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A new solution to an old mystery: Why isn't the interior of our solar system spinning faster?

The key to solving a long-standing mystery about thin disks of gas orbiting young stars: the movement of a small number of charged particles. This is claimed in a new Caltech study

The orbits of the main bodies in the solar system. Courtesy of CALTECH
The orbits of the main bodies in the solar system. Courtesy of CALTECH

The key to solving a long-standing mystery about thin disks of gas orbiting young stars: the movement of a small number of charged particles. This is claimed in a new Caltech study.

These rotating disks of gas, called accretion disks, exist for tens of millions of years and are an early stage in the evolution of solar systems. They contain a small fraction of the mass of the star around which they revolve: imagine a Saturn-like ring the size of the solar system. They are called accretion disks because the gas in these disks moves slowly in a spiral path inward towards the star.

Astrophysicists have long recognized that when this spiraling inward occurs, it should cause the radial interior of the disk to spin faster and faster, according to the law of conservation of angular momentum. To understand the basic idea of ​​conservation of angular momentum, think of ice skaters spinning: when their arms are extended, they spin slowly, but when they close their arms to their body, they spin faster and faster.

The law of conservation of angular momentum means that the angular momentum in the system remains constant, and the angular momentum is proportional to the velocity times the radius. So if the skater's mass is concentrated around a smaller radius because he has attached his arms to his body, then the only way to maintain a constant angular momentum is to increase the speed of rotation.

The inward spiral motion of the adsorption disc is analogous to a skater attaching the arms to the body, so the inside of the adsorption disc should rotate faster. Astronomical observations do show that the interior of an accretion disk does rotate faster, but curiously less quickly than the law of conservation of angular momentum predicts.

Collisions between neutral atoms and a much smaller number of charged particles may explain why the interior of solar systems rotates faster.

Scientists have explored many possible explanations for why the angular momentum of an accretion disk is not conserved over the years. Some have speculated that friction between the inner and outer rotating parts of the adsorption disk may be slowing down the inner region. But calculations show that adsorption discs have very little internal friction. According to the current dominant hypothesis, magnetic fields cause a phenomenon called "magneto-rotational instability" which causes the formation of magnetic and gaseous turbulence (turbulence) - and in fact creates friction that slows the rotation speed of the gas moving inward in a spiral.

Paul Blanc, a professor of applied physics at Caltech, began investigating the problem by analyzing the trajectories of individual atoms, electrons, and ions in the gas that makes up an adsorption disk. His goal was to determine how the individual particles in the gas behave when they collide with each other, and also how they move between collisions, to see if it is possible to explain the loss of angular momentum without using turbulence. As he explained, the basic behavior of the parts that make up adsorption discs - charged particles (electrons and ions) are affected by gravity and magnetic fields, while neutral atoms are only affected by gravity. This difference, he suspected, was the key.

for the scientific article

More of the topic in Hayadan:

4 תגובות

  1. Shmuel Turgeman, the skater spins around himself

  2. interesting
    It is clear that over time the roles these rings have and their positive effects on the planet and the rest of the solar system will be discovered
    It's just a matter of process
    Little by little the marvelous complexity of the star system and the impossible are discovered
    Unless there is an intelligent intention for everything
    What are your deeds, O Lord?

  3. I didn't understand the example of the skater opening his hands or closing them. In both cases its center of mass is in the same place and the radius does not change. As in the position of the spread of the hands, there is one hand that is farther from the center of the circle (in the Shoah to the body) so there is also one hand that is closer to the center of the circle.

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