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Super Massive Blackholes.



 
 
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  #1  
Old February 16th 04, 01:40 AM
Bill Jones
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Default Super Massive Blackholes.

Generally, when the BH stops 'feeding', substantial portion of its
galaxy will remain.

Is it possible that BH's exist which have 'eaten' their entire
galaxies?
If so, what might be the properties of such BH's?

regards, Bill J.
  #2  
Old February 18th 04, 12:40 PM
Phantom
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Default Super Massive Blackholes.

i think a major property of a BH that has 'eaten up' its entire galxy, is
that it sould be MASSIVE


"Bill Jones" wrote in message
om...
Generally, when the BH stops 'feeding', substantial portion of its
galaxy will remain.

Is it possible that BH's exist which have 'eaten' their entire
galaxies?
If so, what might be the properties of such BH's?

regards, Bill J.



  #3  
Old February 18th 04, 01:31 PM
Gordon D. Pusch
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Default Super Massive Blackholes.

(Bill Jones) writes:

Generally, when the BH stops 'feeding', substantial portion of its
galaxy will remain.


Indeed. The masses of all the central supermassive black holes we have
inferred to exist all seem to be around mere 0.2% of the host galaxy's mass.
Explaining why supermassive black hole masses are proprotional to the host
galaxy's mass and why the constant of proprotionality is so small is one of
the top 10 question about galaxy formation currently being studied by
astrophysicists.


Is it possible that BH's exist which have 'eaten' their entire
galaxies?


Highly unlikely. Black holes are not some sort of "Cosmic Vac-U-Suck(tm);"
they can only "eat" something that is _already_ on a collision course for
their event horizons. Once they have "eaten" all such objects, they stop
growing, until a rare chance gravitational interactions happen to perturb
a star onto an orbit that will collide with the black hole.

Furthermore, on a cosmic scale, even the largest supermassive black hole
ever inferred still has a diameter that is quite small compared with the
mean distances between stars --- even in the relatively "crowded" stellar
environment of a galactic core. Since even the central supermassive
black hole represents a miniscule taget for even a star to hit, unless
a gravitational perturbation essentially "drops" the start almost perfectly
straight inward to within a microscopic fraction of a percent, the star
with miss the central black hole and simply continue on its new orbit
until it interacts with something else. Since the probability of even
_one_ star getting thrown into an orbit that hits the black hole is very,
very small, the probability that _ALL_ of them could get thrown into such
almost perfectly radial orbits is utterly negligible.


If so, what might be the properties of such BH's?


They would have very large masses and diameters --- for a black hole.
However, their diameters would still be utterly negligible compared
to a galaxy, and they would not exert any more gravitational force
than the original galaxy that they "ate" did.


-- Gordon D. Pusch

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  #5  
Old February 19th 04, 05:01 AM
J. Scott Miller
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Default Super Massive Blackholes.

Bill Jones wrote:
Generally, when the BH stops 'feeding', substantial portion of its
galaxy will remain.

Is it possible that BH's exist which have 'eaten' their entire
galaxies?
If so, what might be the properties of such BH's?

regards, Bill J.


Black holes, supermassive or "normal" operate only on their local environment.
At interstellar distances, the gravitational pull of such an object is no
different than a mass or collection of masses of normal material of the same
mass. For example, at the core of our galaxy may exist a supermassive black
hole with mass on the order of 1 to 5 million times the mass of the Sun. Its
gravitational pull is no different on us than if there were 1 to 5 million
stars, all with the mass of our Sun, located in the same spot. We are under no
immediate threat of being pulled in there because of our forward momentum in our
orbit around the center of the galaxy. The same is true for the rest of the galaxy.

So, the probability is quite low that a supermassive black hole would have had
the time to both form and gobble up its host galaxy in the lifetime estimates of
our universe.

 




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