A spinning binary radio pulsar proves Einstein's theory

James Marshall
February 1, 2020

The findings confirm the prediction of general relativity and allowed the team to constrain the white dwarf's rotational speed. The pulsar is located 10,000 to 25,000 light-years from Earth in the constellation Musca (the fly), which is near the famous Southern Cross constellation.

This imply, multiple times each moment, a "lighthouse beam" of radio waves transmitted by this pulsar clears past our vantage point here on Earth.

“This pulsars orbit is very special.

The pulsar orbits the white dwarf in a tight, fast orbit less than 5 hours long, hurtling through space at about 620,000 mph (1 million km/h), with a maximum separation between the stars barely larger than the size of our sun, study lead author Vivek Venkatraman Krishnan, an astrophysicist at the Max Planck Institute for Radio Astronomy in Bonn, Germany, told Space.com.

The white dwarf is the size of the Earth but 300,000 times its density; the neutron star, only 20 kilometers in diameter, is about 100 billion times the density of the Earth. People can utilize this to delineate way of the pulsar as it circles the white diminutive person, by timing when its heartbeat lands at our telescope and knowing the speed of light.

Contrasted and white smaller people, pulsars are in another group out and out.

"Systems like PSR J1141-6545, where the pulsar is younger than the white dwarf, are quite rare", Venkatraman Krishnan said. The answer came from an unexpected direction and leads back over 100 years in the development of theoretical physics. Throughout the following two decades, it became apparent that the stars' motion required Einstein's General Theory of Relativity to clarify their intricate dance. To put it simply, the rotation of a mass swirls the space-time in its vicinity, an effect commonly known as “frame-dragging”.

Later in 1918, Josef Lense and Hans Thirring - with substantial support from Albert Einstein - calculated this effect for our Solar System using general relativity. While frame-dragging has been detected by satellite experiments in the gravitational field of the rotating Earth, its effect is tremendously small and challenging to measure.

White dwarfs, remnants of dead stars, can spin very quickly, rotating every minute or two, rather than every 24 hours like Earth does. It is expected to rotate around its own axis within a few minutes.

"One of the first confirmations of frame-dragging used four gyroscopes in a satellite in orbit around the Earth, but in our system the effects are 100 million times stronger", said Dr. Norbert Wex, a researcher in the Max Planck Institute for Radio Astronomy.

“With the help of atomic clocks, we were able to perform highly accurate measurements of the arrival times of the pulsar signals at the Parkes and UTMOST radio telescopes.

Since 2001 the team of scientists would visit Parkes several times a year to map this system's orbit. As space and time get dragged, the pulsar's orbit has slowly changed its orientation over time.

The white dwarf drags space-time, which then causes the pulsar's orbital plane to "tilt" as well. However, the Lense-Thirring precession should still cause, over these 20 years, precession of the pulsar's path of about 150 km.

"After ruling out a range of potential experimental errors, we started to suspect that the interaction between the white dwarf and neutron star was not as simple as had been assumed to date", said Dr. Willem van Straten, from the Auckland University of Technology.

In everyday life, frame-dragging is both undetectable and inconsequential, as the effect is so ridiculously tiny.

"There's only two confirmed binary systems like that where the white dwarf is known to have formed before the other companion", she said.

The resulting "frame-dragging" effect proves another aspect of Einstein's theory of relativity.

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