What makes a supernova go boom? I’ve just been at a meeting on ways to observe such stellar explosions at the Royal Society in London, where there was a session discussing this question.

Type Ia supernovae result from the explosion of white dwarf stars and are now celebrated for their role in revealing that the expansion of the universe is accelerating. Textbooks say that they can form in one of two ways: The first (known as the single-degenerate model) is when a white dwarf -- itself an extremely dense star and thus gravitationally hungry -- rips matter from a binary companion until its own mass exceeds a critical limit (the Chandrasekhar mass, about 1.38 times the mass of the sun), triggering nuclear fusion and an explosion. Since they all explode when they hit the same mass, they explode with the same energy and peak luminosity, which means they can be used as "standard candles" for measuring distance -- that is, just by looking at how bright (or faded) they are, you can calculate how far away they must be. The second theorized way that fusion could be triggered is through the merger of two white dwarfs that have a combined mass that is greater than the Chandrasekhar limit (the double-degenerate model).

But that standard story contains a few gaping plot holes, as Marten van Kerkwjik of the University of Toronto pointed out at the meeting. First, there don’t seem to be enough white dwarfs in close binaries to explain the number of Type Ia supernovae seen. Also, even in theory, explosions triggered in these ways do not naturally produce the mix of elements seen in observations -- unless you tweak the theory to make it fit. Oh, and the standard candle thing? They aren’t so much "standard" as "standardizable" as van Kerkwjik also noted (that is technically, they aren’t identical -- a consideration that was well understood and accounted for the in the dark energy discovery). All of these factors, van Kerwjik says, "cast doubt on the standard picture."

In 2010, van Kerkwjik and colleagues suggested an alternative theory: The merger of two carbon-oxygen white dwarfs can lead to Type Ia supernovae, even if their combined mass is less that the Chandrasekhar mass limit (arXiv:1006.4391v3). Simulations show that a merger of two white dwarfs, each with a mass of around 60 per cent of the sun could lead to an explosion that provides a better match with observations. (Follow up simulations by van Kerkwjik and others here.)

It’s going to be hard to prove that van Kerkwjik’s idea is correct with actual observations, however, since his predictions tend be "negative." For instance, if you look at a supernova remnant and *fail* to find evidence of a companion from which matter was accreted, then that’s consistent with his alternative model -- but doesn’t stand as proof for it. Astronomers have been searching for such evidence -- see for example, "An absence of ex-companion stars in the type Ia supernova remnant SNR 0509-67.5", Schaefer &Pagnotta, Nature 481, 164-166 (12 January 2012), which seems to at least rule out the single-degenerate models for that particular supernova.

The take-home message seemed to be that Type Ia supernovae are even more of a mixed bag than previously thought. Now variety may be the spice of life, but these supernovae have been lauded as standard candles because they all seem to be doing the same thing. The suggestions that things aren’t quite that simple don’t seem to affect the conclusion that the expansion of the universe is accelerating -- at least Brian Schmidt, who won a share of the Nobel for the discovery and who was sitting alongside van Kerkwjik on the discussion panel didn’t seem to be sweating. But since so much of our understanding of the past and future of the universe is tied to these entities, it might be a good idea to work out what’s going on with them.

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I think it just goes to show how much we really don't know, alongside our tendency to imagine explanations for what we see.

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There a big candles and bigger ones and also those very little , the intensity of their flames is not in relation with the volume of the candle but to the wick of the candle, so by assuming that our candles in the sky were all of the same luminosity , was I think already a mistake. Now we are going to understand that the volume of the candle can change, next we will find out that the constituation of the candle is also influencing the luminosity, then the wick and further on. Altogether this would imply that our "measurements" of the universe are not founded on the right data, what does this mean for the growing inflation ?

think free

Wilhelmus

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I should think that two in spiraling white dwarfs would have a different luminosity time dependent profile than a white dwarf that exceeds the Chandrasekhar limit by siphoning off material from a companion. I looks as if we have SNIa SNIb, … down a bit of the alphabet.

LC

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I read this very interesting blog: I don't knew the importance of the type Ia supernovas to measure distance measure (Universe expansion).

I think that is usual in the Universe the presence of double systems (Jupiter is nearly a star), and I think that can be possible that the spiral trajectory of the double star can be obtained from a fluid dynamic system.

If there is a double system (stars with different mass) with the centre of gravity inner to one of the star, then the different movement of one star (inner parts more rigid of the extern parts, and significant tidal forces) can produce a reduction of the kinetic energy of the star (inner spiral movement) increasing the star emission (fluid dynamic friction).

If this is true then it is possible a type Ia supernova with Chandrasekhar star with a spiraling great star, or a spiraling Chandrasekhar star with a little star: I think that it is possible a measure of the primer measuring the emission of the spiraling emission of one (spectrographic separation of the emission components).

I share this imperfect idea because it is necessary too time to verify all, numerical programs, nuclear chemical reaction, fluid dynamic, Chandrasekhar primer time, etc.

Saluti

Domenico

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Dear Zeya Merali

I read your paper on separation space and time.

We work on that foe a last few years, see

http://phys.org/news/2012-04-physicists-abolish-fourth-di
mension-space.html

yours sincerely, amrit

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Supernova study backs both single-degenerate and double-degenerate models:

http://www.cfa.harvard.edu/news/2012/pr201214.html

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Nuclear physics experiment could provide SN insight:

http://www.apollon.uio.no/english/articles/2012/supe
rnova.html

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Ms. Merali: Forgive me for going off topic here, but I recently read your article at Discover concerning Einstein not having gone far enough. One thing I wanted to point out, but there was no place to do so there -- Faust by Goethe is a play not a poem. Also, I enjoy your work and read it when I find it.

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