View source for PSR J1946+2052

{{Short description|Binary pulsar–neutron star system}}
{{Use dmy dates|date=March 2023}}
{{Starbox begin 
| name = PSR J1946+2052
}}
<!-- {{Starbox image 
| image = 
| caption = 
}} -->
{{Starbox observe 
| epoch = [[J2000.0]]
| constell = [[Vulpecula]]
| ra = {{RA|19|46|14.130}}<ref name="Simbad"/>
| dec = {{DEC|+20|52|24.64}}<ref name="Simbad"/>
| appmag_v = 
}}
{{Starbox character 
| class = [[Pulsar]] + [[Neutron star]]
| appmag_1_passband = 
| appmag_1 = 
| b-v = 
| u-b = 
| variable = 
}}
{{Starbox astrometry 
| radial_v = 
| prop_mo_ra = 
| prop_mo_dec = 
| parallax = 
| p_error = 
| dist_ly = 
| dist_pc = {{val|3500|-|4200}}
| dist_footnote = <ref name="Stovall2018"/>
| absmag_v = 
}}
{{Starbox detail 
| source = <ref name="Stovall2018"/>{{rp|page=4}}
| component1 = PSR J1946+2052 A
| mass = {{val|1.31|p=<}}
| radius_km = 
| luminosity = 
| temperature = 
| rotation = {{val|16.9601753230|(2)|ul=ms}}
| age_myr = ≈ 290
|
| component2 = PSR J1946+2052 B
| mass2 = {{val|1.18|p=>}}
| luminosity2 = 
| temperature2 = 
| metal_fe2 = 
}}
{{Starbox orbit
| reference = <ref name="Stovall2018"/>{{rp|page=4}}
| primary = PSR J1946+2052 A
| name = PSR J1946+2052 B
| period_unitless = {{val|0.07848804|(1)|ul=d}}<br/>{{val|1.88371296|(24)|ul=h}}
| axis_unitless = {{val|728000|ul=km}} (mean separation){{efn|name=semimajor|Orbital separation distance ([[semi-major axis]] from primary) calculated with [[Kepler's Third Law]]: <math>a = \sqrt[3]{\frac{GMT^2}{4\pi^2}}</math> given total system mass <math>M</math> {{=}} 2.50 {{Solar mass}} and orbital period <math>T</math> {{=}} 0.07848804 d.<ref name="Stovall2018"/>{{rp|page=4}} Stovall et al. (2018) determined a minimum projected semi-major axis of {{val|1.154319|(5)}} [[light second]]s ({{val|346056|(1)|u=km}}) from radio pulsation timing.<ref name="Stovall2018"/>{{rp|page=4}}}}
| eccentricity = {{val|0.063848|(9)}}
| inclination = 
| node = 
| periastron = [[Julian day|JD]] {{val|2457989.502943|(3)}}<br/>{{nowrap|24 August 2017 00:04:14 [[UTC]]}}
| periarg = 
| k1 = 
| k2 = 
}}
{{Starbox catalog 
| names = PSR J1946+2052
}}
{{Starbox reference
|Simbad=PSR+J1946%2B2052
}}
{{Starbox end}}

'''PSR J1946+2052''' is a short-period [[binary pulsar]] system located {{convert|3500–4200|pc|ly|sigfig=2|lk=on|order=flip}} away from Earth in the [[constellation (astronomy)|constellation]] [[Vulpecula]]. The system consists of a [[pulsar]] and a [[neutron star]] orbiting around their common [[Barycenter|center of mass]] every 1.88 hours, which is the shortest [[orbital period]] among all known double neutron star systems {{asof|2022|lc=y}}.<ref name="Sengar2022"/>{{rp|page=5784}} The [[general theory of relativity]] predicts their orbits are gradually decaying due to emitting [[gravitational waves]], which will eventually lead to a [[neutron star merger]] and a [[kilonova]] in 46 million years.<ref name="Stovall2018"/><ref name="AASNova-20180226"/><ref name="Pol2019"/>

