A new picture combining data from four NASA telescopes is helping to solve the mystery of the "guest star"—a supernova spotted 2,000 years ago by Chinese astronomers.
Formally known as RCW 86, the supernova remnant we see today is two to three times bigger than expected, based on current understanding of how such stellar remains expand.
Now, infrared data from NASA's Spitzer Space Telescope suggest that the explosion happened in a cavity in the surrounding cloud of gas and dust. With no material to slow it down, the supernova's debris spread quickly, leading to the remnant's unusually large size.
Space Pictures This Week: Red Auroras, Mars Avalanche
A mysterious "guest star," southern auroras, and a toothy nebula feature among this week's best space pictures.