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Scientists have figured out why the corona of the Sun is hotter than its surface

Scientists have figured out why the corona of the Sun is hotter than its surface

(ORDO NEWS) — Astrophysicists have proposed a solution to the “problem of heating the solar corona” – a sharp increase in temperature that occurs when moving away from the surface of a star. To do this, scientists combined two previously existing theories that explained this effect by turbulent flows and magnetic waves.

As a general rule, the further we move away from a heat source, the colder it gets. However, this pattern does not work for the Sun.

The temperature on the surface of a star reaches six thousand degrees Celsius, and at a distance of only a few hundred kilometers from it, a sharp increase in temperature occurs. The corona of the Sun can already heat up to one and a half million degrees Celsius, creating a stream of ionized particles – the solar wind, reaching our planet.

Scientists from the University of Otago (New Zealand) have found a possible reason for this unusual effect. The results of their study are published in the journal Nature Astronomy.

Previously, astrophysicists believed that this sudden temperature jump was due to the star’s magnetic fields, but it was not clear exactly how they heat the gas. The issue was known as the “corona heating problem”. There were several hypotheses describing exactly how the energy of the magnetic field is converted into heat.

One of the most popular was that the heating was caused by turbulent currents inside the star’s atmosphere, which carried energy into the corona. Proponents of the second called special ion-cyclotron magnetic waves the cause.

But none of these hypotheses is consistent with the observational results. Low-frequency turbulence, which can carry energy from a star into its atmosphere, has been observed by spacecraft.

However, it cannot explain why ions in the corona of the Sun heat up more than electrons. Such an effect could be caused by high-frequency ion-cyclotron waves, but they are not enough to heat the gas to such high temperatures, and their source is not entirely clear.

To find the answer, scientists used a supercomputer to run a six-dimensional simulation of the coronal gas. It turned out that both hypotheses can be combined into one. The two processes are connected by the recently discovered physical effect of the “spiral barrier”.

It limits the heating of the electrons, preventing the turbulent cascade of energy from descending from the level of the ions. In this case, the stopped energy of the turbulent flow is converted by the spiral barrier into ion-cyclotron waves.

When scientists simulated turbulence capable of generating enough ion-cyclotron waves to heat the corona, they found vortices on the surface of the star that resemble those actually observed by the Nasa Parker Solar Prob spacecraft, which recently entered the solar corona.

Understanding the processes that take place in the atmosphere of the Sun is necessary because of the huge influence of the solar wind on our planet.

The result of the interaction of the solar wind with the Earth‘s magnetic field is a variety of events – from the northern lights to radiation that can destroy satellites, and geomagnetic storms that damage power systems.


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