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X.ray bursters are a class of binary stars which are
luminous in X-rays. They contain a neutron star and a low-mass companion star. The companion fills its Roche lobe and therefore the neutron star is accreting matter from it. The inflowing gas forms an accretion disk around the neutron star. Sometimes X-ray bursters show a sudden
increase in their X-ray luminosity, called X-ray burst. All properties of the X-ray bursts can be explained
assuming that they result from nuclear fusion on the surface of a
neutron star. The accumulated hydrogen-rich gas forms a layer on the
surface. This layer ignites spontaneously as the pressure at the bottom of the layer is high enough.
Luminous X-ray bursts can be considered standard candles, as the
mass of neutron star determines the luminosity of the burst. Therefore, comparing the observed X-ray flux to the predicted value,
relatively accurate distances can be determined. Observations of X-ray bursts allow also the determination of the radius of the
neutron star.
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