Talk:Supernova
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First line
The first line seems to imply that Supernovae result in the formation of new stars. It should state that it forms a bright object that some may have interpreted as a "new" star in the past. The confusion is particularly troubling since Supernova are actually a result of the stellar dying process.
- That's a good point. I made some edits to the article. Etymology is now in a separate paragraph; the intro now focuses on what a supernova is, rather than on the origin of the name. -- Curps 21:03, 12 Mar 2005 (UTC)
Unfortunately, the intro now describes only Type II SNe, and ignores Type I (WD thermonuclear) SNe. It also probably should not focus on the star formation aspect, as that is both somewhat controversial (eg see Hester et al. 2004, Science) and secondary to the phenomenon. Mordecai-Mark Mac Low 00:58, 30 Mar 2005 (UTC)
I have grabbed the relevant text from supernova remnant, which was more accurate. The deleted text is here Mordecai-Mark Mac Low 17:17, 2 Apr 2005 (UTC):
- There are at least two different types of supernova which have different triggering mechanisms which are described in detail below. However, the general pattern of a supernova explosion is that it occurs when a star finally exhausts its thermonuclear fuel, the delicate virial balance between energetic thermal expansion due to fusion and compression due to gravity is lost.
I also rewrote the rest of the introduction:
- removed triggered star formation (see my comments above) and emphasized heavy element production, which was the real point of that paragraph
- moved the definition of "foe" to its own entry, which was only a stub. This unit is only used by some specialists in the subject (I have been working on SNe my entire career, and had never encountered it; it shows up only three or four times in the last five years in a full text search on NASA ADS). Mordecai-Mark Mac Low 17:17, 2 Apr 2005 (UTC)
Supernovas or Supernovae?
Which is the correct plural form? I personally prefer the Latin, but I'm not sure as to which is more appropriate. Christopher 07:12, Feb 17, 2005 (UTC)
- Well I prefer "supernovas" (and changed the article), but Google seems to indicate that "supernovae" is more popular. Hmmm. It sounded archaic to me. -- Curps 07:16, 17 Feb 2005 (UTC)
- The Latin form "supernovae" is used by scientists who study supernovae :-), and is the form found in all current refereed technical literature. Most astronomers use the Church Latin pronunciation of "super-noe-vee", rather than the classical Latin "super-noe-why". If you want to follow the scientific community here, you should use "supernovae". Let me also point out that the astronomers who work on supernovae use ergs as the unit of energy, not Joules. I modified this page many months ago so that it mentioned ergs, but I've obviously been overridden. It does make some sense to pick the same set of units as most other scientific fields, so I decided to let it go. -- Michael Richmond, Feb 18, 2005
- The Astrophysical Journal, to many of our annoyance, does use the 's' plural rather than the 'e' plural. Mordecai-Mark Mac Low 00:58, 30 Mar 2005 (UTC)
Why is 1044 rendered as an image here?
Regarding Type Ia, it says the fusion produces the shockwave. Is that correct? Doesn't the matter colliding in the center produce a shockwave, which then ignites fusion and causes the light emission? --AxelBoldt
I'm not an expert on supernovae, but from the last i've heard, the problem is that we don't know the exact mechanism. We aren't even sure if it is one white dwarf or the collision of two.And regarding the mechanism, there are theories of "detonation" and of "deflagration", that I think have to do with where it starts and how does it expand. I didn't write the particular bit about Ia for that reason, probably it would be more accurate that we don't know, and that there are several possible mechanisms. --AN
One of my astrophysics texts says that a Type Ia supernova occurs before the white dwarf reaches the Chandresekar limit. Rather than the collapse of electron degeneracy and the production of a neutron star, the Ia supernova occurs at around 1.3 solar masses, where the temperature and pressure at the center of the star is sufficient to ignite carbon-burning fusion. Because it is intensely degenerate, however, the dwarf can't respond to the new energy source in its core by expanding, so the core gets hotter, and the carbon-burning reaction faster, until enough energy is released to blow the star utterly apart with no neutron star or black hole remnants.
