Exploding stars reveal never-before seen patterns

WASHINGTON - Astronomers have for the first time, observed post star explosion pauses, flickers and flares- patterns that aren’t yet accounted for in our current understanding of how these eruptions occur.

Using data from a sensitive instrument aboard a satellite that images the entire sky every 102 minutes, they studied four of these stars, or novae, that exploded so violently their light would have been visible without a telescope and measured their brightness over the course of the outburst.

The instrument they used - the Solar Mass Ejection Imager - was developed by a team led by astrophysicist Bernard Jackson at the Center for Astrophysics and Space Sciences at the University of California, San Diego, to study the sun. Rebekah Hounsell, a graduate student at Liverpool John Moores University in Britain made the measurements while visiting UC San Diego.

The team makes detailed maps of stellar light, including its brightness. In those maps Hounsell identified the four novae by finding points of light that rapidly brightened and dimmed over the course of days.

Other astronomers had observed a pause in the brightening of novae, or “pre-maximum halt” before, but some thought it an anomaly. The precise time-scale and repeated observations of the current study confirms it, they 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.

Astronomers typically characterize novae’s changing light with curves smoothly fit to more sporadic observations, but the rapid cadence of the solar imager captured glimmers that hadn’t been observed before. All flickered as their light dimmed and one nova, the slowest of the four to dim, flared brightly twice after reaching its peak luminosity.

These novae are white dwarf stars that steal matter, in the form of hydrogen, from a companion star, often an aging, expanding red giant. As hydrogen accumulates the white dwarf’s gravity pulls it in and condenses it until it ignites, setting off a runaway nuclear fusion reaction.

“Before 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,” UC San Diego’s Jackson said.

“The instrument assures that the brightest and most rapidly evolving novae - ones that brighten and then fade within a few days - are not overlooked,” said Allen Shafter, astronomy professor at San Diego State University.

“The high time resolution of these observations has opened up a new window into the study of novae in our galaxy.”

The team report their observations in The Astrophysical Journal. (ANI)