The four supernovae discovered by the Palomar Transient Factory. Left: before explosion. Right: after explosion. From top to bottom, the supernovae are PTF09atu, PTF09cnd, PTF09cwl, and PTF10cwr.  [Credit: Caltech/Robert Quimby/Nature]

New Class of Stellar Explosion Sings the Blues

9 Jun , 2011 by

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A team of astronomers led by the California Institute of Technology (Caltech) have discovered a new, ultra-bright class of supernova – and it really sings the blues. Possibly one of the most luminous observable objects in the Cosmos, these new types of stellar explosions may help us better understand the origins of starbirth, unravel the mysteries of distant galaxies and even look back into the beginnings of our Universe…

“We’re learning about a whole new class of supernovae that wasn’t known before,” says Robert Quimby, a Caltech postdoctoral scholar and the lead author on a paper to be published in the June 9 on-line issue of the journal Nature. Not only did the team locate four instances of this new class, but the study also helped them unravel the questions behind two previously known supernovae which apparently belong in the same category.

As a graduate student at the University of Texas, Austin, Quimby came to the astronomy forefront in 2007 when he reported the brightest supernova ever found: 100 billion times brighter than the sun and 10 times brighter than most other supernovae. At the time, it was a record. Categorized as 2005ap, it had a rather strange spectral signature – a lack of hydrogen. But Quimby wasn’t the only one in the “class” doing homework, because the Hubble Space Telescope also detected an enigmatic event listed as SCP 06F6. It, too, had an unusual spectrum, but nothing led researchers to surmise it to be similar to 2005ap.

Enter Shri Kulkarni, Caltech’s John D. and Catherine T. MacArthur Professor of Astronomy and Planetary Science and a coauthor on the paper. They enlisted Quimby as a a founding member of the Palomar Transient Factory (PTF) – a project which scans the skies for unrecorded incident flashes of light which could signal possible supernova. With the eye of the 1.2-meter Samuel Oschin Telescope at Palomar Observatory, the colleagues went on to discover an additional four new supernovae events. Measuring the spectra with the 10-meter Keck telescopes in Hawaii, the 5.1-meter telescope at Palomar, and the 4.2-meter William Herschel Telescope in the Canary Islands, the astronomers discovered that all four objects had an unusual spectral signature. Quimby then realized that if you slightly shifted the spectrum of 2005ap—the supernova he had found a couple of years earlier—it looked a lot like these four new objects. The team then plotted all the spectra together. “Boom—it was a perfect match,” he recalls.

From there it didn’t take long to learn to sing the blues. The astronomers quickly figured out that by shifting the spectrum of SCP 06F6 caused it to align with previous findings. The results showed all six supernovae to be a similar type – all with very blue spectra – with the brightest wavelengths shining in the ultraviolet. This was the missing link that connected the two previously unexplained supernovae. “That’s what was most striking about this—that this was all one unified class,” says Mansi Kasliwal, a Caltech graduate student and coauthor on the Nature paper.

Even though astronomers now know these supernovae are related, the rest remains a mystery. “We have a whole new class of objects that can’t be explained by any of the models we’ve seen before,” Quimby says. “What we do know about them is that they are bright and hot—10,000 to 20,000 Kelvin; that they are expanding rapidly at 10,000 kilometers per second; that they lack hydrogen; and that they take about 50 days to fade away—much longer than most supernovae, whose luminosity is often powered by radioactive decay. So there must be some other mechanism that’s making them so bright.”

What could they be? One simulation leads to a pulsational pair-instability and the next points towards a magnetar. No matter what the answer is, the result is the illumination aids astronomers in studying distant dwarf galaxies, allowing them to measure the spectrum of the interstellar gas and uncover their composition. The findings could also “shed light” on what ancient stars may have been like… stretching back into the very beginnings of our Universe. “It is really amazing how rich the night sky continues to be,” Kulkarni says. “In addition to supernovae, the Palomar Transient Factory is making great advances in stellar astronomy as well.”

Original Story Source: California Institute of Technology.


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Ivan3man_At_Large
Member
Ivan3man_At_Large
June 9, 2011 2:42 AM

Er… Tammy, I think that the image caption should read: “[Top]: before explosion. [Bottom]: after explosion. From [left] to [right], the supernovae are PTF09atu, PTF09cnd, PTF09cwl, and PTF10cwr.” =^..^=

Don Alexander
Member
Don Alexander
June 9, 2011 1:05 PM
Nice to see Robert’s paper is finally out, it took 1.5 years of refereeing… @IVAN3MAN_AT_LARGE: While you are correct, I note the original image in the paper was arranged to match the now incorrect caption. There’s quite a few inconguities in the article… “Possibly one of the most luminous observable objects in the Cosmos” – GRB afterglows can be up to FOURTEEN magnitudes more luminous – though only for seconds. What is probably meant is that the total light output of the phenomenon is among the largest known (for transient sources). “on a paper to be published in the June 9 issue of the journal Nature.” – Actually, it was published online-only, and not yet in the actual… Read more »
Anonymous
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Anonymous
June 9, 2011 10:35 PM

Great article – very interesting…

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