Terme de Glossaire
In light emission, X-rays posess a shorter wavelength and therefore have more energy than UVs which are themselves more energetic than visible light. In astrophysics, the emission of X-rays has been studied since the second half of the twentieth century. They are absorbed by the atmosphere, so it was necessary to wait for the first space observations to detect them. The weak X-ray emissions of the Sun first led to the belief that stars emitted very few of them, but several years later, while preparing for the Apollo emissions, researchers serendipitously observed a strong X-ray emission coming from the Scorpion constellation. Since then, the study of X-rays has become a separate field of astrophysics.
Since 1999, the satellites Chandra (for NASA) and XMM-Newton (for the ESA) are entirely devoted to the emission of X-rays. They have enabled more in-depth studies of massive stars, and the measurement of the rotation of black holes.
