From Popular Mechanics
A pair of extremely fast stars locked in a shared orbit have let scientists measure naturally occurring frame dragging for the first time.
Frame dragging is a consequence of general relativity, and studying it could help scientists understand subatomic particle bonds and more.
This special binary system is so fast that it produces measurable results over a much shorter time.
A team of astrophysicists from around the world has been following an unusual pair of spinning stars for almost 20 years, and now they say the binary system is persuasive evidence of frame dragging. In a new paper in Science, the researchers say the white dwarf and neutron star that spin extremely fast together form an edge case to demonstrate relativity.
"Relativistic frame dragging" is an offshoot of Einstein's general theory of relativity-the idea that individual objects in the curvature of spacetime cause changes within that spacetime-where scientists observe that objects with energy can cause spacetime to bend and bunch in order to absorb the extra energy.
In this case, a special binary system is so forceful and sped up that the effects are more visible to scientists. The system, named PSR J1141-6545, is made of two stars: "One is a white dwarf, the size of the Earth but 300,000 times its density; the other is a neutron star which, while only 20 kilometres in diameter, is about 100 billion times the density of the Earth," the press release says.
Something so tiny and extremely dense, especially in a conjoined spin with a second star that itself would be considered quite small and quite dense in any other circumstance, ends up spinning so fast that it bends and wobbles. The tiny neutron star is a pulsar, meaning it emits a steady beam of light that can be tracked as it spins, like when the sun's reflection off a metal object points directly in your eyes as you walk past.
Monitoring the frequency of these spinning pulses lets scientists begin to make an overall picture of how the neutron star is orbiting. All pulsars are useful for research into astrophysics because of the way their size and density makes them behave extremely. In this case, the pulsar is locked in a tight and extremely fast orbit, and over the last two decades, scientists have watched this orbit evolve rapidly compared with other objects in space that are larger, slower, and generally operating on a longer scale of time.
All of this means that for the first time, astrophysicists have recorded evidence of the predicted phenomenon of frame dragging. If spacetime is colloquially indeed a "fabric," it's an elastic one, where spinning objects receive that stored energy back from the fabric of spacetime itself. And objects within spacetime can pass energy back and forth the same way, making it both convenient and attractive, literally, to join into energy-saving pairs like this binary system.
The orbit of the two stars continues to drift and change, like a spinning figure skater who accelerates by pulling in their limbs. It's this change in speed and orientation that let scientists observe the frame dragging, in the form of an observable spin change called the Lense-Thirring effect. "This detection is consistent with an evolutionary scenario in which the [white dwarf (WD)] accreted matter from the pulsar, spinning up the WD to a period of <200 seconds," this research team concludes.
Scientists have longed for evidence of frame dragging in the wild, so to speak, because the idea could explain a lot of things we don't understand yet about relativity, gravity itself, and forces that affect everything from celestial objects to subatomic particles. By observing a forceful and extremely fast binary star, these scientists have recorded what they say is the first such evidence, and the first step toward better understanding the universe.
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