Astronomers have observed unexpected patterns in the light emitted by exploding stars, or novae.
Using data from the Solar Mass Ejection Imager on the Coriolis satellite, which images the entire sky every 102 minutes, they studied four stars which exploded so violently that their light would have been visible from Earth without a telescope. Ther team measured their brightness over the course of the outburst.
They found that three of the novae stalled before reaching a peak, and all flickered or flared as the explosions ran their course.
Other astronomers had previously observed a pause in the brightening of novae - a 'pre-maximum halt' - but some thought it an anomaly. The precise time-scale and repeated observations of the current study confirms that this does take place, the authors say.
"The reality of this halt as found in all three of the fast-declining novae observed is a challenge to detailed models of the nova outburst," said astrophysicist Mike Bode of Liverpool John Moores University.
Two independent teams of theorists have already begun to refine their models of how novae explode in response.
The team speculates that the post-peak flares may correspond to changes in the dynamics of that reaction that still need to be explained.
"Before [Rebekah] Hounsell looked through these data, most novae were observed only after their peak luminance. The instrument's very even cadences and uniformly exposed images allow us to trace the entire evolution of these explosions as they brighten and dim," said Bernard Jackson of UC San Diego.