Old Hubble telescope data yields new supernova discovery
More than two decades of Hubble observations have produced more than 25 terabytes of data. Thanks to the wealth of information stored in the Hubble data archive, astronomers can easily revisit old images in an effort to better understand new discoveries.
Now, astronomers have used the archive to find the progenitor of a mysterious type of supernova, dubbed Type 1ax, which is less energetic and much fainter than its Type Ia cousin.
A Type 1a supernova occurs when a white dwarf siphons material off a companion star, building an additional layer of hydrogen on its surface that will eventually trigger a runaway reaction that detonates the accumulated gas.
The most popular explanation for Type 1ax supernovae is that they鈥檙e created in the same way, except the explosion doesn鈥檛 completely tear the white dwarf into pieces. Instead, the white dwarf ejects roughly half of its mass. It becomes battered and bruised, leaving behind a hot core composed of carbon and oxygen.
鈥淎stronomers have been searching for decades for the progenitors of Type Ia鈥檚,鈥� said Saurabh Jha from Rutgers University in a聽. 鈥淭ype Ia鈥檚 are important because they鈥檙e 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鈥檚 and normal Type Ia鈥檚 make understanding Type Iax progenitors important, especially because no Type Ia progenitor has been conclusively identified.鈥�
So after the team observed the weak supernova, dubbed SN 2012Z, in the Lick Observatory Supernova Search, they dug through Hubble鈥檚 archive. Fortuitously, Hubble had observed the supernova鈥檚 host galaxy, NGC 1309, in 2005, 2006, and 2010, before the supernova outburst.
Curtis McCully, a graduate student at Rutgers and lead author on the team鈥檚 paper, reprocessed the pre-explosion images to find an object at the supernova鈥檚 position.
鈥淚 was very surprised to see anything at the supernova鈥檚 location,鈥� said McCully. 鈥淲e expected that 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.鈥�
The pre-supernova observations reveal a bright, blue source the team calls S1. McCully and colleagues concluded that they were most likely seeing a star that had lost its outer hydrogen envelope, revealing its helium core. But they don鈥檛 think it鈥檚 a type of star that was about to explode, rather it鈥檚 the companion that fed the white dwarf鈥檚 outburst.
The most likely explanation involves a binary star system where each star detonates mass to the other over time.
The team acknowledges that they can鈥檛 totally rule out other possibilities for the object鈥檚 identity, including that it was simply a single, massive star that exploded as a supernova. To settle any uncertainties the team plans to use Hubble again in 2015. Hopefully by then the supernova should fade enough to get a better look at what remains.
罢丑别听聽appear in the journal Nature Thursday.
聽is a freelance science journalist. She holds two B.A.'s from Whitman College in physics-astronomy and philosophy, and an M.S. in astronomy from the University of Wyoming. Currently, she is working toward a second M.S. from NYU's Science, Health and Environmental Reporting program.
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