View source for Hulse–Taylor pulsar

{{Short description|Pulsar in the constellation Aquila}}
{{further|Binary pulsar|Tests of general relativity}}
{{Starbox begin
 | name     = PSR B1913+16
}}
{{Starbox observe
 | epoch    = [[B1950.0]]
 | constell = [[Aquila (constellation)|Aquila]]<ref>{{cite constellation|PSR J1915+1606}}</ref>
 | ra       = {{RA|19|13|12.4655}}
 | dec      = {{DEC|+16|01|08.189}}
}}
{{Starbox astrometry
 | dist_ly  = 21,000
 | dist_pc  = 6,400
}}
{{Starbox detail
 | source   = <ref name="wtf1981">{{cite journal |last1=Weisberg |first1=J. M. |date=October 1981 |title=Gravitational waves from an orbiting pulsar |journal=Scientific American |volume=245 |issue=4 |pages=74–82 |doi=10.1038/scientificamerican1081-74 |bibcode=1981SciAm.245d..74W |last2=Taylor |first2=J. H. |last3=Fowler |first3=L. A.}}</ref>
 | mass     = 1.441 
 | rotation = 59.02999792988 ms
}}
{{Starbox catalog
 | names = [[Pulsar|PSR]]&nbsp;[[B1950.0|B]]1913+16,<ref name=SIMBAD/> PSR&nbsp;[[J2000.0|J]]1915+1606,<ref name=SIMBAD/> {{nowrap|Hulse–Taylor [[binary pulsar]]}},<ref>{{Cite encyclopedia |title=Pulsars |encyclopedia=Encyclopedia of Science |publisher=Enscience |url=http://enscience.me/pulsar/ |last=Ramaswami |first=Ashwin |archive-url=https://web.archive.org/web/20160308044739/http://enscience.me/pulsar/ |archive-date=2016-03-08 |url-status=dead}}</ref> {{nowrap|Hulse–Taylor [[star system|system]]}},<ref>{{Cite web |last=Wanjek |first=Christopher |date=2005-05-30 |title=Orbiting Stars Flooding Space With Exotic Gravitational Waves |url=http://www.nasa.gov/vision/universe/starsgalaxies/collide_whitedwarf_prt.htm |url-status=dead |archive-url=https://web.archive.org/web/20220125171545/https://www.nasa.gov/vision/universe/starsgalaxies/collide_whitedwarf_prt.htm |archive-date=2022-01-25 |access-date=2020-12-07 |publisher=[[NASA]]}}</ref> {{nowrap|Hulse–Taylor [[binary star|binary]]}}, {{nowrap|Hulse–Taylor [[pulsar]]}},<ref name=DavidDarling-HulseTaylorPulsar>{{Cite encyclopedia |url= http://www.daviddarling.info/encyclopedia/H/HulseTaylor.html |title= Hulse-Taylor Pulsar (PSR 1913+16) |publisher= The Worlds of David Darling |encyclopedia= Encyclopedia of Science }}</ref> {{nowrap|[[Russell Alan Hulse|Hulse]]–[[Joseph Hooton Taylor, Jr.|Taylor]] PSR}}<ref name=SIMBAD>{{cite simbad |title= PSR J1915+1606}}</ref>
}}
{{Starbox reference
 | Simbad = PSR+J1915%2B1606
}}
{{starbox end}}

[[File:PSR B1913+16 periastron shift graph.svg|thumb|right|200px|Evidence of orbital decay in PSR B1913+16.<ref name="wt2005">{{cite conference |url=http://aspbooks.org/custom/publications/paper/328-0025.html |title=The Relativistic Binary Pulsar B1913+16: Thirty Years of Observations and Analysis |last1=Weisberg |first1=J.M. |last2=Taylor |first2=J.H. |author-link2=Joseph Hooton Taylor, Jr. |date=July 2005 |publisher=[[Astronomical Society of the Pacific]] |publication-place=[[San Francisco]] |book-title=Binary Radio Pulsars |pages=25 |location=[[Aspen, Colorado]], United States |editor=F.A. Rasio |editor2=I.H. Stairs|conference=ASP Conference Series |volume=328 |arxiv=astro-ph/0407149 |bibcode= 2005ASPC..328...25W  }}</ref> The data points indicate the observed change in the time of [[periastron]] with date, relative to a system not undergoing decay. The parabola illustrates the theoretically expected change according to [[general relativity]].]]

