Pulsar planets are

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

s that are orbiting

pulsar A pulsar (''pulsating star, on the model of quasar'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its Poles of astronomical bodies#Magnetic poles, magnetic poles. This radiation can be obse ...

s. The first such planets to be discovered were around a

millisecond pulsar A millisecond pulsar (MSP) is a pulsar with a rotational period less than about 10 milliseconds. Millisecond pulsars have been detected in radio pulsar, radio, X-ray pulsar, X-ray, and gamma ray portions of the electromagnetic spectrum. The leadi ...

in 1992 and were the first extrasolar planets to be confirmed as discovered. Pulsars are extremely precise clocks and even small planets can create detectable variations in pulsar traits; the smallest-known

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...

is a pulsar planet. They are extremely rare, with only half a dozen listed by the

NASA Exoplanet Archive The NASA Exoplanet Archive is an online astronomical exoplanet catalog and data service that collects and serves public data that support the search for and characterization of extra-solar planets (exoplanets) and their host stars. It is part of ...

. Only special processes can give rise to planet-sized companions around pulsars, and many are thought to be exotic bodies, such as planets made of

diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Diamond is tasteless, odourless, strong, brittle solid, colourless in pure form, a poor conductor of e ...

, that were formed through the partial destruction of a companion star. The intense radiation and winds consisting of

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

positron The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...

pairs would tend to strip atmospheres away from such planets, thus making them unlikely abodes for life.

Formation

The formation of planets requires the existence of a

protoplanetary disk A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may not be considered an accretion disk; while the two are sim ...

, most theories also require a "dead zone" within it where there is no turbulence. There,

planetesimal Planetesimals () are solid objects thought to exist in protoplanetary disks and debris disks. Believed to have formed in the Solar System about 4.6 billion years ago, they aid study of its formation. Formation A widely accepted theory of pla ...

s can form and accumulate without falling into the star. Compared to young stars, pulsars have a much higher luminosity and thus the formation of a dead zone is hindered by the

ionization Ionization or ionisation is the process by which an atom or a molecule acquires a negative or positive Electric charge, charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged at ...

of the disk by the pulsar's radiation, which allows the magnetorotational instability to trigger turbulence and thus destroy the dead zone. Thus, a disk needs to have a large mass if it is to give rise to planets. There are several processes that could give rise to planetary systems: * "First-generation" planets are planets that orbited the star before it went

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

and became a pulsar: Massive stars tend to lack planets, possibly due to the difficulty in detecting them around very bright stars but also because the radiation from such stars would destroy the protoplanetary disks. Planets orbiting within about four

astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

s of the star risk being engulfed and destroyed when it becomes a red giant or red supergiant. During the supernova, the system loses about half of its mass and unless the pulsar is ejected in the same direction as the planet was moving at the time of the supernova, the planets are likely to detach from the system. None of the known pulsar planet systems are likely to have formed in this process. * "Second-generation" planets from material that falls back on the pulsar after a supernova: The material could theoretically reach a mass comparable to that of a protoplanetary disk, but is likely to dissipate too fast to allow the formation of planets. There are no known examples of planets around young pulsars. * "Third-generation" planets: A companion star is destroyed through the interaction with a pulsar, forming a low-mass disk. Pulsars can emit energetic radiation that heats the companion star, until it overflows its Roche lobe and is eventually destroyed. Another mechanism is the emission of

gravitational wave Gravitational waves are oscillations of the gravitational field that Wave propagation, travel through space at the speed of light; they are generated by the relative motion of gravity, gravitating masses. They were proposed by Oliver Heaviside i ...

s, which shrink the orbit until the companion star (in these cases often a

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

) breaks up. In a third mechanism, the pulsar penetrates the envelope of a larger star, causing it to break up and form a disk around the pulsar. Disks formed in these processes are much more massive than these formed through fallback and thus persist for longer times, allowing the formation of planets. They also contain heavy elements that are essential building blocks for planets, and part of the disk will be accreted by the pulsar and spins it up in the process. Alternatively, a light white dwarf is destroyed by the interaction with a more massive one; the light white dwarf gives rise to a debris disk that generates a planet while the larger white dwarf becomes a pulsar. * A companion star may be destroyed during the interaction with a pulsar but leave a planet-sized remnant, such a system is known as a "black widow". * Finally, it is possible that planets from companion stars or rogue planets are captured by a pulsar, or that a pulsar merged with the original host star of the planets. The latter process would form a "

common envelope In astronomy, a common envelope (CE) is gas that contains a binary star system. The gas does not rotate at the same rate as the embedded binary system. A system with such a configuration is said to be in a common envelope phase or undergoing comm ...

