of the black holes gravitational waves and gravitational lens effects, Albert Einstein’s theory of general relativity made many predictions that have been experimentally validated over time. However, some of these predictions are less known than others. This is the case with the Lense-Thirring effect, which describes a phenomenon of space-time training around very dense objects in very fast rotation. Launched in 2004, NASA’s Gravity Probe B satellite made it possible to confirm this phenomenon experimentally in 2011. And recently, astrophysicists have once again been able to confirm the Lense-Thirring effect around a white dwarf as part of a binary system.
In everyday life, this phenomenon is both undetectable and inconsequential, because the effect is ridiculously small. Detecting the spacetime entrainment caused by the rotation of the Earth requires satellites such as the $ 750 million Gravity probe B and detecting angular changes in gyroscopes equivalent to one degree every 100 ‘000 years approximately.
Fortunately, the Universe contains many natural gravitational labs where physicists can observe Einstein’s predictions in detail. This new study, published in the journal Science, reveals evidence of the Lense-Thirring effect on a much larger scale, using a radio telescope and a unique pair of compact stars spinning around each other at breakneck speeds.
A white dwarf and a pulsar to confirm the Lense-Thirring effect
The movement of these stars would have made astronomers perplexed at Newton’s time, because they move in a distorted space-time, and require the general theory of relativity of Einstein to explain their trajectories. One of his lesser-known predictions of this theory is that rotating bodies carry space-time with them. The faster an object turns and the more massive it is, the more powerful the drive.
White dwarfs are a great place to study this process. They are similar in size to Earth but hundreds of thousands of times more massive. They can also rotate very quickly, up to one revolution per minute. The training caused by such a white dwarf would be about 100 million times more powerful than that of Earth.
Illustration showing the Lense-Thirring effect in a white-pulsar dwarf binary system. Credits: Mark Myers / OzGrav ARC Center of Excellence
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Twenty years ago, CSIRO’s Parkes radio telescope discovered a unique star pair made up of a white dwarf (about the size of Earth but about 300,000 times more massive) and a radio pulsar. Pulsars consist of neutrons closely related, which makes them incredibly dense. In addition, they spin much faster than white dwarfs: 150 revolutions / minute for the pulsar studied by the authors.
PSR J1141-6545: an ideal gravitational laboratory for studying general relativity
This means that, 150 times per minute, a beam of radio waves emitted by this pulsar scans our point of observation here on Earth. Astrophysicists can use it to map the path of the pulsar as it orbits the white dwarf, timing when its pulse arrives at the telescope, and knowing the speed of light. This method revealed that the two stars orbit each other in less than 5 hours.
This pair, officially called PSR J1141-6545, is an ideal gravitational laboratory. Since 2001, researchers have used Parkes several times a year to map the orbit of this system, which has a multitude of gravitational effects.
Although PSR J1141-6545 is several hundred quadrillion kilometers (one quadrillion is a million billion), the data shows that the pulsar rotates 2.54 times per second, and that its orbit varies in space. This means that the plane of its orbit is not fixed, but rotates slowly.
On the same subject : The study of a pulsar confirms one of the predictions of general relativity
Binary system: the companion star allows the acceleration of the rotation of the white dwarf
When pairs of stars are born, the most massive one dies first, often creating a white dwarf. Before the second star dies, it transfers matter to its white dwarf companion. A disc forms when this material falls towards the white dwarf, and over tens of thousands of years it accelerates the latter until it makes a full revolution every few minutes.
Many binary systems involve a giant star and a white dwarf, the latter accreting matter from the former. This accretion leads to an acceleration of the rotation of the white dwarf. Credit: Pearson Ed
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In rare cases like this, the second star can then explode into a supernova, leaving behind a pulsar. The rapidly spinning white dwarf carries space-time with it, rocking the pulsar’s orbital plane as it moves. This tilt is what astrophysicists have observed through the mapping of the pulsar’s orbit.
Sources: Science
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