Original | Emily Conover
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The only pair of pulsars known has just revealed a wealth of unique cosmic insights.
For 16 years, scientists have been observing the pair of pulsars, or neutron stars that pulsate. In a paper published Dec. 13 in Physical Review X, physicists said the measurements confirmed that Einstein's theory of gravity, known as general relativity, reached a new level of precision and hinted at the subtle effects of the theory.
Pulsars are spinning dead stars made up of dense neutrons that appear to flicker on and off because their lighthouse-like beams of radiation regularly sweep across The Earth. These changes in pulse time can reveal the motion of pulsars and the effects of general relativity. While physicists have discovered many individual pulsars, the only pair of known pulsars orbiting each other is this one. In 2003, the discovery of the dual-pulsar system J0737-3039 opened up possible new avenues for testing general relativity.
One of the pulsars rotates about 44 times per second, while the other rotates about every 2.8 seconds. The slower pulsar dimmed in 2008 due to a strange phenomenon in general relativity that rotated its beam out of view. The researchers will continue to monitor the remaining visible pulsars and then combine the new data with the old observations to improve the accuracy of the measurements.
Here are five takeaways from the new study:
1. Einstein was right in many ways.
With this pair of pulsar binary stars, we can simultaneously perform five independent tests of general relativity to test whether the various properties of the orbit conform to the predictions of Einstein's theory. For example, the researchers measured the rate at which the orbital elliptical rotated or precessed to see if it was consistent with expectations. The result is that all the parameters conform to Einstein's theory.
What's more, Scott Lansheim, an astrophysicist at the National Radio Observatory in Charlottesville, Virginia, said, "Every individual test of general relativity has become so precise that ... Higher-order effects of general relativity must be included to match the data. "This means that the measurements are so precise that they suggest subtle properties of gravity."
2. Gravitational waves are draining energy.
Observations show that the orbit of the pulsar is shrinking. By measuring the time it takes for the pulsar to complete its orbit each time, the researchers determined that the pair shortens the distance for the pulsars by about 7 millimeters per day.
This is because pulsars, when in operation, excite gravitational waves, which are ripples of space-time that vibrate outward and take away energy. This apparent contraction was first discovered in a galaxy with one pulsar and one neutron star in the 1970s, providing early evidence for the existence of gravitational waves. But the new results are 25 times more accurate than previous measurements.
3. Pulsars are losing mass.
There is also a subtle effect that will change this track. Pulsars gradually slow down over time and lose their rotational energy. Because energy and mass are two sides of the same coin, this means that faster pulsars lose about 8 million tons of mass per second.
Kramer said: "When I first realized this, I was really stunned. While this sounds like a lot, the loss of mass only affects minor adjustments to the track. Previously, scientists could ignore this effect in their calculations because the change was very small. But now the measurement of the orbit is accurate enough, so it makes sense to take it into account.
4. We can know the direction of rotation of the pulsar, which implies its origin.
When a pulsar's light passes through its companion, by studying the timing of the pulse, scientists can know in which direction the faster pulsar is rotating. The results showed that the pulsar rotated in the same direction as its orbit, which provided clues to the formation of the pair's binary stars.
The two pulsars begin with successive explosions of adjacent stars. Normally, when a star explodes, the remnants it leaves behind are washed away, causing them to split apart. The faster pulsar rotates in the same direction as its orbit, meaning that the explosion that formed the pulsar didn't shake it too much, which helps explain how the binary system remains intact.
5. We have clues about the radius of the pulsar.
It is well known that gravitational effects cause the ellipsoid of an orbit to precede or rotate about 17 degrees per year. But in the new study, a subtle adjustment was involved. As the pulsar spins, it acts like a spinning dancer's twisted skirt, dragging the structure of space-time behind it, thus altering the spiral.
This drag effect means that the faster pulsar must have a radius of less than 22 kilometers, and if more precise in future work, this estimate will help reveal the physics of the extremely dense neutron star material that makes up the pulsar.
original:
https://www.sciencenews.org/article/pulsar-dead-stars-general-relativity-einstein