Talk:Supernova/Archive 2

Length of page
As there is now a comment about the length of this page, and the longest articles on the talk page are to do with timing etc, can some of the information be put onto the article page itself - or a general timelines of astronomical events page be created. (Items would include star and planet formation, and ending.)

Edit:
The article stated that iron was the most tightly bound element. This is not true, as the wikipedia article on iron points out. Its almost the heaviest, so I merely changed the world "The" to "Among" "the most tightly bound elements". The rest of the statements seemed mostly correct, but calling Iron the "bottom of the hill" may be misleading. Someone with more knowledge should take a glance at it. &#91;Tycho?] 03:43, 12 December 2005 (UTC)

our? our?!!!
The absolute arrogance of this article is ridiculous. It's completely unprofessional to use self-references in the article, and there's no excuse for it. Say "human species", not "our species", "Milky Way Galaxy" not "our galaxy". For goodness sake, I'm getting tired of this. Furthermore, distances should be cited as "X light years away from Earth, and not merely "X light years away". We're not that arrogant, are we? -- Natalinasmpf 18:55, 26 December 2005 (UTC)


 * Actually, there's a perfectly good excuse for it; Wikipedia's editors and readers are currently exclusively humans on Earth, with no reason to expect that to change in the near future, so it's a safe assumption to make. I happen to agree with you that it's preferable to be more specific simply for the sake of specificity and would support the sort of changes you're discussing here for that reason, but let's not flip out over it and start insulting previous contributors based on an unsupported assumption of bad faith. I note, BTW, that you made the same sort of inclusive assumption with "We're not that arrogant, are we?" - who's "we?" :) Bryan 20:20, 26 December 2005 (UTC)


 * Well that was in the edit summary, not the article itself (i.e. in discussion is perfectly acceptable). I am not accusing previous editors, just that after editing the first person out of the article for the zillionth time I get tired, so it's mainly more of a rant to people who come across it. I do assume good faith, by the way. ;-) -- Natalinasmpf 00:04, 27 December 2005 (UTC)

link to big bang
I don't think it's superfluous to link to the big bang theory. For millenia humans have asked "what are we made of, and how did that material come to be?". Our current best understanding of the answer is standard cosmology, in which supernovae play the absolutely critical role of producing and dispersing heavy elements required for life on Earth. I think it's perfectly natural for this article to link to the big bang. Flying fish 18:11, 13 January 2006 (UTC)

The point is that supernova production of heavy elements is independent of the standard cosmology, even if the contrary may not be true. SN production of heavy elements could as easily proceed in a steady state cosmology, for example. It may be appropriate to note in the article on the Big Bang that the lack of heavy element production during the initial fireball is OK, because of SN and stellar production. Mordecai-Mark Mac Low 00:30, 18 January 2006 (UTC)

Cleanup required for Type II section
The section covering Type II supernovae looks like it started as a fairly long section, and was then subjected to a massive addition of material by a user with lots of enthusiasm but not much experience writing terse encyclopedia-style prose. I've compacted the first half of it a bit, but the second half still needs attention, and the whole section could stand an editing/rewrite pass after that (even the part I revised takes about twice as long to present its information as it should, as I kept the original structure).

The only information change I made was to remove the description of the specific fusion chain listed. The chain listed was hydrogen to helium, helium to carbon (via triple-alpha), carbon and helium to oxygen, oxygen to neon, neon to magnesium, magnesium to silicon, silicon to iron. The chain I'd previously heard of was hydrogen to helium, helium to carbon, carbon to neon, neon to oxygen (by photodissociation, I think?), oxygen to silicon, silicon to iron. Both my old reference and the enthusiastic edit's material seem suspect to me, so I'd appreciate it if a lurking astrophysicist could describe the actual chain as it's presently understood, and list a few references to prevent future confusion. --Christopher Thomas 04:41, 30 January 2006 (UTC)


 * I am honestly fairly confused by the use of the word "sun" in this section. It begins by mentioning that stars more massive than our sun evolve differently. Then it uses the word "sun" in conjunction with a description of an evolution of a star.  I do not know if this description refers to our sun or a star that will evolve into a Type II supernova.  Someone please clarify this.  If the word "sun" here refers to our sun, then it belongs in a different category, as this category is about Type II supernovae.