The PSR J1946+2052 system was discovered by [[radio astronomer]]s on 19 July 2017, during a survey for pulsars with the [[Arecibo Observatory]]'s {{convert|305|m|ft|adj=on|sigfig=3}} radio telescope at [[Arecibo, Puerto Rico]].<ref name="Stovall2018"/><ref name="AASNova-20180226"/> The primary component of PSR J1946+2052 system, the pulsar, has a rotation period of 17 milliseconds and an estimated mass below 1.31&nbsp;[[solar mass]]es. The invisible neutron star companion likely has a lower mass of at least 1.18&nbsp;solar masses, which amounts to a total system mass of approximately 2.50 solar masses, making PSR J1946+2052 potentially the lowest-mass double neutron star system known {{asof|2022|lc=y}}.<ref name="Sengar2022"/>{{rp|page=5784}}

== Discovery ==
The PSR J1946+2052 system was discovered by [[radio astronomer]]s on 19 July 2017, during the [[PALFA Survey]] for pulsars in the [[Milky Way]]'s [[galactic plane]] with the [[Arecibo Observatory]]'s {{convert|305|m|ft|adj=on|sigfig=3}} radio telescope at [[Arecibo, Puerto Rico]].<ref name="Stovall2018"/>{{rp|page=2}} A search in archival imagery shows that PSR J1946+2052 was not detected in [[infrared]] to [[gamma-ray]] wavelengths.<ref name="Stovall2018"/>{{rp|page=3–4}}
<!-- == Visibilty == -->

== Location and distance ==
PSR J1946+2052 is located in the [[northern celestial hemisphere]] in the [[constellation]] [[Vulpecula]]. Its [[Equatorial coordinate system|equatorial coordinates]] based on the [[Epoch (astronomy)#Julian dates and J2000|J2000 epoch]] are [[Right ascension|RA]] {{RA|19|46|14.13}} and [[Declination|Dec]] {{DEC|+20|52|24.6}}; these are indicated in its [[Pulsar#Nomenclature|pulsar identifier]] PSR J1946+2052. In [[galactic coordinates]], it lies in the Milky Way's galactic plane with a galactic latitude 1.98° south and a galactic longitude 57.66° east from the [[Galactic Center]].<ref name="Simbad"/><ref name="Stovall2018"/>{{rp|page=4}} The time delay between different [[frequency|frequencies]] of PSR J1946+2052's radio pulses indicates a [[dispersion measure]] of {{val|93.965|0.003|ul=pc/cm3}}, which suggests a distance between {{convert|3500–4200|pc|ly|sigfig=2|lk=on|order=flip}} from Earth, depending on the electron [[number density]] in the [[interstellar medium]] between the pulsar system and Earth.<ref name="Stovall2018"/>{{rp|page=4–5}} It is unlikely in the near future that PSR J1946+2052's distance could be determined more precisely with direct methods such as [[very-long-baseline interferometry]] or [[hydrogen line]] [[absorption (electromagnetic radiation)|absorption]], as it is too faint and distant.<ref name="Stovall2018"/>{{rp|page=5}}

