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CATEGORY: Blog [back]
TOPIC: Exploding the Supernova Paradigm [refresh]
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FQXi Administrator Zeeya Merali wrote on Apr. 24, 2012 @ 15:14 GMT
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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John Merryman wrote on Apr. 24, 2012 @ 16:16 GMT
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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Edwin Eugene Klingman replied on Apr. 25, 2012 @ 19:36 GMT
John, my dear friend, how else could we arrive at explanations?

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John Merryman replied on Apr. 30, 2012 @ 17:32 GMT

I wasn't dismissing the imagination, but pointing out it lays at the heart of theory. The problem is with the scaffolding we build up around such premises which makes them rigid beyond original intention and thus difficult to re-examine. It is punctuated equilibrium applied to theory. Ideas start small and many die there, but the more successful ones invariably build a retinue whose proponent's careers depend on defending the original premise and find cracks and anomalies in the structure to be career opportunities to patch, rather than reasons to examine the integrity of the structure. The real irony here is that this is such a basic and natural phenomena, but one which modern physics, in its youthful glory, does not consider itself to be subject. When the dust does finally settle, the field will be a little more humble and a bit wiser.

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Anonymous replied on Apr. 30, 2012 @ 20:08 GMT

Edwin Eugene Klingman

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Wilhelmus de Wilde wrote on Apr. 25, 2012 @ 14:21 GMT
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


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Lawrence B. Crowell wrote on Apr. 26, 2012 @ 01:07 GMT
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.


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Domenico Oricchio wrote on Apr. 27, 2012 @ 21:14 GMT
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.



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Lawrence B. Crowell replied on Apr. 28, 2012 @ 13:56 GMT
The observable difference could only be measured in the time domain profile of the supernova event itself. Anything observable prior to that is many orders of magnitude smaller. An SNI is basically a fusion bomb with 1.4 solar masses ~ 3x10^{30}kg. A man made hydrogen bomb involves some 50-100 kg of fusion material. So any possible signal that might exist prior to this event is tiny in comparison. This would be I suspect found in the profiles for SNIs that are due to slow accretion of material from a companion and from a coalescence of two white dwarfs.


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Domenico Oricchio replied on Apr. 28, 2012 @ 14:37 GMT
I thought a pre-ignition phase (not yet supernova) of a double star system: if the fluid dynamic theory is true (only the reality is true) then the spiraling reduce the distance between the stars, and the greater star spiraling (around the inside-star center of gravity of the binary system) increasing the distance from the center of gravity until the surface of the star; the spectrographic emission of a double star contain the information of the convention (thermal transport of energy); Is it possible measure the spectrum, and to find the friction trace in the emission? This is possible only if the friction is great in the pre-ignition instants, or if there is an eclipsing binaries (indirect distance measure).



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Domenico Oricchio replied on Apr. 29, 2012 @ 11:26 GMT
I wish correct some things.

If the fluid dynamic (or other effects) is true for the merger in type Ia supernovas, then these effect are true for each binary system (high luminosity binary system): it is possible to verify in the binary catalog these stars.

If it exist a merger movement of giant star (and little star), then it is possible to write software using three parameter dynamic (masses and age of the stars), so it is possible to verify the parameter that give merger (the distance between stars can be arbitrary).

It is possible to verify the merger movement (spiraling) in visible binaries stars: if this movement is measurable, then must be a theory that explain the movement for each binary system.

It is possible to measure a very little distance reduction in the solar system (Sun-Jupiter)?



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amrit wrote on Apr. 28, 2012 @ 06:57 GMT
Dear Zeya Merali

I read your paper on separation space and time.

We work on that foe a last few years, see

yours sincerely, amrit

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Zeeya replied on Apr. 28, 2012 @ 19:51 GMT
Hi Amrit,

I'll take a look at the link, thank you. By the way, which article of mine on the separation of space and time are you referring to?

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Pentcho Valev replied on Apr. 28, 2012 @ 20:13 GMT

Do you really claim that length contraction is not a consequence of Einstein's 1905 light postulate? If yes, it would be easy to contradict you.

