Talk:Supernova/Archive 1

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Holistic article

This article by a "holistic" organisation claims to have an alternative explanation for supernovae which differs from the scientific explanation. Rnt20 11:32, 8 September 2005 (UTC)

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)

Incorrect description of "timeline"

Be aware that the years listed are only the years in which the supernovae were first observed. The supernovae themselves occurred much earlier, their light taking hundreds or thousands of years to reach Earth.

The statement supernovae occurred much earlier is misleading, in the light of the theory of relativity. Because there exists a reference frame in which the explosion and observation happen almost simultaneously. This is a common mistake when discussing light originating from distant objects. The distance between objects depends on the frame of reference and so does the time taken. It is misleading to say that supernovae occurred much earlier when the event occurrence and observation are on the same light cone. I propose that this statement be dropped from the article.

I think you're being excessively nitpicky here. I'll just change the second sentence a bit to make it less misleading. Bryan 04:37, 21 September 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)

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Why is 10⁴⁴ rendered as an image here?

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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

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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

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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?

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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

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JahMon 12:48, 17 October 2005 (UTC) says: I think supernovae is misspelled once in the type1a part

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] 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 $M_{sun}$. 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 $10^{55}$ erg places a good, and sound upper bound on energy, or more than $10^{51}$ 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/abs/astro-ph/0409035, http://arxiv.org/abs/hep-ph/9901300. 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 $10^{58}$ erg. For a SN of 8 $M_{sun}$ the number is probably more like $10^{53}$ which is about 1 $M_{sun}$. 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. $10^{44}$ is a conversion (not sure why this page uses Joules) from $10^{51}$ erg which is a relativly conservative lower bound from the literature on this subject. Your numbers are correct also, $M_{sun}\approx 10^{47}J,10^{54}$ 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, $M_{sun}=10^{54}$ 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. If the binding energy is several solar masses $10^{54}$, then $M_{NS}=5M_{sun}$ can release this amount of Energy. Note, SN events occur in objects with larger than $8M_{sun}$. 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)

IAA Physicist. $M_{NS}=1.4M_{sun}$, not $5M_{sun}$. The subscripted NS in this case stands for the 'neutron star' that remains. The rest of the ~10 solar masses of the progenitor gets blown off in the explosion. If the explosion fizzles and doesn't blow off the rest of the star, you don't get a neutron star much more massive than this--it collapse into a black hole so quickly that almost no neutrinos (and hence no energy) would escape. -- DMPalmer 19:12, 4 January 2006 (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)

This is incorrect. Look at (Bruenn, S. W. 1985, ApJS, 58, 771). Most of the neutrino flux is generated by electron capture as the core neutronizes. Pair annihilation, plasmon decay, photoneutrino, and bremsstrahlung are second order effects. The thing about thermal processes is that they generate identical amounts of neutrinos and anti-neutrinos and roughly the same number of each species. Electron capture produces only electron neutrinos and that is why most of the energy that comes out is in the form of electron neutrinos.

Roadrunner 22:38, 16 March 2007 (UTC)

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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?

Volcanic eruptions can (sometimes) be predicted a short time in advance—by noting that the top of a mountain is bulging, for example. Likewise, one can identify candidate stars for supernova explosions. Finding a red or blue supergiant undergoing variability—changes in brightness—might plausibly indicate that the star is fusing carbon and hence near the end of its "life cycle". An exceptionally strong stellar wind might also be a clue that the reactions inside the star's core are becoming extreme and that the star will soon go foom. Naturally, what an astronomer calls "soon" might be a thousand Earth years (astronomy and astrophysics typically deal with much longer timescales). I've seen speculations that both Betelgeuse and Eta Carinae are in the pre-supernova phase, with some relatively small number of centuries to go.