" which eventually breaks down to form a disk from which planets can develop.

Implications

The formation scenarios have consequences for the planets' composition: A planet formed from supernova debris is likely rich in

metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...

s and radioactive isotopes and may contain large quantities of

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

; one formed through the break-up of a

would be carbon rich and consist of large amounts of

; an actual white dwarf fragment would be extremely dense. , the most common type of planet around a pulsar is a " diamond planet", a very low-mass

. Other objects around pulsars could include

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

comet A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...

s and planetoids. More speculative scenarios are planets consisting of strange matter, which could occur much more close to the pulsars than ordinary matter planets, potentially emitting

s. Planets can interact with the magnetic field of a pulsar to produce so-called " Alfvén wings," these are wing-shaped electrical currents around the planet which inject energy into the planet and could produce detectable radio emissions.

Observability

Pulsar A pulsar (''pulsating star, on the model of quasar'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its Poles of astronomical bodies#Magnetic poles, magnetic poles. This radiation can be obse ...

s are extremely precise clocks and

pulsar timing Methods of detecting exoplanets usually rely on indirect strategies – that is, they do not directly Astrophotography, image the planet but deduce its existence from another signal. Any planet is an extremely faint light source compared to its ...

is highly regular. It is thus possible to detect very small objects around pulsars, down to the size of large

s, from changes in the timing of the pulsar hosting them. The timing needs to be corrected for the effects of the motions of Earth and the Solar System, errors in the position estimates of the pulsar and of the travel times of the radiation across the interstellar medium. Pulsars spin and slow down over time in highly regular fashion; planets alter this pattern through their gravitational attraction on the pulsar, causing a

Doppler shift The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described t ...

in the pulses. The technique could in theory be also used to detect exomoons around pulsar planets. There are limitations to pulsar planet visibility, however; pulsar glitches and changes in the pulsation mode can mimick the existence of planets. The first extrasolar planets to be discovered (in 1992 by Dale Frail and Aleksander Wolszczan) were the pulsar planets around PSR B1257+12. The discovery demonstrated that exoplanets can be detected from Earth, and led to the expectation that extrasolar planets might not be uncommon. the least massive known extrasolar planet (

PSR B1257+12 A PSR B1257+12 b, alternatively designated PSR B1257+12 A, also named Draugr, is an extrasolar planet approximately away in the constellation of Virgo. The planet is the innermost object orbiting the pulsar Lich, making it a pulsar planet in t ...

, only ) is a pulsar planet. However, the size and particular spectroscopic traits makes actually visualizing such planets very difficult. One potential way to image a planet is to detect its transit in front of the star: in case of pulsar planets, the probability of a planet transiting in front of pulsar is very low because of the small size of pulsars. Spectroscopic analyses of planets are rendered difficult by the complicated spectra of pulsars. Interactions between a planetary magnetic field, the pulsar and the thermal emissions of planets are more likely avenues of getting information on the planets. Pulsar planets have been invoked to explain certain astronomical phenomena, such as

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

bursts from soft gamma repeaters.

Occurrence

only about half-dozen pulsar planets are known, implying an occurrence rate of no more than one planetary system per 200 pulsars. Most of the planet formation scenarios require that the precursor be a binary star with one star much more massive than the other, and that the system survives the supernova that generated the pulsar. Both these conditions are rarely met and thus the formation of pulsar planets is a rare process. Additionally, planets and their orbits would have to survive the energetic radiation emitted by pulsars, including

gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

s and energetic particles ("pulsar wind"). This would be particularly important for

s that were spun up by accretion, while they formed X-ray binaries; the radiation emitted under these circumstances would evaporate any planet. Pulsars remain visible for only a few million years, less than the time it takes for a planet to form, thus limiting the chance of observing one. Based on the known occurrence rate of pulsar planets, there might be as many as 10 million of them in the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

. All known pulsar planets are found around

s, these are old pulsars that were spun up through the accretion of mass from a companion. there are no known planets around young pulsars; they are less regular than millisecond pulsars, increasing the pulsar timing error and thus making planet detection more difficult.

