Scientists affiliated with the Warsaw University Observatory have become the first in the world to capture the lead up to the explosion of a classical nova, the explosion itself and the aftermath.

A research paper published in the journal Nature reveals how they captured the event and how they think their work could improve our understanding of the theory of star hibernation. The nova in question exploded in 2009, but the team had luckily been looking at the section of sky it was located in as part of another project.

classical nova
Image source: Wikimedia Commons

Binary system explodes in classical nova in 2009

Nova Centauri 2009 just so happened to be located in that particular patch of sky, and the explosion inspired the scientists to look back at images they had captured earlier in order to put together a timeline. Unlike a supernova, a classical nova does not mean that the star is destroyed. Instead it means that material that was being collected from its companion star is burned away in a thermonuclear explosion.

“Thanks to our long-term observations, we observed the nova a few years before and a few years after the explosion,” Przemek Mróz, the study’s first author and a PhD student at the Warsaw University Astronomical Observatory, told the BBC. “This is very unusual, because generally novae only attract attention when they are very bright – when they are in eruption.”

This particular nova was part of a binary star system which consisted of white and red dwarf stars. The white dwarf was slowly collecting material from the red dwarf until a tipping point was reached, leading to the explosion.

By looking at images from before the explosion, scientists were able to observe how the brightness of the stars fluctuated as mass was transferred. This continued up to six days before the nova exploded.

Cyclical explosions suggested

The researchers were also able to observe how the rate of mass transfer became far greater just after the explosion. The team also reveals that the brightness is still far greater, although it looks to be going down now.

As a result of the research it has been suggested that hibernation periods are built into events such as classical novae. This is due to the fact that brighter and dimmer periods were observed over the six years in the lead up to the explosion.

Hibernations are when very little activity occurs in a binary system. Their existence suggests that the explosions are cyclical, taking place on repeated occasions over the course of millions of years.

“The entire system survives the nova explosion… so the whole process starts again,” said Mr Mróz. “After thousands of years, our nova will awake and explode again but no one will be able to see it.”

Astronomers call for further research

The researchers will keep an eye on the binary system in order to see whether the mass transfer rate decreases. If it does it would bolster their theory.

However other scientists are not convinced by the findings.  “The thing is still just cooling down at the moment – it’s not yet steady. So we don’t yet know what the long-term brightness is going to be, post outburst, because really we’re still seeing the end of the outburst,” said Christian Knigge from the University of Southampton, who wants to see more data.

However he did hail the work. “As observations, as a test bed for our theories of how these explosions work – this really is fantastic. We can really measure what the brightness and the conditions were before the eruption; we can use this to inform how we model the eruption; we have a nice measure of how long it takes to decline – and we’re going to keep following this,” said Knigge.