First Evidence of Nova Cycle Found Due to Explosion

A star explosion gave scientists the first evidence that the ten thousand to one million year evolution of a nova is a cycle, as hypothesized.

Astronomers at the University of Warsaw were rewarded for their patience when six years of observing the classical nova V1213 Cen (Nova Centauri 2009) culminated in a nova eruption. V1213's explosion is the first direct evidence in support of the nova hibernation hypothesis, as described by a new study published in Nature.

Classical novae, such as V1213, consist of two stars orbiting a common center to create a binary system. Within the system the white dwarf star accumulates particles from a secondary star of lower mass in a process known as accretion.

From 2003 to 2009, the team of astronomers watched the hibernating star. Occasional smaller explosions, called dwarf nova outbursts, indicated the low mass-transfer rate to the white dwarf present during hibernation.

"Dwarf nova outbursts appear when the mass-transfer rate between the stars is unstable, so each little bump in the light curve is produced by a portion of matter falling onto the surface," said Przemek Mróz, the lead author of the study, in a report by Space.com.

Changes in mass-transfer rate can be viewed by the changing brightness of the star. A decreased mass-transfer rate results in a dimmer star, with eruptions causing temporary brightening.

In 2009, V1213 awoke. A change in accretion to prehibernation levels led to the nova explosion.

Nova explosions are perhaps better described as a large-amplitude brightening. Neither star in the binary system dies - the mass-transfer rate increases to prehibernation levels, resulting in a brighter star.

The light curve generated by observation of V1213 pre and posteruption support the hibernation hypothesis. This support is the first evidence for life cycle of novae.

Following the hibernation hypothesis, V1213 will maintain increased mass-transfer rates for a significant period of time before entering a decrease in mass-transfer that could take up to a million years and would eventually put the nova back into hibernation.