The Hubble telescope is back with another cool discovery. One of the universe’s most powerful phenomenons, the supernova, was previously thought to have always destroyed stars. New observations from the Hubble offer evidence that supernovas can leave behind a “zombie star” according to astronomers.

These latest observations could help expand the understanding of the mysterious supernova known as a Type Iax supernova. What’s so special about a Type Iax supernova? They occur when one star dumps enough fuel onto a dying companion star, a white dwarf, to trigger a massive nuclear explosion. While the explosion is massive, a portion of white dwarf survives. There’s just one problem for scientists. They have never actually seen it.

“Astronomers have been searching for decades for the star systems that produce Type Ia supernova explosions,” said scientist Saurabh Jha of Rutgers University in Piscataway, New Jersey.

“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.”

Type Iax supernovas are incredibly rare as far as cosmic events go. Around 30 Iax supernovas have been spotted by scientists.

SN 2012Z

This is the supernova researchers have their eyes on. The supernova was discovered in the galaxy NGC 1309 by the Lick Observatory Supernova Search in early 2012. In a stroke of luck, the Hubble’s Advanced Camera for Surveys observed NGC 1309 for several years before the supernova. Before and after images helped scientists compare the effects of the supernova.

Curtis McCully, lead author of the team’s paper published in the journal Nature, said, “I was very surprised to see anything at the location of the supernova. We expected the progenitor system would be too faint to see, like in previous searches for normal Type Ia supernova progenitors. It is exciting when nature surprises us.”


So, what are we seeing in the picture above? The team concluded the image from 2013 is light of a star that lost its outer hydrogen envelope and has an exposed helium core. Plans are in the works for the team to use the Hubble again in 2015. By then, the supernova’s light should have dimmed enough to reveal if there is a zombie star and a helium companion to confirm the team’s hypothesis.

The NASA press statement offers one theory for what could have transpired at SN2012Z.

One possible explanation for the unusual nature of SN 2012Z is that a game of seesaw ensued between the bigger and smaller of the star pair. The more massive star evolved more quickly to expand and dump its hydrogen and helium onto the smaller star. The rapidly evolving star became a white dwarf. The smaller star bulked up, grew larger and engulfed the white dwarf. The outer layers of this combined star were ejected, leaving behind the white dwarf and the helium core of the companion star. The white dwarf siphoned matter from the companion star until it became unstable and exploded as a mini-supernova, leaving behind a surviving zombie star.


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