Modeling the Light Curve of an X-ray Binary
![x-ray binary](../../../Images/basic/gamma/accretion.gif)
Artist's conception of an X-ray binary,
showing the normal star and disk of gas surrounding the neutron
star. X-rays are emitted in the region nearest the neutron star.
X-ray binaries are two-star systems composed of one normal star and a
"compact star" (usually a neutron star or a black hole). X-ray
binaries emit x-rays because gas from the normal star flows
toward the compact star . As it gets near the compact star, the gas
density and pressure increase, causing a rise in temperature of the
gas. The gas gets hot enough (a few million degrees) to glow in
x-rays. This leads us to a fundamental concept.
Fundamental Concept:
- The more gas there is, the brighter an x-ray binary will shine in
x-rays
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By brightness, we also mean the intensity of the x-rays. Since most
x-ray satellites count the number of x-rays from a source, we would
also say that more gas leads to more x-rays.
The brightness of some x-ray sources is constant. But the brightness of
others can vary.
You now have an idea for why the x-ray intensity from an x-ray binary
might vary. Our next step is to become familiar with the Hera
software and a light curve data set for GX301-2. After that, we will
look for a period in the data.
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