The '''Hulse–Taylor pulsar''' (known as '''PSR B1913+16''', '''PSR J1915+1606''' or '''PSR 1913+16''') is a [[binary star system]] composed of a [[neutron star]] and a [[pulsar]] which orbit around their common [[Barycenter|center of mass]]. It is the first [[binary pulsar]] ever discovered.

The pulsar was discovered by [[Russell Alan Hulse]] and [[Joseph Hooton Taylor Jr.]], of the [[University of Massachusetts Amherst]] in 1974. Their discovery of the system and analysis of it earned them the 1993 [[Nobel Prize in Physics]] "for the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation."<ref name="npp1993">{{cite web |title=The Nobel Prize in Physics 1993 |publisher=[[Nobel Foundation]] |url=https://www.nobelprize.org/prizes/physics/1993/press-release/ |quote=for the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation |access-date=2018-10-27}}</ref>

==Discovery==
Using the [[Arecibo Observatory|Arecibo]] 305 m dish, Hulse and Taylor detected pulsed [[Radio frequency|radio]] emissions and thus identified the source as a pulsar, a rapidly rotating, highly magnetized [[neutron star]]. The neutron star rotates on its axis 17 times per second; thus the pulse period is 59 [[millisecond]]s.

After timing the radio pulses for some time, Hulse and Taylor noticed that there was a systematic variation in the arrival time of the pulses. Sometimes, the pulses were received a little sooner than expected; sometimes, later than expected. These variations changed in a smooth and repetitive manner, with a [[Orbital period|period]] of 7.75 hours. They realized that such behavior is predicted if the pulsar were in a [[Binary system (astronomy)|binary orbit]] with another star, later confirmed to be another neutron star.<ref>{{cite journal|last1=Weisberg|first1=J. M.|last2=Nice|first2=D. J.|last3=Taylor|first3=J. H.|title=Timing Measurements of the Relativistic Binary Pulsar PSR B1913+16|journal=The Astrophysical Journal|date=20 October 2010|volume=722|issue=2|pages=1030–1034|doi=10.1088/0004-637X/722/2/1030|bibcode=2010ApJ...722.1030W|arxiv=1011.0718|s2cid=118573183}}</ref> 

==Star system==
The pulsar and its neutron star companion both follow [[elliptical orbit]]s around their common center of mass. The period of the orbital motion is 7.75 hours, and the two neutron stars are believed to be nearly equal in mass, about 1.4 [[solar mass]]es. Radio emissions have been detected from only one of the two neutron stars.

The minimum separation at [[periastron]] is about 1.1 [[solar radii]]; the maximum separation at [[apastron]] is 4.8 solar radii. The orbit is inclined at about 45 degrees with respect to the plane of the sky. The orientation of periastron changes by about 4.2 degrees per year in direction of the orbital motion (relativistic precession of periastron). In January 1975, it was oriented so that periastron occurred perpendicular to the line of sight from Earth.<ref name="wtf1981"/><ref name="tw82">{{cite journal |last1=Taylor |first1=J. H. |last2=Weisberg |first2=J. M. |date=1982 |title=A new test of general relativity – Gravitational radiation and the binary pulsar PSR 1913+16 |journal=Astrophysical Journal |volume=253 |pages=908–920 |doi=10.1086/159690 |bibcode=1982ApJ...253..908T}}</ref>