"To illustrate the difference between the two views of time, Sorli and Fiscaletti consider an experiment involving two light clocks. Each clock's ticking mechanism consists of a photon being reflected back and forth between two mirrors, so that a photon's path from one mirror to the other represents one tick of the clock. The clocks are arranged perpendicular to each other on a platform, with clock A oriented horizontally and clock B vertically. When the platform is moved horizontally at a high speed, then according to the length contraction phenomenon in 4D spacetime, clock A should shrink so that its photon has a shorter path to travel, causing it to tick faster than clock B. But Sorli and Fiscaletti argue that the length contraction of clock A and subsequent difference in the ticking rates of clocks A and B do not agree with special relativity, which postulates that the speed of light is constant in all inertial reference frames. They say that, keeping the photon speed the same for both clocks, both clocks should tick at the same rate with no length contraction for clock A."

Pentcho Valev

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Pentcho Valev replied on Apr. 29, 2012 @ 08:26 GMT

The following quotation clearly suggests that, if there is no length contraction, Einstein's 1905 light postulate is false:

Relativity and Its Roots, Banesh Hoffmann: "Moreover, if light consists of particles, as Einstein had suggested in his paper submitted just thirteen weeks before this one, the second principle seems absurd: A stone thrown from a speeding train can do far more damage than one thrown from a train at rest; the speed of the particle is not independent of the motion of the object emitting it. And if we take light to consist of particles and assume that these particles obey Newton's laws, they will conform to Newtonian relativity and thus automatically account for the null result of the Michelson-Morley experiment without recourse to contracting lengths, local time, or Lorentz transformations. Yet, as we have seen, Einstein resisted the temptation to account for the null result in terms of particles of light and simple, familiar Newtonian ideas, and introduced as his second postulate something that was more or less obvious when thought of in terms of waves in an ether."

Pentcho Valev

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Zeeya wrote on May. 8, 2012 @ 13:01 GMT
Supernova study backs both single-degenerate and double-degenerate models:

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Lawrence B. Crowell replied on May. 8, 2012 @ 16:09 GMT
The question we can ponder is whether there are observable signatures between the two sources. The single-degenerate source offers to my mind a precise energy value for the SN1. The double seems likely to be less certain, for two white dwarf stars with m ~ 1.5M_{sol} probably creates a much larger "fusion core" than a single white dwarf that exceeds the Chandrasekhar limit.

Cheers LC

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Anonymous replied on May. 10, 2012 @ 21:02 GMT
Hi Lawrence and Zeeya,

It is an interesting topic. These cosmological spheres are fascinating.

The mass, the density, the volume, the vel. of rot spin,vel. of rot orb,linear velocity, the pression, the ...these things are fact we have to consider that the stars evolve also. They live in fact in a simplistic vue.

Let's resume the evolution of a binar system with two stars.In fact we can class their evolution in considering the steps of the process of binar systems.

Let's imaine two stars , a more massive and an other. The evolution of this interaction is under the time in 10^6 years considering an exchange of mass.What I find very fascinating is the oscillation, periodical of evolution.The stars during their interaction implies a dance of these two stars.The stars interact with a specific road.They become in fact on the line time different.The massive star for example become a big red and the other take the gas.The rotations after still imply two stars in sphericality. The velocities increase. After we have the creation of a white dwarf during that the years pass.The nova appears after 12 10^6 years of interactions of mass. The exchange of mass permits a SN on the line time.

The rotations are essential like the V,the m,THE ROTATIONS,...If I take my equations about the E, we have an imrpovement of E=mc², because the 3 motions of spheres must be inserted. If we consider that it exists a constant between all physical spheres, so we can see the relation with mcosV=constant considering that c is the linear velocity,s spinal velocity,o orbital velocity. if the E=m(c³o³s³) that is why we can say that it exists a force between all spheres, so F=S s1s2/r² can be imrpoved. Now we can class the exchange of mass between the systems. An improtant thing is that we must consider that the light turns in the other sense than mass. And that the serie of uniquity is finite and begining from the main central sphere for the two main systems, the hv, the m. That permits to analyze the polarizations of evolution of a star also.

