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Two recent papers have shed light on dark matter within our own Milky Way and cast doubt on two popular theories: Modified Newtonian Dynamics and Superfluid Dark Matter. In both of these theories, additional forces come into play to try to explain the velocities of stars within our galaxy other than simple dark matter. And both of them predict that stars should be moving vertically with respect to the galactic plane at accelerations that we do not observe while a simple Cold Dark Matter halo can explain those measurements. Can these theories recover?
Firstly, why do we think dark matter exists at all?
There are quite a few reasons, actually. The first reason, which was discovered in the 1930s, is that galaxies don’t rotate at the right speeds if all they contain is the luminous matter we can see. Here is a picture of how we think galaxies should rotate versus how they actually rotate.
We can tell how fast stars are rotating because they are made of mostly hydrogen. Hydrogen emits light at a very particular wavelength of 21 centimeters and, if that wavelength is shifted to a smaller wavelength (blue-shifted) we attribute that shift to the star moving towards us, and if it shifted to a larger wavelength (red-shifted) we know it is moving away.
We can combine all the observations of red and blue shifts of stars to determine how fast they are moving. The problem is that we see stars in the outer rims of galaxies moving so fast they should be breaking free of the galaxy’s gravitational pull, but they don’t. Instead, galaxies rotate almost like a record on a record player, with the outer stars moving much faster than the inner ones.
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Dark matter?
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James' World 2 
May 07, 2023 @ 06:29:23
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May 08, 2023 @ 07:58:35
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