More than 100 years ago, after Einstein proposed general relativity, many astronomers put forward the hypothesis that general relativity could be validated by astronomical observations, and the drag effect of the coordinate system was one of them. Today, general relativity has long been verified, but the weak coordinate system drag effect has not been observed and confirmed. Finally, in a study published in the journal Science, a team led by Australia’s Sweeburn University of Science and Technology confirmed the effect for the first time from a rare binary system.
Astronomers have observed coordinate system drag for the first time through the Parks radio telescope. (Photo: Mark Myers ARC Centre for Excellence for Copyright Wave Discovery )
In 1916, Einstein published a general theory of relativity with far-reaching implications for modern physics. But at the beginning of the general relativity, many physicists were skeptical of this – after all, such subversive theories can only be truly accepted by scholars through observational verification.
It is well known that 100 years ago, British scientist Eddington tested general relativity for the first time with the famous total solar eclipse experiment. But beyond that, many physicists have predicted other effects that general relativity can cause. The coordinate system is towed, and is one of them.
In 1918, two Austrian physicists, Josef Lense and Hans Thirring, realized that if general relativity were established, any celestial body would have a drag effect on the surrounding space-time as it turned around. This phenomenon is called coordinate system drag (Frame-dragging) or inertial system drag.
The following example can help us understand the above phenomena. We pour edges the sticky syrup into a bowl and press a spherical lollipop in. What happens when we quickly turn the lollipop stick? The syrup around the lollipops begins to rotate. Similarly, any celestial body that is spinning around its space-time will shift. However, the syrup is dragged by friction, while the gravitational field is dragged by the drag of time and space.
Although theoretically plausible, it is extremely difficult to actually observe the phenomenon. The coordinate system drag effect is too weak. Almost throughout the 20th century, efforts to find this effect in the universe have been fruitless.
In the 1990s and early 2000s, scientists tried to detect the earth’s rotation of space-time drag with a sufficiently sensitive instrument. To this end, NASA has launched the LAGEOS satellite experiment and gravitational detection B experiment, through the gyroscope and other sensitive means to find this effect. These two experiments, especially the gravitational detection B experiment, have yielded results consistent with general relativity predictions. But the error control of these experiments has not been as expected.
Rare Dual Star System
Because the coordinate system of the small, slow-moving Earth is too weak to drag, astronomers are turning their attention to the more distant universe, hoping to observe it in large mass objects that rotate at high speeds.
In 1999, Australian astronomers through the Parks radio telescope discovered a special binary system in the southern cross constellation, 2,000 light-years away. The binary system, called PSR J1141-6545, consists of a white dwarf star and its companion pulsars. Neutron stars are only 20 kilometers in diameter and have a mass greater than the entire solar system. The white dwarf is slightly smaller than the neutron star and is about the same size as Earth.
A binary system of white dwarfs and pulsars orbiting them. (Photo: Mark Myers ARC Centre of Excellence for El Sei On Wave Discovery)
For astronomers, this binary system provides an excellent place to observe the drag effect of the coordinate system.
On the one hand, the white dwarf has a rotation period of only a few minutes, and the high-speed rotating white dwarf produces a coordinate system drag effect that is 100 million times more than Earth’s.
Of course, this effect alone is not enough for telescopes on Earth to observe. At this point, pulsars orbiting the white dwarf become the key. Pulsars are fast-rotating neutron stars, like lighthouses on the surface of the sea, where their magnetic poles continuously emit radio beams as they rotate. For observers on Earth, this beam of signal is like a precise clock, faithfully recording the orbit of the pulsar. If the interval between signals changes, it means that the orbit of the pulsar has shifted. This offset, on the other hand, is a window into the search for the drag effect of the coordinate system.
Another factor that is not allowed or lacking is the extremely rare birth process of PSR J1141-6545. Dual-star systems consisting of white dwarfs and neutron stars are common, but in such systems, neutron stars are often the first to form. The white dwarf’s more “older” binary system, which counts PSR J1141-6545, has so far confirmed only two.
In such a system, a star is the first to die, forming a white dwarf. White dwarfs acquire the gaseous matter of the companion star and rotate and accelerate;
This is important because PSR J1141-6545 retains the typical magnetic field characteristics of pulsars compared to ordinary binary systems, helping astronomers distinguish their orbital information.
Discover the signal
This system, which brings together all the advantages, naturally becomes the focus of the research team. Since 2000, australia’s Parks telescope and the UTMOST radio telescope have been observing it continuously in the hope of finding evidence of long-term changes in orbital parameters.
In 2015, they finally observed a faint shift in the orbit. But that’s not enough – other factors, in addition to this effect, can also have an impact, such as the rotation itself, which compresses the neutron star more “flat” and changes its gravitational field. Therefore, through data processing, the team sifted other factors from the signal to find long-term, gradual changes in the direction of the orbital plane — such a signal that other effects could not be explained.
The next question is, is this rare twin-star birth valid? Computer simulations confirm this possibility. The astronomers found Thomas Tauris of a university in Aarhus, Denmark, and simulated the process. The study found that systems similar to PSR J1141-6545 were entirely possible after strict restrictions on the initial mass and orbit of the two stars.
The team reported the findings in a recent paper published in the journal Science.
The study finally provides accurate astronomical observational validations for a century-long hypothesis, and once again confirms general relativity. In addition, the discovery of the drag effect of the coordinate system has other implications for modern astronomy.
As the densest substance in the universe, the components of neutron stars are never answered definitively. Venkatraman Krishnan, the study’s lead author, said the effect should also be observed in a binary system made up of two pulsars. Such observations could help scientists confirm the exact volume of these pulsars, revealing their mysterious inner composition.