== Origin ==
[[File:Double Neutron Star Formation - noirlab2303b.jpg|thumb|Infographic depicting the evolutionary stages of double neutron star systems]]
Double neutron star systems such as PSR J1946+2052 are thought to have formed from the asynchronous evolution of two high-mass stars in a wide binary system.<ref name="Sengar2022"/>{{rp|page=5782}}<ref name="Pol2019"/>{{rp|page=1}} The higher-mass star first evolves and explodes in a [[supernova]], leaving a neutron star remnant in an eccentric mutual orbit with the surviving companion star. As the companion star evolves into a [[supergiant]] and expands beyond its [[Roche lobe]], it begins transferring mass to the neutron star, which energetically [[Accretion (astrophysics)|accretes]] the material and spins up to a [[rotation period]] of a few milliseconds, becoming a recycled [[millisecond pulsar]] and an [[X-ray binary]]. The aging companion star eventually engulfs the pulsar in a gaseous [[common envelope]] and their mutual orbit begins to circularize and shrink due to [[drag (physics)|drag forces]] within the envelope.<ref name="Sengar2022"/>{{rp|page=5782}} The pulsar continues accreting and strips the companion star of its hydrogen [[Circumstellar envelope|envelope]], turning it into a [[helium star]].<ref name="Tauris2015"/><ref name="Sengar2022"/>{{rp|page=5788}} The helium star eventually explodes in an [[ultra-stripped supernova]] with minimal ejecta, resulting in a low [[momentum]] kick that leaves the resulting neutron star pair bound in a low-eccentricity orbit around each other.<ref name="Stovall2018"/>{{rp|page=4}}<ref name="Sengar2022"/>{{rp|page=5791}} The second-born neutron star from this supernova is expected to pulsate for only a few million years before its rotation slows down sufficiently for its pulsation mechanism to [[Pulsar#Formation, mechanism, turn off|turn off]]. On the other hand, the first-born pulsar is expected to continue pulsating for billions of years thanks to the high [[angular momentum]] it had acquired from accretion.<ref name="Sengar2022"/>{{rp|page=5783}}

== Physical characteristics ==
The total mass of the PSR J1946+2052 system is {{val|2.50|0.04|ul=solar mass}}, which is determined from the components' mutual [[orbital period]] using [[Kepler's third law]]. This is potentially the lowest mass measured for a double neutron star system {{asof|2022|lc=y}}, though it could be tied with [[PSR J1411+2551]] ({{val|2.538|0.022|u=solar mass}}) within uncertainty bounds.<ref name="Stovall2018"/>{{rp|page=4}}<ref name="Sengar2022"/>{{rp|page=5784}} Although the individual component masses have not been measured directly, the [[binary mass function]] constrains them to be {{val|1.31|u=solar mass|p=<}} and {{val|1.18|u=solar mass|p=>}} for the pulsar and companion, respectively. A more detailed analysis of the [[Einstein delay]] ([[gravitational time dilation]] and [[Doppler shift]] effects) in the pulsar's pulsation timing would enable a more precise measurement of both components' masses.<ref name="Stovall2018"/>{{rp|page=4}}

=== Pulsar ===
The pulsar is the only [[electromagnetic radiation|electromagnetically]] detectable component of the PSR J1946+2052 system. It pulsates in radio wavelengths 59 times [[Hertz|per second]], corresponding to a rotation period of 17 milliseconds. Due to the generation of electromagnetic radiation by its rotating [[magnetic field]], the pulsar is gradually losing [[rotational kinetic energy]] at a spin-down [[luminosity]] of {{nobr|{{val|7.5|e=33}} [[erg]]s per second}} ({{val|7.5|e=26|ul=W|}} or {{val|2.0|ul=solar luminosity}}) and its rotation period is increasing at a rate of {{val|9|2|e=-19}} seconds per second. This is a relatively low spin-down rate for a neutron star, which suggests the pulsar must have a weakened surface magnetic field strength of {{convert|4e9|G|T|lk=on}}. This weakened magnetic field is thought to be the result of the pulsar having accreted matter from a past companion star, which accumulated onto the pulsar's surface and buried its original surface magnetic field. This indicates that the pulsar is the first-born stellar remnant of the PSR J1946+2052 system. The pulsar is estimated to have a [[Neutron star#Spin down|characteristic age]] of 290 million years, assuming it only experienced constant spin-down to its present rotation period.<ref name="Stovall2018"/>{{rp|page=4}} However, this is likely not accurate to pulsar's true age because it underwent rotational spin-up through accretion in the past.<ref name="Pol2019"/>{{rp|page=4}}

