A new theoretical study argues that sheet-like structures in the gravitational field can break apart and reconnect in new arrangements, much as magnetic field lines do when they unleash solar flares, Live Science reported. The work, published Oct. 28 in Physical Review D, is built entirely on Albert Einstein's theory of general relativity. It spells out when this "gravitational reconnection" can happen, offers a way to measure how fast it proceeds, and suggests a change in how gravity and matter trade energy. The process could even play a role in black hole collisions, the researchers said.
Magnetic field lines are normally "frozen" into the plasma that makes up stars and can be stretched, but not cut. Where that rule breaks down, they can snap and rejoin, releasing energy in bursts such as solar flares. "In plasma physics, reconnection has become an essential part of our understanding of how magnetic fields reorganize and exchange energy with matter," Luca Comisso, an astrophysicist at Columbia University and first author of the study, told Live Science. "Could something similar be true for gravity?" Gravity and magnetism describe very different aspects of nature, he said, "so there's no obvious reason to expect them to behave alike." But when Einstein's equations are written in a particular mathematical form, some of the same principles appear. Comisso and co-author Felipe Asenjo, a physicist at Adolfo Ibáñez University in Chile, used a framework known as the tetrad formulation, in which certain aspects of gravity can be expressed through quantities that resemble electric and magnetic fields.
In a prior study in Physical Review Letters earlier this year, the same researchers suggested that gravitational fields can form two-dimensional structures called gravitational field sheets. One dimension stretches through space and the other through time, so a snapshot at any instant catches each sheet as a line, like the field lines drawn around a magnet. Under certain conditions those sheets evolve without breaking. In the new paper, the team found that this is not always the case. "Gravitational field sheets can break and reconnect in a different arrangement, much like magnetic field lines do in plasmas," Comisso said. Breaking the frozen-in rule does not, by itself, guarantee reconnection. Sometimes the sheets merely slip relative to the flow that carries them. Genuine reconnection happens only when no such alternative flow exists.
The researchers also derived equations for how quickly reconnection can occur and how it affects the transfer of energy and momentum. In general relativity, gravity and matter can trade energy and momentum, with only their combined total conserved. Reconnection changes the local rate of that exchange and can create or destroy gravitational helicity, a measure of how twisted and interlinked the sheets are. "Everything follows from Einstein's general relativity," Comisso said. The finding does not require new physics, and it has not yet been observed in nature. It is a new reading of equations that have already passed more than a century of tests, with possible implications for violent events such as colliding black holes.