A binary star system consisting of two neutron stars, one of which is a pulsar, orbiting each other
A pulsar binary is two neutron stars, one of which isPulsar, a binary system formed by orbiting each other around each other.The term is also used to mean circling any other star.There are 120 known pulsar binaries.However, astronomers reserved the term "this pulsar binary" for the first pulsar binary that was discovered, and it is also called PSR 1913+16 (PSR stands for pulsar) according to its number in the celestial table.This pulsar binary provides the most accuratetest。[1]
Pulsar binary PSR1913+16 was founded in 1974 byUniversity of MassachusettsOfRussell Hulse (Russell Hulse) andJoseph Taylor (Joseph Taylor)Puerto RicoOfArecibo Radio Telescope Found.Huls was a graduate student at that time, and was in charge of the daily work of a project to search for pulsars with the telescope.His mentor, Taylor, was the general manager of the project. In the summer of 1974, he regularly flew from Amherst, Massachusetts, to Arecibo.The discovery they made that summer was extremely important, and in 1993, both were obtained by the research of pulsar binariesNobel Prize。[1]
Discovery process
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On August 2, the instrument recorded a very weak signal, which was the first sign of the existence of the pulsar binary.If the signal is even 4% weaker, it will be lower than the built-in cut-off level of the computer search program and will not be recorded.This source is particularly interesting because its period is very short, only 0.059 seconds, which is the second fastest pulsar known at that time.But it was not until August 25 that Huls was able to use itArecibo telescopeObserve this object in more detail.
After August 25, Huls made a series of observations on the pulsar for several consecutive days and found that its changes were very special.Most pulsars are super accurate clocks, with the beat period accurate to 6 or 7 decimal places;This period seems to be erratic, with daily variations of up to 30 microseconds (a huge "error" for pulsars).By the beginning of September 1974, Hoose understood that these changes are also periodic in themselves, and can be explained by the Doppler effect caused by the pulsar moving around a companion star in a strict orbit.
Taylor flew to Arecibo to participate in this research. He worked with Huls to find out that the orbital period of the pulsar moving around its companion (the "year" of the pulsar) is 7 hours and 45 minutes, and the maximum speed of the pulsar movement (according toDoppler effect）300 kilometers per second is one thousandth of the speed of light, while the average speed of flying around the companion star is about 200 kilometers per second.At this amazing speed, the length of the orbit that was completed in less than 8 hours was about 6 million kilometers, roughly the circumference of the sun.In other words,PulsarThe average distance from the companion star is approximately equal to the radius of the sun, so the entire binary system can just be placed inside the sun.
research meaning
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All pulsars areneutron star；For this object, its orbital parameters indicate that the companion star must also be a neutron star.One of the key tests of general relativity isMercuryOfPerihelion precession, isEinsteinTheory rather thanIsaac NewtonGravitational theoryPredicted orbital displacement.The two researchers calculated that this effect ("near star" displacement) of the pulsar binary PSR1913+16 is about 100 times stronger than that of Mercury.Moreover, Mercury orbits the sun only four times a year, while this pulsar can orbit the companion star 1000 times a year, which provides much more opportunities to study this effect.The measurement was completed in time, and the results proved that the near star precession of the pulsar binary was exactly consistent with the prediction of Einstein's theory - this was the first direct test of general relativity using extrasolar objects.Combining the near star displacement measurement results with the orbital data of the binary star system, the mass of the two stars in the system was finally determined to be 2.8275 times the mass of the sun with unprecedented high accuracy.
But this is just the beginning of using this pulsar binary as a laboratory to test and apply Einstein's theory.Further observations lasting for several months show that the accuracy of the pulsar as a clock is extremely high as long as the changes caused by orbital motion are deducted.Its 0.05903 second cycle only increases by 1/4 nanosecond (a quarter of a billionth of a second) in a year - equivalent to a clock that is only 4% slower in a million years.
