Hercules X-1
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Artist's impression of Her X-1. Credit:
D. Klochkov
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An X-ray pulsar that is a member of
an eclipsing binary system with an orbital
period of 1.7 days; it lies about 15,000 light-years away in the constellation
Hercules. The visible component has been identified
as the blue variable HZ Herculis, whose spectrum varies from late A or early
F to B. Her X-l has a pulsation period of 1.2378 seconds, presumed to be
its rotation period, and shows a 35-day quasi-periodicity in the X-ray region
(but not in the optical). It is thought to move in a nearly circular orbit,
to be accreting matter from HZ Her, and to have a mass of about 0.7 solar
mass. The orbital period is stable, but the pulsation period is speeding
up at a rate of about 1 part in 100,000 per year. The X-ray eclipse lasts
0.24 days.
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