Two Supernova Questions

Up until the supernova in the Larger Magellanic Cloud, theory suggested that there were two types of supernovae: the total implosion-explosion of a white dwarf growing beyond Chandrasekhar’s Limit, and the implosion-explosion of a red giant that had produced a non-exothermically-fusible iron core.

As I understood the reports, the particular star that supernova’ed was a “blue giant” – a star towards the top of the main sequence – and that this would cause substantial rethinking of what caused supernovae.

First question: Did this prove out to be true, and if so, have they determined a new generally-accepted theory for their causes?

Second question: A popular work on novae and supernovae published before 1987 suggested that the three most probable relatively nearby stars to “go” were, in order, Eta Carinae, Betelgeuse, and Mira, with Ras Algethi and a couple of other red giants farther down the list. Can anyone speak to which stars are now considered most likely? Is it the same three?

First answer: Current models do incorporate 1987a, although I don’t know the details of how. It didn’t really take all that long to update the models, though.

Second answer: Eta Carinae has already done something or another; last I understood it was considered a sort of planetary nebula. It’s not expected to do anything else sudden and dramatic. Meanwhile, I don’t know if it’s the Number 1 candidate, but Betelgeuse is definitely very close to supernova: A former professor of mine who studied it estimated that we would see it go sometime within the next thousand years, which means that there’s actually a decent chance that it’s already blown.

SN 1987A is considered a Type II supernova. The thing that was unusual about it was the star was not a red giant but rather a hot blue star. The adjustments in theory that had to be made was to account for the fact that a star could reach the end of its life without being a red giant. It turns out that Sanduleak -69 202 (the name of the star) was a red giant at one time, but then lost the outer parts of its atmosphere and so what we saw before the boom was it’s core, which is much hotter than the atmosphere it lost. So it looked like a blue giant.

Just to add my two cents worth-- the progenitor of Sn87A was a blue supergiant, and was clearly unusual for many reasons, not the least of which was its color. Also, the rings around it have never been adequately explained; although forming rings is understood, it’s not understood why the middle ring is so dense. This indicates the progenitor was odd in some way. One possibility is that there was a smaller star or possibly planet that was consumed by the star, speeding it up. No one knows, though.

The star Sher 25 is a bit hotter and more massive than 87A, and will definitely blow in the next 20,000 years (that’s how long 87A’s progenitor took to explode once it became a blue giant). I have not heard that Betelgeuse will go in 1000 years. Chronos, is there a paper about that?

Anyway, on my site I have info about 87A and Sher 25 (scroll down a bit for the latter).

Thanks to all three of you. (This is my fourth attempt at answering you – I was involuntarily logged off before the post “took” three times in succession. So please forgive the tardiness in answering.)

Chronos, I was under the impression that what had happened to Eta Carinae in the 1840s had resulted in the throwing off of a planetary nebula (or the origins of one) and that Eta Carinae was still considered a good candidate for going supernova, with an enormous stellar wind and non-periodic pulsations, etc. Phil’s second (Sher 25) link tells a lot about that star. Bad Astronomer, I for one would welcome anything you care to post about Eta Carinae; I find that object fascinating.

Apparently the misunderstanding I had about Sanduleak pre-supernova status was from misinterpreting blue giant star as blue-giant star (i.e., class O main sequence star) rather than as implying blue supergiant star.

So what are the chances it’ll wipe us out when it blows?

Not very high. It’s about 150 parsecs away – which means something like 500 light years, in round numbers. Radiation from it will be about as strong as from the full moon, give or take an order of magnitude – in any case, much brighter than any other point source in the sky. Radiation impinging on Earth will increase by some small but significant amount – but the atmosphere will block most of the harmful rays. In short, unless you’re subject to moonburn or right at the edge of your acceptable lifetime radiation intake, you would do better to avoid microwaves than to worry about Betelgeuse.