Talk:SN 1987A

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Talk.Origins says 169,000 light years? http://www.talkorigins.org/indexcc/CF/CF210.html --Shernren 09:13, 30 March 2006 (UTC)

I calculated the distance myself by the light echo method, and arrived at a much smaller value for the distance. Refer http://www.geocities.com/peaceharris/sn1987a

FYI - "Peace Harris" (Selva Harris) is arguing his position from a young earth creationist (i.e., religious) perspective. His article is not from the professional science literature, nor reflective of it, nor has it had any peer review of any kind from professional astrophysicists. (Greeneto 02:18, 8 June 2006 (UTC))

Changed "planetary nebula" to "supernova remnant". A planetary nebula is a separate astronomical phenomenon from that of a supernova remnant. A PN is formed by the mass lost by a pre-white-dwarf star over a number of episodes, while a SNR is formed by the expanding blast wave from a supernova, e.g. SN 1987a. -- April

Oh, okay! I stand corrected. Is this a recent re-designation? IIRC, I have come across books which use the term "planetary nebula" to describe the Crab, etc. --CYD

No problem! And by the way, thank you for your additions on this subject, one near and dear to my li'l heart. :) To answer your question... it's not a recent designation, per se, but the classification of given objects may be recent. I wouldn't be surprised if the Crab was thought to be a planetary nebula before it was shown to be a supernova remnant. Of course, the term planetary nebula is a horrific misnomer to begin with, as it has about zero to do with planets... hm, maybe I should put in a paragraph on that... :) -- April

The neutrino burst of a supernova takes several seconds. How should it be possible to measure the neutrino speed by to detectors on earth? If the 2 detectors measure neutrinos of different energy range and there is some neutrino mass different from zero than some delay between the corresponding bursts are expected which can be measured if they are larger than the bursts itself. But I don't know if this played a role in this case. --Wolfgangbeyer 08:37, 13 Apr 2004 (UTC)

I removed the part on the "source of regret to astrophysicists": I don't think the energy resolution was that low (except maybe IMB) and the time difference between the clocks of each detector wouldn't have allowed the measurement of the speed of the neutrinos (it is a tiny fraction below that of light). Synchronized timing would help to determine roughly the direction of the supernova by triangulation, and also it would allow coincidence measurement in the framework of SNEWS. --Fleurot 03:03, 6 Oct 2004 (UTC)

Contents 1 Antineutrinos 2 SN 1987A erro SN 1987 3 Background Level and neutrino/antineutrino distinction 4 iron sun extlink 5 Refutation of YEC 6 where was it visible?

[edit] Antineutrinos

From the short antineutrino article it seems that some people think that neutrinos are identical to antineutrinos. With that in mind, how did the neutrino detectors differentiate between neutrinos and antineutrinos during the SN 1987A event? Is it possible that they just detected neutrinos and not any antineutrinos(or vice-versa)? Intangir 20:53, 12 Apr 2005 (UTC)

We don't expect the same reactions to occur with neutrinos or antineutrinos. For example, IMB and Kamiokande II were filled with light water, so they saw mostly anti-neutrinos via the reaction nubar+p->n+e⁺. Neutrinos react with light water moslty via electron scattering, which has a much lower cross-section.

The fact that neutrinos could be their own anti-particles is for the moment a hypothesis which would violate lepton-number conservation. Experiments are on their way.  :)

--Fleurot 20:15, 14 Apr 2005 (UTC)

Ahhh, ok. So they are theoretically different, we just haven't observed the difference yet...

I am trying to learn more about the SN 1987A evidence against antimatter-antigravity claims to incorporate that into the exotic matter article(that article sorely needs some counterarguments). Did IMB and Kamiokande II also observe neutrino electron scattering along with antineutrino events during the supernova? I have had a hard time finding a websource which goes into more detail about the antimatter gravity aspect of the SN than Gravitational effects on antimatter, do you know of any other good sources? Intangir 03:39, 16 Apr 2005 (UTC)

The usual assumption until recently was that neutrinos were one particle, and antineutrinos were another particle, the antiparticle of neutrinos. However, all neutrinos appear to have one "handedness" (quantum spin), and all antineutrinos appear to have one other "handedness". This is difficult (though not necessarily impossible) to explain within the mathematical frameworks of the theories being built around that time. More recently, it's been proposed that they're different manifestations of one type of particle. Until we have a universally accepted and well-tested Grand Unified Theory, we're not going to be sure which is the case. The fact remains that, from an observational point of view, neutrinos and antineutrinos act as if they are different particles (antiparticles of each other), carrying lepton number and participating in normal and reverse beta decay. --Christopher Thomas 18:35, 3 April 2006 (UTC)

Question: How come the neutrinos reached earth three hours before the visible light? Were they emitted several hour earlier?

