2023-07-21 21:00:00
[사이테크+] Two-faced white dwarf ‘Janus’ discovered… “Hydrogen on one side, Helium on the other side” US research team “Observation of hydrogen and helium alternately every 15 minutes… The reason for the surface split is a mystery” (Seoul = Yonhap News) Reporter Lee Joo-young = When a star the size of the Sun consumes all of its hydrogen, only the core remains at the end and becomes a white dwarf. However, the discovery of a white dwarf with half of the star covered with hydrogen and half with helium is arousing curiosity. On the 22nd, Dr. Ilaria Caiazo of the California Institute of Technology (Caltech), USA, discovered a white dwarf with two faces (ZTF J203349.8+322901.1), in which the side made of hydrogen and the side made of helium are observed alternately as the star rotates, in the scientific journal Nature on the 22nd. said it did A white dwarf is the final appearance of a sun-sized star. As these stars get older, they consume all of their hydrogen in nuclear fusion, expand and become red giants, then lose all the gas on the surface and contract their cores to become high-temperature, high-density white dwarfs. Because of the strong gravity of a white dwarf, heavy elements sink to the center and the outer surface is surrounded by remaining hydrogen and helium. The sun is expected to go through this process in 5 billion years to become a white dwarf the size of the Earth. The research team nicknamed this two-faced white dwarf star ‘Janus’ after the Roman god. The star was first observed by the Palomar Observatory’s wide-area astronomical observation instrument, the Zwicky Instant Capture Facility (ZTF), operated by the California Institute of Technology. They found that the star’s brightness changed rapidly and confirmed that Janus rotates every 15 minutes through follow-up observations using the ‘Canary Large Telescope’ (GTC) instrument and the Palomar Observatory instrument in the Canary Islands, Spain. Then, observations at the WM Keke Observatory in Mauna Kea, Hawaii, captured only hydrogen and helium wavelengths alternately observed in the spectrometer at regular intervals when Janus rotated. This means that half of the star is covered with hydrogen and half with helium. However, it is not known why Janus is in this state. The research team proposed one hypothesis, saying that this is the first time such a white dwarf has been discovered, and that we may be witnessing a rare phenomenon in white dwarf evolution. “In some, but not all, white dwarfs, the surface of a star undergoes a transition from hydrogen to helium,” said Dr. Caiazo. What happens remains a mystery. “The answer may lie in the magnetic field,” said Dr. Caiazo. “The magnetic field can inhibit the mixing of matter. Magnetic fields around stars tend to be asymmetric or one side is stronger, so mixing does not occur on the side where the magnetic field is stronger, so there can be only hydrogen.”<저작권자(c) 연합뉴스, 무단 전재-재배포 금지>
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