| Topic: |
Science > Physics |
| User: |
"Michael J. Strickland" |
| Date: |
08 Mar 2006 02:04:14 PM |
| Object: |
Galactic Core Black Holes |
Large star clusters in the center of galaxies could comprise
a black hole. The only requirement for a black hole is high
mass, not high density.
I've calculated that 3.8e9 suns (sun density stars) in a cluster
of radius 1.07e13 m (= 0.001 ly, or about twice Pluto's orbit
radius) would have sufficient mass to comprise a black hole.
This is a rather low density black hole. It would have
an average density of 1/1000 the sun.
The stars would be spaced about 7 million km apart and orbit their
common center of mass.
None of these stars would be anywhere near black hole density by
themselves but the cluster would be.
The radius of a black hole is proportional to sqrt[1/rho] so
the density could be reduced (spacing increased) further with
an increase in cluster radius. Every hundredfold decrease in
density would require only a 10 fold increase in cluster radius.
To me, this star cluster scenario seems more plausible than the
solitary supermassive black hole at the galactic core that you often
hear about.
--
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Michael J. Strickland
Quality Services
703-560-7380
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| User: "Eric Gisse" |
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| Title: Re: Galactic Core Black Holes |
08 Mar 2006 02:18:52 PM |
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Michael J. Strickland wrote:
Large star clusters in the center of galaxies could comprise
a black hole. The only requirement for a black hole is high
mass, not high density.
I've calculated that 3.8e9 suns (sun density stars) in a cluster
of radius 1.07e13 m (= 0.001 ly, or about twice Pluto's orbit
radius) would have sufficient mass to comprise a black hole.
This is a rather low density black hole. It would have
an average density of 1/1000 the sun.
The stars would be spaced about 7 million km apart and orbit their
common center of mass.
None of these stars would be anywhere near black hole density by
themselves but the cluster would be.
The radius of a black hole is proportional to sqrt[1/rho] so
the density could be reduced (spacing increased) further with
an increase in cluster radius. Every hundredfold decrease in
density would require only a 10 fold increase in cluster radius.
To me, this star cluster scenario seems more plausible than the
solitary supermassive black hole at the galactic core that you often
hear about.
Mabey. It might have started out that way, but it certaintly didn't
last.
But do you really think a system of roughly 4 *billion* stars stuffed
inside a volume within an order of magnitude of our solar system would
end up as anything other than a black hole?
How would that many stars in that small of area even form in the first
place?
--
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Michael J. Strickland
Quality Services
703-560-7380
---------------------------------------------------------------
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| User: "Sam Wormley" |
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| Title: Re: Galactic Core Black Holes |
08 Mar 2006 03:07:31 PM |
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Michael J. Strickland wrote:
Large star clusters in the center of galaxies could comprise
a black hole. The only requirement for a black hole is high
mass, not high density.
I've calculated that 3.8e9 suns (sun density stars) in a cluster
of radius 1.07e13 m (= 0.001 ly, or about twice Pluto's orbit
radius) would have sufficient mass to comprise a black hole.
Schwarzschild Radius with your numbers
http://www.google.com/search?q=%282*G*3.8*10%5E9*1.98892*10%5E30+kg%29%2Fc%5E2+in+AU
http://www.google.com/search?q=%282*G*3.8*10%5E9*1.98892*10%5E30+kg%29%2Fc%5E2+in+light+years
If your mass is within its Schwarzschild Radius is it
what we describe as a black hole
http://scienceworld.wolfram.com/physics/SchwarzschildRadius.html
and will collapse to a singularity (for the non rotating case).
Singularity Theorem
http://scienceworld.wolfram.com/physics/SingularityTheorem.html
Black Hole
http://scienceworld.wolfram.com/physics/BlackHole.html
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| User: "Henning Makholm" |
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| Title: Re: Galactic Core Black Holes |
08 Mar 2006 02:32:53 PM |
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Scripsit "Michael J. Strickland" <qualityser@worldnet.att.net>
I've calculated that 3.8e9 suns (sun density stars) in a cluster
of radius 1.07e13 m (= 0.001 ly, or about twice Pluto's orbit
radius) would have sufficient mass to comprise a black hole.
This is a rather low density black hole. It would have
an average density of 1/1000 the sun.
If sufficiently many stars get close enough together to form an event
horizon (= a black hole), they will quickly be drawn together by their
mutual gravity, and the density would grow towards infinity at a
singularity.
See the Penrose-Hawking singularity theorems.
The stars would be spaced about 7 million km apart and orbit their
common center of mass.
They couldn't. Inside the event horizon, there are _no_ stable orbits.
--
Henning Makholm "There is a danger that curious users may
occasionally unplug their fiber connector and look
directly into it to watch the bits go by at 100 Mbps."
.
