A pulsar has just confirmed another piece of the general relativity puzzle Einstein predicted, and it’s the first real detection of an effect known as ‘frame dragging.’ And it’s kind of a big deal.
Frame dragging, or lense-thirring, basically states that spacetime will churn like honey around a rotating body with gravitational mass. We've seen traces of the effect before around the Earth, but we're fairly gravitationally tiny, so the effect was hardly definitive.
Enter the pulsar in question. In January 2020, scientists published their observations of just such a special case. The scientists watched a binary star system with some unusual qualities. One star is a white dwarf about the size of the Earth but much chunkier, about 300,000 times the density. And this white dwarf is spinning so fast it completes a rotation in a matter of minutes. That mass and speed means it drags space-time around it much more strongly than Earth does.
This system moves so comparatively quickly that we can literally observe its evolution, in this case using the Parkes and UTMOST radio telescopes in Australia. Their orbit has drifted slightly over time, and the only possible explanation is frame dragging.
Find out the answer and more in this Elements.
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Lense–Thirring frame dragging induced by a fast-rotating white dwarf in a binary pulsar system
Frame dragging is a predicted phenomenon in general relativity, whereby a rotating mass drags the surrounding spacetime around with it. Venkatraman Krishnan et al. analyzed timing observations of PSR J1141-6545, a young pulsar in a binary orbit with a white dwarf. Modeling the arrival times of the radio pulses showed a long-term drift in the orbital parameters. After considering possible contributions to this drift, they concluded that it is dominated by frame dragging (the Lense-Thirring effect) of the rapidly spinning white dwarf. These observations verify a prediction of general relativity and provide constraints on the evolutionary history of the binary system.
Einstein's Warped View of Space Confirmed
Any object with mass warps the space-time around it, in much the same way as a heavy object deforms a stretched elastic sheet, explained study leader Ignazio Ciufolini of the Universitá di Lecce in Italy. If the object spins, another distortion is introduced, "in the same way as the elastic sheet would be twisted by a spinning heavy wheel on it." If the space around Earth is being frame-dragged, then satellites ought to be caught up in the deformation, scientists reasoned.
White dwarf causes strange relativity effect called frame dragging
The easiest way to understand frame dragging is to imagine sticking something in a pool of water and starting to rotate it. As the speed of the rotation increases, the water will begin to swirl around the object. Something similar happens when a massive object is rotating, except the fluid it's rotating in is space-time itself.