Magnetic Turbulence – Warming The Solar Winds.
In this more modern age, we think we know a great deal about the Sun. However, there are still many mysteries to be solved. Our star itself is a mystery unfolding.
As the solar wind escapes into the Solar System, it should cool down, but that’s not the case. Even with no particle collisions to dissipate energy, it continues to heat. Now, new research led by University of Warwick physicist Dr. Kareem Osman may help shed some light on this solar riddle. Throughout the Universe, a force is present – turbulence. It can be found in galaxies, accretion disks, stellar winds, stars and even in interstellar matter. Here on Earth we can see the power behind turbulence in its role of shaping the evolution of laboratory plasmas – a state which diminishes between fusion devices.
Because we can study this interaction, we gain insight as to how turbulence can cause changes in space. Thanks to our new solar orbiting satellites, we can study the solar wind and the near-Earth environment. This research has uncovered the fact that the solar wind is considerably hotter than expected as a “normal” outflow from the Sun and scientists theorize turbulence may be the answer. If we have the answer, then just what is the riddle? In the case of astrophysical plasma, it should be so dissipated that its particles don’t collide. So, if it is “collisionless” then how does it heat?
The new research led by Dr. Kareem Osman at the University of Warwick’s Center for Fusion, Space and Astrophysics has revealed how turbulence may heat the solar wind. He says:
“Turbulence stretches and bends magnetic field lines, and often two oppositely directed field lines can come together to form a current sheet. These current sheets, which are distributed randomly in space, could be sites where the magnetic field snaps and reconnects transferring energy to particle heating.There are also many more ways that current sheets can heat and accelerate the plasma.”
When it comes to current sheets, the researchers set a limit on their strength and then measured how the proton strength compared to the sheet strength.Their results produced current sheets with enhanced temperatures – the strongest of which where also the hottest.
Even though this experiment gave the desired results, the researchers are also quick to point out that a current sheet itself doesn’t provide a lot of heating.
Together, current sheets are responsible for about half the solar wind internal energy and only about a fifth of all the solar wind data. The strongest of all only account for about 2% and are responsible for just a little more than a tenth of the system’s internal energy. To add to the mystery, the researchers also found that heating isn’t evenly distributed in solar wind current sheets!
“These results suggest magnetofluid turbulence drives intermittent dissipation through a hierarchy of coherent structures, which collectively could be a significant source of coronal and solar wind heating.” says Dr. Osman.
Original Story Source: University of Warwick News Release.
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