Typographic problem
I don't know anything about supernovae, and I have a problem reading this article due to the type letter used in Wikipedia. Uppercase letter I (vowel i) is identical to lowercase l (consonant L). So I can't distinguish whether type Ia supernovae are L-a or i-a. I think this should be cleared up in the article. Diego Moya 11:42, 8 February 2006 (UTC)


 * This is something that is governed by your browser settings, not by Wikipedia. --Christopher Thomas 18:54, 8 February 2006 (UTC)

Possible threats to earth
In this section, I read the quote, "The probability of a Type Ia within 100 parsecs is about 1 per billion years or less. Thus it is likely that a nearby Type Ia about 100-1000 parsecs away has occurred several times within the history of life on Earth, about 500 million years ago, but is unlikely to occur anytime within the lifespan of the human species."

Is not such an event being "unlikely to occur" during the human species' lifespan an example of Gambler's fallacy? That is, of course, unless prior supernovae affect the chance of more occurring - which I believe is not typically the case.


 * Looking at that passage, the thing I couldn't make sense of was the phrase "about 500 million years ago." That makes it sound like there were several nearby type Ia's about 500 million years ago (talk about a bad day!). If the passage is interpreted that way, then the rest of the sentence does sound like a gambler's fallacy. But I think that phrase was just misleading, and its intended meaning is unknown, so I've removed it. KarlBunker 02:21, 27 March 2006 (UTC)

According to an article in LASNews (not authorative, but informative), "For a supernova explosion to endanger Earth, it would have to be within 30 light years. And according to Fields, no massive stars within that range are threatening to explode." 'Fields' is Brian Fields, an astronomer at the University of Illinois. ( User:Ceyockey ( talk to me ) 21:44, 8 April 2006 (UTC)

Supernova and the creation of the solar system
I feel that in addition to the threats to earth, we could have a section on how a supernova can create the kind of shock-wave of the molecular hydrogen clouds that form new stars. The element enrichment of such clouds is important as it explains many of the elements composing the earth. It has been proposed that the solar system, formed at latest count 4567.17 billion years ago, was formed by such a supernova event about 20-30 million years earlier (aparently protoplanetary discs last up to 25 million years).

Also I don't know what the literature suggests, but from the chemical composition of the Solar System, it should be possible to work out whether the triggering event for the Solar System was a Type I or a Type II supernova.

Any thoughts anyone

John D. Croft 03:19, 20 June 2006 (UTC)


 * Would the chemical signature appear in the composition of the solar system, or did the supernova just trigger the collapse of an existing molecular cloud via a shock wave? Also I think there are other mechanisms besides supernovae that can trigger the collapse of giant molecular clouds. &mdash; RJH (talk) 19:39, 28 September 2006 (UTC)

Type Ia luminosity curve
''The similarity in the shapes of the luminosity profiles of all known Type Ia supernovae has led to their use as a standard candle in extragalactic astronomy. The cause of this similarity in the luminosity curve is still an open question.'' I thought it was pretty well established that type Ia supernovae have similar luminosity curves because they all come from the same phenomena (a white dwarf gaining mass to beyond the Chandrasekhar limit). As a result, they all have about the same mass, follow the same path to detonation, and convert about the same amount of matter to energy in their explosions. user:Jsc1973


 * Yes I believe you are correct, although I understand there has been some recent work on explosion asymmetries that may be relevant. &mdash; RJH (talk) 19:34, 28 September 2006 (UTC)

Animation of Supernova collapse in crossection
The image of the supernova crosssection attached to this site is useful. But is there an animation anywhere of the process of collapse (in cross section) from the phase of helium burning through to implosion and subsequent explosion? WOuld be fascinating.

Also, regarding the iron core - how long does it take for the star to explore once iron is created? That is, after the silicon converts to iron, and iron-fusion attempts to begin - are we talking weeks of seconds. Also, typcially how much iron is then dispersed in the explosion? —The preceding unsigned comment was added by 193.120.81.130 (talk • contribs) on 12:25, 11 August 2006.


