Epoch B1950.0 Equinox B1950.0
|Right ascension||19h 13m 12.4655s|
|Declination||16° 01′ 08.189″|
PSR B1913+16 (also known as PSR J1915+1606 and PSR 1913+16) is a pulsar (a radiating neutron star) which together with another neutron star is in orbit around a common center of mass, thus forming a binary star system. In 1974 it was discovered by Russell Alan Hulse and Joseph Hooton Taylor, Jr., of the University of Massachusetts Amherst. 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."
The system is also called the Hulse–Taylor binary pulsar after its discoverers.
Using the Arecibo 305m antenna, Hulse and Taylor detected pulsed 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 milliseconds.
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 period of 7.75 hours. They realized that such behavior is predicted if the pulsar were in a binary orbit with another star.
Star system 
The pulsar and its neutron star companion both follow elliptical orbits 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 masses. 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. In the case of PSR B1913+16, 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. 
The orbit has decayed since the binary system was initially discovered, in precise agreement with the loss of energy due to gravitational waves predicted by Einstein's general theory of relativity. The ratio of observed to predicted rate of orbital decay to be 0.997±0.002. The total power of the gravitational radiation (waves) emitted by this system presently, is calculated to be 7.35 × 1024 watts. For comparison, this is 1.9% of the power radiated in light by our own Sun. (Another comparison is that our own Solar System radiates only about 5000 watts in gravitational waves, due to the much larger distances and orbit times, particularly between the Sun and Jupiter).
With this comparatively large energy loss due to gravitational radiation, the rate of decrease of orbital period is 76.5 microseconds per year, the rate of decrease of semimajor axis is 3.5 meters per year, and the calculated lifetime to final inspiral is 300,000,000 years. 
- Mass of companion: 1.387 MSun
- Orbital period: –7.751939106 hr
- Eccentricity: –0.617131
- Semimajor axis: 1,950,100 km
- Periastron separation: 746,600 km
- Apastron separation: 3,153,600 km
- Orbital velocity of stars at periastron (relative to center of mass): 450 km/s
- Orbital velocity of stars at apastron (relative to center of mass): 110 km/s
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, and that tighter bounds will be difficult to attain with current knowledge of these figures. They 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 figure-of-eight shape.
In popular culture 
Science fiction writer Arthur C. Clarke offhandedly speculated, in his television series Mysterious World, that this pulsar was the Star of Bethlehem. He ended the 12th episode with the line, "How romantic if even now we can hear the dying voice of the star which heralded the Christian era."
See also 
- wikisky.org SKY-MAP for 19:15:28 / +16:06:27 (J2000 position)
- Weisberg, J. M.; Taylor, J. H.; Fowler, L. A. (October, 1981). "Gravitational waves from an orbiting pulsar". Scientific American 245: 74–82. Bibcode:1981SciAm.245...74W. doi:10.1038/scientificamerican1081-74.
- Weisberg, J.M.; Taylor, J.H. (July 2005). "The Relativistic Binary Pulsar B1913+16: Thirty Years of Observations and Analysis". In F.A. Rasio and I.H. Stairs (eds.). ASP Conference Series 328. Aspen, Colorado, USA: Astronomical Society of the Pacific. p. 25. arXiv:astro-ph/0407149. Bibcode:2005ASPC..328...25W.
- "The Nobel Prize in Physics 1993". Nobel Foundation. Retrieved 2011-03-12. "for the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation"
- Taylor, J. H.; Weisberg, J. M. (1982). "A new test of general relativity - Gravitational radiation and the binary pulsar PSR 1913+16". Astrophysical Journal 253: 908–920. Bibcode:1982ApJ...253..908T. doi:10.1086/159690.
- Taylor, J. H.; Weisberg, J. M. (1989). "Further experimental tests of relativistic gravity using the binary pulsar PSR 1913 + 16". Astrophysical Journal 345: 434–450. Bibcode:1989ApJ...345..434T. doi:10.1086/167917.
- Weisberg, J. M.; Nice, D. J.; Taylor, J. H. (2010). "Timing Measurements of the Relativistic Binary Pulsar PSR B1913+16". Astrophysical Journal 722: 1030–1034. arXiv:1011.0718v1. Bibcode:2010ApJ...722.1030W. doi:10.1088/0004-637X/722/2/1030.