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| User: "Michael J. Strickland" |
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| Title: Re: Galactic Core Black Holes |
10 Mar 2006 01:46:40 PM |
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"Henning Makholm" <henning@makholm.net> wrote in message
news:87d5gwoex6.fsf@kreon.lan.henning.makholm.net...
Scripsit "Michael J. Strickland" <qualityser@worldnet.att.net>
I've calculated that 3.8e9 suns (sun density stars) in a cluster
of radius 1.07e13 m (= 0.001 ly, or about twice Pluto's orbit
radius) would have sufficient mass to comprise a black hole.
This is a rather low density black hole. It would have
an average density of 1/1000 the sun.
If sufficiently many stars get close enough together to form an event
horizon (= a black hole), they will quickly be drawn together by their
mutual gravity, and the density would grow towards infinity at a
singularity.
Not if they were orbiting their common center of mass (at orbital velocity).
See the Penrose-Hawking singularity theorems.
Do these theorems apply to a collection of discrete masses or only to a
single mass? I've never seen the type of black hole I'm considering
discussed, only single, contiguous mass black holes.
The stars would be spaced about 7 million km apart and orbit their
common center of mass.
They couldn't. Inside the event horizon, there are _no_ stable orbits.
This may be true for a single mass black hole where the gravitational force
increases as you move inside the event horizon, but does it apply to the
type I'm considering (a collection of masses) where the gravitational force
decreases as you move inside the event horizon?
Picture a cluster of stars, slightly less than the aggregate mass required
for a black hole, orbiting their common center of mass. Then a few
additional stars come flying by and enter into orbit about the cluster
resulting in sufficient mass to produce the black hole. Since these stars
are outside the inner stars and do not provide any gravitational force on
the inner stars (shell theorem), how can they render the orbits of the inner
stars unstable?
....
--
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Michael J. Strickland
Quality Services
703-560-7380
---------------------------------------------------------------
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| User: "Henning Makholm" |
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| Title: Re: Galactic Core Black Holes |
10 Mar 2006 05:17:54 PM |
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Scripsit "Michael J. Strickland" <qualityser@worldnet.att.net>
"Henning Makholm" <henning@makholm.net> wrote in message
If sufficiently many stars get close enough together to form an event
horizon (= a black hole), they will quickly be drawn together by their
mutual gravity, and the density would grow towards infinity at a
singularity.
Not if they were orbiting their common center of mass (at orbital velocity).
They cannot. There are no stable orbits inside an event horizon/
See the Penrose-Hawking singularity theorems.
Do these theorems apply to a collection of discrete masses or only to a
single mass?
Probably they are formulated for a continuous distribution of mass.
I've never seen the type of black hole I'm considering
discussed, only single, contiguous mass black holes.
That is because the configuration you are imagining is not possible
according to the SR field equations.
They couldn't. Inside the event horizon, there are _no_ stable orbits.
This may be true for a single mass black hole where the gravitational force
increases as you move inside the event horizon, but does it apply to the
type I'm considering (a collection of masses) where the gravitational force
decreases as you move inside the event horizon?
It is true for essentially any configuration where there is a closed
event horizon.
Picture a cluster of stars, slightly less than the aggregate mass required
for a black hole, orbiting their common center of mass. Then a few
additional stars come flying by and enter into orbit about the cluster
resulting in sufficient mass to produce the black hole. Since these stars
are outside the inner stars
Why do you suppose that they can remain "outside"? If they can, it
will be because they are not heavy enough to cause an event horizon in
the first place.
--
Henning Makholm "No one seems to know what
distinguishes a bell from a whistle."
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| User: "Eric Gisse" |
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| Title: Re: Galactic Core Black Holes |
08 Mar 2006 05:31:49 PM |
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Henning Makholm wrote:
Scripsit "Michael J. Strickland" <qualityser@worldnet.att.net>
I've calculated that 3.8e9 suns (sun density stars) in a cluster
of radius 1.07e13 m (= 0.001 ly, or about twice Pluto's orbit
radius) would have sufficient mass to comprise a black hole.
This is a rather low density black hole. It would have
an average density of 1/1000 the sun.
If sufficiently many stars get close enough together to form an event
horizon (= a black hole), they will quickly be drawn together by their
mutual gravity, and the density would grow towards infinity at a
singularity.
See the Penrose-Hawking singularity theorems.
The stars would be spaced about 7 million km apart and orbit their
common center of mass.
They couldn't. Inside the event horizon, there are _no_ stable orbits.
mmm..probably.
I have often wondered, but have no way of proving, whether it is
possible for a multibody system of black holes to have stable, in any
meaningful sense of the word, orbits within the event horizons. It is
cut-and-dry as to what happens to a lone object inside a black hole,
but less so when there is more than one object and their masses are
comparable to the black hole itself.
--
Henning Makholm "There is a danger that curious users may
occasionally unplug their fiber connector and look
directly into it to watch the bits go by at 100 Mbps."
.
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