 * An animation seems like a neat idea, but I can't even see the non-animated cross-section you mentioned in the article (was it in one of the external links?). I can produce an animation, but I'd want to check with some of the lurking astrophysics-types first, because I've seen different versions of the fusion sequence (one I'd originally heard was hydrogen/helium/carbon/neon/oxygen/silicon/iron, but a different one was mentioned in past versions of the article).


 * My understanding is that the iron core reaches the Chandrasekhar limit in a few days once fusion to iron starts, but I could be misremembering. The total amount of iron produced is about 1.4 solar mases, but I have no idea how much is dispersed (vs. being transmuted to form part of the neutron star), or how much is produced by fusion induced by the shockwave or intense neutron radiation during collapse. As the sun formed from supernova remnants, the fraction of iron in its composition should give you a lower limit to the fraction (relative to hydrogen) produced by a typical supernova.--Christopher Thomas 17:32, 11 August 2006 (UTC)

Merge Near-Earth Supernova into Supernova
The subsection on Near earth supernovas is larger than the main article on near earth supernovas. There's no real reason not to merge. The Smilodon 02:43, 18 September 2006 (UTC)


 * As creator of the Near-Earth Supernova article, I agree. - R_Lee_E [[Image:Flag of the United States.svg|25px]] (talk, contribs) 16:58, 18 September 2006 (UTC)


 * I went ahead and merged the page. Thanks. &mdash; RJH (talk) 22:24, 18 September 2006 (UTC)

Possible new subdivision in Supernova 1a types
http://www.spaceref.com/news/viewpr.html?pid=20858 Thought to probably keep this in mind when and if it becomes official, SNLS-03D3bb would be the culprit, thanks, CarpD 9/20/06

Origin of the word "nova"?
There are two claims for the originator of the word "nova": the first claim states that it comes from the title of Johannes Kepler's book De Stella nova in pede Serpentarii (under Observation history); the second claim is under Notable supernovae which states that it was taken from the title of Tycho Brahe's book De Nova Stella ... Resolution, anyone? Daen 23:11, 24 September 2006 (UTC)


 * I'd be inclined to credit Tycho, since Kepler was his pupil and his Kepler's title was undoubtedly influenced by Tycho's earlier work. Then again it is uncertain what role Kepler's work played in popularizing the word. In the 1866 MNRS publication by Huggins, where the first spectrum of a nova was measured, he used the word "new" rather than nova. So it is not clear at what date the term came into popular usage, although the online etymology dictionary gives a year of 1877. There is a Astronomische Nachrichten paper from that year using the word "Nova" in its title. &mdash; RJH (talk) 16:34, 25 September 2006 (UTC)
 * The text has been modified. &mdash; RJH (talk) 19:31, 28 September 2006 (UTC)

Supernovae as cosmic ray sources
I read the article twice hwever I didn't find any statement about the fact that there are some evidences (SN1987A) and many theoretical works (trying to find out where I Put the exact references) that point at supernovae as some of the celestial bodies producing high energy cosmic rays via a second order fermi mechanism. Probably a little paragraph should be added about this in the interstellar impact section, explaining how the shockwaves produced by a collapsing supernova can explain high energy cosmic rays near their ankle point (anout 10^20 eV if I remember corectly) Tatonzolo 13:00, 28 September 2006 (UTC)


 * This would make a good addition to the "Interstellar impact" section, and a precursor to "Impact of supernovae on Earth". (Is there a better name than "Interstellar impact"?) I added this to the "to-do" list. Thank you for the suggestion. &mdash; RJH (talk) 19:31, 28 September 2006 (UTC)


 * It is not supernovae that are thought to be the source of cosmic rays, but supernova remnants. See e.g., http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v416/n6883/abs/416823a_fs.html, for some background on this (this result for this particular supernova remnant was later discredited, but the general principal / motivation still stands.) Note also SNRs these are the proposed source of cosmic rays below the knee (10^15 eV), not the ankle. Nobody knows what produces cosmic rays above the knee; something big and extragalactic, presumably. Tubbs334 19:35, 29 September 2006 (UTC)


