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Pulsar Timing Method

Pulsar Timing is the method that was used in 1992 by Aleksander Wolszczan and Dale Frail to detect the first confirmed exoplanets. These exoplanets orbit a pulsar, which is a rapidly rotating neutron star. A neutron star is the extremely dense remnant of a star that exploded as a supernova. As they rotate, pulsars emit intense electromagnetic radiation that is detected on Earth as regular and precisely timed pulses, which are so regular they are more accurate than an atomic clock. Known pulsars have rates ranging from a few miliseconds to several seconds, depending on the speed of the star's rotation. Slight regular variations in the timing of the pulses indicate that the pulsar is moving back and forth, orbiting the center of mass of a system with one or more planets. Astronomers can deduce the orbit as well as the mass of these planets by precisely measuring irregularities in the timing of the pulsars. The method is so sensitive that it can detect planets as small as one tenth the mass of Earth! However, pulsars are relatively rare celestial objects and as of November 2022, 48 extrasolar planets have been discovered by this method. Life as we know it could not survive on these pulsar orbiting planets because the high-energy radiation emitted by the pulsars there is extremely intense.

Pulsar timing method diagram showing a planet orbiting a pulsar and how this causes a slight but regular change in the pulsation period. The diagram also shows that from the observer's viewpoint, the pulsar appears to flash periodically as it rotates, when the emitted beam of radiation from the pulsar faces directly towards the observer.

Pulsar timing method diagram. The emitted electromagnetic radiation from a rotating pulsar is detected as regular and precisely timed pulses on Earth. Slight variations in the pulsation period indicate the pulsar is orbiting a center of mass due to one or more orbiting planets. Image credit: Alice Hopkinson, LCO