New Solar Telescope Captures the Interior of the Dark Cores of Sunspots

A new telescope has captured the first-ever detailed view of the interior structure of umbrae, the dark patches in the center of sunspots. The images reveal dynamic magnetic fields responsible for the plumes of plasma that emerge as bright dots interrupting their darkness.

The new, high-resolution images were taken through the Big Bear Solar Observatory's (BBSO) New Solar Telescope (NST). These images reveal the atmosphere above the umbrae to be finely structured, consisting of hot plasma intermixed with cool plasma jets as wide as 100 kilometers.

"We would describe these plasma flows as oscillating cool jets piercing the hot atmosphere," said Vasyl Yurchyshyn, one of the researchers, in a news release. "Until now, we didn't know they existed. While we have known for a long time that sunspots oscillate-moderate resolution telescopes show us dark shadows, or penumbral waves, moving across the umbra toward the edge of a sunspot-we can now begin to understand the underlying dynamics."

The oscillating jets, called spikes, result from the penetration of magnetic and plasma waves from the sun's photosphere, which is the atmospheric layer of the sun that gives off light. These spikes then travel outward along magnetic tubes into the abutting chromosphere.

Sunspots form when strong magnetic fields rise up from the convection zone, a region beneath the photosphere that transfers energy from the interior of the sun to its surface. At the surface, the magnetic fields concentrate into bundles, which prevent the hot rising plasma from reaching the surface. The energy deficit causes the magnetic bundles to cool down to temperatures about 1,000 degrees lower than their surroundings. They therefore appear darker against the hotter, brighter background.

There are openings in the umbra, though, from which plasma bursts out as lava does from a volcano's side vents. These plumes create the bright, nearly circular patches that are called umbral dots. In contrast, sunspots have strong magnetic fields and fewer openings.

"These measurements tell us about the speed, temperature and pressure of the plasma elements we are observing, as well as the strength and the direction of the solar magnetic fields," said Yurchyshyn. "Thus we were able to find that spikes, or oscillating jets, are caused by chromospheric shocks, which are abrupt fluctuations in the magnetic field and plasma that constantly push plasma up along nearly the same magnetic channels."

The findings are published in The Astrophysical Journal.

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