Mini-Supernova Creates a Zombie Star
When a relatively weak supernova tries to obliterate a star that just refuses to die, it leaves a zombie star. Researchers from Rutgers University detected a progenitor system at the site of a mini-supernova blast, which may indicate that it left a fragmented white dwarf that they called a "zombie star."
Even amateurs know this one.
[Credit: Sony Pictures Releasing]
The research team found a "luminous" blue progenitor star, or the star that caused the explosion of the white dwarf, in pre-explosion Hubble photos. The qualities of the progenitor star indicated that the supernova may have been Type lax, which is a so-called "mini-supernova. Unlike the related, more powerful type of supernova, Type la, a Type lax supernova does not completely destroy its star.
"Astronomers have been searching for decades for the star systems that produce Type Ia supernova explosions," said Saurabh Jha of Rutgers University. "Type Ia's are important because they're used to measure vast cosmic distances and the expansion of the universe. But we have very few constraints on how any white dwarf explodes. The similarities between Type Iax's and normal Type Ia's make understanding Type Iax progenitors important, especially because no Type Ia progenitor has been conclusively identified. This discovery shows us one way that you can get a white dwarf explosion."
From the paper: "The leading models for type Iax supernovae are thermonuclear explosions of accreting carbon–oxygen white dwarfs that do not completely unbind the star, implying that they are 'less successful' versions of normal type Ia supernovae, where complete stellar disruption is observed. Here we report the detection of the luminous, blue progenitor system of the type Iax SN 2012Z in deep pre-explosion imaging. The progenitor system's luminosity, colours, environment and similarity to the progenitor of the Galactic helium nova V445 Puppis suggest that SN 2012Z was the explosion of a white dwarf accreting material from a helium-star companion."
The researchers were surprised to find evidence of the Type lax supernova, as they are usually not bright enough to see. "It is exciting when nature surprises us," said Curtis McCully, a graduate student at Rutgers and lead author of the paper. They hope to observe the area with the Hubble again in 2015 in order to find definitive evidence of the remnant dwarf star and confirm their hypothesis.
"Back in 2009, when we were just starting to understand this class, we predicted these supernovae were produced by a white dwarf and helium star binary system," said team member Ryan Foley of the University of Illinois at Urbana-Champaign. "There's still a little uncertainty in this study, but it is essentially validation of our claim."
If their hypothesis is proven correct, then their findings will help contribute to a more complete understanding of white dwarf death and the relationship between the Type la supernova and its stranger cousin, the lax.