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Astronomers Explode Virtual Supernova
Posted by
CowboyNeal
on Thu Mar 22, 2007 11:27 PM
from the safest-detonation-yet dept.
from the safest-detonation-yet dept.
DynaSoar writes "Scientists at the University of Chicago's Center for Astrophysical Thermonuclear Flashes have created a simulation of a white dwarf exploding into a type 1a supernova. Using 700 processors and 58,000 hours, they produced a three second movie showing the initial burst that is thought to be the source of much of the iron in the universe. Understanding these supernovas is also important to testing current cosmological theories regarding dark matter and dark energy, as their brightness is used as a measurement of distance, and discrepancies found in the brightness of very distant supernovas consistently seem to indicate a change in the speed of expansion of the universe over time."
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movie links on the UC site (Score:5, Informative)
for all alternative OS users out there.
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Psssh! (Score:5, Funny)
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Re:Psssh! (Score:5, Funny)
Parent
Simulated KaBoom? (Score:2)
There was supposed to be a simulated Ka-Boom. A simulated earth shattering Ka-Boom.
SciTechPulse. Geek News Netcast. Hot Polynesian Geek Chick Silulu. [scitechpulse.com]
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58000 hours (Score:4, Interesting)
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Researcher #1: Ooops! It crashed... darn!
Researcher #2: Crap! After 6 years!...
Researcher #1: Oh wait.. I have an idea!...
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Re:58000 hours (Score:5, Informative)
Parent
Re:58000 hours (Score:4, Informative)
Yep, definitely nowhere in the story. Not anywhere. Definitely not in plaintext, sitting there, waiting to be read
Parent
Re:58000 hours (Score:4, Insightful)
Parent
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Re:58000 hours (Score:5, Interesting)
For a brief overview (based on Fowler's Nobel Prize lecture) on element formation... This is all from memory (and I am not a physicist) so do your own verification. Basically small stars burn Protium (1H). These fuse to product 2He which immediately decays into Deuterium (2H), emiting a positron. This P-P process eventually allows Deuterium to fuse forming the stable 4He.
As the amount of Helium in a star increases, it eventually becomes possible for Helium to fuse. The only problem is that 8Be is unstable and alpha decays almost immediately back into He. However, you get a small amount of 8Be sitting around for a while, and it can fuse with 4He to produce 12C (Carbon-12). From here things get interesting...
For stars with more than about 1.1 times the mass of our sun, The carbon becomes the basis for Helium production, replacing the P-P process. The basic process (called the CNO cycle) involves single captures of protons (2 of which decay into neutrons and positrons) and then the alpha decay back into 12C. In short this allows Carbon to act as a sort of catalyst for Hydrogen fusion. All elements heavier than Carbon are produced using one of a number of processes. These include fast proton capture, slow proton capture, and alpha capture. The problem is that these become endothermic at the point of Iron. So while smaller stars can produce some of the heavier elements, they are limited in the quantities they can produce. Supernovas, however, can rapidly create much larger quantities of heavier elements.
Also note that at a point in the distant past, stars were more massive than they generally are today. This means that at different points in the history of the universe, we saw large amounts of heavier elements generated.
So this is all quite interesting. I am sure at that many hours we are probably talking about a pretty detailed atomic model. The movie probably shows noting near what the simulation shows.
Parent
A face in the explosion (Score:3, Informative)
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Very Subtle (Score:5, Funny)
They probably got Federal Funding for this by explaining it was "like sticking a giant firecracker up a giant frog"
The horror! (Score:3, Funny)
Moo (Score:2, Informative)
Shouldn't that be supernovae?
No, it's an English word (Score:4, Informative)
In fact, the word is built out of two Latin adjectives, literally it means an "abovenew". Invented words follow this rule, hence the plural of octopus is octopuses, of satellite is satellites, and of millennium is millenniums. The plural of "vertebra" is "vertebrae" because it is an actual Latin word, not an invented modern one.
Incidentally, while pursuing this very pedantic note, "satellites" is correct plural but the singular of the original word is "satelles". And the original word is pronounced sat-ell-it-ees. We are a long way from Latin.
Parent
Uh, not quite... (Score:2)
The word nova in the astronomical context comes from Tycho Brahe, a Danish astronomer who was writing in Latin at the time. The plural is novae, not novas. Although supernova is an English construction, the etymology is derived more directly from this Latin word than other modern inventions. Although both plural forms are strictly correct due to the artificial construction, supernovae is used predominantly in our field.
Linguistics (Score:2)
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Strictly speaking, super (as a preposition of space or location, in this case) takes nova in the ablative case, so the ending on nova is a long a (ahhhhh). If we were writing in Latin I don't know that we'd use the -ae ending for the plural at all. In fact, I'm not sure what the plural would be.
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Is it April Fools Day already? (Score:5, Funny)
Nice blanket statement (Score:3, Insightful)
Bob: But we'll never get funding with a three second image. This thing had to have caused something useful .. ... how about something specific like Kevin Federline?
Joe: Well, um
Bob: No, panders too much to popular culture.
Joe: That's too bad because my next thought was heavy metal music. Oh, how about some type of boring "metal" like iron ore. It's in some vitamins too which will interest the average consumer.
Bob: That'll do. We have to get the funding proposal out by noon.
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more detail (Score:5, Informative)
The progenitors of SNIa are most likely white dwarfs composed of carbon nitrogen and oxygen, probably with a companion star from which they are stripping matter. They are very compact on the order of a few thousand kilometers at most, and really dense - more than the mass of the sun. They aren't hot enough to support fusion - they are supported by Pauli pressure; quantum mechanics doesn't allow two electrons in the same state at the same time so though gravity tries to compact these objects there is a Pauli pressure outward to balance it.
