Some massive stars, which expand and emit red light after entering the twilight years, are called "red supergiants". They continue to evolve and will become "supernovae". A supernova explosion means that the life of a star will come to an end.
Recently, the Purple Mountain Astronomical Observatory of the Chinese Academy of Sciences and Tsinghua University jointly captured the moment of 1 hour after the death of a massive star for the first time, and witnessed the strange phenomenon of very early shock wave radiation turning from red to blue for the first time, providing a new clue for unraveling the mystery of star death. The results were published online in Nature on December 14.
The supernova explosion "That Flash" was photographed
Located about 22 million light-years from Earth, Galaxy M101 is one of the closest galaxies to Earth and has long been a favorite subject for astronomy enthusiasts due to its unique windmill shape.
On May 19 of this year, Japanese amateur astronomer Koichi Itagaki took a photo of a supernova explosion at SN101ixf in the M2023 galaxy. Wang Xiaofeng, a professor at Tsinghua University and a visiting researcher at the Purple Mountain Observatory, realized the significance behind the supernova discovery, and his joint research team quickly contacted astronomy enthusiasts and obtained color images covering the pre- and post-explosion periods.
How valuable these images are for scientific research depends on the scientist's ability to "decipher" them.
△SN2023ixf very early optical metering data. b-d: Single-band metering data extracted from RGB color images. i-o: The rapid evolution of SN2023ixf from red to blue can be seen from 1.4 hours to 5.7 hours after the explosion of the synthetic supernova.
Astronomy enthusiasts use detectors that have not undergone rigorous specifications and standardized testing, and there are certain differences from scientific-grade detectors for professional astronomical research, and it is not easy to obtain valuable data from them.
However, it is worth the effort to "decipher". According to the researchers, massive stars usually produce core-collapsing supernovae due to the termination of nuclear fusion at the end of their evolution. The shock wave caused by the gravitational collapse can break through the star's outer atmosphere for a short period of time, producing instantaneous radiation. These very early radiation signals are key to revealing the shock wave propagation process, supernova explosion asymmetry, and the peristellar environment. However, at present, the international observation of supernova shock radiation is very scarce, especially the lack of multi-band information, which leads to the fact that human understanding of supernova is still very limited.
Interpreting color images to reveal the "last ray" of the stellar twilight
The team of Ph.D. students at Tsinghua University, Li Gates, and Li Wenxiong, a postdoctoral fellow at the National Astronomical Observatories of the Chinese Academy of Sciences, successfully extracted the multi-band photometric data from the observation data of astronomy enthusiasts for the first time, and obtained reliable SN2023ixf extremely early multi-color photometric data.
These data shed light on the anomalous color evolution of early shock wave radiation, laying the groundwork for important discoveries. Hu Maokai, a postdoctoral fellow at the Purple Mountain Observatory, and Yang Yi, a postdoctoral fellow at the University of California, Berkeley, were responsible for the model fitting part of early radiation.
After considering the physical processes such as shock wave radiation, peristellar dust ablation, and peristellar matter interaction, the multi-band photometric and temperature evolution of early shock radiation of SN2023ixf is reasonably explained.
△Fitting of SN2023ixf extremely early multi-band light curves. By combining the physical processes such as shock wave breakthrough, extinction caused by rapid ablation of dust, and peristellar matter interaction, the multi-band light variation curve of SN2023ixf during the rising period can be reasonably explained.
The Purple Mountain Observatory postdoctoral fellows Tianrui Sun and Lei Hu and Ph.D. student Jian Chen used the Antarctic Survey Telescope AST3-3 and the Yao'an High Precision Telescope (YAHPT) at the Yao'an Observatory of the Purple Mountain Observatory to carry out fast follow-up observations of SN2023ixf, and obtained a good multi-band light curve during the rising period, which provided important observation data for the circumferential environment of SN2023ixf and provided important help for model fitting.
△南极巡天望远镜AST3-3
The color images reveal the entire process of a red supergiant star about 85 million times the size of the Sun from death to eruption, forming the supernova 2023ixf explosion. Detailed multi-band observations clearly show the strange phenomenon of red shock waves that break out of the cocoon at the very early stage of the red supergiant explosion and gradually transform into blue. This never-before-seen color image subverts the traditional theoretical framework of the expectation that the moment of star death is accompanied by a blue shock wave breakthrough.
The research team believes that the gradient shock wave from red to blue indicates that the star was dying and was surrounded by a thick dust shell. As the shock wave spread rapidly, the dust was destroyed in just a few hours. The shock wave breakthrough from red to blue is like lifting a thick veil of dust that envelops a dying star. This research has significantly advanced the understanding of the late evolution and death of massive stars, a common and mysterious spectacle in the universe.
△ Yao'an high-precision telescope
Perhaps we have a chance to see a supernova explosion with the naked eye
Supernova explosions are one of the most spectacular astronomical events in the universe, and will the average person have a chance to observe them with the naked eye?
It's possible. There have been many records of supernova explosions in ancient China, the most famous of which is a magical celestial phenomenon during the Northern Song Dynasty. Jingde three years (AD 1006) April Wuyin, Zhou Boxing saw, out of the south, riding the official west once, like a half moon, there are mangjiao, Huanghuang can be identified, the library building east. According to the records of the "History of the Song Dynasty and the Astronomical Chronicles", this supernova can shine at night when it is brightest, and can be used to distinguish objects at night, and it lasted for a year and four months before disappearing.
According to foreign historical sources, Japan, Iraq, Egypt and Europeans have also seen this supernova shining in the night sky. Modern astronomers refer to the supernova seen in 1006 as "Supernova 1006" (SN 1006).
Today, astronomy enthusiasts are staring at Betelgeuse in the constellation Orion, which is considered "the most promising supernova". Currently, the star is still in the state of a red supergiant, about 640 to 724 light-years away from Earth, and can be seen with the naked eye. Scientists believe that it is nearing the end of its life cycle. But due to the complexity of the star's evolutionary process, no one can say for sure exactly when it exploded, perhaps in a few years, or hundreds of thousands of years later.
Modern Express + reporter is Zhong Yin
(Photo courtesy of the Purple Mountain Observatory of the Chinese Academy of Sciences)
(Proofread by Xu Yuanhua)