OK, after seeing a couple of fireworks ads the other day, several of us got talking about what you could do to put on a really big fireworks display. Things got pretty silly pretty quickly, but the question that came up was, when the Andromeda galaxy celebrates its independence day in the year 201,776, what might they use? Or, to turn it into a General Question, “What is the biggest explosion someone could reasonably expect to see?”
Here’s a list I came up with. (Bear in mind that I only had enough physics to get through Engineering back in my college days and am at best an armchair astronomer, so I’m probably wrong somewhere on this list.)
Conventional Explosives - Just standard fireworks scaled up a few orders of magnitude. I know the military has some really big bombs but I’m not quite sure how far they go. I suspect there is a practical upper limit on how big a conventional explosive can be because (I suspect) past a certain point the part of the explosive that has already gone off blows the rest of it apart before it can react.
Nuclear Explosives - Most people’s idea of a really big explosion. (The conversation that inspired this post got stared when someone wondered if you could produce a country-wide “fireworks display” by setting off nuclear devices in orbit). I suspect the upper limit here would be that, past a certain point, only so much of the fissionable/fusionable material could react before the force of the explosion blew it apart. (And, yes, I know that a star can be thought of as a fusion reaction that keeps exploding, but it doesn’t exactly match most people’s idea of an “explosion”.)
Supernova - Now these are big. I assume that the bigger the star, the bigger the resulting supernova. But, past a certain mass you don’t have a star anymore; you have a neutron star/black hole. So that marks the upper limit there.
Collapsing Black Holes (?) - Here is where we are getting beyond my knowledge level. If I remember correctly, Black Holes can somehow slowly lose mass. When its mass drops below a certain level, it ceases to be a Black Hole and suddenly all the matter and energy within it are released at once. I would guess this is bigger than a Supernova but I don’t know if this is even a valid theory anymore.
The Big Bang - Well, there was only one of these and I doubt anyone was around to see it, so it doesn’t count.
And, some things I didn’t know where to put them.
A) Matter/Antimatter Collison - I know this releases a lot of energy, but I don’t know how big it could get. If, for example, a matter planet and an antimatter planet were to collide, they would start reacting when they first touched. At some point, the energy release would push them apart again. (Or, for that matter, gravity may tear them apart before they hit, which gives us a bunch of small explosions instead of one big one.) I would guess this would fall somewhere between 2 and 3 above.
B) Neutron Stars - Do these do anything? I know there is an energy release as matter falls into them but beyond that I really don’t know. (That’s what a Pulsar is, isn’t it? Not sure if that would count for our explosion definition or not.)
So, anyone have any ideas or input? I’ve only got a few days until the 4th, so I need to start working on my plans…
Nah, your Type II supernova is going to deliver a bigger bang than a gamma ray burster or a black hole. Take for instance SN94D. It released about 10^41 J of energy and the temperature at the core reached about 3E12 K.
The limiting factor on man-made nuclear explosives is currently the “why bother?” factor. A megaton bomb can destroy a city. A hundred megaton bomb can destroy… A city. After a certain point, you just can’t flatten things any further. There probably is an upper bound, but I’m not sure what it would be.
On supernovas, the transition from star to black hole/neutron star is exactly what causes the supernova. In other words, any star that goes supernova is above that limit. There are still practical limits on how big a star will form in the first place, though: Too much mass available, and you’re likely to just get two stars.
With black holes, you’re referring to evaporating black holes, not collapsing ones. A black hole will eventually release a great deal of energy (equal to its original mass times c[sup]2[/sup]), but the part at the end (what one might call an explosion, though there’s no hard cutoff as to what counts as the end stage) is much dimmer than a supernova or even an ordinary star (though still much brighter than anything man-made)
And we can still see the Big Bang, though not with visible light, and it’s not very impressive any more. The Big Bang happened everywhere, so you can look in any direction to see it. But it happened long enough ago that the light has all cooled off to microwaves. And there was only one, so maybe that shouldn’t count.
I’m not sure anyone knows exactly what they are, but quasars are apparently the brightest objects in known space. A quasar 10 parsecs away would appear as bright as our sun. That’s mighty bright.
Quasars are believed to be galaxies with supermassive black holes in the core. Are you sure you don’t mean 10 megaparsecs? If a galaxy was 10 parsecs away (which isn’t many times further than the nearest star), we would be considered part of it.
Take that Wikipedia article with a grain of salt… 3C273 is indeed the brightest quasar in apparent magnitude, but I’m pretty sure that it’s not the brightest absolute. A decent quasar would be as bright as the Sun as far away as 100 pc or so. And while quasars are part of galaxies, the quasar engine itself is smaller than the Solar System, so it does make sense to talk about being 100 pc away from a quasar.
One way of looking at the Big Bang is to consider it an event that is still taking place. (After all, any answer you give to “When did it end? / When did it become simply The Universe?” is entirely arbitrary.
So the universe in its entirety as one hell of a big fireworks display.
As tanstaafl said, there is a limit to how large a star can get, but it’s not because it will collapse into a black hole. The limit is due to the fact that the bigger a star gets, the more light it puts out. If you add more matter to a star, at some point the light pressure will be strong enough to overcome the star’s gravity and blow the outer layer of its atmosphere away from the star. This is known as the Eddington Limit.
Now it turns out that the Eddington Limit varies depending on the composition of the star. The more heavy elements in the star, the lower the Eddington limit. In the early universe, there were few heavy elements, so the stars coiuld get bigger than they can today. The upper limit seems to have been about 150 solar masses, whereas now the limit is somewhere around 60 to 90 solar masses. When one of those monsters go boom, you get a hypernova which is basically a super-dooper supernova. The current theory about GRBs is that most of them are caused by hypernovae from the early universe.
