It keeps going, and going…

The massive size of the remnant is not its only claim to fame. Indeed, M31N 2008-12a also now holds the title of most frequently recurring nova, as it erupts at least once a year. "When we first discovered that M31N 2008-12a erupted every year, we were very surprised," said co-author Allen Shafter of San Diego State University in a press release . This is because most recurrent novae only explode about once a decade.But despite the fact that the white dwarf has spent the past million years or so exploding annually, researchers don't think it will last forever. Once the white dwarf surpasses the Chandrasekhar limit — which is about 1.4 times the mass of the Sun — it will irreparably blow itself apart as a supernova or collapse down into a neutron star.According to theory, white dwarfs that are approaching the Chandrasekhar limit should undergo frequent nova explosions, resulting in gigantic remnants. And because that's exactly what astronomers see happening around M31N 2008-12a, they think this star may be priming up for a supernova explosion itself. However, you and I likely will not be around to witness it."In less than 40,000 years," the study says, "the underlying composition of the white dwarf will be revealed incontrovertibly when either a type Ia supernova or an accretion-induced collapse of the white dwarf to a neutron star is observed."If the researchers are able to find other examples of huge remnants around different novae, they think they may learn a bit about type Ia supernovae. Because type Ia supernovae have very predictable brightnesses (which is why they're called standard candles ), by studying them, researchers can pin down cosmic distances with extreme accuracy. Ultimately, this helps them better understand how the universe grows and evolves over time."They are, in effect, the measuring rods that allow us to map the visible universe," said Shafter. "Despite their importance, we don't fully understand where they come from."So for now, Shafter and his colleagues are working hard to determine whether super-remnants like M31N 2008-12a are the exception, or the rule. And if they're as common as some think, then the next step becomes improving our ability to spot them.