What causes solar flares?

Why do solar flares occur?
21 January 2020

Interview with 

Gregory Fleishman, New Jersey Institute of Technology




Solar flares are areas of unusual brightness in the Sun. Now we have a better idea what causes them. Adam Murphy reports…

Adam - At the heart of our solar system, the Sun pumps out incomprehensible amounts of energy, that allow life on this planet to exist. But sometimes that energy gets a little more concentrated into what's called a solar flare.

Gregory - What happens fundamentally, some energy is very quickly being released and converted to various forms of energy; energy of motion, energy of heating and energy of energetic charged particles. And this manifests a phenomena which we call a solar flame.

Adam - That's Gregory Fleishman from the New Jersey Institute of Technology explaining a solar flare. But the scale of these things is spectacular as well. A single flare can release more than a billion, billion joules of energy, and is capable of sending particles streaming all the way here to Earth. But what is actually going on in the Sun? How do solar flares get going?

It wasn't something we had a very strong idea about, what the catalyst was, but using an array of telescopes in California looking at the microwave radiation the Sun is giving off, just like the energy in a microwave oven, Gregory's work may shine a light on it.

Gregory - What we found, we found that the magnetic field at the flare location decays very quickly and very strongly. For example, in the beginning of a flare in a given location, you may have magnetic field. We quantify magnetic fields in units called Gauss. So for example, initially you observed 1000 Gauss and after this release, the magnetic field dropped by a factor of five. It's only 200 Gauss and all this 800 Gauss of magnetic field, like 80% of magnetic field strengths disappeared, and transferred to other forms of energy. And these other forms of energy is energy of accelerated charged particles. It's energy of heated plasma and also energy of microscopic motions, also observed from the same location.

Adam - The Sun's magnetic field is very strange. Unlike Earth's magnetic field, which is roughly the same shape as a bar magnet, the Sun's magnetic field twists and turns and changes, and it looks like these play a key role in the generation of solar flares. And as these fields twist and scrunch and collide and combine, they give off huge amounts of energy. And these telescopes in California give us a new level of detail with which to measure solar flares.

Because the thing about flares is that we can't predict them. And if particles from a particularly strong one hit the Earth at the wrong time, they could damage the communication systems the planet relies on. And this work could be the first step towards predicting them.

Gregory - We are quantifying now what we could call "nowcasting", so we can analyse it in almost real time, and we can predict severe space weather effects. We can predict what will happen in the space plasma close to the Earth produced by such flares.


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