Confirmed pulsar planets

, - , M62H b , , , , ~ , ~ , , - , PSR B1257+12 b , () , 0.19 , 25.262 , 0 , ~ , ~ , - , PSR B1257+12 c , () , 0.36 , 66.5419 , 0.0186 , ~ , , - , PSR B1257+12 d , () , 0.46 , 98.2114 , 0.03 , ~ , , - , PSR B1620-26 b , , 23 , 34,675 , ~ , ~ , , - , PSR J1719-1438 b , , 0.0044 , 0.090706293 , 0.06 , ~ , , - , PSR J2322-2650 b , , 0.0102 , 0.322963997 , 0.0017 , ~ , , - , PSR J1748-2021H b , , 0.0111 , 0.360787526 , ~ , ~ , ~ , - , PSR J0636+5129 b , , 0.0036 , 0.0665513392 , ~ , 60 , , - , PSR J1807-2459 A b , , ~ , 0.07 , ~ , ~ , ~ , - , PSR B1802-07 b , , 0.008098 , 0.071092 , 0.0000003 , ~ , ~ , - , PSR J1211-0633 b , , 0.0116 , 0.38634962 , ~ , ~ , ~ , - , PSR J0312-0921 b , , 0.00465 , 0.0975 , ~ , ~ , ~ , - , PSR J1824-2452G b , , 0.004875 , 0.1046 , 0.0000003 , ~ , ~ , - , PSR J1928+1245 b , , 0.005825 , 0.1366347269 , ~ , ~ , ~ , - , PSR J1824-2452M b , , 0.00854 , 0.242519219 , ~ , ~ , ~ , - , PSR J1630+3550 b , , ~ , 0.315863166 , 0.00042 , ~ , ~ , - , PSR J2241-5236 b , , ~ , 0.1456722395 , ~ , ~ , ~ , - , PSR J1311-3430 b , , ~ , 0.065115 , ~ , ~ , ~ , -

M62H is a millisecond

located in the constellation

Ophiuchus Ophiuchus () is a large constellation straddling the celestial equator. Its name comes from the Ancient Greek (), meaning "serpent-bearer", and it is commonly represented as a man grasping a snake. The serpent is represented by the constellati ...

. It is located in the

globular cluster A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...

Messier 62, at a distance of from Earth. The pulsar was discovered in 2024 using the

MeerKAT The meerkat (''Suricata suricatta'') or suricate is a small mongoose found in southern Africa. It is characterised by a broad head, large eyes, a pointed snout, long legs, a thin tapering tail, and a brindled coat pattern. The head-and-body ...

radio telescope A radio telescope is a specialized antenna (radio), antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the r ...

. M62H has a rotational period of 3.70 milliseconds, meaning it completes 270 rotations per second (270 Hz). Its planetary companion has a minimum mass of and a median mass of , assuming a mass of for the pulsar. Its minimum density is of 11 g/cm. Assuming the median mass, it implies a maximum radius of . The planet takes just to complete an orbit, and is located at a distance equivalent to 0.49% of an

from M62H.

PSR B1257+12

The pulsar PSR B1257+12, parsecs away in the constellation

Virgo Virgo may refer to: Arts and entertainment * Virgo (film), a 1970 Egyptian film * Virgo (character), several Marvel Comics characters * Virgo Asmita, a character in the manga ''Saint Seiya: The Lost Canvas'' * ''Virgo'' (album), by Virgo Four, ...

, was confirmed to have planets in 1992 based on observations made with the

Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science F ...

