Illustration of a planetary system around the pulsar PSR1257+12 (bright object at top right). Two planets with masses of 2.8 and 3.4 terrestrial masses were detected orbiting at a distance of 0.47 and 0.36 AU from the pulsar (1 AU = 1 Astronomical Unit - about 150 million km). The interaction between the planets and the pulsar was detected as a periodic change in the rotational period of the pulsar. Pulsars are neutron stars and their main feature is the emission of a flash of energy concentrated into a narrow beam. They are usually found in binary stellar systems and their strong gravitational force extracts gas (pink clouds) from their companion star. Reference: Nature Vol. 355 9-1-1992 pag. 145.