The Big Picture: NuSTAR telescope shows the sun blasting out X-rays

Pop quiz, hotshot: What do you get when you heat gas above 3 million degrees Celsius? High-energy X-rays, of course -- just the kind that NuSTAR was launched to detect. The space telescope took a break from hunting black holes to snap its first-ever shot of the sun. When that X-ray image (blue and green) is overlaid onto an infrared photo from the Solar Dynamics Observatory (in orange), it shows how X-rays relate to high-temperature solar activity like flares and sunspots. Scientists want to figure out why the sun's corona (outer atmosphere) is 1 million degrees Celsius, while the surface is a mere 6,000 degrees Celsius -- a discrepancy that's like a "flame coming out of an ice cube," according to NASA. Though it might sound risky to point the world's most sensitive high-energy X-ray telescope at the sun, it's actually quite safe -- our star emits plenty of X-rays, but very few of the high-energy type.

[Image credit: NASA/JPL]