. The system consists of one tiny planet with a mass of Earth masses and two Super-Earths with masses and times that of Earth, assuming that the pulsar has a mass of 1.4 solar masses. They most likely formed from a protoplanetary disk, probably generated from the partial destruction of a companion star.

Computer simulation Computer simulation is the running of a mathematical model on a computer, the model being designed to represent the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be determin ...

s have shown that the system should be stable for at least one billion years and that exomoons could survive in the system. The system resembles the inner

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

; the planets orbit the pulsar at distances comparable to that of Mercury to the Sun and may have comparable surface temperatures. Reports of additional bodies in this system might be due to solar disturbances.

PSR J1719−1438

A cthonian planet with a mass comparable to Jupiter but less than 40% of its radius orbits the pulsar PSR J1719-1438. This planet is probably the

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

-rich remnant of a companion star that was evaporated by the pulsar's radiation and has been described as a "diamond planet".

PSR B1620−26

A circumbinary planet with a mass of Jupiter masses orbits around PSR B1620-26, a binary star consisting of a pulsar and a

in the

M4. This planet may have been captured into the pulsar's orbit, a process which is particularly likely within the packed environment of a globular cluster, and may be about 12.6 billion years old, making it the oldest-known planet. Its existence may demonstrate that planets can form in

-poor medium including the globular clusters.

PSR J2322−2650

PSR J2322-2650 seems to have a roughly Jupiter-mass companion. The radiation from the pulsar could be heating it to about ; a light source observed close to the pulsar may be the planet. This pulsar is considerably less luminous than many, which may explain why the planet has survived to this day.

Debris disks and precursors

Timing variations of the pulsars

PSR B1937+21 PSR may refer to: Organizations * Pacific School of Religion, Berkeley, California, US * Palestinian Center for Policy and Survey Research * Payment Systems Regulator in the United Kingdom * Physicians for Social Responsibility, US Political par ...

and PSR J0738-4042 may reflect the existence of an

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...

around the pulsars, and collisions between asteroids or

s and pulsars have been proposed as an explanation for the phenomenon of fast radio bursts, the

gamma ray burst In gamma-ray astronomy, gamma-ray bursts (GRBs) are extremely energetic events occurring in distant galaxies which represent the brightest and most powerful class of explosion in the universe. These extreme electromagnetic emissions are second ...

GRB 101225A and other types of pulsar variability. There are no known

debris disk A debris disk (American English), or debris disc ( Commonwealth English), is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris ...

s around pulsars, although the

magnetar A magnetar is a type of neutron star with an extremely powerful magnetic field (~109 to 1011 T, ~1013 to 1015 G). The magnetic-field decay powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays.Ward; Br ...

s 4U 0142+61 and 1E 2259+586 have been suggested to harbour them. The white dwarf–pulsar binary PSR J0348+0432 may be a system that could develop pulsar planets in the future. The existence of a dust cloud at the pulsar Geminga that may be a precursor to planets has been proposed.

Candidates

There were earlier reports of pulsar planets which were either retracted or considered unconvincing, such as the 1991 "discovery" of a planet around PSR B1829-10 which turned out to be an artifact caused by the motion of the Earth. The existence of planets around the pulsar PSR B0329+54 has been debated since 1979 and is still unresolved . PSR B1828-11 has been conclusively established to display magnetospheric activity that mimicks planets, without having any, and a planet candidate around the pulsar Geminga was later attributed to timing noise. , - , PSR B0329+54 b , () , 10.26 , 10,140 , 0.236 , ~ , , - , PSR B1828-11 a , () , ~ , 231 , 0.14 , ~ , ~ , - , PSR B1828-11 b , () , ~ , 498 , 0.23 , ~ , ~ , - , PSR J1555-2908 c , () , ~ , 4,500 , 0.27 , ~ , ~ , - , PSR B0525+21 b , () , 10.35 , 10,132 , 0.96 , ~ , ~ , - ,