 * Which brings up a question I had: should the supernova remnant page be merged with supernova? Right now it's awfully brief, although I could see it having significant material for an expansion. &mdash; RJH (talk) 21:14, 29 September 2006 (UTC)


 * The supernova remnant page indeed needs a lot added to it (something I can look into at some stage). However, I don't think it should be merged with the supernova page, as they are distinct (albeit related) phenomena. The energy and light we see from a supernova comes from radioactive decay of newly synthesized elements; the light we see from a supernova remnant comes from the kinetic energy of the outwardly moving debris interacting with their surroundings. E.g. if a star exploded in a vacuum, you would get a supernova but not a supernova remnant. So they are different beasts. Tubbs334 21:24, 29 September 2006 (UTC)


 * Err now wait a moment... supernovae do explode in a vacuum. I would assume a remnant is a remnant, regardless of whether it emits energy or not. But no matter. &mdash; RJH (talk) 22:42, 29 September 2006 (UTC)


 * Supernovae will usually expand into the interstellar medium or into the progenitor star's stellar wind. It is the interaction with this surrounding material that produces a supernova remnant. I.e., what you see for hundreds of thousands of years after the explosion is the surrounding swept up material, not the explosion itself. Tubbs334 00:22, 30 September 2006 (UTC)


 * You're right Tubbs, however I think it's worth mentioning in this article too that Supernova and their remnants are responsible for producing high energy cosmic rays, maybe linking the remnants page.. Tatonzolo 21:38, 30 September 2006 (UTC)


 * That sounds fine to me. Although note that (i) the connection between supernova remnants and cosmic rays is strongly suspected but is yet to be proven, and (ii) the cosmic rays in question are, relatively speaking, not of high energy; nobody knows yet what causes the high energy ones. Tubbs334 03:07, 1 October 2006 (UTC)


 * ok Tubbs, I made some reserches about some good reference about our discussion: i found on some manuals that there are hints of the Fermi 2nd mechanism to explain accelerations up to 10^16-18 eV (well below the knee) and here is an article about evidence of acceleration in supernovae remnants at 10^14 ev (I've not checked the references of the article or where it is referenced to get newer and up to date articles) here is the link. Tatonzolo 10:14, 12 October 2006 (UTC)

Since it is the supernova remnants that are the suspected source of the high-energy cosmic rays, and as we have agreed not to merge the page on supernova remnants onto this page, I'm going to strike the "Supernovae as high energy cosmic ray sources via a second order fermi mechanism" to-do item from here. Thanks. &mdash; RJH (talk) 20:21, 12 December 2006 (UTC)

List of doomsday scenarios
Could use votes to save this article, thanks MapleTree 22:38, 28 September 2006 (UTC)
 * It appears that the page was doomed. &mdash; RJH (talk) 15:17, 10 October 2006 (UTC)

Core collapse section
Reading the section I had some concerns about some statements, so I checked my books and so on before posting this: it is stated As the core collapses, it heats up, producing high energy gamma rays which decompose iron nuclei into helium nuclei and free neutrons  actually I dind't find any possible source of gamma rays in the collapse, at energies around Chandrasekhar limit the atoms are almost completely ionized and emission of gammas from nuclei is at least unfavoured.. From what I can see from my sources (looked at some astro particle and astrophysics) the way the neutrons are produced is via inverse beta decay since the degenerate fermi gas has enough energy to open the inverse beta decay. Apart from this it would be interesting to state that the neutrinos are prone to matter oscillation inside the dense matter of the nova (it should have been observed thanks to some muon neutrinos presents among the neutrino events observed by Kamiokande experiment with 1987A neutrinos) (I have to double chek the statement about the observation though)) Apart from this I think that the statement core collapse phase is known to be so dense and energetic that only neutrinos are able to escape is misleading, since the neutrinos escape is due to their weak interaction with matter making it possible for them to escape without further interactions, actually even photons would be able to escape in long times (as happens in the solar core... after all we are seein the photons produced in the core about a million years ago) Tatonzolo 09:39, 29 September 2006 (UTC)