Candidates imminent & 'local' to us could include Rho Cassiopeiae [2], Betelgeuse [3], Antares [4], Eta Carinae [5], or even this Kitt Peak Downes star [6] Imminent here can mean sometime between now and the next 10000 years (except for the last listed). There is one possible predictor [7] The Yeti 20:03, 5 January 2007 (UTC)

If you had a spaceship relatively close to the star, you could probably get a much more precise "advance warning" by watching the neutrino flux. Because neutrinos pass through matter far more easily than photons do, the neutrino flood from the core implosion will arrive sooner than the flash. The difference may be as much as several hours. How you detect neutrinos depends upon how advanced your spaceship is. In Star Trek they do this in a slick, automagical, treknobabble way: regular tricorders cannot sense neutrinos, but Geordi's VISOR can. (This was a plot point, once.) If you don't have subspace sensors or other Trek gizmonics, you could try capturing a comet nucleus from the nearest Oort cloud. This would give you a block of ice the size of Manhattan or thereabouts, which you could wrap in a protective sunscreen and surround with photomultiplier tubes. Most neutrinos would pass through the comet ice without interacting, but the odd particle may strike and produce a tiny flash of light. (Dealing with the comet's impurities would of course be an issue, but with a supergiant star close at hand you may be able to melt the comet and re-freeze it in some fashion. Look up water's specific heat and heat of fusion.) Just before the big boom, you'd see a sharp rise in the number of tiny flashes.

This is essentially a frozen version of the Super-Kamiokande neutrino detector. The "Icecube" project involves trying the same concept using a section of the Antarctic icecap. (So they better make it work before global warming kicks in!) See the SNEWS project for an explanation of how people are trying to use this neutrino detector technology to get advance warnings of supernovae we could see here, on Earth.

It is probably misleading to put regular novae and supernovae in the same category, the way you do by writing "(super)nova". A garden-variety nova occurs when the accretion disk of a white dwarf in a binary star system undergoes a nuclear fusion explosion: matter falling onto the dwarf from its companion star gets squeezed tight enough to fuse. This is probably more difficult to predict without telescopic observations of the star system itself. The same goes for the type of supernova where the mass falling onto the white dwarf pushes it past the Chandrasekhar limit and makes it implode.

How far away would a (sf) spaceship (protected against normal radiation and space debris of course) have to be to avoid damage?

Let's see. A ballpark figure for the total energy output is 10⁴⁴ joules. The radiation intensity can be computed by dividing the total energy by the area through which the energy flows. In this case, that "Gaussian surface" is a sphere drawn around the exploding star at the radius where you've parked your spaceship. Writing I for the intensity, E for the energy and r for the spaceship's radius,

$I={\frac {E}{4\pi r^{2}}}.$

Note that the intensity falls with the square of the radius (inverse-square law). This tells you what your shields have to handle. I don't know how strong those shields will be, but here's a reasonable supposition, in terms of David Weber's Honorverse. A typical warship in the Royal Manticoran Navy can travel at speeds up to .6 c (six-tenths the speed of light). At higher velocities, the ship's particle shielding can't cope with the stuff impacting it. Plowing into a hydrogen atom at that speed makes it look like a cosmic ray. (And don't even think about a dust particle. . .)

OK. To get an order-of-magnitude estimate, let's assume interstellar space contains one H atom per cubic centimeter. Moving at relativistic velocities introduces a correction factor due to Lorentz contraction. At .6 c, distances parallel to the direction of motion are contracted by a factor of 1.25; that is, a 1-meter stick moving at .6 c looks 0.8 meters long. The apparent density of hydrogen atoms is therefore one atom per every 0.8 cubic centimeters, a higher density than observed when stationary. The molar mass of hydrogen is about 1 gram, so each hydrogen atom masses about 1.7e-27 kg. (That's 1 divided by Avogadro's number.) That mass is "enhanced" by the same Lorentz factor as before,

$\gamma ={\frac {1}{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}=1.25,$

giving a mass (as observed by the spaceship) of

$m=m_{0}\gamma \approx 2.1\times 10^{-27}{\rm {\ kg}}.$

The kinetic energy of this speeding hydrogen atom is given by its total energy minus its rest energy. Using Einstein's famous formula, this works out to be

$K=mc^{2}-m_{0}c^{2}=m_{0}(\gamma -1)c^{2},$

which when you plug in the numbers gives

$K=3.7\times 10^{-11}{\rm {J}}.$

Each atom carries a kinetic energy K, and every time the ship traverses 0.8 cm of space, it impacts one atom per square cm. Multiplying the ship's speed (meters per second) by the atom density (1/m³) by the energy per atom (joules) gives an energy flux in joules per square meter per second:

$\Phi =v\rho K\approx 5.4\times 10^{3}{\frac {\rm {J}}{{\rm {m}}^{2}{\rm {s}}}}.$

Note that here we've got a flux involving units of time. To make a meaningful comparison, we need to know how the supernova's energy blast is distributed over time—basically, we need a figure for how long the supernova lasts. Each type of SN has its own characteristic "light curve", since they brighten and dim in different ways which depend upon their internal physics. Much of the light for a Type II SN, which I expect is what you want your spaceship to monitor, actually comes from the radioactive decay of elements produced by the SN shock wave, isotopes of cobalt and nickel to be more precise. Not wanting to get into any truly ugly math, I think we can take a total of 60 days for the SN to pour out the really impressive part of its energy. 60 days is 5.2e6 seconds, for a (very rough) average emission rate of 2e37 joules per second.

We can now compute the "safe distance" by seeing at what radius this 2e37 J/s is spread out to the extent that the ship's particle shielding can handle the flux. Using the formula I gave above (the inverse-square relation), this works out to be

$r={\sqrt {\frac {2\times 10^{37}}{4\pi \cdot 5.4\times 10^{3}}}}$ m

or about 1.7e16 meters. This is about a light-year and a half!

I should note that all this depends upon the strength of the particle shielding. These figures are probably close to right for the Honorverse's ships. (In the Honorverse, you could probably get a lot closer by "rolling ship" when your neutrino detector registers an imminent explosion, placing your impeller wedge between yourself and the blast. However, that's a bit beside the point, and I've seen the same rough figures for starship acceleration and speed limits in other SF 'verses. For example, Star Trek full impulse is 0.2 c, so you could re-do the calculation for v/c = 0.2 and see how strong the Enterprise's navigational deflector has to be. Ditto for Isaac Asimov's Nemesis, etc., etc.)

Anville 2 July 2005 17:17 (UTC)

I know novae and supernovae are different beasties - but assumed the calculations would follow the same principle (but bigger star = bigger explosion = keep further away to start with). I suspect that "Don't argue with a potential exploding star" is valid whether it is going to go nova, supernova or hypernova.

Having a spaceship with time travelling capacity (ie the ability to move through time in a non-linear manner, as the Tardis or H. G. Wells' machine do would help - or one which can jump into alternative universes.

If there is a list of "Common problems with science fiction stories" which has a section on novae and their bigger relatives please link it here.

—The preceding unsigned comment was added by 212.85.6.26 (talk • contribs) on 17:55, 24 October 2005.

Because I'm bored, I'll add my two cents worth to this thread:

• You wouldn't need a detector right next to the supernova if you had a neutrino observatory on the world you were trying to get a warning for. Earth's current neutrino detectors were able to pick up Supernova 1987A's neutrino burst, and they are now networked to act as a Supernova Early Warning System (warning for astronomers to get telescope fixes, not of any impending disaster).
• If you have FTL ships, you'd get more advance notice of the supernova, but you'd still probably be in the next star system over (so as to hide from the imminent bang, unless you can enter FTL fairly quickly). But useful FTL travel (or even communication) wrecks so much of physics that I prefer to assume STL.
• For surviving the explosion, let's assume that you have 10 T per m^2 of hull plating, and that you can afford to have it soak about 3 MJ/kg (it ends up glowing white-hot). This gives about 3e+10 J/m^2 energy absorption. This amount of shielding will also stop enough radiation that your passengers might live (depends on how much extremely-high-energy radiation is produced). I'm assuming that the neutrino flux at the ship's distance is low enough not to do anything, which might not be a valid assumption.
• We can assume that a supernova will release between 1e+44 J (lower bound cited) and 1e+47 J (rest energy of Sol). I'm very skeptical of more energy than that being released by anything short of a hypernova. Gravitational potential energy released by compacting into a neutron star is high, but it's at most between 2 and 4 solar masses and doesn't release all of its energy. Any form of fusion energy releases at most about 1 solar mass in energy even with a 100-solar-mass star completely transmuted. Stars much above 140 solar masses can't form (unstable due to too much radiation pressure), and anything above around 40 would collapse into a hypernova anyways.
• We'll assume the supernova explosion is spherically symmetrical. This doesn't actually hold, but it's an adequate approximation. This means the explosion energy is uniformly distributed over 12.6 r^2 square metres of area. Tying that to the shielding energy limits gives:

