Where have all the Milky Way's supernovas gone? Contrary to what would seem a basic survival instinct, many astronomers are positively keen to get more catastrophic, solar-system-busting explosions in our home galaxy. But until recently, a good Jerry Bruckheimer space opera hasn't appeared to reach Earth since the seventeenth …
... we're not seeing more Supernovas in our own Galaxy because they've already occurred and dissipated to the point of relative invisibility (ie: they're just dust now).
Consider: when we look at other galaxy, we are looking far back in time. (Andromeda is 2.5 million LY, so when you look at it you see it as it was 2.5 million years ago.)
Maybe supernovas were once very common (which is why we can observe them in other galaxies) but today are very are rare. Our own galaxy is only about 100,000 LY wide (and about 1000 LY thick, according to our best estimates).
The remnants of a supernova are light, radiation, and matter. It's this same matter that later forms planets (and us - don't forget, you're made of stardust!). In other, very distant galaxies, we see the light and radiation, but don't forget they occurred millions of years ago.
If we were in one of those other galaxies, we would be able to observe the supernovas of the Milky May. Maybe we don't see many here because the light and radiation has already passed, and all that's left is the dust.
"(We later had to look up the terms he was using to identify that he was, in fact, being racist rather than just plain crazy.)"
Finally, a purpose for the Racial Slur Database!
Are supernovae dangerous?
How far away would a supernova have to be for the intensity of radiation it produced to fall below the level that would fry us?
Yes, Tim - your conjecture would be correct IF the number of super nova dropped in the last few million years and did so equally across the universe. There is no reason to believe that both of those items happened. This leave two simpler reasons
1) There are fewer nova in the Milky Way - again no real good reason for this - but one strange result is reasonable.
2) We are having a hard time seeing them thru the dust - a very likely issue. There is less dust between us and Andromeda there there is between us and the center of the milky way.... which seems to be correct. For example, there is reason to believe that there are very large black holes at the center of galaxies - we can't see the center of our own galaxy - so we do not know.
Now where DID I leave the flying saucer?
@ Tim Brown
Tim, I'm pretty sure that the NASA scientists would have thought of that. They would be looking at Galaxy's that at the moment in time that we are seeing them are the same age as us. ie, if Galaxy A is 10 millions years old, and the Milky Way is 5 million years old then they would only look at Galaxy A for the comparison of numbers of supernova if Galaxy A was 5 million light years away, so we would be seeing Galaxy A when it was 5 million years old.
Lets face it NASA may hire people who are crazy (diaper astronaut lady) or have no common sense (the lady who gave out personal deatils to a 419er from her work computer) but they dont tend to hire overtly stupid people...
... God placed the supernovae into other galaxies for us to watch some nice stellar fireworks and not into our own galaxy because they'd harm His creation if too close...
2.5e6 years is far too short for any measurable change in the rate of supernovas.
There are stars made out of hydrogen left over from the big bang, and eventually such stars will be few and far between. When such stars supernova, the release huge clouds of gasses including a variety of elements - not just hydrogen.
The sun formed about 4.5e9 years ago, from gasses ejected from supernovas. The sun will supernova in about 3.5e9 years, and the gasses ejected will eventually form new stars. Stars are still forming in our galaxy, and this is not going stop any time soon. There will be plenty of supernovas to watch in the next billions of years.
(Maybe aliens put up some dust clouds to protect us from supernova ratiation ;-)
Not likely. First of all, 2.5 million years is a tiny fraction of the lifetime of a galaxy. Observation of the two satelite galaxies of ours (the Large and Small Magellanic Clouds) also suggest a higher rate, and they are far closer than the Andromeda Galaxy (157,000 ly and 197,000 ly respectively). Unless all galaxies evolve in exact synchrony, your scheme is not very likely. Furthermore, we can estimate the number of supernova candidates from the spectral types of stars. In so-called starburst galaxies the fraction of supernova candidates is higher than average, but our galaxy seems to be quite regular in this sense. I think interstellar dust and gas are the main culprits in not seeing them
All Sing (sorry :-D)
It was just a star
but it caught my eye
now I'm irradiated
and my 'dermus is fried
Blame it on the supernova (blame it on ... the supernova)
....[big hook exits stage left with LaeMing in tow]
"The sun will supernova in about 3.5e9 years..."
Nope. It's not big enough. It'll go: red giant -> whitedwarf/planetary nebula -> black dwarf (not the same as a black hole).
> The sun will supernova in about 3.5e9 years
I'm sure that quoting numbers in exponential format makes you sound plausible, but this statement is wrong. The sun is too small to end its life in a supernova by about a factor of ten.
"There will be plenty of supernovas to watch in the next billions of years."
Well, you might be willing to wait around to see 'em, but I'm a busy man. Got things to see, people to do. Let me know how they work out for you.
Supernova = Boring
I thought they were going to release evidence of ancient civilizations on Mars, not some boring old supernova palaver.
So when our sun goes supernova, will the global warming folks finally stop whinging?
They suffer years of geek-hating abuse at school, do years of sex-less college and then University, then finally get a job in the super-competitve field of high level astronomy at NASA.
Finally, after suffering a life of ridicule to be taken seriously, a couple of jocks embarass them among their peers by shouting about their vaginas.
@ global warming
no, the global warming folks will probably stop living well before when the sun goes red giant and our orbit lies near or within the radius of the sun.
Our sun is too miserably small and insignificant to ever go supernova. ;-D It will bloat out to a red giant and swallow us though. Humanity will be a hardly noticed and long forgotten smear on one speck of dust in the vastness of time-space by then.
Who left all this dust lying around my star system?
"it exploded about 28,000 years ago — or yes, 28,140 years if you're a stickler for detail"
I am so please give months, days, hours, minutes, seconds please..
Mines the one with the big target on it
Re: Are supernovae dangerous?
The only two stars near to us which are likely to go supernova within the next few million years are Betelgeuse (427 light years away) and Eta Carinae (7500-8000 LY), Some scientists think the latter could go at any time now. Neither are thought to threaten earth.