## Cosmic Clocks: Galaxies Behave Like Clocks, Rotating Once Every Billion Years

Discussion of the astronomical and cosmological aspects of a universe of motion.
duane
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### Cosmic Clocks: Galaxies Behave Like Clocks, Rotating Once Every Billion Years

http://www.sci-news.com/astronomy/galax ... 05817.html

Cosmic Clocks: Galaxies Behave Like Clocks, Rotating Once Every Billion Years
It’s not Swiss watch precision, but regardless of whether a galaxy is very big or very small, if you could sit on the extreme edge of its disk as it spins, it would take you about a billion years to go all the way round.

He said that by using simple maths, you can show all galaxies of the same size have the same average interior density.

“Discovering such regularity in galaxies really helps us to better understand the mechanics that make them tick — you won’t find a dense galaxy rotating quickly, while another with the same size but lower density is rotating more slowly.”

Cosmic clocks: a tight radius–velocity relationship for H i-selected galaxies

if Galaxy A has a radius of 1,
Galaxy B has a radius of 2,
and Galaxy C has a radius of 1/2
and all do a revolution in 1 billion years

then is the speed of the outer edge
determined by a cosmic (time) factor
rather than the amount of "dark matter" within?

bperet
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### Re: Cosmic Clocks: Galaxies Behave Like Clocks, Rotating Once Every Billion Years

duane wrote:
Thu Mar 15, 2018 12:40 pm
then is the speed of the outer edge determined by a cosmic (time) factor rather than the amount of "dark matter" within?
The outer edge is probably not rotating, at all. I'd bet what is being measured is the stellar equivalent of Brownian motion, which is why they all appear to rotate at the same speed.

If you look at our solar system (aka "galaxy") from far away, the outer edge does not appear to move, either, because it is a whirlpool--spinning fastest at the sun and virtually not at all on the edge.
Every dogma has its day...