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well, black holes are somewhat off-topic here, but no matter [img]smile.gif[/img]
actually, unless i've missed some big discovery lately, mini-black holes are only being theorised on for now, as there is no real mechanisem known to explain their creation. the black holes that more or less certainly exist are the remains of massive stars that end their lives in a supernova explosion. when nuclear reactions in the star's core stop, the core collapses under it's own gravitational pull until not even light can escape it's immense gravity. the 'point of no return', beyond which escape velocity exceeds the speed of light, is the event horizon and that is what is usually referred to as the size of the black hole. so the 'radius' of a black hole the mass of a few sun's masses is actually a few kilometers.
there are probably also black holes in the centers of most galaxies, those have masses on the order of millions of times the mass of our sun and are about the size of our solar system.
p.s., just to comment on what Mirac wrote...
indeed, there really are quite a lot of bodies a few meters in size hiting our planet, but these bodies are weak enough to break up very high up in the atmosphere, so the explosions they cause aren't a threat to us. and i'm not talking firecracker-type explosions here, rather think 'little boy' or 'fat man' size explosions! all thanks to our precious atmosphere that guards us from yet another cosmic danger [img]smile.gif[/img] .
as for the near misses - iirc there was an asteroid some 300 meters across that a few years ago missed the earth by only about 50.000 or 100.000 kilometers! that is incredibly close (the moon is on average 386.000 kilemeters away) and an asteroid this size could easily devastate an entire continent.
[ 09-02-2003, 05:51 PM: Message edited by: frudi_x ]
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