As the mass increases, the brightness of the star increases


Supernova explosion scene (left) and the parent star before the supernova explosion ⓒ anglo australian observatory
Supernova explosion scene (left) and the parent star before the supernova explosion ⓒ anglo australian observatory

A heavy star as defined in astronomy refers to a star with a mass of approximately eight times the mass of the sun. So, how are the characteristics of these heavy stars different from those of relatively small stars like the sun? It is also said that the moment such a star dies from old age, it causes a supernova explosion or becomes a black hole.


The more researchers study space, the more my curiosity increases, and the 6th lecture of Space Opera, an event that can solve such a curiosity, was held online on the 7th and received enthusiastic responses from participants


Professor Yoon Seong-cheol of Seoul National University's Department of Physics and Astronomy, presented on the subject of ``supernova, neutron stars, and heavy stars that become the mother of black holes, was filled with a feast of knowledge that satisfies the thirst of participants wondering about the cause of the black hole.


Organized by the Chaos Foundation, established with the aim of popularizing science, this event was designed with the intent to view everything related to space, including the solar system, planets, and galaxies, from a variety of perspectives from experts.


As the mass increases, the brightness of the star also increases.


Prior to the full-scale lecture, Professor Yoon said, if you look closely at the stars shining in the sky, you can see that they are all different. For example, like Rigel in the constellation Orion, the more blue the star is, the higher the temperature and mass of the star.


The relationship between a star's mass and its brightness is one of the laws of astrophysics. As a law that grasps a phenomenon in which the brightness of a star increases a lot even with a slight increase in mass, British astronomer Arthur Eddington discovered.


Professor Yoon introduced, when a star heavier than the sun completes the hydrogen fusion reaction, it becomes a huge red supergiant like Betelgeuse. It collapses into a black hole and dies.


Interestingly, of the hundreds of billions of stars in our galaxy, heavy stars make up only 0.5%, but heavy stars play a very important role in the history of the universe and the origin of life.


According to Professor Yun's explanation, the evolution to heavy stars all began with the nuclear fusion of hydrogen. In fact, astronomers in the past have questioned how stars, including the sun, can produce so much energy for a long time.


In the case of the sun alone, it has continuously released 4 trillion watts of energy every year for 4.5 billion years, because it was an energy system that was difficult to interpret at the level of science and technology in the past.


The scientist who solved such a question was Arthur Eddington, the one I introduced earlier. In the 1930s, he proposed the hypothesis that the solar energy source would be a hydrogen fusion reaction, based on Einstein's theory.


Later, German astronomer Hans Bethe succeeded in proving this theoretically in 1939. Since then, nuclear fusion has been studied along with fission during the development of the atomic bomb, and the first hydrogen bomb test in history was conducted in 1952, confirming that the solar energy source is a hydrogen fusion reaction.


Heavy stars lead to supernova explosions


Last year, NASA and the European Space Agency (ESA) drew attention by releasing images of shock waves emitted when a supernova explodes and dies in space 2,400 light-years away using the Hubble Space Telescope.


The exploding supernova is about 20 times the mass of the Sun and the scientists who filmed it estimated that the remnant of the supernova explosion was the outermost edge of the shock wave from the explosion 20,000 years ago.


A supernova refers to a phenomenon in which a star that is dark enough to be difficult to observe in ordinary times suddenly causes a large explosion and increases in brightness. When a star explodes, it suddenly brightens and looks like a new star. Among them, it is called a supernova because its brightness is particularly bright.


Professor Yoon explained, Supernovae are hundreds of millions of times brighter than the sun, and as many as hundreds of billions of times brighter.


He also mentioned the existence of gamma rays following the supernova explosion. Gamma rays are one of the deadliest cosmic radiations, and scientists estimate that gamma rays may have been involved in at least one of several major extinctions that Earth has experienced.


In fact, according to data released last year by researchers at the University of Illinois in the United States, it is highly likely that cosmic radiation from a supernova explosion is the cause of the mass extinction that occurred about 360 million years ago.


Because of the gamma rays that contributed to the global extinction, people are often worried about the tragedy again. However, a review by Dutch researchers in the past reveals that the Earth is safe from gamma-ray explosions.


He said, at the conclusion of the presentation, Professor Yoon said, Kilonova is the observational evidence that neutron stars collided.

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