Dwarf outshines star

The star Sirius is the brightest star visible in the northern hemisphere. As realized in 1862, the star has a companion - a small, faint, hot star known as a white dwarf. White dwarfs represent the end stages of the evolution of relatively "low mass" stars (i.e. stars which have a mass near that of our Sun): they're actually the remains of the evolved star's core. They pack about 1 solar mass into a volume the size of the earth, which means that they are extremely dense, and have strong gravitational fields. When young they are very hot (with temperature of 10 thousand to 100 thousand degrees), hot enough to emit X-rays. The X-ray image above was taken with the High Resolution Camera (HRC) on the Chandra (X-ray observatory). In this X-ray image the white dwarf companion is much brighter than the visual primary star. The bright "spokes" in the image are produced by X-rays scattered by the support structure of the Low Energy Transmission Grating (LETG) which was in the optical path for this observation. This observation is particularly fitting, since the namesake of the Chandra Observatory, Subrahmanyan Chandrasekhar, developed the theoretical understanding of the structure of white dwarfs.

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Page Author: Dr. Michael F. Corcoran
Last modified February 25, 2001