While pulsars are certainly compact objects, the true gravitational heavyweights are black holes. “But we’ll never find what, if anything, is wrong with relativity unless we keep trying. “In all likelihood, general relativity will pass this as well,” he says. Ransom expects the results by mid-2015, but he isn’t betting against Einstein. The results will be 20 times - possibly 100 times or more - more precise than ever before. In this way, the researchers expect to test whether the strong equivalence principle holds. If, by contrast, the rates were to vary, the pulsar’s orbit would be distorted, and Ransom and his colleagues could use the timing of the pulses to detect this distortion. (Part of an ordinary star or white dwarf also exists as this energy, but a much smaller fraction.) Einstein’s theory predicts that such energy should experience the same gravitational attraction as matter, meaning that Ransom’s pulsar and the white dwarf orbiting near it would be drawn toward the system’s third star at the same rate. When a star collapses into an ultradense object like a pulsar or black hole, some of its matter turns into what’s called gravitational binding energy. The system’s unique geometry will allow the scientists to examine general relativity’s strong equivalence principle, which states that gravity accelerates all objects at the same rate, regardless of their density. Scott Ransom and his colleagues at the National Radio Astronomy Observatory are using the Green Bank Telescope in West Virginia to track the rotation of this odd pulsar, designated PSR J0337+1715. One of these recently discovered pulsars, with a highly unusual orbit involving two other stars known as white dwarfs, can now help physicists test a different prediction of general relativity. Over a 30-year study period, the Hulse-Taylor pulsars spiraled toward one another at exactly the rate Einstein predicted.Įver since Hulse and Taylor stumbled upon their pulsars in 1974, astronomers have turned up thousands more throughout the galaxy. Over time, however, the outgoing gravitational waves would deplete a binary system’s energy, causing the objects to spiral in toward each other. Called gravitational waves, these undulations are so tiny that one passing through Earth would jostle us by far less than the diameter of a proton. Einstein predicted that as dense objects like pulsars orbit each other, they should create ripples in space-time, similar to ripples in a lake. One of the more famous general relativity tests to date involved a pair of pulsars, technically named PSR B1913+16 but better known as the Hulse-Taylor binary pulsar (after Russell Hulse and Joseph Taylor, who won the 1993 Nobel Prize in Physics for its discovery). They’re so tightly packed that a pulsar the mass of our sun would be compressed to a sphere with a diameter about the length of Manhattan. ![]() These extreme objects advertise their presence with intense beams of radiation, sweeping through the sky like cosmic lighthouses, with a regularity rivaling Earth’s best clocks. They aim to detect how gravity behaves in the highly warped regions of space-time near superdense collapsed stars called pulsars. New telescopes and detectors are helping astronomers look far beyond the solar system, where nearly all tests so far have occurred. With today’s advanced instruments, astronomers can for the first time search the universe’s gravitational extremes for relativity’s possible breaking point. Yet most physicists are still betting on that one man. And huge gravitational wave detectors will scan thousands of galaxies for tiny ripples in the cosmic fabric of space-time.Įach of these experiments - some of the most ambitious ever conceived - will test a theory that one man worked out a century ago with pencil and paper. A global effort will soon photograph, for the first time, a black hole. ![]() Powerful telescopes are already looking for minute hiccups in the whirring of stellar corpses called pulsars. “This is where general relativity really gets going,” says Cornish.
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