Scientists have discovered a new type of supernova, called the Type 1ax.

Previously, only two types of supernova were thought to exist in the universe: the core collapse and Type 1a. A Type 1a supernova involves a disrupted white dwarf, while a core-collapse supernova involves the explosion of a star approximately 10 to 100 times the size of our own sun. The Type 1ax supernova, however, is characteristically different from both.

Like the Type 1a supernova, the new Type 1ax also involves a white dwarf, though it is less forceful and also fainter, having about one-hundredth its brightness. The Type 1ax is also rarer, about one third as common as the Type 1a. Interestingly, a white dwarf can actually survive the new type of supernova explosion, unlike in the Type 1a. This makes it more of a mini-supernova.

"The star will be battered and bruised, but it might live to see another day," said lead researcher Ryan Foley. "It's the runt of the supernova litter," he added.

In terms of what causes the explosion, it could be a result of the helium layer being ignited in the companion star, causing the white dwarf to explode via a shock wave. Or, the white dwarf may ignite on its own due to density and temperature alterations caused by its helium shell.

The researchers categorized the new supernova by examining 25 examples. They found that none appeared in elliptical galaxies, which are populated by old stars. This indicated that the new supernovae are located in young star systems.

The fact that the new supernova hasn't been discovered until now is not attributed to the fact that it is fewer in number, but rather to its faintness.

"For more than a thousand years, humans have been observing supernovas," Foley said. "This whole time, this new class has been hiding in the shadows."

Findings of the study are published in the Astrophysical Journal and can be found online.