Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site ucbvax.BERKELEY.EDU Path: utzoo!watmath!clyde!burl!ulysses!ucbvax!space From: REM%IMSSS@SU-AI.ARPA (Robert Elton Maas) Newsgroups: net.space Subject: nearby supernovas etc. Message-ID: <8603020306.AA00249@s1-b.arpa> Date: Sat, 1-Mar-86 22:08:44 EST Article-I.D.: s1-b.8603020306.AA00249 Posted: Sat Mar 1 22:08:44 1986 Date-Received: Sun, 2-Mar-86 19:19:14 EST Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 107 GWS> Date: 28 Feb 86 09:56:08 GMT GWS> From: brahms!gsmith@ucbvax.berkeley.edu (Gene Ward Smith) GWS> Subject: Sirius Supernova? GWS> Sirius A is about 2.3 solar masses (all I am saying is off the top of GWS> my head, I am hoping the experts will settle this one) and this is too GWS> small for iron core collapse, carbon detonation, etc. Thanks for the correction. I think I was remembering something I read more than five years ago, before we realized that although 1.4 solar masses or so is the limit for iron-core collapse, there's an awful lot of solar wind loss during the red giant stage so it takes more like ten or twenty solar masses at the outset to end up with 1.4 at the critical time. (Or was it 2.4? I forget?) I stand corrected, no supernova at all ever in Sirius. By the way, in latest Sky&Telescope there's a note on Sirius being reddish in recorded history (in fact about 600 AD), because at that time its white-dwarf companion was in the red giant stage. It's hard to believe the conversion from red giant to white dwarf could occur so quickly, although with Sirius gobbling most of the loose hydrogen as fast as it is shed, and ionizing & light-pressure-shoving the rest of the emitted hydrogen, I could imagine it within the realm of possibility. Any news since S&T publishing date on that topic that you know of? GWS> When Sirius is in its giant stage, it will presumably give some matter GWS> up to Sirius B. If this becomes a big deal, it looks like the usual GWS> nova (not supernova) situation. Well, even not being a supernova, it could upset Earth and not well enough protected space colonies a bit if it does. But of course, as I pointed out, it won't be any where near Earth then. GWS> Once more off the top of the old head, I recall Betelguese and Antares GWS> as being both about 400 light years away; hardly close enough to sterilize GWS> the planet Earth or whatever. I'm not sanguine. I understand the visible light flux from either will be about 3 magnitudes brighter than Venus as viewed from Earth, easily visible in day (or was that 3 magnitudes brighter than full moon?? Nah.) Due to the thermal cutoff of blackbody radiation being up in the gamma rays or at least x-rays, the x-ray flux will be tens of times more intense than the visible light. Right? That would play havoc with upper atmosphere and half-protected space colonies. GWS> Eta Carinae (?) is even closer to supernova. How close? (My guess of <1000yrs for Betelguese and Antares was a rather gross ballpark figure; would appreciate better estimate if you have it, likewise for Eta Carinae or whatever.) But up here in Northern hemisphere I'm not too worred about Eta Carinae -:) GWS> Sirius right now is firmly on the main sequence. No argument there, that was my position all along, why its demise isn't at all soon. GWS> ... one tenth the time of the Sun on the main sequence; i.e., GWS> about a billion years. I must have mis-remembered somehow. Thanks for correction. Ok, that proves my point even more, in a billion years not only will Sirius have drifted even further from Sun, but it'll be moot because the Sun will already be roasting Earth to death. GWS> How much has gone? I don't know, but why do you assume most of it? No, I assumed somewhere in middle, just had total life on main sequence wrong. What star could I have been thinking of that lives only one million years? Deneb is the most massive/bright star I know of nearby enough to be first magnitude, but even it must be at least 100,000 years if Sirius is 1 million years, right? GWS> What gives with you people making plans 100 or 200 million years in GWS> advance, anyway? I beg to differ. If current theory says we have only 200 million years before we roast, and that isn't enough time for fossil fuels to be re-supplied, then there's a reasonable chance it's absolutely urgent to get into space this time around instead of blowing our chance and having to wait for the next round of fossil fuels. We might be mistaken, worrying unnecessarily, but if we're right why blow it? Some people pray to God because if he exists it's worthwhile and if not it doesn't hurt. I think the argument for getting into space based on current theory is a lot better than the reasons for praying. GWS> Grow up, folks! Sorry, I beg to differ again. We are grown up, we are seriously considering the longterm survival of our species, based on current theories of the prognosis of the Universe, rather than just living for today and not giving a damn for the future. If we're wrong, we're wrong, but it's not because we aren't grown up, it's because current theory is wrong. In general, the best survival technique is to make use of the current scientific theories tempered with awareness of how new the theories are and how they might be wrong. Ignoring current theories completely is foolish in my opinion. Committing suicide just because the Heat Death will likely get us in the end anyway, is equally foolish. There's a middle ground where we guard against disasters our current theories predict, without totally giving up in cases our theories say we'll die anyway. If we were totally sure of the 200,000 year limit hence the 50-year practial limit, it would be right to enslave the world's economy to have a crash program to get space developed ASAP. As it is I'm content to generally push for space development, being ready to institute a crash program if our 5th-generation computers tell us absolutely for sure how the Sun really works inside and what or prognosis is.