New observations of the Sun could help develop a better solar thermometer

(ORDO NEWS) — A sophisticated new observation of a cold zone on the Sun’s surface could help scientists develop a new kind of solar thermometer.

A team of astrophysicists led by researchers from the University of Glasgow used observations from the ALMA observatory in Chile for the first time to estimate the temperature of a solar prominence.

Solar prominences are zones of plasma on the surface of the Sun, which are held by its powerful magnetic fields at a temperature much lower than in neighboring regions.

While temperatures on the surface of the Sun can exceed a million degrees Kelvin, temperatures at the centers of solar prominences typically range from 5,000 to 8,000 degrees. They can exist for several weeks before becoming unstable and bursting out into space.

In a paper published in Monthly Notices of the Royal Astronomical Society: Letters, the researchers describe how they used the ALMA observatory’s ability to generate high-resolution images of the Sun using data collected from an array of radio antennas.

This process, known as interferometry, allowed them to conduct a detailed study of the temperature of the solar prominence that occurred on April 19, 2018.

They studied data from the H-alpha and 3 mm regions of the electromagnetic spectrum, allowing them to measure the optical thickness and brightness temperature of the prominence over a period of about two hours.

These observations allowed them to create images of the prominence’s spine, outlining the spiky structures at the edges of its plasma envelope. An analysis of its brightness showed that the temperature of the plasma contained in the spine is between 6,000 and 7,000 degrees Kelvin.

The prominence was also measured by two other observatories, one on Earth and the other in space. The Bialkow Observatory at the University of Wroclaw in Poland took measurements of the prominence at the same time as the Atmospheric Imaging Assembly aboard NASA‘s Solar Dynamics Observatory spacecraft.

The team correlated the observational data from both stations with the ALMA results and found a high degree of agreement, indicating the reliability of the ALMA results as an estimate of the shape and temperature of the prominence.

Dr Nicolas Labrosse of the School of Physics and Astronomy at the University of Glasgow is the lead author on the paper. Dr. Labrosse said: “Solar prominences are one of the clearest illustrations of how magnetic fields shape our Sun’s atmosphere, creating and controlling much colder plasma patterns in an almost unimaginably hot environment.

“Understanding how solar prominences form and evolve over time , will help us answer a number of fundamental questions about how our Sun works, as well as others like it throughout the Universe.

Unraveling these answers will also help us better understand how to use magnetic fields to manipulate plasma here on Earth in environments such as future fusion reactors.”

“We are very pleased that we have been able to demonstrate for the first time the possibility of making high-resolution measurements of solar prominences using ALMA interferometry data.

Although in this case we used only two ALMA bandwidths, expanding our observations to other bands will allow us to make even more detailed observations, which could take us one step closer to building a better solar thermometer.”

Dr. Labrosse is the co-author of a second paper, led by astrophysicists from the Czech Academy of Sciences, published in The Astrophysical Journal Letters, which also reviews ALMA solar prominence data.

Dr. Labrosse added: “The two papers were written independently but show complementary results on how we can use ALMA to measure the temperature of solar prominences.

“The second paper shows that there are still unresolved structures in our ALMA data – prominences. which have a characteristic spatial scale less than the ALMA resolution.

This is interesting because we can learn more about how prominences form and how the building blocks of prominences relate to what we observe with our instruments at current resolution.”

“Taken together, the results of this work suggest that we can learn a lot from ALMA’s data on solar prominences. We look forward to future collaborations with our research partners to make further measurements with ALMA.”

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