Scientists believe they have solved the mystery of why the inner solar system rotates much more slowly than the laws of physics suggest.
The Solar System’s inner ring contains thin layers of gas and dust known as accretion disks, which spiral around young stars that are slowly moving inward.
If this is done in a spiral, according to the laws of angular momentum, the inner part of the disk should spin faster—like a figure skater spinning faster with his arms tucked in than with his arms out.
While observations have shown that the inner portion of an accretion disk spins faster, it’s not moving as fast as predicted.
Researchers have found many possible explanations for this behavior: whether it’s friction between the inner and outer rotating parts of the accretion disk, or magnetic fields creating a “magnetorotatory instability” that produces gas and magnetic turbulence that slows the rate of rotation of the inward spiral gas.
Neither of these explanations satisfied Paul Bellan, a professor of applied physics at Caltech, as calculations show that accretion disks have negligible internal friction and turbulence is “of concern”.
Professor Bellan began by analyzing the trajectories of individual atoms, electrons and ions in the gas that made up the disk to see how the particles behaved during collisions and how they moved between collisions.
Using a simulation of about 40,000 neutral and about 1,000 charged particles that could collide with each other, as well as gravity and magnetism.
“This model had just the right amount of detail to capture all the essential features,” says Professor Bellan, “because it was large enough to behave just like trillions and millions of colliding neutral particles, electrons and ions that make up a star in orbit orbiting magnetic field.”
The simulation showed that collisions between neutral atoms and charged particles would cause positively charged ions to spiral inward while negatively charged electrons spiraled outward. Analysis of this behavior showed that angular momentum is not conserved, but a force called “canonical angular momentum” is.
The canonical angular momentum is the sum of the original ordinary angular momentum plus an additional quantity that depends on a particle’s charge and the magnetic field. There is no difference between these forces for neutral particles, but charged particles can change drastically due to the large magnetic crowd.
The charge difference increases momentum of both positive and negative particles increases their canonical angular momentum, with neutral particles losing angular momentum and moving inward.
This small difference has an enormous ripple effect on a scale as large as the solar system, requiring only one particle in a billion to be charged to explain the observed loss of angular momentum of the neutral particles.
This movement makes the disc resemble a giant battery – with a positive terminal near the center and a negative terminal around the edge. This creates a tremendous electrical flux and propels astrophysical jets shooting in both directions; these have been observed by astronomers for over a century without ever knowing the force behind their origin.
The research paper “Neutral-charged-particle Collisions as the Mechanism for Accretion Disk Angular Momentum Transport” was published in Astrophysical Journal.