The inner solar system rotates much more slowly than the laws of modern physics predict, and a new study may help explain why.
A thin disk of gas and dust, known as an accretion disk, spirals around young stars. These disks, where the planets form, contain excess star-forming material that is a fraction of the star’s mass. According to the conservation law of angular momentum, the inner part of the disk should rotate faster as the material slowly rotates inward toward the star, similar to how figure skaters rotate faster as they approach. arms to his body.
However, previous observations have shown that the inner solar system, the region of the solar system which extends from the ground in the asteroid belt and includes the terrestrial planets – does not rotate as fast as predicted by the conservation law of angular momentum. Using new simulations of a virtual accretion disk, scientists at the California Institute of Technology (Caltech) have demonstrated how accretion disk particles interact.
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“The angular momentum is proportional to the velocity for the radius, and the law of conservation of angular momentum states that the angular momentum in a system remains constant,” Caltech researchers wrote in a statement. “So if the skater’s radius decreases because they’ve stretched their arms, the only way to keep the angular momentum constant is to increase the rotational speed.”
So why not preserve the angular momentum of the inner accretion disk? Previous research suggested that friction between accretion disk regions or magnetic fields that generate turbulence (and create friction) may slow the rate of rotation of the falling gas, according to the statement.
“That worried me,” Paul Bellan, a professor of applied physics at Caltech and co-author of the study, said in the statement. “People always want to blame turbulence for phenomena they don’t understand. Right now there’s a big craft industry arguing that turbulence is responsible for getting rid of the angular momentum of accretion disks.”
To better understand angular momentum loss, Bellan studied the trajectories of individual atoms, ions, and gas in an accretion disk and, in turn, how particles behave during and after collisions. While the charged particles – electrons and ions – are affected by both gravity and magnetic fields, neutral atoms are only affected by gravity.
The researchers used computer models to simulate an accretion 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. edge of the accretion disk. Meanwhile, the neutral particles lose angular momentum and exhale inward toward the center.
In turn, the accretion disk acts as a giant battery, with a positive terminal near the center of the disk and a negative terminal at the edge of the disk. These terminals generate powerful currents, or jets of material, that enter space from both sides of the disc.
“This model had the right amount of detail to capture all the essential features because it was big enough to behave like trillions and trillions of neutral particles, electrons and ions colliding around a star in a magnetic fieldBellan said in the statement.
Computer simulations suggest that while the angular momentum, the canonical angular momentum, the sum of the original ordinary angular momentum plus an additional amount that depends on the charge of a particle, and the magnetic field are lost, it is conserved, according to the statement.
“Because the electrons are negative and the cations are positive, the inward motion of the ions and the outward motion of the electrons, which are caused by collisions, increases the canonical angular momentum of both,” they said. explain the researchers in the statement. “Neutral particles lose angular momentum as a result of collisions with charged particles and move inward, which compensates for the increase in the canonical angular momentum of charged particles.”
Their findings were published the 17 of May a Astrophysics Journal.
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