Supernova solved

In 185 A.D., Chinese astronomers recorded a bright ''guest star'' in the night sky. By the 1960s, astronomers figured out that the guest star was in fact a supernova, and identified the remains of the stellar explosion.

And in 2011, a team of astrophysicists led by NC State researchers solved the mystery of what caused this explosion and why this particular remnant is so very large.

Supernova remnant RCW 86 is much larger than it should be – in fact, if it could be seen in the sky, it would take up more space than our full moon.

''This supernova remnant got really big, really fast,'' says Brian J Williams, post-doctoral research scholar at NC State. ''It's two to three times bigger than we would expect for a supernova that was witnessed exploding nearly 2,000 years ago. Now, we've been able to finally pinpoint the cause.''

To do so, astronomers used NASA's Spitzer Space Telescope and Wide-field Infrared Survey Explorer (WISE) to take infrared readings of  RCW 86. That data, as well as previous observational data from NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton Observatory, showed that the stellar explosion took place in a hollowed-out cavity, which allowed material expelled by the star to travel much faster and farther than it would have otherwise.

The infrared data were also used to confirm what triggered the explosion that brightened the skies in 185 AD According to the data, the event is a Type Ia supernova, which means that a star like our sun died relatively peacefully, shrinking into a dense star called a white dwarf. The white dwarf is thought to have later blown up in a supernova after siphoning matter, or fuel, from a nearby star.