Can someone verify or refute this?
Supernova models are a current topic of research. Subchandrasekhar explosions are one of the possibilities discussed. That there is no remanent in a Ia is something I do not remember from the top of my head, but it is possible. But, I repeat, i do not think there is an unanimous agreement on SN Ia mechanism (at least last time i went to a research talk on the subject, one or two years ago).--AN
American Indians?
What's the deal with the claim that American Indians saw the 1054 supernova? Did they leave any records? Does anyone has a reference to this fact? Gadykozma 19:26, 13 Sep 2004 (UTC)
- Petroglyphs exist which depict a bright star in the proper position, and which can be dated to the supernova's time. The first such image to be discovered was found by William Miller, Palomar Observatory's chief photographer, and Helmut Abt, an astronomer. This glyph, at White Mesa, Arizona, was found back in the 1950s; since then, a dozen more have turned up. My favourite is one at Chaco Canyon, New Mexico.
- Laurence A. Marschall's book The Supernova Story (Plenum: 1988, ISBN 0-306-42955) has more information, including a nice photograph. Marschall also summarizes why Europeans didn't observe the "guest star" the way the Chinese (and probably the Anasazi) did. In mid-July, just two weeks after the estimated explosion date, Pope Leo IX excommunicated the Eastern Orthodox patriarch. "At such a time, the wisest course was probably to keep mum about any omens in the sky." Not an altogether convincing theory, I admit, but one with a certain odd appeal, rather like an episode from a James Burke documentary.
- Anville 23:26, 13 Sep 2004 (UTC)
- This article [1] (http://www.astronomy.pomona.edu/archeo/outside/chaco/nebula.html) also has a picture and background information on the Anasazi supernova petroglyph at Chaco Canyon.
- Anville 19:15, 26 Sep 2004 (UTC)
Supernova outputs more energy than several Solar masses ?
The second paragraph says that a Supernova can output energy equivalent to several solar masses. This can't possibly be true. Fusion produces a lot energy. Still, Fusing of Hydrogen atoms to Helium turns less than 1 percent of the mass to energy.. Supernova#Type II explains this. Fusing of heavier elements produces relatively less energy. So, for a Supernova to output the energy equivalent of several Solar masses wouldn't it have to mass hundreds of times the mass of our Sun? But the maximum size of a star is about 150 Solar Masses. So, this section is plainly wrongd
The energy that is getting converted is the gravitational binding energy of the star, not the nuclear energy of the atoms. The SN is occuring because the nuclear energy is exhausted. Also, SN occur in stars of > 8 <math>M_{sun}<math>. I looked at the language in this paragraph again, "as many as several Solar masses of energy or more than 10^44 joules." As many as several solar masses or <math>10^{55}<math> erg places a good, and sound upper bound on energy, or more than <math>10^{51}<math> erg is a lower bound and is confirmed even in the conservative literature. Lets not miss the point that SN are extremely energetic events. All of the above information is confirmed by astro-ph literature, see my comments below. I dont think a change is required here. John187 15:51, 18 Mar 2005 (UTC)
- A supernova doesn't produce its energy by nuclear fusion, at least not in the conventional sense. The energy of a supernova is produced when its core collapses into a neutron star, producing a tremendous amount of neutrinos and a powerful shockwave that heats up the remaining stellar atmosphere and blows it away. This is a much more efficient process than ordinary nuclear fusion. Bryan 02:07, 18 Mar 2005 (UTC)
- I just reread the article and I'm a little less certain now, though. The section on type Ia supernovae says they occur when a white dwarf passes the Chandrasekhar limit, which as far as I'm aware means it should then collapse into a neutron star. This is supported by parts of that section (eg, "In the case of a nova, the infalling matter causes a fusion reaction of material near its surface but does not cause the star to collapse") but another part says "The energy release from the thermonuclear burning (~1044 joules)" which has exactly the problem with it that you point out. So do type Ia supernovae generate their energy via collapse into a neutron star, or is it via thermonuclear reactions? My gut says it must be via collapse into a neutron star, but I'm not an expert in this field so I'm reluctant to dive in and change it. The section on type II supernovae is as I expected it to be, though, and matches what I said above about core collapse. Bryan 02:19, 18 Mar 2005 (UTC)
