X-ray Binary Stars
If human eyes could see X-rays rather than optical light, we would see a very different sight when looking at the sky. We would be overwhelmed by a few hundred very bright stars, mostly concentrated towards the center of our galaxy. Most of these stars would be X-ray binaries, where a black hole or neutron star is devouring material from its companion star. Because humans do not see naturally in the X-ray spectrum, we invented telescope observatories to expand our vision capabilities, and to provide a unique probe into how the universe operates under extreme physical conditions.
X-ray binaries are a special class of binary stars. They are made up of a normal star and a collapsed star (a white dwarf, neutron star, or black hole). These pairs of stars produce X-rays if the stars are in close enough proximity that material is pulled off the normal star by the gravity of the dense, collapsed star. The additional material accreted onto the surface must go through a violent transition region called the "boundary layer." In the boudary layer, friction within the disk heats up the accreting material to temperatures exceeding a million degrees, and forces the material to spiral down gradually onto the white dwarf surface. Scientists think the X-rays primarily come from the boundary layer.
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Last Modified: December 2010
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