A thin disk of gas and dust – known as an accretion disk – orbits young stars. These disks, where planets form, contain the remnants of star-forming material that makes up a small fraction of the star’s mass. According to the law of conservation of angular momentum, the inner part of the disk should rotate faster as the spiral material slowly spins inward toward the star, similar to the way ice skaters spin faster when they bring their arms close to their bodies.
However, previous observations have shown that the inner solar system – a region Solar System that extends from the sun to the asteroid belt and includes terrestrial planets It does not rotate as fast as predicted by the law of conservation of angular momentum. Using new simulations of a hypothetical accretion disk, scientists at the California Institute of Technology (Caltech) have demonstrated how particles in the accretion disk interact.
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Caltech researchers wrote in a permit. “So if a skater’s radius decreases because they’ve pulled their arms inward, the only way to keep angular momentum constant is to increase their rotational speed.”
So why isn’t the angular momentum of the internal accretion disk conserved? Previous research suggested that friction between regions of the accretion disk or magnetic fields that generate turbulence (and create friction) may slow the spinning speed of the leaking gas, according to the statement.
“It worried me,” Paul Bilan, a professor of applied physics at Caltech and co-author of the study, said in the statement. “People always want to blame turbulence on phenomena they don’t understand. There is a large household industry currently arguing that turbulence explains the disposal of angular momentum in accretion disks.”
To better understand the loss of angular momentum, Bellan studied the trajectories of individual atoms, ions, and gas in an accretion disk, and thus, how particles behave during and after collisions. During charged particles – Electrons And ions – affected by both gravity And magnetic fields, only neutral atoms are affected by gravity.
The researchers used computer models to simulate a cumulative disk of 1,000 charged particles colliding with 40,000 neutral particles in magnetic and gravitational fields. They found that the interaction between neutral atoms and a much smaller number of charged particles results in positively charged ions, or cations, spiraling inward and negatively charged particles, or electrons, moving outward toward the edge of the accretion disk. Meanwhile, the neutral particles lose angular momentum and rotate inward toward the center.
In turn, the accumulator disk acts like a giant battery, with a positive tip near the center of the disk and a negative tip at the edge of the disk. These stations generate strong currents, or jets of material, that travel in them outer space from both sides of the disc.
“This model contained just the right amount of detail to capture all the key features because it was large enough to behave just like trillions or trillions of colliding neutral particles, electrons and ions orbiting a star in magnetic fieldBilan said in the statement.
Computer simulations indicate that while the angular momentum is lost, the canonical angular momentum — the sum of the original normal angular momentum plus an additional quantity dependent on the particle’s charge and magnetic field — is conserved, according to the statement.
“Because the electrons are negative and the cations are positive, the internal movement of the ions and the external movement of the electrons, resulting from the collisions, increases the fundamental angular momentum of both,” the researchers explained in the statement. “Neutral particles lose angular momentum as a result of collisions with charged particles and move inward, balancing the increase in the primary angular momentum of charged particles.”
Their findings were published on May 17 in Astrophysical Journal.
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