$r={\sqrt {\frac {E}{12.6\cdot 3\times 10^{10}}}}$

• Plugging in upper and lower limits on E gives a minimum safe distance of about 2e+16 m to 5e+17 m, or somewhere between 2 and 50 light-years for a ship that doesn't have another star to hide behind.

Enjoy! --Christopher Thomas 05:36, 30 January 2006 (UTC)

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?

Not particularly. The physics I deal with is typically much more terrestrial, so I don't have much offhand knowledge about supernova element production. However, the process sounds reasonable: californium can be produced by bombarding curium with alpha particles, and curium in turn is made by α-bombarding plutonium. Plutonium forms when uranium-238 undergoes neutron capture, and I know supernovae can produce uranium nuclei. Since there are several intermediate steps, I'd expect the overall amount of californium to be relatively small. (Of course, there may be other synthesis pathways I don't know about and thus haven't considered.)

Remember that technetium was first obtained synthetically, but it has since been observed in trace quantities in terrestrial uranium ores (thanks to spontaneous fission) and in red giant stars. Neither of which changes the fact, of course, that any experiment you do on Earth which requires technetium will probably use a synthetic source: it's so much easier to get Tc from spent nuclear fuel rods than from any "natural" source that the element may be considered, for practical purposes, "synthetic".

Anville 2 July 2005 16:08 (UTC)

The back-story of californium, however, is that someone (Burbidge, Hoyle, Burbidge, Christy and Fowler, 1956) noticed that the decay time of supernovae was comparable to that of Californium 254 (55 day half-life). They suggested that the late stages of a supernova were due to the decay of radioactivity. As it turns out, they were right, but the specific isotopes were 56Ni which decays (6.2 day half-life) to 56Co which decays (77 days) to stable 56Fe.

DMPalmer 00:41, 18 December 2005 (UTC)

Timescale of Events

The article, under the Type II explantion states that a core the size of the sun collapses in a fraction of a second. To me that's saying that:

core the size of the sun = R = 695,000km (roughly) fraction of second = 1s/??

If light travels around 197,000km/s, how can matter possible collapse over a distance of 695,000km in less than a second? As far as I know, matter cannot travel faster than light even in the core collapse associated with a supernova, OR in the expanding shockwave following a supernova. In fact, comparing the expanding shockwave's apparent speed to it's known near realative speed is a good measure for it's distance.

Core collapse does take a fraction of a second, but the core is 10-20 km only. The shockwave reaches a velocity of the order of 10% of the speed of light (which is 300,000 km/s) --Fleurot 20:04, 12 July 2005 (UTC)

Perhaps it should be clarified. When I read the article I assumed it was talking about the entire star, depsite the impossibility of that. It should be described what part of the star is collapsing and when (I dont have the knowledge to make this sort of edit myself) [Tycho?] 03:45, 12 December 2005 (UTC)

I just clarified that the core is more massive than the Sun, but with a diameter comparable to Earth's. (The neutron star left behind after the collapse is ~12 km radius.) The details of what gets ejected and under what circumstances you get a neutron star+ejecta vs. a black hole that swallows the entire star are still being worked out (computational relativistic hydrodynamics is not simple). However, when you get a neutron star + ejecta the stuff that falls in to form the neutron star (vs. the stuff that eventually flies out) is originally within or near this core diameter. -- DMPalmer 01:07, 18 December 2005 (UTC)

As an extra question, if the basic model of collapse is believed understood, except for the neutrino transfer in the "first second", could someone add a section, "timeline of collapse", which details the stages leading up to collapse, and during and after explosion, and the timescale upon which each occurs? Thanks FT2 (Talk) 14:08, 4 May 2006 (UTC)