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Hubble spots a ‘zombie star’: What it is and why it matters

With the help of the Hubble Space Telescope, a team of researchers has spotted a “zombie star” lurking in deep space. What is this astronomical equivalent of the walking dead, and how did it get there?

The story involves a rare type of cosmic explosion, detective work and a NASA first.

It began 110 million years ago in a double-star system in the depths of space. A burned-out white dwarf star was sucking energy from its healthy blue companion star, feeding off of it until — boom! Supernova. Often, this explosion of the dwarf star is a cataclysm, reducing it to smithereens.

But not always. There’s a less common and less destructive type of supernova whose discovery was announced only last year. In this cosmic event, the dwarf star survives, albeit “battered and bruised,” a shadow of its former self - or, as NASA puts it, a zombie star.

This mini-supernova, known as SN 2012Z, lies in galaxy NGC 1309. It was discovered in January 2012 in the Lick Observatory Supernova Search. A team of researchers, including Rutgers scientist Saurabh Jha, Rutgers grad student Curtis McCully and Ryan Foley of the University of Illinois at Urbana-Champaign, studied this faint star. Members inspected archival data from Hubble and found the telescope had looked at this galaxy years before, between 2005 and 2010.

They focused in on these pre-explosion images and “were able to pinpoint the actual star system that later exploded,” Anton Koekemoer, a Hubble astronomer at the Space Telescope Science Institute, told the Los Angeles Times. “This is the first time that this has been done for this important class of supernova.”

Why are these supernovae so important? Dubbed Type Iax, they are closely related to Type Ia, the type that reduce a dying dwarf star to smithereens.

Type Ia supernovae are used as a tool for measuring immense distances in space. They also help astrophysicists determine the expansion of the universe.

But despite decades of searching, astronomers have never actually seen a Type Ia star before it exploded, because they’re too faint.

That makes the discovery of this zombie star even more special.

“Since both the Iax and Ia types involve white dwarfs,” Koekemoer said, “and since no Ia has yet been imaged directly before its explosion, this makes this particular Iax discovery very interesting.”

Although Iax supernovae are less common, astronomers have located the aftermath of another blast. In January 2013, NASA says, Hubble took images of supernova 2008ha, 69 million light-years away in galaxy UGC 12682. Images show an object that could be the surviving dwarf star or its companion. Now they’ll go looking for an image from its past.

Astronomers, in fact, have identified more than 30 mini-supernovae, according to NASA.

That’s a lot of potential space zombies.

The team’s findings on SN 2012Z will appear in the Aug. 7 edition of the journal Nature.

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