Thursday, October 15, 2020
I never believed in "Dark Matter". Like that 10% of the matter in the universe is in stars, and 90% is not seen
Well, if the other 90% is not visible, how do you know it is there? I just didn't believe one could know.
Then I read that galaxies are spinning too quickly, like there is more of a gravitational force pulling them together than expected, which allows them to spin faster.
But how do you know the galaxies are spinning too quickly, they don't change much in even 100 years. Then I read up. Hydrogen burning in stars emits light a very specific frequency. A galaxy rotating with some stars moving towards you, and some away will have a doppler shift in this precise frequency. Sort of like a train when blowing its horn goes past you, you hear the drop in frequency from higher to lower. So the spread out of this frequency tells you how fast the galaxy is spinning.
They are spinning too fast, so there is some "dark matter" helping pull them together, allowing them to spin faster.
Pretty cool if you have a background in physics, ... and I do.