Taylor, Joseph Hooton, Jr. (1941-) is an American astrophysicist and radio astronomer acclaimed for discovering the first binary pulsar, a system of two collapsed stars that emit tremendous energy as they rotate rapidly around one another. Taylor's work in this area, done in collaboration with American physicist Russell Alan Hulse, gave the first true indications of gravitational waves as predicted by Albert Einstein's general theory of relativity. In 1993, Taylor and Hulse jointly received the Nobel Prize in physics for their discoveries.
Taylor, the second son of Joseph and Sylvia Evans Taylor, was part of a large, extended Quaker family. From the time he was 7, the family lived on his paternal grandfather's farm in New Jersey, and there, with his brother Hal, he had his first experiences with radio transmitters and receivers. The brothers constructed multiple variations of working ham radio equipment using their own ingenious mix of abandoned television parts and army surplus odds and ends, and experimented with erecting several radio antennae on the roof of the family home.
In school, Taylor was naturally drawn to the sciences, particularly math, and also participated in many sports. He attended Moorestown (New Jersey) Friends School and then Haverford College, both Quaker institutions. At Haverford, he concentrated on physics and began to study radio astronomy in greater depth. As a senior honors project, Taylor built a working radio telescope, using as one of his guides the Radio Amateur's Handbook, by then well known to him.
After receiving his B.A. degree from Haverford in 1963, Taylor was admitted to Harvard as a graduate student. There he did work in astronomy, applied mathematics, and physics, and ultimately began thesis research in radio astronomy, working under Alan Maxwell. He was awarded his Ph.D degree in astronomy in 1968, after which he spent an additional year at Harvard as a research fellow and lecturer in that discipline. From 1969 until 1980, Taylor was a member of the faculty of the University of Massachusetts at Amherst, rising from assistant professor to associate professor in 1973, and becoming full professor in 1977. He then joined the physics department of Princeton University in 1980. He remains at Princeton, being named the James S. McDonnell Distinguished University Professor of Physics there in 1986.
Taylor first began the work that led to his Nobel Prize in the early 1970's. At that time, Hulse, one of his graduate students, was looking for a suitable thesis project, and together they came to the idea of investigating pulsars. Pulsars, discovered in 1967, by British astronomers Joceyln Bell (later Jocelyn Bell Burnell)and Antony Hewish, are rapidly rotating neutron stars created by the explosions of supernovas—stars that, in exploding, briefly emit huge amounts of energy and light.
Pulsars are known to have extremely small diameters relative to most other stars—in some cases no more than 6.2 miles (10 kilometers) across—but at the same time they have tremendous mass, often as great or greater than that of the sun. Because they are also surrounded by a powerful magnetic field, radio waves are emitted only from their poles, in narrow, cone-shaped beams. As a pulsar spirals through space, these radio waves are picked up on the earth as pulses, much like the intermittent beams emitted from lighthouses.
Because of the weakness of these pulsar radio signals as they sweep past the earth, however, huge radio telescopes are required to detect them. Therefore, Taylor and Hulse chose to conduct their own pulsar search at Puerto Rico's Arecibo Observatory, which houses the world's largest single-element telescope—equipment having a massive 1,000 foot- (305 meter-) diameter. In the course of their work together, Taylor and Hulse found 40 new pulsars, but their history-making discovery occurred on July 2, 1974.
On that date, their analysis of the incoming data indicated a pulsar exhibiting unusual behavior. Whereas all previously known pulsars had been recorded as having an invariable pulsation rate, the signals from this particular pulsar occurred in irregular periods. However, though the rate of pulsation alternately increased and decreased over time, the men found that these changes occurred at a constant average value, leading them to suspect the existence of a companion body pulsating along with the pulsar itself. Unexpected though their findings were, the scientists were able to conclude that these two bodies were both neutron stars, and of similar weight, each about 1.4 times heavier than the sun.
In further calculating the possibilities of such a binary system—two pulsars orbiting each other at high velocity—Taylor and Hulse determined that the distance between the two objects would be several times the distance between the earth and the moon. They named their find, the first binary pulsar ever discovered, PSR 1913 + 16, PSR standing for “pulsar” and the numbers indicating its location in the sky. Its discovery was soon to produce a revolutionary ripple within the world of radio astronomers and astrophysicists. After calculating the orbit of the binary pulsar based on its pulse sequence, Taylor and Hulse continued to observe and record its behavior. They found that the two stars were gradually drawing closer together—their orbit was contracting—while at the same time they were rotating with ever-increasing speeds. They also determined that the system's eight-hour orbit was decreasing by about 75 millionths of a second per year. This collective data provided the first experimental confirmation that there was a magnetic component to gravity—that Albert Einstein's predicted gravitational waves did in fact exist.
This prediction was part of Einstein's 1915 general theory of relativity, a generalization and extension of his earlier theory of special relativity. Whereas special relativity presents the physics behind space and time, general relativity also addresses the effects of gravitational forces, superseding the theories put forth by Isaac Newton. According to general relativity, the powerful electromagnetic field created by two bodies rotating rapidly around one another would cause the emission of these so-called gravitational waves. The theory further states that the loss of energy caused by these radio waves would in turn bring the two bodies increasingly closer together.
No one had found any physical confirmation of these predictions prior to the discovery of PSR 1913 + 16, but about four years after that event, Taylor was able to report that the dual bodies of the binary pulsar were in fact rotating toward each other at a rate so consistent with Einstein's calculation as to exhibit only about 0.5 percent inaccuracy. Although the technology to observe gravitational waves has yet to be developed, the coincidence between Einstein's theoretical calculations and the observed orbital values, gathered over a 20-year observation of PSR 1913 + 16, provides convincing evidence of the existence of such waves, and gives powerful support to the general theory of relativity itself.
There has been another profound effect of Taylor and Hulse's discovery. Gravity is the oldest known natural force, but because the earth's gravitational field is so weak, it has been extremely difficult to study. Any deviations from Newton's theory of gravity have been virtually impossible to detect. But the discovery of binary pulsars, with their relatively huge deviations, made feasible a new branch of astronomy altogether, gravitational wave astronomy, in which scientists can now study the effects and gather data on phenomena that would otherwise be impossible to observe or even to suspect the existence of.
Taylor himself has continued the search for and study of binary pulsars. He discovered a second one in 1985, with a research assistant, and has since found others. With his associates, Taylor has also measured several other of Einstein's general relativity predictions in this “laboratory in the sky,” with equally accurate results. Dozens of other relativity effects remain to be measured, but Einstein's theory continues to stand up to the tests.
The value of Taylor's work has been recognized in many prizes and appointments in addition to his Nobel award. In 1980, he was the recipient of the Dannie Heineman Prize given by the American Astronomical Society and the American Institute of Physics. In 1985, he was awarded both the Henry Draper Medal and the Tomalla Foundation Prize in gravitation and cosmology, and in 1992, received the Wolf Prize in Physics. Taylor is also a fellow of the American Academy of Arts and Sciences and a member of the American Philosophical Society and the National Academy of Sciences