=== Companion ===
The companion was discovered from the periodic Doppler shifting in the pulsar's pulsation frequency, due to the orbital motion of the pulsar induced by the companion. It is inferred to be a neutron star, consistent with its high mass and expected evolutionary history.<ref name="Stovall2018"/>{{rp|page=4}} Having formed last in an ultra-stripped supernova of its progenitor star, the companion should be younger than the pulsar and likely did not undergo rotational spin-up through accretion.<ref name="Pol2019"/>{{rp|page=4}} The companion does not exhibit radio pulsations, either because its electromagnetic beams do not point towards Earth or its pulsation mechanism has turned off.<ref name="Stovall2018"/>{{rp|page=2}}<ref name="Sengar2022"/>{{rp|page=5783}} Since it could not be detected directly, very little is known about the companion's properties.<ref name="Stovall2018"/>{{rp|page=2}}

== Orbit ==
The components orbit about their common [[center of mass]], or [[barycenter]], in a period of 1.88 hours. This is the shortest orbital period among all known double neutron star systems {{asof|2022|lc=y}}.<ref name="Sengar2022"/>{{rp|page=5784}} In 2017, the system was losing {{val|0.13|u=solar luminosity}} ({{val|5.0|e=25|u=W}}) of energy to [[gravitational wave]] emissions and its orbital period was decreasing at an [[Derivative|instantaneous rate]] of {{val|1.78|e=-12}} seconds per second.<ref name="Stovall2018"/>{{rp|page=4–5}} The orbital decay rate will progressively increase in magnitude as the components spiral closer to each other, and will lead to a [[neutron star merger]] in 46 million years.<ref name="Stovall2018"/>{{rp|page=4}} [[Integral|Integrating]] the components' orbital decay backwards in time shows that their mutual orbit had an eccentricity less than 0.14 and a period less than {{convert|0.17|d|h}} before the companion's progenitor star went supernova.<ref name="Stovall2018"/>{{rp|page=4}} The orbiting neutron stars of the PSR J1946+2052 system experience relativistic [[apsidal precession]] at a very high rate of {{val|25.6|0.3}} degrees per year, making it also the fastest-precessing double neutron star system known.<ref name="Stovall2018"/>{{rp|page=4}}

== Merger ==
Within milliseconds after merging, [[atomic nuclei]] inside the neutron stars undergo [[rapid neutron-capture process|rapid neutron capture]], producing copious [[neutrino]]s and numerous elements heavier than iron in the process.<ref name="Fujibayashi2020"/>{{rp|pages=1, 18}} For low-mass neutron star mergers like PSR J1946+2052, these heavy elements are predicted to predominantly consist of lighter [[nuclide]]s with [[atomic mass number]]s less than ''A'' < 130, with small amounts of [[lanthanides]] and heavier nuclides accounting for 0.2%–0.4% of the remaining [[nucleosynthesis|nucleosynthesized]] mass.<ref name="Fujibayashi2020"/>{{rp|pages=19, 23}} Up to {{val|0.1|u=solar mass}} of these heavy elements are predicted to be ejected outward at about 0.1 times the [[speed of light]], due to the extreme angular momentum and heating involved in the merger.<ref name="Fujibayashi2020"/>{{rp|pages=1, 14}} These heavy elements would then be intensely irradiated by the merger-produced neutrinos about 0.1 seconds later, becoming accelerated to speeds over 0.3 times the [[speed of light]].<ref name="Fujibayashi2020"/>{{rp|pages=13}} Over time, these ejected heavy elements undergo [[radioactive decay]] and produce electromagnetic radiation from [[infrared]] to [[ultraviolet]] wavelengths, generating a [[kilonova]].<ref name="Fujibayashi2020"/>{{rp|pages=1}}

