I once asked an astrophysicist how far one would need to be from a supernova to be safe. He opined that he wouldn’t care to be much closer than 10 parsecs (a little less than 33 light-years). A check of other sources gives a wide variety of estimates, but it doesn’t signify, The main point is that whatever range you pick, the dangers from neighboring supernovae are virtually unpredictable…and inescapable.
What dangers? Well, aside from debris and radiation (all serious problems) the main danger is fast neutrinos, which may damage DNA. Whether neutrinos (which can’t be defended against by any known means) travel faster than light speed, as reported by CERN, is still under adjudication. If they do, they’ll arrive faster than the other dangers. Gamma rays, for example, travel at the speed of light (and can be defended against, with difficulty). Dust-sized and larger particles, (which can be defended against, with less, but still substantial difficulty), travel slower than light. So IF high-energy neutrinos travel faster than light, they might serve as warning for problems to come, if nothing else.
But what is the risk? Well, estimating this sort of thing is always problematic. Whether or not it turns out that nothing CAN travel faster than light, the best we can do is estimates. What we can do is figure out how many stars likely to go supernova there are in the danger zone, and try to determine from astronomical observations what stages of their development they are (each and all) in. We can’t do much better than estimates on when they will blow, because we don’t have enough information. But it’s not only a lack of information. It may be simply impossible to give a precise date, no matter how much information we have. Part of the problem is that the stars may be close enough to do damage, but not close enough for anything like real-time observations.
Another problem is that, while we have a fairly comprehensive catalog of the stars nearby, and of their sizes and ages, and while we have a fairly good understanding of how supernovae occur, and though we have a fairly good understanding of the average lifespan of stars of various types and sizes, it’s not good enough to predict an exact date. Likely it never will be. So we have to go by averages. We know that the larger stars are the type that go supernova, and that they have substantially shorter lifetimes than smaller stars like the sun (which never will explode, by the way. It will expand to a much larger size, for a while, But this expansion will be slow–in the range of millions to billions of years). We even know why larger stars last a shorter time than smaller stars. It’s the same reason a big fire burns out faster than a small one–bigger objects ‘burn’ (read ‘fuse’ for stars) faster because there’s more fuel, and the reactions can take place more frequently. In other words, they burn faster because they burn hotter.
What we don’t know, and perhaps can’t know, is a precise timetable. Estimates place the supernova of a nearby star at ‘about every 24 million years’. But even if we knew the uncertainty of this estimate (± a million years? ± a thousand years? Even (and this has happened in estimates), ± a billion years?), we’d still need to know things like ‘when did it happen last?’. And though such impacts leave evidence, collecting such evidence on Earth (with its constantly recycling crust) is difficult, to say least. It might be easier to collect that sort of evidence on the Moon, with lower levels of erosion, etc. But there are no current plans, as far as I know, for such an expedition.
So we have to fall back on estimates. If we assume that such an event happened recently (in the current Quaternary Era, which is to say less than 3 million years ago), we can assume that we have about 20 million years to prepare. Plenty of time, right? But if the most recent event was further back than that…well it could be any time from ‘right about now’ to the aforementioned 20 million years.
So what can be done about it? Well, even allowing for the most generous preparation time, the best solution is to spread out into the cosmos, as widely as possible. That’s a long-term project, and we have problems that are (probably) more immediate. But it’s still an important back-burner problem. So if you feel you haven’t enough to worry about, here’s something to be mulling about in the spare time.
For today’s more obscure problem, I’m still not sure where I heard a joke from the Soviet era in Russia. The quote is along the lines of “In the event of a nuclear attack, put a sheet over your head and walk slowly to the graveyard. But don’t walk quickly. You wouldn’t want to start a panic.”
treraia 