Thread: Black Holes
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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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