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Black Holes



 
 
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  #1  
Old April 13th 19, 12:15 AM posted to sci.astro
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Default Black Holes

Will a black hole in a galaxy ever consume their entire galaxy. If so are there any known galaxies that are almost consumed by their black hole?

In a spiral galaxy is it the black hole that causes the spiraling, like water down a plug hole?

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  #2  
Old April 13th 19, 05:04 PM posted to sci.astro
Martin Brown[_3_]
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Default Black Holes

On 13/04/2019 00:15, wrote:
Will a black hole in a galaxy ever consume their entire galaxy. If so
are there any known galaxies that are almost consumed by their black
hole?


No. It will only consume any stars that happen to venture too close and
find themselves in a tightly bound and ultimately decaying orbit. They
are not the deranged cosmic vacuum cleaners of science fiction.

Eventually it will consume all the material available to it and become
quiescent - visible only by the effect that it has on light passing by.

If our sun suddenly turned into a black hole then the planets would all
still orbit pretty much as they did before. I suspect Mercury would be
frame dragged a bit more but further out it would be business as usual
(apart from there being no sunlight any more).


In a spiral galaxy is it the black hole that causes the spiraling,
like water down a plug hole?


No. They are density waves of star formation in the galactic disk. There
are plenty of elliptical galaxies with no spiral structure as well.

Galaxy collisions can shake things up a lot - then when two massive
black holes merge you get very spectacular fireworks and gravity waves
that are detectable on Earth.

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Martin Brown
  #3  
Old April 17th 19, 09:36 PM posted to sci.astro
Steve Willner
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Default Black Holes

In article ,
Martin Brown writes:

No. [Black holes] will only consume any stars that happen to
venture too close and find themselves in a tightly bound and
ultimately decaying orbit.


Also gas clouds if they are in tightly bound orbits.

They are not the deranged cosmic vacuum cleaners of science
fiction.


Indeed!

Eventually it will consume all the material available to it and become
quiescent - visible only by the effect that it has on light passing by.


Also by its gravitational effect on nearby stars and gas clouds. I
suppose that's not strictly "visible" in the sense Martin meant, but
have a look at https://www.youtube.com/watch?v=AZhUQl-wmq0 and read
the caption. These stellar orbits are how the mass of the Galactic
center black hole is known.

Galaxy collisions can shake things up a lot - then when two massive
black holes merge you get very spectacular fireworks and gravity waves
that are detectable on Earth.


"Gravitational waves." The term "gravity waves" means something else
entirely. Hard to keep straight, though, if you don't often use
these terms.

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