The sun is an identifiable and inescapable landmark in the sky above the Earth, illuminating our world. Nevertheless, only a minimal portion of this light is visible to human eyes, which see just a portion of the electromagnetic spectrum. 

Recent investigations by NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) have shown that our star emits high-energy radiation that our eyes cannot detect.

In a picture provided by NASA on Friday, February 10 (opens in a new tab), patches of high-energy X-ray radiation caught by the NuStar telescope appear as vivid blue dots. 

Data from NuStar is merged with observations of low-energy X-rays obtained by Japan's Hinode satellite, shown in shades of green, and ultraviolet images captured by NASA's Solar Dynamics Observatory (SDO), shown in shades of red.

Solving the coronal heating problem of the sun

NuStar's observations are beneficial since they indicate the sun's hottest regions. Scientists believe that the random distribution of these very hot patches throughout the sun's surface might help solve one of the sun's oldest and most urgent mysteries: why the sun's upper atmosphere, the corona, is so much hotter than its surface.

This is true everywhere in the sun except when moving from the corona, which may reach temperatures of up to 3.6 million degrees Fahrenheit (2 million degrees Celsius), to the photosphere, which can be as much as 500 times cooler, at around 6,200 degrees Fahrenheit (3,700 degrees Celsius).

NASA explains (opens in new tab) that this is as startling as the air surrounding a fire being 100 times hotter than the flames themselves

 when the sun's heat escapes from its core.

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Nanoflares, little bursts of heat and light in the sun's atmosphere, might cause this surprise warming. They are smaller than typical solar flares, but like their more significant relatives, they create material above the average coronal temperature.

Standard flares may not occur often enough to heat the corona; however, nanoflares may occur more frequently, perhaps frequently enough to create this extra heating.

Individual nanoflares are too weak to detect the sun's light output. Still, NuSTAR can detect radiation from high-temperature material formed by a large number of nanoflares occurring in the same region simultaneously. This may enable solar physicists to determine the frequency of nanoflares, how they release energy, and whether or not they cause coronal heating.

The data for this new mosaic picture was gathered. At the same time, NASA's sun-touching spacecraft, the Parker Solar Probe, made its 12th close encounter with the star, speeding into the outer edges of its corona and getting closer than any other vehicle.

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Researchers may correlate visual activity on the sun with samples of the solar atmosphere taken by the Parker Solar Probe by correlating NuSTAR's sun views with data gathered during the up close and personal encounters of the probe.

Despite the fact that NuSTAR was initially meant to detect distant objects and events beyond the solar system, such as collapsing stars and black holes, it might potentially provide a great deal of information about the sun. 

Since this telescope can only observe a portion of the sun from its orbit around the Earth, the picture comprises 25 photographs acquired in June 2022 that have been pieced together.