Every day, astronomers learn more about the stars spread around the cosmos, but there’s still plenty to learn about the star closest to Earth. NASA has released a new composite image of the Sun featuring data from the NuSTAR space telescope. It reveals some of the hottest areas of the Sun, which may help scientists unravel a stellar mystery that has remained unsolved for decades.
NuSTAR is a powerful orbiting X-ray observatory. It was launched in 2012 to study distant energy sources like supermassive black holes and collapsing stars. However, it can also peek at the Sun’s X-ray output. Because NuSTAR is focused on distant objects, it has a narrow field of view that cannot fit the entire Sun. However, the team decided to take a full disk image in June 2022. The result is a mosaic image made up of 25 individual frames.
The image above includes data from more than NuSTAR. The Red comes from the infrared camera on NASA’s Solar Dynamics Observatory, the green is a map of low-energy X-rays from the Japanese Aerospace Exploration Agency’s Hinode mission, and the blue is from NuSTAR’s observation of high-energy X-rays. As you can see, there’s not very much blue in the image. Below, you can see all three layers separated.
The Sun appears different depending on who’s looking. From left, NASA’s NuSTAR sees high-energy X-rays; the Japanese Aerospace Exploration Agency’s Hinode mission sees lower energy X-rays; and NASA’s Solar Dynamics Observatory sees ultraviolet light. Credit: NASA/JPL/JAXA
NASA believes the NuSTAR data could help scientists understand why the Sun’s corona is so hot. While the Sun’s surface is a toasty 5,500 degrees Celsius, the corona reaches scorching temperatures of more than 1 million degrees Celsius. The Sun’s heat radiates out from the core, so no one is certain how the star’s atmosphere ends up so much hotter than the surface. Solar flares don’t happen often enough to keep the corona so hot, but nanoflares might be the key. That’s what you’re seeing in the blue regions above.
Individual nanoflares, small eruptions originating deep inside the Sun, are too faint compared with the blazing brightness of the Sun to appear in today’s instruments. However, NuSTAR can detect the high-energy output when multiple nanoflares occur close together. This could help physicists determine how often nanoflares happen and how much energy they release.
The June 2022 observations also coincided with the Parker Solar Probe’s 12th pass through the corona, which will help to connect observed nanoflare activity with the actual conditions in the Sun’s atmosphere. This spacecraft still has a few years of expected operation ahead of it, so it could still gather additional data to contribute to solving the mystery once and for all.
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