The elemental abundances of most known stars do not match that predicted for low-mass star mergers, suggesting that low-mass star mergers must be rare occurrences.<ref name="Fujibayashi2020"/>{{rp|page=23}} The low total mass of the PSR J1946+2052 merger will likely form a strongly magnetized [[supramassive neutron star]]<!-- "supra" is not a typo --> remnant that slightly exceeds the {{val|2.1|-|2.4|u=solar mass}} [[Tolman–Oppenheimer–Volkoff limit]].<ref name="Fujibayashi2020"/>{{rp|page=2}}<ref name="Sarin2021"/>{{rp|page=8}} This supramassive neutron star would be unstable as the [[centrifugal force]]s that prevent its [[gravitational collapse]] will diminish due to the loss of angular momentum to gravitational waves and other [[magnetohydrodynamics|magnetohydrodynamic]] processes.<ref name="Sarin2021"/>{{rp|page=3}} The supramassive neutron star would survive for only a few seconds before collapsing into a [[black hole]].<ref name="Fujibayashi2020"/>{{rp|page=12}}

== See also ==
* [[GW170817]], first neutron star merger discovered
* [[Hulse–Taylor binary]], first pulsar in a binary system discovered
* [[PSR J0737−3039]], first double pulsar binary system discovered
* [[PSR J1930–1852]], double neutron star system with the longest known orbital period

== Notes ==
{{notelist}}

== References ==
{{reflist|refs=

<ref name="Simbad">{{cite web
  |title      = PSR J1946+2052 -- Pulsar
  |url        = https://simbad.u-strasbg.fr/simbad/sim-id?Ident=PSR+J1946%2B2052
  |work       = [[SIMBAD]]
  |publisher  = [[Centre de données astronomiques de Strasbourg]]
  |accessdate = 3 Mar 2023}}</ref>

<ref name="Tauris2015">{{cite journal
  |first1 = Thomas M. |last1 = Tauris
  |first2 = Norbert |last2 = Langer
  |first3 = Philipp |last3 = Podsiadlowski
  |title      = Ultra-stripped supernovae: progenitors and fate
  |journal    = Monthly Notices of the Royal Astronomical Society
  |date       = August 2015
  |volume     = 451
  |issue      = 2
  |pages      = 2123–2144
  |doi-access = free
  |doi        = 10.1093/mnras/stv990
  |arxiv      = 1505.00270
  |bibcode    = 2015MNRAS.451.2123T}}</ref>

<ref name="Stovall2018">{{cite journal
  |display-authors = etal
  |first1 = K. |last1 = Stovall
  |first2 = P. C. C. |last2 = Freire
  |first3 = S. |last3 = Chatterjee
  |first4 = P. B. |last4 = Demorest
  |first5 = D. R. |last5 = Lorimer
  |first6 = M. A. |last6 = McLaughlin
  |title      = PALFA Discovery of a Highly Relativistic Double Neutron Star Binary
  |journal    = The Astrophysical Journal Letters
  |date       = February 2018
  |volume     = 854
  |issue      = 2
  |pages      = 6
  |id         = L22
  |doi-access = free
  |doi        = 10.3847/2041-8213/aaad06
  |arxiv      = 1802.01707
  |bibcode    = 2018ApJ...854L..22S}}</ref>

<ref name="AASNova-20180226">{{cite news
  |title      = PALFA Discovers Neutron Stars on a Collision Course
  |url        = https://aasnova.org/2018/02/26/palfa-discovers-neutron-stars-on-a-collision-course/
  |first = Susanna |last = Kohler
  |work       = AAS Nova
  |publisher  = American Astronomical Society
  |date       = 26 February 2018
  |accessdate = 3 March 2023}}</ref>

<ref name="Pol2019">{{cite journal
  |first1 = Nihan |last1 = Pol
  |first2 = Maura |last2 = McLaughlin
  |first3 = Duncan R. |last3 = Lorimer
  |title      = Future Prospects for Ground-based Gravitational-wave Detectors: The Galactic Double Neutron Star Merger Rate Revisited
  |journal    = The Astrophysical Journal
  |date       = January 2019
  |volume     = 870
  |issue      = 2
  |pages      = 11
  |id         = 71
  |doi-access = free
  |doi        = 10.3847/1538-4357/aaf006
  |arxiv      = 1811.04086
  |bibcode    = 2019ApJ...870...71P}}</ref>