- A couple points....First here are two references on the subject, http://arxiv.org/PS_cache/astro-ph/pdf/0409/0409035.pdf, http://arxiv.org/PS_cache/hep-ph/pdf/9901/9901300.pdf. To begin to think about this one needs to realize that the energetics and densities involved in Supernova formation are way beyond any of the "typical" physics thinking people might be familiar with, even including fusion. The collapse is so energetic that nothing but neutrinos can escape the advancing stellar material. This creates a kind of pressure cooker where by any mechanism where mass converts to energy that we typically think of, this energy can not escape until it gets converted into a neutrino somehow. So, unless a process can create neutrinos, we can pretty much ignore it. Even though neutrino production is extremely supressed, its the only way for energy to escape and this is how the supernova must emit its energy. The key point is that to understand the supernova you must understand the neutrino. The energetics are sufficiently high, that pair creation and annilation are occuring spontaneously, and neutrino creation will occur in about 1/10000 the rate of e+e- so this is probably the mechanism for most of the neutrino formation. This all must occur in a 10s window. Despite these limits however, there are alot of things yet to be understood about this process. The energetics are likely high enough that SN involve physics beyond the Standard Model. John187 15:33, 18 Mar 2005 (UTC)
- That sounds like an excellent bit of explanation to put into the article itself. Doing so now. :) Bryan 00:37, 19 Mar 2005 (UTC)
- I do agree that "several" solar masses sounds astonishing. It depends on the mass of the collapsing star of course, but you have to remember that our Sun is an average to small star. A typical figure given for the energy release of a SN is <math>10^{58}<math> erg. For a SN of 8 <math>M_{sun}<math> the number is probably more like <math>10^{53}<math> which is about 1 <math>M_{sun}<math>. I'll look at the language to see if it needs softened a bit. The point is these SN generate a HUGE amount of energy even by stellar scales. These are some of the most energetic events we can imagine. John187 15:33, 18 Mar 2005 (UTC)
- Just to make sure I understand this: the speed of light is c=299,792,458 m/s, the mass of the sun is m=1.9891 × 10^30 kg, therefore one solar mass corresponds to E = m * c^2 = 1.788^{47} Joule. Do you get the same numbers? If the calculation is correct, then 10^44 Joule is less then one permille of a solar mass and the text would contradict itself. --Jochen 01:33, 19 Mar 2005 (UTC)
- Please have a look at the 2nd paragraph of this discussion. <math>10^{44}<math> is a conversion (not sure why this page uses Joules) from <math>10^{51}<math> erg which is a relativly conservative lower bound from the literature on this subject. Your numbers are correct also, <math>M_{sun} \approx 10^{47} J, 10^{54}<math> erg. The sentence in consideration still reads correctly. "as many as several solar masses or more than 10^44 J" You have to read it as an upper limit and a lower limit. Every star does not have the same mass. I think we are hashing apart this sentence a bit much. Nobody has a crystal ball to look into supernova to see what happens, these numbers are order of magnitude type estimates to explain what we think is probably going on, for more details you have to go to the astro-ph literature, I've already quoted several good papers. John187 03:27, 19 Mar 2005 (UTC)
- Hi John, just a few remarks. 'not sure why this page uses Joules': Joules is the SI unit, so it should be used. 'every star does not have the same mass': "solar mass" means "mass of the sun", otherwise it would be "stellar mass". 'upper limit and a lower limit': I read "as many as several solar masses" as "more than 1.788 × 10^{47}". --Jochen 11:25, 19 Mar 2005 (UTC)
- Sure. My point about the Joule is that Astrophysics is standardized to CGS units. The "standard" unit of energy in Astrophysics is the Erg. Also, in the context used above, <math>M_{sun} = 10^{54}<math> erg is being used as a unit of energy. None of the discussion above has anything to do with our sun, per se. As to the total energy, have a look at equation (1) in this article (http://arxiv.org/PS_cache/hep-ph/pdf/0306/0306056.pdf). If the binding energy is several solar masses <math>10^{54}<math>, then <math>M_{NS} = 5 M_{sun}<math> can release this amount of Energy. Note, SN events occur in objects with larger than <math> 8 M_{sun}<math>. So saying that SN release several solar masses of energy is very conservative. John187 16:13, 20 Mar 2005 (UTC)
- IANA Physicist. But this still excites great skepticism in me. Conservation of Energy, Conservation of Mass... Where does the energy come from? As I see it, nuclear fusion or gravitational contraction are the two choices. My understanding is that pushing a proton and electron together to form a neutron takes a lot of energy. It doesn't release energy.
