2023-10-21 22:11:27
Image of a neutron star with strong magnetic force, provided by ESO/L. Calçada A neutron star is an ultra-dense celestial body formed when a star explodes. It seems that earthquakes similar to those on Earth are occurring there as well. Moreover, it is said to have a magnitude (M) of 17 or more. Professor Tomonori Toya of the University of Tokyo and his colleagues analyzed observation data from a radio astronomical observatory and published the findings in a British academic journal. When a star 8 to several dozen times more massive than the Sun burns out, it finally explodes into a supernova. What is left behind is a small celestial body called a neutron star. It is a star whose density is unimaginably high, with even its atoms being crushed by its great gravity. It has a radius of about 10 km, but it weighs as much as the sun. 1 billion tons per cubic centimeter. One cup of ochoko weighs as much water as the entire Lake Biwa. Another feature is that it has a strong magnetic field. A strange phenomenon called “high-speed radio burst,” in which sharp radio waves of about one-thousandth of a second are emitted from this neutron star, has been discovered and has been actively researched over the past 10 years. I don’t know the cause yet. Toya and colleagues analyzed data from a total of 7,000 fast radio bursts observed by the Arecibo Observatory in Puerto Rico and the FAST Observatory in China. The results showed that bursts tended to occur in clusters rather than in separate bursts. After the first burst occurs, several bursts often follow. It’s like the aftershocks of an earthquake. So, when we investigated the probability of subsequent bursts occurring after the first one, we found that it fits perfectly with the “Omori-Utsu law,” which expresses the probability of aftershocks occurring. Another common feature with earthquakes was that there was no relationship between the size of the initial burst and the subsequent bursts. Toya says, “It’s hard to imagine that this kind of coincidence could happen by chance, because earthquakes occur in a similar way to the Earth.” It is thought that the surface of a neutron star has a crust made up of neutrons that are solidified like crystals. This crust is pushed and distorted by the strong magnetic field generated inside the star, and when it can no longer withstand it, it cracks and earthquakes occur. A portion of the energy released then becomes a high-speed radio burst. A neutron star has a radius of about 10 km, but the gravity on its surface is 100 billion times that of Earth, and even a small fault can release a huge amount of energy. The energy of the high-speed radio wave burst alone is said to be equivalent to M17.5. The original size should be even larger. It’s an incredible earthquake. “If we make further comparisons with earthquakes on Earth, we may be able to explore the state of matter inside neutron stars,” Toya hopes. (Osamu Nagai)
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