b , () , 11 , 11,400 , 0.2 , ~ , ~ , - , PSR J2007+3120 b , () , ~ , 723 , <0.38 , ~ , ~ , - , PSR J0337+1715 (AB) b , () , ~ , 3,000 , ~ , ~ , ~ , - , SGR 1806-20 b , () , 0.85 , 238 , 0.992 , ~ , ~ , - , PSR B1540-06 b , () , ~ , 1,473 , 0.12 , ~ , ~ , - , PSR B1714-34 b , () , ~ , 1,417 , 0.14 , ~ , ~ , - , PSR B1826-17 b , () , ~ , 1,102 , 0.35 , ~ , ~ , - , PSR B0144+59 b , () , ~ , 319 , 0.45 , ~ , ~ , - , PSR B1727-33 b , () , ~ , 350 , 0.26 , ~ , ~ , - , PSR B2053+36 b , () , ~ , 1,013 , 0.4 , ~ , ~ , - , PSR J1758-1931 b , () , ~ , 719 , 0.43 , ~ , ~ , - , PSR J1843-0744 b , () , ~ , 650 , 0.4 , ~ , ~ , - , PSR J1904+0800 b , () , ~ , 946 , 0.18 , ~ , ~ , - , PSR J2216+5759 b , () , ~ , 117 , 0.41 , ~ , ~ , - , PSR J1947+1957 b , () , ~ , 1,070 , 0.56 , ~ , ~ , - , PSR B1931+24 b , () , ~ , 5,180 , 0.25 , ~ , ~ , - , PSR B0823+26 b , () , ~ , 28 , 0.37 , ~ , ~ , - , SWIFT J1756.9-2508 b , , 0.0012346 , 0.0379907 , ~ , ~ , ~ , - , PSR J2007+3120 b , , ~ , 723 , ~ , ~ , ~ , - , PSR B0943+10 b , , 1.8 , 730 , ~ , ~ , ~ , - , PSR B0943+10 c , , 2.9 , 1,460 , ~ , ~ , ~ , -

Habitability

Pulsars emit a very different radiation spectrum than regular stars, with very little optical or

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

radiation but large amounts of

ionizing radiation Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...

and

pairs, which are generated by the pulsar's magnetic field as it spins. Additionally, remnant heat from before the pulsar's birth, heating of the pulsar's poles from its own radiation and from mass accretion processes drives the emission of

thermal radiation Thermal radiation is electromagnetic radiation emitted by the thermal motion of particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation. The emission of energy arises from a combination of electro ...

and

neutrino A neutrino ( ; denoted by the Greek letter ) is an elementary particle that interacts via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small ('' -ino'') that i ...

s. The electron-positron pairs and X-rays are absorbed by planetary atmospheres and heat them, driving intense atmospheric escape that can strip them away. The presence of a planetary magnetic field could mitigate the impact of the electron-positron pairs. Habitability is conventionally defined by the equilibrium temperature of a planet, which is a function of the amount of incoming radiation; a planet is defined "habitable" if liquid

can exist on its surface although even planets with little external energy can harbour underground life. Pulsars do not emit large quantities of radiation given their small size; the

habitable zone In astronomy and astrobiology, the habitable zone (HZ), or more precisely the circumstellar habitable zone (CHZ), is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressu ...

can easily end up lying so close to the star that tidal effects destroy the planets. Additionally, it is often unclear how much radiation a given pulsar emits and how much of it can actually reach a hypothetical planet's surface; of the known pulsar planets, only these of PSR B1257+12 are close to the habitable zone and , no known pulsar planet is likely to be habitable. Additional heat sources may be radioactive isotopes such as

potassium-40 Potassium-40 (K) is a long lived and the main naturally occurring radioactive isotope of potassium. Its half-life is 1.25 billion years. It makes up about 0.012% (120 parts-per notation, ppm) of natural potassium. Potassium-40 undergoes four dif ...

formed during the supernova that gave rise to the pulsar and

tidal heating Tidal heating (also known as tidal working or tidal flexing) occurs through the tidal friction processes: orbital and rotational energy is dissipated as heat in either (or both) the surface ocean or interior of a planet or satellite. When an objec ...

for planets with close orbits. Radiation from outside sources such as companion stars would also add to the energy budget.

Notes

References

Sources

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * {{Portal bar, Astronomy, Stars, Outer space Types of planet Pulsars