Artist's concept of a binary system

Introduction to X-ray Binaries

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What are X-ray Binaries?

Binary star systems contain two stars that orbit around their common center of mass. Many of the stars in our galaxy are part of a binary system. A special class of binary stars is the X-ray binaries, so-called because they emit X-rays. X-ray binaries are made up of a normal star and a collapsed star (a white dwarf, neutron star, or black hole).

How does X-ray Astronomy Fit In?

X-ray binaries were discovered by rocket flights in the 1960s. These objects were bright in X-rays but were rather faint optically. More observations with Uhuru showed them to be pulsating regularly and to show X-ray eclipses when observed for longer periods. The only explanation was a close binary system in which a rapidly spinning neutron star was responsible for the X-rays. Because the binary periods were so fast, it was recognized that these systems must be so close as to be interacting, with mass exchanged from the "normal" star to the compact star. As the matter falls in toward the compact object, it is heated to X-ray temperatures.

There are two main types of X-ray binaries: Massive X-ray Binaries (MXRBs) and Low-Mass X-ray Binaries (LMXBs). In MXRBs, material is transferred via a strong stellar wind from a massive O- or B-type star to the compact object. In LMXBs, the lower mass stars don't have strong stellar winds. They require "Roche lobe overflow" to transfer matter to the compact object. This occurs through the inner Lagrangian point, L1.

Further Binary Resources and References

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