Physicists Say Gravity Can 'Break and Reconnect' Like Magnetic Fields in Solar Flares
Columbia and Chilean researchers rewrote Einstein's equations to look like plasma physics and found a process that moves energy from gravitational fields into matter.
More than a century after Einstein wrote the equations that describe gravity, physicists are still finding new ways to read them. Luca Comisso, an associate research scientist in Columbia University's departments of Astronomy and Physics, and Felipe A. Asenjo of Universidad Adolfo Ibáñez in Chile report that gravitational field structures can break and reconnect, in a process they call "gravitational reconnection." When it happens, energy moves out of the gravitational field and into matter. The work appears in Physical Review D.
The idea borrows from plasma physics. In a plasma, magnetic field lines get dragged, stretched and twisted until the stress becomes too great. "Magnetic reconnection is when these field lines, in some specific configuration, break and reattach in a different configuration," Comisso said. "When they break and reconnect, they release energy." It is the process behind solar flares and one of the most important energy-release mechanisms in astrophysics, taking energy from the magnetic field and handing it to particles.
Gravity can do something similar, the researchers argue, though the geometry is different. "Because space-time is four-dimensional rather than three-dimensional, gravity involves something like field 'sheets' rather than field lines," Comisso explained. Adding one dimension to a line gives a plane. The sheets are mathematical structures, not physical objects, but their reconnection describes a route by which gravitational energy can be transferred to matter.
The insight came from rewriting Einstein's equations. Over the past few years, physicists have developed a formulation that is mathematically equivalent to the original but expressed in different variables. Written that way, the equations of gravity look a great deal like those governing plasmas, the gases that make up the sun, fuel fusion experiments and fill much of interstellar space. Comisso has spent his career on plasmas, and he and his colleagues applied those methods to gravity.
The new paper, "Reconnection of Gravitational Fields," builds on an earlier Physical Review Letters paper with Maricarmen A. Winkler that identified previously unrecognized rules constraining how space-time can bend, stretch and evolve. "Einstein's equations contain constraints on how space-time can evolve that are not immediately apparent," Asenjo said. "By revealing these hidden new properties, we can begin to understand the fundamental rules governing how this gravitational reconnection process behaves."
Why it matters comes down to how astrophysicists work now. To learn what happens when two black holes collide, they run enormous supercomputer simulations from chosen starting conditions and see what emerges. Those results are used to predict the gravitational-wave signals that detectors such as LIGO are built to measure. Near merging black holes, gravity is so strong and space-time so distorted that the behavior is extraordinarily hard to calculate.
The researchers say their approach offers a way to identify rules the fields must obey without running the full calculation. "It helps us predict some patterns of the space-time," Comisso said. "Even without doing the full calculation, we know that space-time needs to behave in a certain way, that it needs to satisfy those constraints."
For now, gravitational reconnection is a theoretical result. The next challenge is to study how the process might unfold in specific settings, such as merging black holes, and whether it produces effects that gravitational-wave detectors could measure. Comisso hopes the approach will eventually help researchers predict how much energy such events release and what signatures they leave.
