Pretty overtired right now so I might be missing something basic here but could this [stellar merger theory - ed] have triggered the supernova and made it different, perhaps explaining the apparent lack of a stellar remnant? Has that hypothesis been advanced for this yet?
What effects – other than turning a red supergiant blue – might that stellar merger have had on the course and outcome of the 1987 a supernova?

On further reflection I guess the time scale for that – millions or at least thousands of years earlier – rules it out as the trigger, probably?

Although I’d still love to see the second question there answered if anyone is still reading and can enlighten us.

In my opinion the ring and the nebula inside are showing an hour-glass structure soon or later revealed as a precessing and spinning jet. DF and A Salis
inAstrophysics and Space Science
Volume 231, Numbers 1-2, 191-194, DOI: 10.1007/BF00658614
Precessing Gamma jets, GRB and the twin rings around SN1987A ..

However the SN1987A neutrino event did help (to some of us) to severely constrains and reject the so called (embarassing or unfortunate ) recent super-luminal claim (Opera-Cern) on neutrino tachyon speed that we now feel coming back to reality…see arXiv:1109.5368 .
Best regards DF

I guess I found the answer to your question. According to The Ultimate Neutrino Page the Neutrinos have been observed on February 23 7:35 UTC. So this is taken as the time SN1987A happened (the Core collapsed).
The light has been seen first on February 24 23:00 UTC. That’s after SN1987A became visible. The light has been there earlier, but someone had to notice that.

As Dutch Railroader explained in #17, the visible event really happened at some time in this window of 39:25 hours.

What are the odds that the first supernova we got to see that was nearby and that we really got to examine in detail with modern astronomy instruments would turn out to be an unusual one, rather than an average one? Could it be that SN1987A was not actually unusual, but just appears unusual to us due to insufficient knowledge about the true diversity of supernovas? And how would this consideration apply to probability statements founded on similar logic, such as “well, this earth-like planet is only 20 light years away, and so for us to find one now, so soon after looking, must mean that earth-like planets are very common in the galaxy”?

Well co-incidence does play a role and the sample size is far too small.

For instance, yellow dwarf stars similar to our Sun make up only around 4% of all stars with nearly all being much cooler, fainter red, white* and (if you call ‘em stars*) brown dwarfs. Yet Alpha Centauri – our nearest stellar neighbour – contains two such stars albeit Alpha Centauri B is an relatively bright, hot and massive example of an orange dwarf.

Toss a dice five times in a row and you’ll get lucky and throw five sixes on occassion – but that won’t be a probable result. Unless the dice is weighted natch!

Only when the sample size grows eg. we’ve made a thorough and complete as possible survey of all the nearby stars and their exoplanets or have a larger list of supernovae do we get a real idea of how typical / likely such things are.

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* Technically speaking you could also argue that white dwarfs are no longer “true” stars but stellar corpses / remnants – although few people do.