| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Virgo[1] |
| Right ascension | 13h 00m 03.1075s[2] |
| Declination | +12° 40′ 55.155″[2] |
| Characteristics | |
| Evolutionary stage | Pulsar |
| Astrometry | |
| Proper motion (μ) | RA: 46.44±0.08[2]mas/yr Dec.: −84.87±0.32[2]mas/yr |
| Parallax (π) | 1.41±0.08 mas[2] |
| Distance | 2,300 ± 100 ly (710 ± 40 pc) |
| Details | |
| Rotation | 6.21853194840048 ms[3] |
| Age | 3±3[3] Gyr |
| Other designations | |
| Lich,[4] PSR 1257+12, PSR J1300+1240, PSR 1300+1240 | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
PSR B1257+12, alternatively designatedPSR J1300+1240,[5] is a millisecondpulsar, 2,300light-years (710parsecs) from theSun, in theconstellationVirgo, rotating at 160.8 times per second (faster than the blade of a blender).[2] It is also namedLich, aftera powerful, fictional undead creature.[6][4]
The pulsar has aplanetary system with three knownpulsar planets, named "Draugr" (PSR B1257+12 b orPSR B1257+12 A), "Poltergeist" (PSR B1257+12 c, orPSR B1257+12 B), and "Phobetor" (PSR B1257+12 d, orPSR B1257+12 C). They were both the firstextrasolar planets to be discovered and the first pulsar planets to be discovered—B and C in 1992 and A in 1994. A is the lowest-mass planet yet discovered by any observational technique, having somewhat less than twice the mass ofEarth's moon.
The convention that arose for designating pulsars was that of using the letters PSR (Pulsating Source of Radio) followed by the pulsar'sright ascension and degrees ofdeclination. The modern convention prefixes the older numbers with a B meaning the coordinates are for the 1950.0epoch. All new pulsars have a J indicating 2000.0 coordinates and also have declination including minutes. Pulsars that were discovered before 1993 tend to retain their B names rather than use their J names, but all pulsars have a J name that provides more precise coordinates of its location in the sky.[7]
On their discovery, the planets were designated PSR 1257+12 A, B, and C, ordered by increasing distance. They were discovered before the convention that extrasolar planets receive designations consisting of the star's name followed by lower-caseRoman letters starting from "b", in order of discovery, was established.[8] However, they are listed under the latter convention on astronomical databases such asSIMBAD and theExtrasolar Planets Encyclopaedia, with A becoming b, B becoming c, and C becoming d.
In July 2014, theInternational Astronomical Union launchedNameExoWorlds, a process for giving proper names to certain exoplanets and their host stars.[9] The process involved public nomination and voting for the new names.[10] In December 2015, the IAU announced the winning names, submitted by the Planetarium Südtirol Alto Adige inKarneid,Italy, were Lich for the pulsar and Draugr, Poltergeist, and Phobetor for planets A, B, and C, respectively:[6][11]
In 2016, the IAU organized aWorking Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars (includingstellar remnants). In its first bulletin of July 2016,[14] the WGSN explicitly recognized the names of exoplanets and their host stars approved by the Executive Committee Working Group Public Naming of Planets and Planetary Satellites, including the names of stars adopted during the 2015 NameExoWorlds campaign. This stellar remnant is now so entered in the IAU Catalog of Star Names.[5]
PSR B1257+12 was discovered by thePolish astronomerAleksander Wolszczan on 9 February 1990 using theArecibo radio telescope. It is amillisecond pulsar, a kind ofneutron star, with a rotation period of 6.2185 milliseconds (9,650 rpm), and was found to have anomalies in the pulsation period, which led to investigations as to the cause of the irregular pulses. In 1992, Wolszczan andDale Frail published a famous paper on the first confirmed discovery of planets outside the Solar System. Using refined methods one more planet was found orbiting this pulsar in 1994.
The pulsar is estimated to have a mass of 1.4 M☉, which is typical for most neutron stars and pulsars. The radius is estimated to be around 10kilometres or 6.2miles (~1.5×10−5 R☉), also common for pulsars and neutron stars. The pulsar is extremely hot, with a surface temperature of up to around 28,856 K (28,583 °C; 51,481 °F). The pulsar formed one to three billion years ago from awhite dwarf merger, a pair of white dwarfs colliding and collapsing to form a rapidly spinning pulsar.[15]
The discovery stimulated a search for planets orbiting other pulsars, but it turned out such planets are rare; only a handful of other pulsar planets have been confirmed.[16]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| A (b / Draugr) | 0.020 ± 0.002 M🜨 | 0.19 | 25.262 ± 0.003 | 0.0 | ~50° | — |
| B (c / Poltergeist) | 4.3 ± 0.2 M🜨 | 0.36 | 66.5419 ± 0.0001 | 0.0186 ± 0.0002 | 53° | — |
| C (d / Phobetor) | 3.9 ± 0.2 M🜨 | 0.46 | 98.2114 ± 0.0002 | 0.0252 ± 0.0002 | 47° | — |
In 1992, Wolszczan and Frail discovered that the pulsar had two planets. These were the first discovery ofextrasolar planets to be confirmed;[17][18] aspulsar planets, they surprised many astronomers who expected to find planets only aroundmain-sequence stars. Additional uncertainty surrounded the system, because of a claim of an earlier pulsar planet aroundPSR 1829-10 that had to be retracted due to errors in calculations. In 1994, an additional planet was discovered.[19] Additionally, this system may have anasteroid belt or aKuiper belt.
The planets are believed to be the result of a second round ofplanetary system formation as a result of twowhite dwarfs merging with each other into a pulsar and a resulting disk of material in orbit around the star.[15] Other scenarios include unusualsupernova remnants or aquark-nova.[20] However, the white dwarf–white dwarf merge model seems to be the most likely cause of the formation of the planets.
In 1996, a possibleSaturn-like (100 Earth mass)gas giant was announced orbiting the pulsar at a distance of about 40 AU (6.0 billion km; 3.7 billion mi).[21] The original hypothesis was retracted; a reinterpretation of the data led to a new hypothesis of adwarf planet one-fifth the size ofPluto orbiting PSR B1257+12. It would have an average orbital distance of 2.4 AU (360 million km; 220 million mi) with an orbital period of approximately 4.6 years.[22][23][24][25] The dwarf planet hypothesis was also retracted because further observations showed that the pulsation anomalies previously thought to reveal a fourth orbital body are "not periodic and can be fully explained in terms of slow changes in the pulsar'sdispersion measure".[24]
