In the 1930s, astronomers observing the night sky discovered a peculiar celestial object. This object exhibited a spectrum that indicated it was both cold, at temperatures of only two to three thousand degrees, and hot, reaching tens of thousands of degrees. This phenomenon of coexisting cold and hot temperatures puzzled astronomers. In 1941, the astronomical community named it a 'symbiotic star.' For decades, astronomers have made significant efforts to unravel this mystery. The late Chinese astronomer and former director of the Beijing Astronomical Observatory, He Maolan, conducted observational studies on symbiotic stars in France during the 1940s and 1950s, followed by contributions from other Chinese astronomers.
Half a century has passed, yet the mystery of symbiotic stars remains unsolved. Initially, some astronomers proposed the 'single star' theory, suggesting that the center of a symbiotic star is a red giant surrounded by a layer of hot nebula. However, the coexistence of the red giant's low temperature and the nebula's high temperature posed a challenge. Others proposed the 'binary star' theory, arguing that a symbiotic star consists of a cold red giant and a hot dwarf star in a binary system. However, due to the limitations of observational technology at the time, it was impossible to directly observe the motion of the binary stars. With advancements in observational techniques, astronomers began to conduct extensive observations of symbiotic stars across X-ray, ultraviolet, visible light, infrared, and radio wavelengths, accumulating a wealth of data. In recent years, high-precision radial velocity measurements and radio observations have provided increasing evidence supporting the idea that symbiotic stars may consist of a low-temperature red giant or supergiant, a high-temperature hot star, and a surrounding common hot nebula.
Some astronomers have proposed a theoretical model suggesting that the low-temperature giant or supergiant in a symbiotic star continuously expands and ejects material, forming a massive accretion disk, which generates strong shock waves and high temperatures during the accretion process. Certain symbiotic stars belong to the nova-like category, frequently undergoing eruptions that increase their brightness by several dozen times. However, the binary star theory has not yet established its position definitively, as the hot star has yet to be directly observed. Future research will focus on enhancing measurements of binary star orbits and further gathering data on cold stars to explore their stability.
Unraveling the mystery of symbiotic stars is crucial for the study of stellar physics and stellar evolution. However, more efforts are needed to fully solve this enigma.
