Abstract
FOUR X-ray sources have been identified1,2 with globular star clusters (NGC1851, NGC6441, NGC6624 and M15). These are the first X-ray sources to be optically identified with the oldest component (age∼1010 yr) of the stellar population of our Galaxy; previous identifications of galactic X-ray sources were mostly with bright, young, Population I stars or with relatively recent supernova remnants. Katz3, Clark4 and Canizares and Neighbours5 have discussed the apparent differences in frequency and population between the globular cluster X-ray sources and other galactic X-ray sources. They have assumed that the X-ray sources in globular clusters are, like the sources identified with Population I stars, binary stars in which a normal companion transfers mass on to a collapsed star, thereby producing X rays.
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