Observatoire de Paris
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Artistic reproduction of an extrasolar planet around a pulsar.
Copyright : Paris Observatory / UFE

In 1970, David Richards noticed an anomaly in the periodicity of a signal from the Crab pulsar, discovered one year before. He proposed three explanations :

  • A precession effect,
  • A vibration of the pulsar
  • or a perturbation due to the presence of a planet with a period of 11 days.

The vibration hypothesis was considered to be the correct one. On the other hand, in 1991, Andrew Lyne published the discovery of a planet around PSR 1829-10, from observations with the radiotelescope of Jodrell Bank.

In January 1992, the same day Lyne retracted his discovery (he didn't take into account the eccentricity of the orbit of the Earth), Alexander Wolszczan announced the discovery of two planets (with a period of 67 days and a mass of 3,4 MJ for the first one, and a period of 90 days and a mass of 2,8 MJ for the second one) around PSR 1257+12 !

This time, the observations of Wolszczan at Arecibo were confirmed by Dale Frail in VLA. Moreover, the study of the system enabled us to highlight a 3:2 gravitational resonance between the two planets.

The existence of these strange planets seemed to be truly real, since in 1994 a second pulsar, PSR B1620-26, was found to have a planet of mass 2,5 MJ.