<ref name="Fujibayashi2020">{{cite journal
  |first1 = Sho |last1 = Fujibayashi
  |first2 = Shinya |last2 = Wanajo
  |first3 = Kenta |last3 = Kiuchi
  |first4 = Koutarou |last4 = Kyutoku
  |first5 = Yuichiro |last5 = Sekiguchi
  |first6 = Masaru |last6 = Shibata
  |title      = Postmerger Mass Ejection of Low-mass Binary Neutron Stars
  |journal    = The Astrophysical Journal
  |date       = October 2022
  |volume     = 901
  |issue      = 2
  |pages      = 27
  |id         = 122
  |doi-access = free
  |doi        = 10.3847/1538-4357/abafc2
  |arxiv      = 2007.00474
  |bibcode    = 2020ApJ...901..122F}}</ref>

<ref name="Sarin2021">{{cite journal
  |first1 = Nikhil |last1 = Sarin
  |first2 = Paul D. |last2 = Lasky
  |title      = The evolution of binary neutron star post-merger remnants: a review
  |journal    = General Relativity and Gravitation
  |date       = June 2021
  |volume     = 53
  |issue      = 6
  |pages      = 55
  |id         = 59
  |doi        = 10.1007/s10714-021-02831-1 
  |arxiv      = 2012.08172
  |bibcode    = 2021GReGr..53...59S}}</ref>

<ref name="Sengar2022">{{cite journal
  |display-authors = etal
  |first1 = R. |last1 = Sengar
  |first2 = V. |last2 = Balakrishnan
  |first3 = S. |last3 = Stevenson
  |first4 = M. |last4 = Bailes
  |first5 = E. D. |last5 = Barr
  |first6 = N. D. R. |last6 = Bhat
  |title      = The High Time Resolution Universe Pulsar Survey - XVII. PSR J1325-6253, a low eccentricity double neutron star system from an ultra-stripped supernova
  |journal    = Monthly Notices of the Royal Astronomical Society
  |date       = June 2022
  |volume     = 512
  |issue      = 4
  |pages      = 5782–5792
  |doi-access = free
  |doi        = 10.1093/mnras/stac821
  |arxiv      = 2204.06869
  |bibcode    = 2022MNRAS.512.5782S}}</ref>

}}

== External links ==
* {{cite journal |display-authors = etal |first1 = T. M. |last1 = Tauris |title = Formation of Double Neutron Star Systems |journal = The Astrophysical Journal |date = September 2017 |volume = 846 |issue = 2 |pages = 58 |doi-access = free |doi = 10.3847/1538-4357/aa7e89 |arxiv = 1706.09438 |bibcode = 2017ApJ...846..170T}}
* {{cite web |title = A New Relativistic Binary System Found by PALFA |url = https://science.nrao.edu/science/meetings/2018/postdoc-symposium/presentations/KevinStovall_NRAO_Postdoc_Symposium2018.pdf |display-authors = etal |first = Kevin |last = Stovall |work = Postdoc Symposium |publisher = [[National Radio Astronomy Observatory]] |date = 19 March 2018}}
* {{cite web |title = Research Interests: Binary Pulsars! |url = https://www3.mpifr-bonn.mpg.de/staff/pfreire/interests.html |first = Paolo |last = Freire |publisher = [[Max Planck Institute for Radio Astronomy]]}}

{{Vulpecula}}
{{Neutron star}}

{{DEFAULTSORT:PSR J1946+2052}}
[[Category:Pulsars]]
[[Category:Double neutron star systems]]
[[Category:Vulpecula]]
[[Category:Astronomical objects discovered in 2017|20170719]]