Scientists Look Inside Central Engine of Solar Flare for First Time

by | Jul 28, 2020 | Daily Space, The Sun | 0 comments

Scientists Look Inside Central Engine of Solar Flare for First Time
IMAGE: Observation of a large solar flare on Sept. 10, 2017 in extreme ultraviolet (grayscale background, by NASA’s Solar Dynamics Observatory) and microwaves (red to blue indicate increasing frequencies, observed by the Expanded Owens Valley Solar Array). Light orange curves are selected magnetic field lines from the matching theoretical solar eruptive flare model. The flare is driven by the eruption of a twisted magnetic flux rope (illustrated by a bundle of color curves threading the dark cavity). Microwave sources are observed throughout the region below the cavity where a large-scale reconnection current sheet — the flare’s “central engine” — is located, providing crucial measurements for its physical properties. CREDIT: NJIT-CSTR, B. Chen, S. Yu; NASA Solar Dynamics Observatory

Astronomy is forever in pursuit of more details, and the more we see, the more we often realize we don’t understand. Even our Sun has phenomena that we struggle to understand even though that star is right beside us.

In another paper in Nature Astronomy, this one with lead author Bin Chen, scientists look into the heart of a solar flare and work to understand what factors power these giant rings and streams of plasma. Using data from the Owens Valley Solar Array, which observes the sun in microwave wavelengths of light, they analyzed a powerful solar flare from 2017. This event generated a 40,000-kilometer sheet of electric current that accelerated electrons to high energies. 

According to Chen: How exactly this happens is not clearly understood, but it is thought to be related to the Sun’s magnetic field. It has long been suggested that the sudden release of magnetic energy through the reconnection current sheet is responsible for these major eruptions, yet there has been no measurement of its magnetic properties. With this study, we’ve finally measured the details of the magnetic field of a current sheet for the first time, giving us a new understanding of the central engine of the Sun’s solar flares.

Specifically, according to co-author Kathy Reeves: We found that there were a lot of accelerated particles just above the bright, flaring loops. The microwaves, coupled with modeling, tells us there is a minimum in the magnetic field at the location where we see the most accelerated particles, and a strong magnetic field in the linear, sheet-like structure further above the loops. 

These sheet-and-loop magnetic structures work together to pump 10-100 billion trillion joules of energy out per second. 

To understand how these fields work together, they used sophisticated computer models that had to match what they saw in detail, including the thin reconnection current sheet and the magnetic field configuration during the eruption. From this model, they could see what underlying physics drives these eruptions and how magnetic fields can generate the plasma inflow/outflow that is seen reconnecting the current sheet.

This is a case of high-resolution images being required to confine a highly detailed analytical model, which in turn gives us a detailed understanding of the physics. Sometimes, we can’t just write down the equations and work out reality, but by combining the too-many equations only a computer model can manipulate with a detailed picture of reality, we can use physics to understand our universe. And sometimes that is enough.

More Information

Center for Astrophysics (CfA) press release 

Measurement of Magnetic Field and Relativistic Electrons Along a Solar Flare Current Sheet,” Bin Chen, Chengcai Shen, Dale E. Gary et al., 2020 July 27, Nature Astronomy (Preprint on arxiv.org)

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