When our sun comes to its ending in five billion years or so, it will fade into a quiescent white dwarf. Bigger stars go out with a bang—those with more than 10 times the mass of our sun collapse with enough vigor to spark a supernova, one of the most energetic events in the universe. For decades astronomers have suspected the existence of a type of stellar explosion that is bigger still—a “pair-instability” supernova, with 100 times more energy than an ordinary supernova. In the past year two teams of astronomers have finally found it, redrawing in a stroke the limit of how big things can be in this universe of ours.

All stars balance gravity with pressure. As light elements such as hydrogen fuse in a star’s core, the reactions generate photons that press outward, counteracting the pull of gravity. In larger stars, pressure at the core is high enough to fuse heavier elements such as oxygen and carbon, creating more photons. But in stars bigger than 100 solar masses or so, there’s a hitch. When oxygen ions begin to fuse with one another, the reaction releases photons that are so energetic, they spontaneously trans­mute into electron-positron pairs. With no photons, there’s no outward pressure—and the star begins to collapse.

One of two things can happen next. The collapse can create even more pressure, reigniting enough oxygen to create a burst of energy. This burst is enough to toss off the outer layers of the star but not enough to create a full supernova. The cycle can repeat itself in pulses—astronomers call this case a “pulsational” pair-instability supernova—until the star loses enough mass to end its life in an ordinary supernova. A team led by the California Institute of Technology’s Robert M. Quimby announced it had identified one of these and has submitted a paper for publication.

If the star is really big—and here we’re talking more than 130 solar masses—the collapse happens so fast and gathers so much inertia that even fusing oxygen can’t stop it. So much energy develops in such a little space that eventually the whole thing blows up, leaving no remnant behind. This is “the real deal, the big stuff,” says Avishay Gal-Yam, an astronomer at the Weizmann Institute of Science in Rehovot, Israel, whose team claims in a recent paper in Nature to have discovered the first full-fledged pair-instability supernova (Scientific American is part of Nature Publishing Group).

Before the findings, most astronomers had argued that gigantic stars in nearby galaxies slough off much of their mass before dying out, precluding a pair-instability supernova. These ideas are being reconsidered, now that these biggest of explosions have announced themselves in spectacular fashion. 

This article was originally published with the title The Biggest Bang Theory.

11 Comments

1. 1. candide 09:25 AM 9/30/10

   "So much energy develops in such a little space that eventually the whole thing blows up..."
   
   How exactly? What are the physics of that - going from a super-fast collapse to "blowing up?"

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2. 2. jtdwyer in reply to candide 10:03 AM 9/30/10

   I agree: the author was doing very well, explaining the nuclear processes in reasonably general terms until, all of a sudden, it just 'blowed up reel good'!

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3. 3. candide 01:40 PM 9/30/10

   It reminds me a bit of the "And then a miracle occurs..." comic:
   
   http://blog.stackoverflow.com/2008/09/then-a-miracle-occurs-public-beta/
   
   I could understand if the authors do not know the process, but at least say that much.

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4. 4. jtdwyer 11:15 PM 9/30/10

   The silly article title "The Biggest Bang Theory: Astronomers Confirm a New Type of Supernova", does a great job of mixing metaphors: Big Bang/Supernova Theory? Supernovas bigger than the Big Bang? What?

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5. 5. galaxy_man 09:49 AM 10/1/10

   The actual explosion from collapse is caused by a rebound effect, which is partly due to the Shandrasekhar(sp?) limit of atomic density, similar to Pauli exclusion but based on physical proximity rather than the occupancy of states. Once atoms are squeezed together to a sufficient degree, it becomes literally impossible for anything else to enter that space with the exception of the formation of a singularity.
   
   Supernovae of stars with a certain mass (a minimum of about 20-30+ solar masses if I'm not mistaken) occur because of a petering out of the nuclear reactions taking place in the star's core which provide enough outward force to repel the outer shells from collapsing into the core under their own weight. When this happens, the shells crush inward and 'bounce' off of the inner core, and are expelled outward in a violent explosion. This is the definition of a type II supernova. I imagine a similar mechanism is at play with these very large novae.

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6. 6. jtdwyer 10:26 AM 10/1/10

   It seemed to me that this type of supernova needed to be placed within the context of other types. Wikipedia/Supernova says (sans references):
   
   "When the progenitor star is below about 20 solar masses (depending on the strength of the explosion and the amount of material that falls back), the degenerate remnant of a core collapse is a neutron star. Above this mass the remnant collapses to form a black hole. (This type of collapse is one of many candidate explanations for gamma ray bursts, possibly producing a large burst of gamma rays through a hypernova explosion.) The theoretical limiting mass for this type of core collapse scenario was estimated around 40–50 solar masses."
   
   "Above 50 solar masses stars were believed to collapse directly into a black hole without forming a supernova explosion, although uncertainties in models of supernova collapse make accurate calculation of these limits difficult. Above about 140 solar masses stars may become pair-instability supernovae that do not leave behind a black hole remnant."

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7. 7. jtdwyer 10:37 AM 10/1/10

   By the way, it's still unclear to me how a 140 Solar mass star could repeatedly eject matter and never leave a black hole remnant: why, when the residual mass reached some threshold above 50 Solar masses would it not immediately collapse into a black hole as a 50+ Solar mass collapsing star would?

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8. 8. Wayne Williamson 06:42 PM 10/1/10

   commenters....i agree with you....
   
   blue giants like this should still follow the normal burning up to iron and then exploding either leaving a neutron star or black hole...(michael moyer...if not please explain)
   
   just got the latest magazine today with the cover pic showed at the top...but doesn't contain this article....
   

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9. 9. Dr. Strangelove in reply to jtdwyer 09:43 PM 10/3/10

   I guess a 140 solar mass star ejects more mass when it blows up that there is not enough mass left to form a black hole.
   
   It ejects more mass through a series of ejections or pulses (pulsational pair-instability supernova) or just one big bang.
   
   Why it blows up and not collapse into a black hole? I guess big stars fuse more oxygen atoms that release photons that exert enough outward pressure for a brief moment before they transmute into electron-positron pairs.

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10. 10. MORMAC999 07:50 PM 10/4/10

    I AM HAPPY THAT`S MODERN THEORY FROM OLD THEORY
    SOME THING HAVE HALF TRUE BESIDE SUPERNOVA
    WAEL MOREICHEH
    POET

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11. 11. jtdwyer in reply to Dr. Strangelove 03:39 PM 10/1/12

    Sorry the long delay in noticing your reply!
    
    Yours seems like a reasonable assessment - perhaps the pressure produced by the continued sporadic fusion of some heavy elements within an enormous core following a partial collapse prevents complete collapse... Please see
    http://en.wikipedia.org/wiki/Pair-instability_supernova

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