NASA's NuSTAR has taken a break from peering into the far-away Universe and used its high-energy X-rays to snap the most sensitive and stunning images of our Sun to date, putting any Christmas displays on Earth to shame.

The NuSTAR, or Nuclear Spectroscopic Telescope Array, mission was launched into space in 2012, designed to detect black holes and other celestial objects found outside our solar system. So why would scientists use the most sensitive high-energy X-ray telescope ever built to take a portrait of the Sun? Well, the Sun may be well-studied and close to home, relatively speaking, but it still has its secrets.

And NuSTAR, which can handle the intense brightness of the Sun without being damaged, unlike other telescopes, may be the key to unlocking some of those secrets. For example, researchers hope to gain insight into the extremely high temperatures found above sunspots - cool, dark patches on the Sun.

But perhaps most intriguing is what they may learn about nanoflares - smaller versions of the Sun's giant flares that erupt with charged particles and high-energy radiation. Nanoflares are only a hypothetical idea, but if they do indeed exist, they may help explain the "coronal heating problem." The corona, or the Sun's outer atmosphere, on average is 1.8 million degrees Fahrenheit (1 million degrees Celsius), while the surface of the Sun is "only" 10,800 Fahrenheit (6,000 Celsius). The sizzling hot corona compared to the relatively cooler surface has been a long-standing mystery among scientists, and NuSTAR could help determine whether nanoflares are the source of this intense heat.

"NuSTAR will give us a unique look at the Sun, from the deepest to the highest parts of its atmosphere," David Smith, a solar physicist and member of the NuSTAR team at University of California, Santa Cruz, said in a statement.

What's more, the telescope's precise X-rays may be able to spot another theoretical enigma - dark matter. Specifically, the dark matter particles called axions, which would appear as a spot of X-rays in the center of the Sun.

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