| Observation data Epoch B1950.0 Equinox B1950.0 |
|
|---|---|
| Constellation | Aquila[1] |
| Right ascension | 19h 13m 12.4655s |
| Declination | 16° 01′ 08.189″ |
| Astrometry | |
| Distance | 21,000 ly (6400 pc) |
| Details [2] | |
| Mass | 1.441 M☉ |
| Radius | 1.4×10−5 R☉ |
| Rotation | 59.02999792988 ms |
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 Princeton University. Their analysis of the system, which strongly suggested that it was losing energy by emission of gravitational waves in accordance with the general theory of relativity, earned them the 1993 Nobel Prize in Physics.[3]
The system is also called the Hulse–Taylor binary pulsar after its discoverers.
Contents |
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.
The pulsar and its companion both follow elliptical orbits around their common center of mass. The period of the orbital motion is 7.75 hours, and the stars are believed to be nearly equal in mass, about 1.4 solar masses.
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).[4] In January 1975, it was oriented such 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 total power of the gravitational radiation (waves) emitted by this system presently, is calculated to be 7.35 × 1024 watts.[5] 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 gravitation wave 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.[2]
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.[6]
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."