Logically speaking, we have an exchange of mass precise and specific. But in the logic of the evolution where m polarises hv.We have an increase of mass for all mass. Even if we have a lost of mass due to the interactions of two stars. It is relevant considering the singularity and the diffusion of matters inside the universe. We can say that these stars produce and diffuse specific matters. Now of course the polarity between m and hv is difficult to see because the planck walls are far of us. But we can extrapolate the serie, finite and precise from the main central sphere.and with my equatiopns about the rotations, that helps !

The laws of Kepler are always a good partner !!!

The aim is to analyze the points of equilibrium. The gravitational waves can help also !

Let's play with the spheres .....:)

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FQXi Administrator Zeeya Merali wrote on May. 9, 2012 @ 16:49 GMT
Nuclear physics experiment could provide SN insight:

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Lawrence B. Crowell replied on May. 11, 2012 @ 17:50 GMT
I will have to think about how this pertains to SNI, for this sounds more directed to SNII or the end of large stars. This result does though give more degrees of freedom or quantum states for nuclear transitions.


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Domenico Oricchio replied on May. 12, 2012 @ 14:10 GMT
I though these days to the nuclear reaction in supernovas, obtaining some vague ideas.

The supernovas are a good instrument to measure the Universe expansion, but I think that are a good instrument to study the inner composition of the stars.

We have some indirect measure of the inner composition, and nuclear reaction, of the stars: I think Sun seismographic tomography, Sun neutrinos emission, etc; but each supernova ignition cause the dispersion of great star, and the spectrographic absorption of the supernova cloud can give a standard measure of the star composition: a statistical study of the cloud can be useful because the supernova have a standard composition (1.4 solar mass with the same age), and a right calibration of the cloud measure can give the inner structure of the companion star (I think a standard like Hertzsprunger-Russel diagram for supernova clouds); there are some differences because of the nuclear reaction (quantum tunneling) induced by the supernova explosion.

I think that a static compression metallic hydrogen, with an accelerator with high luminosity, can give (using for example beta+ decay, or neutron injection) an induced proton decay to obtain a fission experiment (extern part of the star simulation) to calibrate the software to the right differential equation for nuclear reaction.



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Lawrence B. Crowell replied on May. 13, 2012 @ 16:38 GMT
A white dwarf star has of course reached the end of its nuclear cycle. The object is about the size of a terrestrial planet such as Earth, but has a mass of .5 to 1.4 times the mass of the sun. The outer layer is mostly carbon, followed by an inner layer of oxygen, followed by a core composed mostly of neon.

If this object is near a companion star, a more ordinary type of star, such that its gravitation pulls of material from the star, the white dwarf mass increases. Once it reaches the Chandrasekhar limit at around 1.4 M_{sol} it implodes and generates a runaway fusion process that liberates lots of energy. Elements are fused up to iron, with a small minority fused in an endothermic process to heavier elements.

The alternative process is where two white dwarf stars are in a mutual orbit. The loss of orbital energy by various processes, the generation of gravitational radiation, friction due to intervening medium of gas or dust and so forth, causes the two to spiral into each other. The coalesced object then enters into a runaway fusion process. This mechanism will differ from that above because the mass of the coalesced fusion core could be larger than the Chandrasekhar limit 1.4 M_{sol}. This could mean the energy released is different and this may not be an appropriate “standard candle.”

The question, which I would imagine some astrophysicists are already working on, is what are the signatures expected for the two processes. Is the time domain of energy release different? The fusion in the second process could involve nuclear processes that occur with different nuclei at this evolves. For instance there could in the second process be much more carbon fusion in the initial moments. It would then be of interest to distinguish between these two events.

Cheers LC

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Jeff Ford wrote on May. 10, 2012 @ 12:13 GMT
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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Zeeya replied on May. 12, 2012 @ 00:30 GMT
You're quite right, of course! In fact, I just missed out on seeing Faust staged, while I was writing that piece, so I'm not sure how "poem" slipped in. I guess the editors felt it was as much a work of poetry as a play, perhaps.

And thank you for saying that you enjoy my other articles too.

There is a Julian Barbour thread somewhere. I guess I should really move this discussion there. :-)

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