I'd like to know this too:D. An explanation should be added to the article, or a reference made to this phenomenon with a link to a relevant article/external link on this subject. I have a possible explanation, entirely unfounded as I am not an cosmologist: neutrino speed (nominally at C in a perfect vacuum) is less affected by the density of the interstellar medium than photons, perhaps? Or maybe they are less readily absorbed or reflected by the ISM, resulting in a noticeable surge in neutrino levels several hours before significant photon emissions? The latter would seem to be logical given that neutrino detection is notoriously difficult to achieve. The former probably just indicates I am totally ignorant of the concept that C is absolute for the density of the medium:D --ChrisJMoor 02:36, 18 December 2005 (UTC)

They are emitted during the core collapse as electrons and protons combine to form neutrons. The light of the explosion is also produced at or after this time. The difference is that neutrinos can escape the collapsing star much more easily than photons, as plasma is mostly transparent to neutrinos, but is opaque to light. As a result, we see a neutrino burst at the time of the explosion, but don't see the glowing shell of expanding stellar material until the shockwave of the explosion reaches the surface of the star. --Christopher Thomas 18:35, 3 April 2006 (UTC)

[edit] SN 1987A erro SN 1987

Com respeito a estrela supernova descoberta no ano de 1987, só deve ser tratada como tal - SN 1987A - caso nesse mesmo ano houvessem além dela outra, desse modo a nova em questão deve ser tratada apenas de SN 1987.

[edit] Background Level and neutrino/antineutrino distinction

According to the article: 'Although the actual neutrino count was only 24, it was a significant rise from the previously-observed background level.'

What was the previously-observed background level? It is important to know this in order to understand the relevance of the observed number. Also, the article neglects to make important distinctions between neutrinos and antineutrinos. I know that most of the observations(maybe all) were infact antineutrinos and not neutrinos. If the only significant rise was in the number of antineutrinos observed then this is not significant evidence that gravity affects matter and antimatter similarly. If this is significant evidence for this(which seems likely), it is very important for this article to give some indication as to how significant. --Intangir 00:59, 3 January 2006 (UTC)

Look up solar neutrino problem. That should give numbers for the background from the sun. Or search for papers on SN1987A neutrino detection, and look at their measurement plots. Background levels also depend on how direction-sensitive the detector is (the Cherenkov light is emitted in a cone in approximately the direction the incident neutrino was travelling). --Christopher Thomas 18:38, 3 April 2006 (UTC)

[edit] iron sun extlink

That link looks crank-ish. Can someone check it out and remove it if appropriate? 67.117.130.181 23:07, 26 November 2006 (UTC)

Yah. It is a completely crank link. You missed the additional link to the crank site by the 2003/2005 gif animation. I'm going to remove that link as well. --Benjamin Franz 16:35, 30 December 2006 (UTC)

[edit] Refutation of YEC

Proofs aside, this paragraph is badly written. Also it makes it seem as speed of light has been decelerating since a lot of time ago. Please check. 01:21, 17 February 2007 (UTC)

Can you be more specific? It states that the speed of light has not changed, so I don't understand the implication you refer to. Maury 15:13, 17 February 2007 (UTC)

Reading it over I saw the problem, and fixed it (I hope). Let me know what you think. Maury 15:24, 17 February 2007 (UTC)

[edit] where was it visible?

Northern Hemisphere or Southern Hemisphere? Both? Thanks,Rich 05:41, 24 February 2007 (UTC)

Southern hemisphere. Declination −69° 16′ 11.79″ (J2000) [1]

This means it would come barely above the horizon around 20N latitude. Tom Ruen 07:57, 24 February 2007 (UTC)