NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) spacecraft – a $180 million black-hole hunter – has obtained its first picture of the Sun, producing the most detailed solar portrait ever taken in high-energy X-rays.

This first solar image from NuSTAR demonstrates that the telescope can in fact gather data about Sun. And it gives insight into questions about the remarkably high temperatures that are found above sunspots – cool, dark patches on the Sun.

Future images will provide even better data as the Sun winds down in its solar cycle.

“NuSTAR will give us a unique look at the Sun, from the deepest to the highest parts of its atmosphere,” said Dr David Smith from the University of California, Santa Cruz, who is a member of the NuSTAR team.

“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 back yard?” added Dr Fiona Harrison of the California Institute of Technology in Pasadena.

While the Sun is too bright for other telescopes such as NASA’s Chandra X-ray Observatory, NuSTAR can safely look at it without the risk of damaging its detectors.

The Sun is not as bright in the higher-energy X-rays detected by NuSTAR, a factor that depends on the temperature of the solar atmosphere.

With NuSTAR’s high-energy views, it has the potential to capture hypothesized nanoflares – smaller versions of the Sun’s giant flares that erupt with charged particles and high-energy radiation.

Nanoflares, should they exist, may explain why the Sun’s outer atmosphere, called the corona, is sizzling hot, a mystery called the ‘coronal heating problem.’ The corona is 1 million degrees Celsius (on average), while the surface of the Sun is relatively cooler at 6,000 degrees Celsius. Nanoflares, in combination with flares, may be sources of the intense heat.

If NuSTAR can catch nanoflares in action, it may help solve this decades-old puzzle.

“NuSTAR will be exquisitely sensitive to the faintest X-ray activity happening in the solar atmosphere, and that includes possible nanoflares,” Dr Smith said.

What’s more, the X-ray observatory can search for hypothesized dark matter particles called axions.

Dark matter is five times more abundant than regular matter in the Universe. Everyday matter familiar to us, for example in tables and chairs, planets and stars, is only a sliver of what’s out there. While dark matter has been indirectly detected through its gravitational pull, its composition remains unknown.

“It’s a long shot, but NuSTAR may be able spot axions, one of the leading candidates for dark matter, should they exist. The axions would appear as a spot of X-rays in the center of the Sun.”

“Meanwhile, as the Sun awaits future NuSTAR observations, the telescope is continuing with its galactic pursuits, probing black holes, supernova remnants and other extreme objects beyond our Solar System.”