us realize the role of science and the reason for space exploration.
Science has two main roles. One is to explain various empirical phenomena through natural laws, and the other is to broaden the horizon of the world of experience. The former makes science obsolete by some. Because once a phenomenon is explained, it is no longer mysterious. Things that once belonged to the sacred realm, such as rainbows, stars, and life, have all been explained and secularized in the name of science. Some will judge that it is worth it because mankind has achieved a brilliant scientific and technological civilization in return, while others will still miss the romance of myths and fantasy.
However, the true value of science goes beyond simply explaining empirical phenomena and developing practical skills through them. As you can see in the example of black holes, science can make our hearts flutter and flutter as much as myths and fantasy. Because science leads us to a new world that mankind has never experienced before.
The vast universe that escaped the celestial theory, the bending of space-time due to gravity, the big bang, and the black hole were all like fantasy at one time. Science has transcended the limits of finite humans through the two wings of ‘logical reasoning’ and ‘creative experimentation and observation’.
Galileo Galilei, the first to observe celestial bodies through a telescope, opened the way for mankind to advance into the vast universe outside the solar system. British astronomer Arthur Eddington brought the theory of general relativity from fantasy to the real world by observing the bending of starlight due to the gravitational field of the sun. The discovery of cosmic background radiation by American astronomers Arno Penzias and Robert Wilson even extended human experience to the Big Bang.
Through the black hole image captured by the EHT research team, we are now experiencing a black hole as well. Black holes are still mysterious and difficult to understand, but we are living in an era of experiencing black holes.
The James Webb Space Telescope (JWST) was sent to space by NASA in December of last year. It is expected that they will find clues about extraterrestrial life. photo source wikipediaSpace exploration in the 21st century will lead mankind to another new world. For example, the ‘James Webb Space Telescope (JWST)’, which was launched at the end of last year and became a hot topic, is highly likely to give humankind evidence that there is life on exoplanets soon. On the 21st, everyone was delighted with the success of the Korean launch vehicle Nuri (KSLV-II). It was a milestone indicating that South Korea was now ready to take the lead in space exploration. In this way, our horizons are expanding.
Seongcheol Yoon, Professor, Department of Physics and Astronomy, Seoul National University
