An X-ray picture of the Sun's atmosphere reveals a number of the hottest regions.

Even on a clear day, human vision cannot perceive all of the light emitted by our nearest star. NASA's Nuclear Spectroscopic Telescope Array has captured a portion of this invisible light, including high-energy X-rays released by the hottest material in the Sun's atmosphere (NuSTAR). 

While the observatory mainly investigates extrasolar phenomena, such as enormous black holes & shattered stars, it has also given researchers insights into our Sun.

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In the composite image, NuSTAR data are depicted in blue.

In contrast, observations by an X-ray Telescope (XRT) somewhat on the Japanese Aerospace Exploration Agency's Hinode mission are depicted in green, as well as the Atmospheric Imaging Assembly (AIA) on NASA's Solar Dynamics Observatory (SDO) is seen in red. 

NuSTAR's extremely tiny field of view prevents it from seeing the complete Sun from Earth's orbit. Therefore, the observatory's view of the Sun is a mosaic of 25 photographs captured in June 2022.

NuSTAR has detected high-energy X-rays in only a few sites in the Sun's atmosphere.

In contrast, Hinode's XRT detects limited X-rays, and SDO's AIA detects ultraviolet radiation – wavelengths emitted throughout the Sun's surface.

Scientists may be able to solve one of the greatest riddles surrounding our nearest star with the help of NuSTAR: why the Sun's outer atmosphere, known as the corona, is at minimum 100 times hotter than on its surface. 

This perplexes astronomers because the Sun's radiation radiates outward from its centre. Like if the air surrounding a fire were one hundred times hotter than the flames.

The genesis of the corona's heat could be nanoflares, minuscule eruptions within the Sun's atmosphere. Flares are massive explosions of light, heat, and particles that various solar observatories can observe. 

Nanoflares are significantly smaller than solar flares, although both types emit much hotter material than the typical coronal temperatures. Regular flares may not occur frequently enough to retain the corona at high temperatures observed by scientists. 

Still, nanoflares might occur so regularly that they jointly heat the corona.

NuSTAR can photoreceptors from high-temperature material believed to be created when a significant number of nanoflares happen in close proximity. This skill allows researchers to look into nanoflares' frequency and energy release mechanisms.

The data used to create these photographs coincided with NASA's Parker Solar Probe's 12th close encounter with the Sun, or perihelion, flying closer to our star than any other spacecraft. 

Making observations with NuSTAR during Parker's perihelion approaches permits scientists to correlate remotely observed activity in the Sun's atmosphere with the probe's firsthand sampling of the solar environment.

More Regarding the Mission,

NuSTAR was introduced on 13 June 2012. It was created in collaboration with the Danish Technical University (DTU) and the Italian Space Agency as a Small Explorer mission headed by Caltech in Pasadena, California, and managed by JPL for NASA's Science Mission Directorate in Washington (ASI). 

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Columbia University, NASA's Goddard Space Flight Facility in Greenbelt, Maryland, & DTU constructed the telescope's optics. The spacecraft was constructed in Dulles, Virginia, by Orbital Sciences Corporation. The mission operations centre for NuSTAR is at the University of California, Berkeley.

In contrast, the official data archive is located at NASA's High Energy Astrophysics Science Archive Research Center. ASI provides the ground station and data archive for the mission. Caltech manages JPL for NASA.