black holes and comets

[gou...@dec-parrot.uucp]

I'm not an expert, I'm asking for an expert answer on behalf of my
six-year-old daughter (who's no expert either). We have access to
independent facts in the form of her encyclopedia (at the least),
but need someone to pull them together somewhat...

The question she asks is, why don't the comets get gobbled up by
black holes out beyond the planets? Or, how probable is it that
any given comet might get thus, er, eaten? (Probably not accurate
to say "destroyed".) Or, how many comets might might thus be
eaten over a period of time?

The answer I gave her was that, as far as anyone knows, black holes
are not all that common, at least not ones that are big enough to
do that kind of damage. We wondered if a black hole that was big
enough (however you want to measure "big") to absorb comets might
be big enough to be detectable in the orbits of the known planets,
thus qualifying as "Planet X" or whatever, that was what Pluto was
supposed to be but apparently isn't after all.

Can anyone shed any light on this for us?

-- Kenn Goutal ...decwrl!dec-rhea!dec-parrot!goutal

[Steve Schlaifer x3171 156/224]

In article <14...@decwrl.DEC.COM>, gou...@dec-parrot.UUCP writes:
> I'm not an expert, I'm asking for an expert answer on behalf of my
> six-year-old daughter (who's no expert either).
>

> The question she asks is, why don't the comets get gobbled up by
> black holes out beyond the planets?
>

Essentially, comets are very close to the sun, stars and black holes, which
are just really big stars that have collapsed into themselves, are very
far away. In the same way that the stars that we see at night don't
have any discernable affect on the motions of the planets or the comets,
black holes also have no affect on the planets or comets. They are just too
far off for their gravity to have much effect. Anything that
was both close enough and big enough to gobble comets, would also cause
very large disturbances in the orbits of the planets which would be easily
detected by modern (or even primitive) instruments.
--

...smeagol\ Steve Schlaifer
......wlbr->!jplgodo!steve Advance Projects Group, Jet Propulsion Labs
....group3/ 4800 Oak Grove Drive, M/S 156/204
Pasadena, California, 91109
+1 818 354 3171

[Michael k Notch]

In article <14...@decwrl.DEC.COM> gou...@dec-parrot.UUCP writes:
>The question she asks is, why don't the comets get gobbled up by
>black holes out beyond the planets? Or, how probable is it that
>any given comet might get thus, er, eaten? (Probably not accurate
>to say "destroyed".) Or, how many comets might might thus be
>eaten over a period of time?
>

I thought about your questions and even though I am not an expert, my answer
is this: if planets like Earth and Jupiter do not get "sucked" into a Black
Hole, that indicates that we may be too far away from a Black Hole.

--
"But... What about Naomi?"

USENET: ihnp4!umn-cs!srcsip!notch Michael k Notch
philabs!srcsip!notch Honeywell SRC/SIP/MVT
MN17-2349
--