Answer: is constant
Explanation:
In order to analyze the velocity of the stars within a galaxy, the <u>galaxy rotation curves</u> (developed by the American astronomer Vera Rubin) are used. These graphs are elaborated as a scatter diagram in which the orbital velocity of the stars present in a galaxy is represented on the Y axis and the distance of these stars to the center of the galaxy on the X axis.
Thanks to this diagram, it has been possible to observe a characteristic behavior in the rotation speed of the stars (and gas) present in the galaxies, which differs from the rules of the orbital movement of the planetary systems postulated by Newton and Kepler.
This means that in these galaxy rotation curves it has been observed that the rotation speed of stars and gas is "constant", regardless of the distance to the center of the galaxy. This discrepancy and these results were then used to demonstrate the existence of dark matter in the universe.
I find that the best answer is the following one:
c. determined by factors outside our control
For example, even though life is very hard in the very hot and the very cold regions, we can't control it: so this is an example of a physical environment that is hard to control.
In comparison, it is often easier to describe than our social environment.
The best and most correct answer among the choices provided by your question is the fourth choice.
The geography of the Mayan civilization different from the geography of Mesopotamian civilization because t<span>he Mayan civilization was not built around a major river.</span>
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