View source for PSR B1620−26

{{Short description|Binary star system in the globular cluster of Messier 4}}
{{Use dmy dates|date=November 2024}}
{{Starbox begin }} 
{{Starbox image 
| image = [[Image:Location of pulsar B1620-26.jpg|250px]]
| caption = The location of PSR B1620−26 (circled)
}} 
{{Starbox observe 
| epoch = [[J2000.0]]
| constell = [[Scorpius]] ([[Messier 4|M4]])
| ra = {{RA|16|23|38.2218}}<ref name=SIMBAD/>
| dec = {{DEC|−26|31|53.769}}<ref name=SIMBAD/>
| appmag_v = 21.30<ref name=SIMBAD/>
}} 
{{Starbox character 
| class = Pulsar + DB
}} 
{{Starbox astrometry 
| dist_ly = 12,400
| dist_pc = 3,800
}}  
{{Starbox detail 
| component1 = PSR B1620-26
| age_gyr = 12.2
| mass = 1.35
| radius = 0.00003
| radius_km = 20.85
| temperature = ≤ 30,000
| rotation = 11.0757509142025 [[millisecond|ms]]
| component2 = WD B1620-26
| age_gyr2 = 12.2
| mass2 = 0.34
| radius2 = 0.01
| radius_km2 = 6,950
| temperature2 = ≤ 25,200
}} 
{{Starbox catalog 
| names = PSR J1623−2631
}}
{{Starbox reference
|Simbad=PSR+B1620-26
}}
{{Starbox end}}

'''PSR B1620−26''' is a [[binary star]] system located at a distance of 3,800 [[parsec]]s (12,400 [[light-year]]s) in the [[globular cluster]] of [[Messier 4]] (M4, NGC 6121) in the [[constellation]] of [[Scorpius]].<ref name=EPEstar>{{cite encyclopedia |url=http://exoplanet.eu/star.php?st=PSR+B1620-26 |archive-url=https://web.archive.org/web/20060621055409/http://exoplanet.eu/star.php?st=PSR+B1620-26 |url-status=dead |archive-date=21 June 2006 |title=Notes for star PSR B1620-26 |author=Jean Schneider |date=2011 |encyclopedia=[[Extrasolar Planets Encyclopaedia]] |access-date=26 September 2011}}</ref><ref name="arzoumanian">{{cite journal | author = Z. Arzoumanian | author2 = K. Joshi | author3 = F. A. Rasio | author4 = S. E. Thorsett | title=Orbital Parameters of the PSR B1620-26 Triple System | journal=Proceedings of the 160th Colloquium of the International Astronomical Union | date=1999 | volume=105 | pages=525 | bibcode=1996ASPC..105..525A |arxiv = astro-ph/9605141 }}</ref><ref name=ESO>{{cite web |url=http://www.eso.org/public/images/m4/ |title=Messier 4 (M4) globular cluster |date=2009 |publisher=[[European Southern Observatory]] |access-date=26 September 2011}}</ref>  The system is composed of a [[pulsar]] ('''PSR B1620−26 A''') and a [[white dwarf]] star (WD B1620−26, or '''PSR B1620−26 B'''). As of 2000, the system is also confirmed to have an [[exoplanet]] orbiting the two stars.

== History ==
The double system (''triple'' including the substellar companion) is just outside the core of the globular cluster. The age of the cluster has been estimated to be about 12.2 billion years.<ref name=aaa143_1>{{cite journal | author=Caputo, F. | author2=Castellani, V. | author3=Quarta, M. L. | title=Reddening, distance modulus and age of the globular cluster NGC 6121 (M4) from the properties of RR Lyrae variables | journal=Astronomy and Astrophysics | volume=143| issue=1 |date=February 1985 | pages=8–12 | bibcode=1985A&A...143....8C
}}</ref> Hence this is the age estimate for the birth of the planet, and two stars.

