Talk:Supernova/Archive 1

message: :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)
thread_title: Holistic article

message: 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)
replies: text: 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)
thread_title:  First line 

message: 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)
thread_title:  Incorrect description of "timeline" 

message: 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)
thread_title:  Moved explanation to type II 

message: 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)
thread_title:  Californium: Created in stars or artificial? 

message: 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)
replies: text: 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)
thread_title:  Timescale of Events