This can't go on forever in these progenitor systems however, and if the white dwarf strips enough matter of its companion to get to ~1.4 solar masses (the Chandrashekar limit) then Pauli pressure isn't strong enough to balance gravity and the star begins to collapse and when that happens pressure and temperature rises and somewhere a nuclear fusion flame ignites. Details about what happens near collapse, and where and how the flame ignites, and how many there are and how they progress are still debated. In this particular model they are considering only a single flame (so far) and its a "gravitationally confined detonation" (GCD - the name of this particular model).
Its a little difficult to get a sense of scale from those videos, though there are numbers in the bottom corner. The flame starts of near or just of center and becomes bubble/mushroom shaped through a Rayleigh-Taylor instability [wikipedia.org] and breaks the stellar surface in under a second. Its less than another second before the ash and flame from the bubble collides at the opposite end of the star. This flame crashing into itself (see video 1) causes compression and a detonation.
Theres been a lot of debate as to whether its a deflagration or a detonation or whether it transitions from one to the other and how and when that happens and us poor graduate students just hope they don't go crazy over details of the progenitors during our qualifying examinations. This is notable because there appears to be a growing number of voices who are saying that a detonation is necessary. These events are so standard because they all become SNIa if they get near 1.4 solar masses. There is a fair bit of diversity (and some just crazy objects) and most of that probably arises from details during the explosion which is why modeling them is partly why the models are so important.
There is still a lot of modeling left to do. This flame is producing a lot of heavy elements (there is O, S, Ca, Mg and Si in the early spectra - the silicon feature is around 6150 angstrom in the rest frame and is the marker of a Ia at low to moderate redshifts). As the outer layers expand and become more transparent you see more of the material produced during the explosion and a lot of this is Nickel (Ni-56) which decays to cobalt and powers the light curve so you get this typically 2 week rise and then a slow fall off. Later times most of the Ni has become cobalt which is decaying to iron and you see these elements in the spectrum. The energies we are talking about here are about 10^45 Joules. A H bomb by contrast is 10^15 Joules so 30 order of magnitude. Unless you can picture 10^30 H bombs going off its hard to get a feeling for this number but thats generally the case with numbers in cosmology.
There are a lot of empirical relations you see from the lightcurve, which are exploited to standardize them (for instance the brighter the supernova, the slower its rate of decline, and there are relations for the colour...) and if a model can replicate them and match the observed lightcurves and spectra then this is a very impressive accomplishment. I skim
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Its a little difficult to get a sense of scale from those videos, though there are numbers in the bottom corner. The flame starts of near or just of center and becomes bubble/mushroom shaped through a Rayleigh-Taylor instability and breaks the stellar surface in under a second. Its less than another second before the ash and flame from the bubble collides at the opposite end of the star. This flame crashing into itself (see video 1) causes compression and a detonation.
I don't get it. The flame expands o
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Virtual Supernova: readable article (Score:2)
I found that passage confu
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I don't get it. The flame expands outward to the surface in less than a second. I am ok so far. Now to do that the material would need to have a lot of momentum in the direction it is going, so how does it suddenly turn around and crash into itself on the other side?>
It is not the material itself that 'turns around', but rather the gas/plasma pressure increase that propagates (at nearly relativistic speeds, no less. The simulated star was earth-sized; imagine traveling to the other side of our planet
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I was going to ask "how do you see it if it doesn't fuse", but then I got smart and read the Wikipedia page on white dwarfs [wikipedia.org] which was really quite good, from a layman's perspective.
Cheers and thanks for the wonderful comment,
-l
10 year project grant pays off (Score:2)
Iron? Am I wrong? (Score:2)
I always thought that iron was produced without the nova and that it was elements that are heavier than iron that were created by the blast. Am I wrong on this?
Counterintuitive (Score:2)
Real ultimate power! (Score:2)
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Just because you throw more resources at a problem doesn't necessarily mean that it gets solved any quicker (in many cases, past a certain point it actually gets slower).
Re:Well that's all fine and good.... (Score:4, Insightful)
Knowledge for knowledge's sake ALWAYS ends up paying off.
Just because we dont know how to make our lives better by virtue of gaining this knowledge now, there's no reason to suppose we'll never know (in fact, history indicates that eventually ALL research pays off to some extent).
If you RTFA and do a slight bit of reasoning (I know, I know, but try), you will see that this research directly helps us understand more of the hydrogen -> helium mechanincs.
Repeat after me:
ALL KNOWLEDGE IS VALUABLE.
KNOWING IS ALWAYS BETTER THAN NOT KNOWING.
Ignorance being bliss was a concept invented to placate the ignorant.
Parent
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Further development in materials and energy sources today relies upon gaining a better understanding of the physics involved. After all, it's hard to do engineering when you don't know the rules. While we have very good models for large-scale physics, we're still lacking at the subatomic level.
The difficulty of subatomic physics is that the particles are so small that their influences are difficult to detect. One way to solve that is
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Plus, keep in mind that this center gets funding from the DoE. I'm sure you can creatively think of other uses for exploring high-energy thermonuclear reactions in high-resolution detail.
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NeoThermic
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I hate to state the obvious but we would go looking for them and if we didn't find them, we would go "back to the drawing board". It's science 101...
1. Observe.
2. Model.
3. Predict.
4. Repeat.
Science is littered with dead models, not to put too fine a point on it but that's how it works. The only belief required says that "the real world exists as something seperate from the internal model created by my brain, commonly called p
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We need to keep the scientific method in mind anytime we read a study. Far too many people are willing to take a study as an absolute truth instead of a new way of seeing an incident. This coupled with the fact that too many people already have a problem with the concept of a law and a theory makes talking about science in a meaningful way fairly hard.
So yes, there is tons to be discovered even in our own backyard but at the same time theories and predictions can be mad