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New Class of Stellar Explosion Sings the Blues

The four supernovae discovered by the Palomar Transient Factory. Top: before explosion. Bottom: after explosion. From left to right, the supernovae are PTF09atu, PTF09cnd, PTF09cwl, and PTF10cwr. Credit: Caltech/Robert Quimby/Nature

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.


Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

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  • 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.” =^..^=

    • Tammy Plotner June 9, 2011, 1:48 PM

      thank you, ivan3man… it was late last night when i did this article and i was rushing a bit to get it in ahead of a storm. (satellite internet does not like lightning.) i flipped the image to make it fit the page better and totally didn’t think. thanks again!

  • Anonymous 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 journal.

    “because the Hubble Space Telescope also detected an enigmatic supernova listed as SCP 06F6″ – The event wasn’t even recognized as a supernova initially, as no redshift could be derived from the mysterious spectrum, leading to a bunch of theories.

    “the colleagues went on to discover four new supernovae events” – PTF has actually discovered about 1000 SNe so far, it’s just that they found what turned out to be four additonal 2005ap-class events.

    “and that they take about 50 days to fade away—much longer than most supernovae, whose luminosity is often powered by radioactive decay.” Erm, as it stands, this is just totally wrong. The paper actually states that these SNe fade FASTER than typical radioactive-decay-driven tails. What must be meant is that they take about 50 (rest-frame) days to even reach peak, which is much longer than normal SNe – so 50 days before they even START fading.

    “One simulation leads to a pulsar” No. Pulsational pair-instability is a mechanism which has nothing at all to do with pulsars.

    • Tammy Plotner June 9, 2011, 2:00 PM

      DAG… thank you for shredding me faster than a supernova. i’ve made a couple of very minor word changes which hopefully makes the article read more correct. the only thing i cannot change is the direct quote about the 50 days, since that is directly from the article and not my wording. it is not an easy job to re-write a technical article and not make any mistakes… and i try to do my best. your critque is always welcome and helps me improve.

      • Anonymous June 9, 2011, 3:16 PM

        I wasn’t blaming you, since I had no idea how much was directly taken from the original press release. And I realized that was a quote from Quimby, either he was misquoted or he tried to somehow make it concise and non-technical and messed up…

        The extremely long-duration, high luminosity of these events is what makes them so important.

        • IVAN3MAN_AT_LARGE June 9, 2011, 8:12 PM

          …, either [Quimby] was misquoted or he tried to somehow make it concise and non-technical and messed up…

          Like when NASA made an arse of themselves with their ‘arsenic-base life‘ 2 Dec. 2010 press release, eh?

  • Anonymous June 9, 2011, 10:35 PM

    Great article – very interesting…