Designated PSR 1913 + 16, the Hulse-Taylor Pulsar was discovered in 1974 by Russell A. Hulse and Joseph H. Taylor. both of Princeton and was the first known binary pulsar system. Hulse-Taylor has a mass very close to that of the Sun, and like other pulsars, it spins very rapidly on its axis, making approximately 17 complete revolutions every second. However, unlike any previously known pulsar, Hulse-Taylor's pulse frequency, which should have rivaled an atomic clock in precision, varied smoothly between 16.958 per second and 16.935 per second over a period of 7.75 hours.

Hulse and Taylor drew the conclusion that the pulsar must be part of a binary system. Further observation confirmed that it was circling a main sequence star of almost equal mass in a remarkable orbit varying from 1.1 to 4.8 solar radii, only a few times greater than the distance from the Earth to the Moon. Realizing that this was a potential jackpot find for theoretical physics, Hulse and Taylor continued observation of the star for a period of several years. Through these observations, they demonstrated that Einstein's theory of General Relativity correctly predicted:

  • Time dilation, measured as the change in frequency of the pulses
  • Orbital precession of a whopping 4 degrees a year more than predicted by Newton's theory
  • Gravity waves radiating from the system, which are a unique prediction or General Relativity. Long-term observation showed that the system was losing energy and that the stars were spiraling in towards each other, decreasing their orbital period at a rate of 75 millionths of a second each year
  • All of these predictions, most notably the gravity waves, were accurate to less than one percent of the predicted value. For their work on this pulsar system, Hulse and Taylor were awarded the Nobel Prize in Physics in 1993.

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