Pulsar planets are

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...

s that are found orbiting

pulsar A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Ea ...

s, or rapidly rotating

neutron star A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...

s. The first such planets to be discovered were around a millisecond pulsar and were the first

extrasolar planets An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, in ...

to be confirmed as discovered.

History

Pulsar planets are discovered through pulsar timing measurements, to detect anomalies in the pulsation period. Any bodies orbiting the pulsar will cause regular changes in its pulsation. Since pulsars normally rotate at near-constant speed, any changes can easily be detected with the help of precise timing measurements. The discovery of pulsar planets was unexpected; pulsars or neutron stars have previously gone supernova, and it was thought that any planets orbiting such stars would have been destroyed in the explosion. In 1991, Andrew G. Lyne announced the first-ever pulsar planet discovered around PSR 1829–10. However, this was later retracted, just before the first real pulsar planets were announced. In 1992,

Aleksander Wolszczan Aleksander Wolszczan (born 29 April 1946) is a Polish astronomer. He is the co-discoverer of the first confirmed extrasolar planets and pulsar planets. Early life and education Wolszczan was born on 29 April 1946 in Szczecinek located in pre ...

and Dale Frail announced the discovery of a multi-planet

planetary system A planetary system is a set of gravitationally bound non- stellar objects in or out of orbit around a star or star system. Generally speaking, systems with one or more planets constitute a planetary system, although such systems may also consi ...

around the millisecond pulsar PSR 1257+12. These were the first two extrasolar planets confirmed to be discovered, and thus the first multi-planet extrasolar planetary system discovered, and the first pulsar planets discovered. There was doubt concerning the discovery because of the retraction of the previous pulsar planet, and questions about how pulsars could have planets. However, the planets proved to be real. Two additional planets of lower mass were later discovered by the same technique, although one has since been retracted. In 2000, the millisecond pulsar PSR B1620−26 was found to have a

circumbinary planet A circumbinary planet is a planet that orbits two stars instead of one. The two stars orbit each other in a binary system, while the planet typically orbits farther from the center of the system than either of the two stars. In contrast, circum ...

(

PSR B1620−26 b PSR B1620−26 b is an exoplanet located approximately 12,400 light-years from Earth in the constellation of Scorpius. It bears the unofficial nicknames "Methuselah" and "the Genesis planet" (named after the Biblical character Methuselah, who, ac ...

) that orbits both it and its companion

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...

, WD B1620–26. This was announced as the oldest planet ever discovered, at 12.6 billion years old. It is currently believed to have originally been the planet of WD B1620–26 before becoming a circumbinary planet, and therefore, while discovered through the pulsar timing method, it did not form the way that PSR B1257+12's planets are thought to have. In 2006, the magnetar 4U 0142+61, located from Earth, was found to have a

circumstellar disk A circumstellar disc (or circumstellar disk) is a torus, pancake or ring-shaped accretion disk of matter composed of gas, dust, planetesimals, asteroids, or collision fragments in orbit around a star. Around the youngest stars, they are th ...

. The discovery was made by a team led by Deepto Chakrabarty of MIT using the

Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003. Operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, ...

. The disk is thought to have formed from metal-rich debris left over from the

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or whe ...

that formed the pulsar roughly 100,000 years ago and is similar to those seen around Sun-like stars, suggesting it may be capable of forming planets in a similar fashion. However, pulsar planets would be unlikely to harbor life as we know it, due to the high amounts of

ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...

and low amounts of visible light emitted by pulsars. In 2011, a planet that is theorized to be the remaining core of a star that orbited a pulsar was announced. It orbits millisecond pulsar PSR J1719−1438, and represents a path to planetary status by evaporation of a star. The planet is estimated to have a density of at least 23 times that of water, a diameter of 55,000 km, a mass near that of Jupiter's, and a 2-hour, 10-minute orbital period at 600,000 km. It is thought to be the diamond crystal core remaining from the evaporated white dwarf, with an estimated weight of .

Formation

There are three types of pulsar planets known so far. The PSR B1257+12 planets were formed out of the debris of a merged companion star that used to orbit the pulsar when it was a white dwarf.Very long baseline interferometry astrometry of PSR B1257+12, a pulsar with a planetary system
/ref> In PSR J1719-1438, the planet most likely is the companion, or what's left of it after being almost entirely blasted away by the extreme irradiation from the nearby pulsar. PSR B1620–26 b is most likely a captured planet.

History

Formation

List of pulsar planets

Confirmed planets

Candidate planets

Protoplanetary disks (fallback disks)

Disproven planets

See also

References