There is a minor dispute about the proper nomenclature rules to use for this unusual star system.  One side regards the A/B convention of naming binary stars as having priority, so that the pulsar is PSR B1620−26 A, the white dwarf companion is PSR B1620−26 B and the planet is [[PSR B1620−26 c]].  The other side considers PSR to apply only to stars which are pulsars, not their companions, so the white dwarf should be named using the WD convention, making the pulsar PSR B1620−26, the white dwarf "WD J1623−266", and the planet "PSR B1620−26 b."  Early articles used the first convention, but star catalogs have been using the second.<ref name=SIMBAD>{{cite simbad|title=PSR B1620-26|access-date=31 January 2018}}</ref><ref name=EPEplanet>{{cite encyclopedia |url=http://exoplanet.eu/planet.php?p1=PSR+B1620-26&p2=b |title=Notes for Planet PSR B1620−2 b |author=Jean Schneider |date=2011 |access-date=24 September 2011 |archive-date=9 November 2011 |archive-url=https://web.archive.org/web/20111109025942/http://exoplanet.eu/planet.php?p1=PSR+B1620-26&p2=b |encyclopedia=[[Extrasolar Planets Encyclopaedia]] |url-status=dead }}</ref> The most recent proposal<ref name="hessman">{{Cite arXiv |eprint=1012.0707 |class=astro-ph.SR |first1=F. V. |last1=Hessman |first2=V. S. |last2=Dhillon |title=On the naming convention used for multiple star systems and extrasolar planets |date=2010 |last3=Winget |first3=D. E. |last4=Schreiber |first4=M. R. |last5=Horne |first5=K. |last6=Marsh |first6=T. R. |last7=Guenther |first7=E. |last8=Schwope |first8=A. |last9=Heber |first9=U. |display-authors=4 |pages=4}}</ref> provides a nomenclature like '''PSR B1620−26 (AB)b''', including capital letters '''A''' and '''B''' in parentheses to identify inner stellar components of binary system, followed by italic letter '''b''' referred to outer planetary companion. In practice, context makes it clear whether the pulsar, the white dwarf, the planet, or the system as a whole is being referred to.

== White dwarf ==
The mass of the white dwarf is 0.34 [[solar mass]]es and orbits at a period of 191 days with an inclination of 55° relative to its pulsar companion.<ref name="ford">
{{cite journal |last=Ford |first=Eric B. |date=1999 |title=Theoretical Implications of the PSR B1620−26 Triple System and itItslanet |journal=The Astrophysical Journal |volume=528 |pages=336–350 |doi=10.1086/308167 |arxiv=astro-ph/9905347v2|s2cid=5856069 }}</ref>
Its age is approximately {{val|480|e=6|140}} years.<ref name="sigurdsson">{{cite journal | author = S. Sigurdsson | display-authors = 4 | author2 = H. B. Richer | author3 = B. M. Hansen | author4 = I. H. Stairs | author5 = S. E. Thorsett | title=A Young White Dwarf Companion to Pulsar B1620-26: Evidence for Early Planet Formation. | journal=Science | date=2003| volume=301| pages=193–196| bibcode=2003Sci...301..193S |arxiv = astro-ph/0307339 | doi=10.1126/science.1086326 | pmid=12855802 | issue=5630| s2cid = 39446560 }}</ref>

== Planetary system ==
[[Image:Jovian planet in globular cluster M4 - calm bystander in stellar drama.jpg|thumb|left|The evolution of the PSR B1620−26 system]]

[[PSR B1620−26 b]] was originally detected through the Doppler shifts its orbit induces on signals from the star it orbits (in this case, changes in the apparent pulsation period of the pulsar).

In the early 1990s, a group of astronomers led by Donald Backer, studying what they thought was a binary pulsar, determined that a third object was needed to explain the observed Doppler shifts. Within a few years, the gravitational effects of the planet on the orbit of the pulsar and white dwarf had been measured, giving an estimate of the mass of the third object that was too small for it to be a star. The conclusion that the third object was a planet was announced by [[Stephen Thorsett]] and his collaborators in 1993.

{{OrbitboxPlanet begin}}
{{OrbitboxPlanet
| exoplanet = [[PSR B1620−26 b|b]]
| mass = 2.5 ± 1
| period = ~36,500
| semimajor = 23
| eccentricity = ''low''
| inclination = 55<sub>−8</sub><sup>+14</sup>
}}
{{Orbitbox end}}

== See also ==
* [[PSR B1257+12]]
* [[Delta Trianguli]]
* [[Pulsar planet]]
* [[List of exoplanets discovered before 2000]] - PSR B1620-26 b

== References ==
{{reflist}}

== External links ==
* [http://www.solstation.com/x-objects/b1620-26.htm '''SolStation''': PSR B1620−26]
* [http://www.space.com/scienceastronomy/oldest_planet_030710-1.html '''SPACE''': Oldest Known World Conjures Prospect of Ancient Life]
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{{Sky|16|23|38|-|26|31|53|12400}}

{{Scorpius}}
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[[Category:Binary stars]]
[[Category:Pulsars]]
[[Category:White dwarfs]]
[[Category:Scorpius]]
[[Category:Multi-star planetary systems|2]]
[[Category:Planetary systems with one confirmed planet]]
{{DEFAULTSORT:PSR B1620-26}}