With the increase of the number of observations, the relevant figures are more and more accurate: the period is 0.059029995271 seconds;The growth rate is 0.253 nanoseconds per year;Orbit period 27906.98163 seconds;The change rate of perigee is 4.2263 degrees per year.Because the period of the pulsar is actually changing, the above highly accurate number is for a specific date, or "epoch", which is September 1, 1974.
On January 10, 2004 (Beijing time), Andrew Rainey, director of the Yodelier Embankment Observatory in the United Kingdom, and others published an article in the latest issue of Science, reporting that they had recognized a rare binary group consisting of two pulsars.Through this unique pulsar binary, we can detect Einstein's theory of relativity and better understand the energy rays produced by pulsars.LondonRoyal Observatory Greenwich Robert Mather believes that this is an extremely important discovery.Although Einstein predicted the existence of gravity waves, he never directly observed gravity waves.Mather said that there are not many sources that can emit sufficient gravity waves. Pulsar binaries are one of the few sources of sufficient gravity waves.
High observation accuracy will soon make more tests and applications of relativity possible.One of the tests involves the prediction of special relativityTime dilation。Since the speed of pulsar moving around the companion star reaches a large part of the speed of light, the observation shows that the "clock" of pulsar is slowing down, and the degree of slowing down is related to its speed.Since the speed per hour is changing along the orbit (from the highest speed of 300 kilometers per second to "only" 75 kilometers per second), this will be reflected in the regular change of the pulsar period in each orbital period.Because the orbit of the pulsar around the companion star is elliptical, its distance from the second neutron star is changing.This means that when it moves from the area with strong gravitational field to the area with weak gravitational field, its timekeeping device should be affected by the regularly changing gravitational field.
The combination of these two effects makes the maximum change of pulsar period in an orbital period to 58 nanoseconds.This variation can be introduced into orbit calculation to determine the mass ratio of two stars.Since the displacement of the near star point indicates that the total mass of the two stars is 2.8275 solar masses, this value, together with the mass ratio of the two stars, gives that the mass of the pulsar itself is 1.42 times the mass of the sun, and the mass of its companion star is 1.4 times the mass of the sun.This is the first accurate measurement of the mass of a neutron star.
However, the biggest victory of studying PSR1913+16 is yet to come.Almost immediately after the announcement of the discovery of this pulsar, there were severalrelativityExperts pointed out that in theory, the pulsar binary should beGravitational radiationThe loss of energy creates ripples in time and space.The loss of energy will cause the pulsar and its companion to hover close to each other, resulting in accelerated orbital motion.
Discovery value
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Test value
Even in the extreme case of pulsar binaries, this effect is very small.It will cause the orbital period (about 27000 seconds) to be reduced by only 10 millionths of a second per year (about 0.0000003 seconds).The theory is straightforward, but the observation must reach unprecedented accuracy.In December 1978, after four years of work, Taylor announced that he had measured this effect, and it was completely consistent with the prediction of Einstein's theory.The accurate prediction of the theory is that the orbital period should be reduced by 75 millionths of a second every year.By 1983, nine years after the discovery of the pulsar binary, Taylor and his colleagues had measured this change with an accuracy of two millionths of a second per year, and the published observation value was 76 ± 2 seconds per millionth per year.Since then, the observation has been further improved, reaching a high degree of consistency with Einstein's theory, with an error of less than 1%.This is the most sensational and comprehensive test of general relativity so far, which actually excludes the possibility of any other theory as a reliable description of the behavior of the universe.The accuracy of the test is so high and the consistency with the theory is so good that general relativity and quantum electrodynamics are ranked as the two most stable disciplines in the whole science.
theoretical value
In principle, the pulsar binary PSR1913+16 and other similar systems provide more accurate time measurement than any artificial clock, including the most accurate atomic clock.If we measure the change of a single pulsar binary only with the atomic clock, we will never be able to prove it.However, if the signals of at least three pulsars are compared with those of the atomic clock and with each other, it should be possible to create a method of using (mutually calibrated) pulsars to improve the timekeeping of the atomic clock.Just as it is possible to define the length of a second by the behavior of cesium atoms rather than by the rotation of the earth, it is not impossible to define the length of a second by a pulsar binary one day.