==Use as a test of general relativity==
The orbit has decayed since the binary system was initially discovered, in precise agreement with the loss of energy due to [[gravitational wave]]s described by [[Albert Einstein]]'s [[general theory of relativity]].<ref name="wtf1981"/><ref name="tw82"/><ref name="tw89">{{cite journal |last1=Taylor |first1=J. H. |last2=Weisberg |first2=J. M. |date=1989 |title=Further experimental tests of relativistic gravity using the binary pulsar PSR 1913 + 16 |journal=Astrophysical Journal |volume=345 |pages=434–450 |doi=10.1086/167917 |bibcode=1989ApJ...345..434T|s2cid=120688730 }}</ref><ref name="wnt2010">{{cite journal |last1=Weisberg |first1=J. M. |date=2010 |title=Timing Measurements of the Relativistic Binary Pulsar PSR B1913+16 |journal=Astrophysical Journal |volume=722 |issue=2 |pages=1030–1034 |doi=10.1088/0004-637X/722/2/1030 |arxiv=1011.0718 |bibcode=2010ApJ...722.1030W |last3=Taylor |first3=J. H. |last2=Nice |first2=D. J.|s2cid=118573183 }}</ref> The ratio of observed to predicted rate of [[orbital decay]] is calculated to be 0.997 ± 0.002.<ref name="wnt2010"/> The total power of the gravitational waves emitted by this system presently is calculated to be 7.35 × 10<sup>24</sup> watts. For comparison, this is 1.9% of the power radiated in light by the [[Sun]]. The [[Solar System]] radiates only about 5,000 watts in gravitational waves, due to the much larger distances and orbit times, particularly between the Sun and [[Jupiter]], and the relatively small mass of the planets.

With this comparatively large energy loss due to gravitational radiation, the rate of decrease of orbital period is 76.5 [[microsecond]]s per year, the rate of decrease of semimajor axis is 3.5 meters per year, and the calculated lifetime to final [[inspiral]] is 300 million years.<ref name="wtf1981"/><ref name="wnt2010"/>

In 2004, Taylor and Joel M. Weisberg published a new analysis of the experimental data to date, concluding that the 0.2% disparity between the data and the predicted results is due to poorly known galactic constants, including the Sun's distance from the [[Galactic Center]], the pulsar's proper motion and its distance from Earth. While there are efforts underway for better measurement of the first two quantities, they saw "little prospect for a significant improvement in knowledge of the pulsar distance," so tighter bounds will be difficult to attain. Taylor and Weisberg also mapped the pulsar's two-dimensional beam structure using the fact that the system's precession leads to varying pulse shapes. They found that the beam shape is latitudinally elongated, and pinched longitudinally near the centre, leading to an overall shape like a figure eight.<ref name="wt2005"/>

In 2016, Weisberg and Huang published further results, still with a 0.16% disparity, finding that the ratio of the observed value compared to the predicted value was 0.9983 ± 0.0016.<ref>{{cite journal |last1=Weisberg |first1=J. M. |last2=Huang |first2=Y. |date=21 September 2016 |doi=10.3847/0004-637X/829/1/55 |title=Relativistic measurements from timing the binary pulsar PSR B1913+16 |journal=The Astrophysical Journal |volume=829 |number=1|page=55 |arxiv=1606.02744 |bibcode=2016ApJ...829...55W |s2cid=119283147 |doi-access=free }}</ref> They name the main driver of this improvement, from 1.8σ to 1σ discrepancy, as being improved galactic constants published in 2014.

==Characteristics==
*Mass of companion: {{Solar mass|1.387}}
* Total mass of the system: {{Solar mass|2.828378(7)}}
* Orbital period: 7.751938773864 hr
* Eccentricity: 0.6171334
* [[Semi-major axis]]: 1,950,100&nbsp;km
* Periastron separation: 746,600&nbsp;km
* Apastron separation: 3,153,600&nbsp;km
* Orbital velocity of stars at periastron (relative to center of mass): 450&nbsp;km/s
* Orbital velocity of stars at apastron (relative to center of mass): 110&nbsp;km/s

==See also==
{{Portal|Astronomy|Physics}}
* [[Binary pulsar]]
* [[PSR J0737−3039]]
* [[Square Kilometre Array]]
* [[Tests of general relativity]]
* [[Quadrupole formula]]

==References==
{{reflist}}

{{Stars of Aquila}}

{{DEFAULTSORT:Hulse-Taylor binary}}
[[Category:Pulsars]]
[[Category:Double neutron star systems]]
[[Category:Aquila (constellation)]]
[[Category:Astronomical objects discovered in 1974]]
[[Category:Stars with proper names]]