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PSR B1620−26 is a binary star about 12,400 light-years away in the constellation Scorpius (M4).
It is theorized that originally B1620−26 A had another, lower mass white dwarf companion, which was ejected when the current B1620−26 B interacted with the original binary system. At that time, B1620−26 B was still a main sequence star, with its planet (PSR B1620−26c). Whereupon, the planet settled into orbit around both stars.
The triple system is just outside the core of the globular cluster. The age of the cluster has been estimated to be about 12.7 billion years. Hence this is the age estimate for the birth of the planet, and two stars.
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Planet system
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PSR B1620−26c was originally detected through the Doppler shifts its orbit induces on signals from the star it orbits (in this case, changes in the apparent pulsation period of the pulsar).
In the early 1990s, a group of astronomers led by Donald Backer, studying what they thought was a binary pulsar, determined that a third object was needed to explain the observed Doppler shifts. Within a few years, the gravitational effects of the planet on the orbit of the pulsar and white dwarf had been measured, giving an estimate of the mass of the third object that was too small for it to be a star. The conclusion that the third object was a planet was announced by Stephen Thorsett and his collaborators in 1993.
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See also
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