- The article also says that a supernova can release as much energy in one burst as our Sun releases in its entire lifetime. Sure, that is creditable. But fusion of Hydrogen to Helium turns less than one percent of the mass to energy. An earlier comment in this thread says that the energy doesn't come from fusion, but from the "core collapse". Well, if that writer meant from gravity, gravity is by far the weakest of the four fundamental forces I learned about in school. -- Geo Swan 20:19, 2005 Mar 20 (UTC)
Moved explanation to type II
Moved the explanation of collapse to type II. Type I's don't produce neutrino bursts.
Removed false statement
- The energetics are sufficiently high that pair creation and annilation are occuring spontaneously but although neutrino/antineutrino creation will occur at only about 1/10000 the rate of electron/positron creation this is probably the mechanism for most of the neutrino formation.
Most of the neutrino formation occurs from electron capture
p + e- = n + nu^e
pair production happens, but it doesn't produce nearly as many neutrinos. It is important since most of the mu and tau neutrinos come from pair production, but it's not that important to the energetics.
- Actually, the original statement is mostly true, yours is not. The neutronization reaction you wrote there is thought to be responsible for about 1% of the total neutrino energy released during a supernova. 99% of the energy is carried by neutrinos created in thermal processes such as pair annihilation, plasmon decay, photoneutrino and Bremsstrahlung. Pair annihilation does dominate at high temperatures.
--Fleurot 19:49, 14 Apr 2005 (UTC)
Also, a typical type II supernova releases 10^53 erg of energy which translates into one solar mass of energy.
Roadrunner 17:15, 1 Apr 2005 (UTC)
Took out the "several solar masses" of energy. A supernova has 10^53 of gravitational binding energy. m = E/c^2. 10^53 / 3x10^10 / 3x10^10 = 10^32 grams. One solar mass is 2 x 10^33 grams.
Also, the "upper bound" for type II supernova comes from gravitation limits. It's an easy calculation to calculate the amount of gravitational energy in the star before and after.
Also took out the section about the neutrino physics not being well understood. The neutrino physics is actually pretty well understood. Its some of the other parts that are nasty.
Softened the part about the standard model. The energies in supernova are high enough so that there could be some weird effects, but nothing really, really weird. The typical energy for a particle in a supernova is tens to hundreds of MeV. This is well below the energy of the big particle accelerators (which can put particles up to tens of TeV) so there is unlikely to be really, really weird physics at this level.
Roadrunner 19:24, 1 Apr 2005 (UTC)
Roadrunner 19:24, 1 Apr 2005 (UTC)
Contradiction with Cataclysmic_variable_star
Here it states that the companion for a type Ia is usually a red giant. Under Cataclysmic_variable_star, it says red dwarf, or sometimes a subgiant.
The supernova and the spaceship
Would it be possible to predict when a star is going to go (super)nova? Or would it fall into the category of events like the volcanic eruptions that are stated to be imminent but of unpredictable actuality?
How far away would a (sf) spaceship (protected against normal radiation and space debris of course) have to be to avoid damage?
Californium: Created in stars or artificial?
It is said on this article that supernovae can produce some of the heaviest elements like californium. But the californium article tells that californium is a synthetic element.
Isn't that disturbing?