White or red?
Sirius is the brightest white star in our galaxy. Why did ancient astronomers say it was red? A group of American astronomers has just proposed a response. They start from the hypothesis that a dwarf star can become super giant and contract it again in a short space.
Sirius is a stable star and his friend the white nano Sirius B. A series of analyses have revealed that Sirius B is composed almost entirely of highly compressed carbon dioxide. Above it there is a thin layer of helium and an atmosphere of hydrogen.
The enormous heat produced by the fusion of helium and hydrogen led to the expansion of the atmosphere and became thousands of times larger than its initial size. The white dwarf became a red giant. When the temperature decreased, the star recovered the initial size. According to this theory, what the Romans knew as the red star of the dog is not their nano friend Sirius.
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