Astronomers have found the first direct evidence that prove the nova hibernation hypothesis, a theory that posits binary star systems undergo cyclical explosion that repeat itself over a period of time.

In a new study published in the journal Nature on Aug. 17, Przemek Mróz, from the Warsaw University Observatory in Poland, and colleagues reported the explosion of a hibernating star. They observed mini outbursts leading up to the classical nova, the final explosion of a white dwarf, the remains of sun-like star that has exhausted its nuclear fuel.

Compared with more powerful supernova explosion which means the death of stars, nova eruptions do not necessarily result in the destruction of the stellar parents.

The nova that astronomers call V1213 Cen, or Nova Centauri 2009 erupted in 2009 but they have been observing its source star since 2003. Using data that were collected years before and after the eruption, researchers were able to learn about the evolution of this particular type of nova.

Classical novas such as the Nova Centauri 2009 happen in binary systems, which consist of two stars orbiting each other. The nova occurs when a white dwarf stars gains matter from the other star over a period of time.

The cycle starts with the hibernation phase, wherein the companion star sends mass in the form of hydrogen to the white dwarf star. The white dwarf cyclically gets brighter, dims and then awakes erupting in a big explosion, an event that creates significant increase in brightness. The process is slow but eventually starts all over again.

Although astronomers observe several classical novae in the Milky Way per year, most of them are faint due to interstellar gas and dust that hide them. Long term observations with this particular nova, however, showed that the white dwarf star experienced periodic brightening since 2003 before the explosion.

The fluctuation in brightness means that during this time, a low mass-transfer occurred between the two stars. Mass transfer rate also increased after the explosion. The system is currently bright but is slow fading. This will continue for a while before the process starts all over again.

"Within the six years before the explosion, the system revealed dwarf nova outbursts indicative of a low mass-transfer rate," the researchers wrote.

"The post-nova is two orders of magnitude brighter than the pre-nova at minimum light with no trace of dwarf nova behaviour, implying that the mass-transfer rate increased considerably as a result of the nova explosion."

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