Tech UPTechnologyConfirmed: a star can 'drag' space-time around it

Confirmed: a star can 'drag' space-time around it

The theory of general relativity is full of strange predictions about how massive bodies affect space and time; But one of the strangest predictions is an effect known as space-time drag .

Now, an international team of astrophysicists led by Australian professor Matthew Bailes of the ARC Center of Excellence at Gravitational Wave Discovery has shown exciting new space-time drag tests, observing how the spin of a white dwarf twists space and space. weather. The effect is so subtle that it was first measured only a decade ago. The data, which provide additional evidence for Albert Einstein’s theory of general relativity, have been published in the journal Science.

In general relativity, gravity is not a force. The presence of a mass bends the space around it, which means that objects moving near the mass deviate from a straight path. The deflection makes it appear that the object is being pulled toward the mass as by a force we call gravity. When a large mass is rotating, the space also rotates slightly in the direction of rotation . This effect is what is known as carry-over.

Thus, for the past 20 years, researchers have been using radio telescopes to track the motion of a pulsar, the dense remnants of a massive star that went supernova, and a spinning white dwarf. The white dwarf about the size of Earth but about 300,000 times heavier and a radio pulsar barely the size of a city but 400,000 times denser.

The pulsar, called PSR J1141–6545 , emits a constant rhythm of radio waves as it spins, and by recording the arrival times of those pulses, the researchers are able to figure out when the pulsar is moving to and from Earth. This exotic stellar pair is located 12,000 light years distant from Earth , in the constellation of La Mosca (Musca).


We can’t put a satellite around the white dwarf, but we don’t need to. Pulsars are incredibly precise clocks, emitting radio waves from their magnetic poles at precise intervals, as we’ve discussed. The team used this score of years of radio data to measure subtle changes in the pulsar’s orbit.

“With the help of atomic clocks, we were able to make very accurate measurements of the arrival times of the pulsar signals at the Parkes and UTMOST radio telescopes,” said Vivek Venkatraman Krishnan of the Max Planck Institute for Radio Astronomy and leader of the work.

According to general relativity, any rotating mass carries spacetime with it. And so it is. A twist in the structure of space-time, predicted by the theory of general relativity, is causing the orbit of a stellar corpse to wobble around another stellar corpse. And this event is helping astronomers reconstruct the last days of these two long-dead stars.

The motion of these stars would have puzzled astronomers in Isaac Newton’s time, as they clearly move in warped spacetime, and require Einstein’s general theory of relativity to explain their trajectories.

The white dwarf and the pulsar orbit each other every five hours, so the drag is quite weak, despite the size of the star. Still, over the course of 20 years, astrophysicists estimated that the pulsar’s orbit would have drifted about 150 kilometers.

“Observations of the J1141-6545 pulsar show such a deviation that, after detailed calculations and ruling out a range of possible experimental errors, it was confirmed to be caused by a change in its orbital orientation,” said study co-author Willem van Straten. They also discovered that the white dwarf rotates on its axis every 100 seconds, confirming the hypothesis of the moment of its formation.

It’s funny, because the normal thing would be for the supernova to explode and then the progenitor of the white dwarf spews gas at the pulsar after the explosion, aligning the spin to orbit. But in this case, the complete opposite has happened: the parent of the pulsar was the one that spewed gas on the white dwarf and then the supernova took place.

Reference: V. Venkatraman Krishnan el al., “Lense – Thirring frame dragging induced by a fast-rotating white dwarf in a binary pulsar system,” Science (2020).… 1126 / science.aax7007

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