 * I'd really appreciate it if you could correct the text as appropriate, and if you had some references that would also be helpful. I'm trying to go through all the sections and get references for everything of note, but I haven't done much of anything on the Classification section yet. (That seemed to be the best-developed section, but now it appears to have a few issues.) Thanks! &mdash; RJH (talk) 14:23, 29 September 2006 (UTC)


 * I will try to work at it in the weekend, and will try to find some references for all the article.Tatonzolo 15:22, 29 September 2006 (UTC)


 * That would be excellent. Thank you. &mdash; RJH (talk) 19:26, 29 September 2006 (UTC)
 * I believe this statement is simply false. It is the shock wave that produces the energy to split the iron atoms into free nucleons. See the to-do list comment I made. Errabee 14:58, 6 October 2006 (UTC)

Confused about energy
The second sentence states that SN release 1017 times the energy of the Sun. This is misleading, because it is comparing the total energy output of a SN (about 1051 erg with the luminosity of the Sun (about 4 x 1033 erg/s). So the statement is true if you compared the SN energy output to the output of the Sun in one second but that is not a particularly meaningful or enlightening comparison. The peak luminosity of SN is about 109 to 1010 times the Sun's luminosity. Furthermore, that does not outshine a galaxy like the Milky Way (it's about a tenth of a big galaxy's luminosity). —The preceding unsigned comment was added by 71.131.208.105 (talk • contribs).
 * How can the sun luminosity be different from it's total energy production? Apart from a minor amount of power (power is the right thing to compare with a supernova, as we want to compare energy produced in thesame amount of time) going into neutrinos, all the rest must be photons. The sun does not send its energy to alternative universes, does it? Even if one defines "luminsity" as the power emitted in the visible electromagnetic spectrum, it's still most of the total solar power. According to the luminosity article, solar luminosity is 3.827×1026 W. I assure you that the total power of the sun's thermonuclear engine is less than 4×1026 W. Friendly Neighbour 18:21, 6 October 2006 (UTC)
 * However, the good question is whether the 1051 erg (1044 J) is really supernova explosion energy (as the article seems to say) or it's peak power. If the former then the comparison is meaningless, if the latter then we have to correct the units to erg/s or W. Friendly Neighbour 18:41, 6 October 2006 (UTC)


 * Yes, I've been meaning to change that into something more meaningful, while still being a value to which any reader can relate. Sorry. The original value for the energy output came from here: http://heasarc.gsfc.nasa.gov/docs/objects/snrs/snrstext.html . It should be fixed now. &mdash; RJH (talk) 19:04, 6 October 2006 (UTC)

Anthropomorphism of White Dwarfs
One part of this just seems rather unprofessional, for lack of a better word.

"Once fusion begins, the white dwarf quickly discovers that its dependence on degeneracy pressure (rather than thermal pressure) to support its weight against gravity carries a heavy price. It is unable to respond to the initial temperature increase by expanding and cooling (because degeneracy pressure is independent of temperature), and thus cannot regulate the burning in the manner of normal stars."

The star doesn't "discover" and cannot "regulate" anything. It is not a living being, it is subject to natural laws, not its own weakness. Also, I think the "comes at a heavy price" part could be redone. I'm not sure enough about my own writing skills to put it on the main article myself, but what about something like "Once fusion begins, the white dwarf is supported by electron degeneracy pressure (rather than thermal pressure), to counter gravitational collapse. Since degeneracy pressure opperates independent of temperature, the star cannot respond through the normal modes of expansion (and thus cooling) as a normal star would." ? Davepetr 07:07, 1 December 2006 (UTC)


 * Yes I found myself somewhat bothered by that statement as well, but I was somewhat reluctant to make the change. I just assumed it was an attempt to make the text more interesting to read. &mdash; RJH (talk) 15:59, 1 December 2006 (UTC)


 * Since there was no counter-argument I reworded the paragraph. Hopefully that does the job. Thanks for the feedback. &mdash; RJH (talk) 22:08, 18 December 2006 (UTC)