A space telescope named NuSTAR, designed to gaze into the farthest realms of the universe, has turned its eye on our own sun to capture a dramatic image of it pouring out high-energy X-rays.

Although designed and launched into space in 2012 to study black holes and cosmic objects at great distances from our own solar system, researchers have long considered its sensitive instruments as ideal candidates to study our sun.

One of those scientists is David Smith, solar physicist and member of the NuSTAR mission team at the University of California, Santa Cruz.

"NuSTAR will give us a unique look at the Sun, from the deepest to the highest parts of its atmosphere," he says.

Smith got in touch with the principal investigator of the mission, Fiona Harrison at the California Institute of Technology in Pasadena, Calif.

"At first I thought the whole idea was crazy," she says.. "Why would we have the most sensitive high-energy X-ray telescope ever built, designed to peer deep into the universe, look at something in our own backyard?"

Smith was able to convince Harrison, explaining while the Sun is much too bright for other telescopes including NASA's Chandra X-ray Observatory, the NuSTAR instrument-- which can look at the Sun in higher-energy X-ray realms where it is not as bright -- could safely look for faint X-ray flashes predicted by theorists without the risk of damaging its detectors.

NuSTAR's first image, released by NASA, Caltech and the space agency's Jet Propulsion Laboratory in Pasadena, has proved that to be true.

When the X-ray image is combined with an infrared photo taken by another space telescope -- NASA's Solar Dynamics Observatory -- it shows those X-rays closely linked to solar activity with high temperatures, such as sunspots and flares.

Astrophysicists have theorized that small versions of those flares, dubbed nanoflares, could be the reason the outer atmosphere of the sun, the corona, is so much hotter than the Sun's surface at 1 million degrees Celsius versus the surface's mere 6,000 degrees, a mystery known as the "coronal heating problem" that is like "flame coming out of an ice cube," NASA says.

If NuSTAR could capture these nanoflares as they occur, the decades-old mystery could be solved, Smith says.

"NuSTAR will be exquisitely sensitive to the faintest X-ray activity happening in the solar atmosphere, and that includes possible nanoflares," he says.

While being prepared for more Sun studies, NuStar will continue to observe the far universe and its black holes, remnants of supernovas and other extreme cosmic objects, NASA says.