In the last few months there have been some developments in the hunt for Dark Matter, unfortunately they tell us what Dark Matter isn't rather than what it is. One of the most popular theories, the idea that Dark Matter is made of sterile neutrinos, now appears to be most likely untrue according to a recent experiment at the MicroBooNE detector at Fermilab. The idea may not be completely dead but it is certainly badly wounded:
Another idea is that Dark Matter doesn't really exist and we need to modify our understanding of gravity, especially General Relativity. That idea has been just about destroyed by the discovery of a very odd type of galaxy called Ultra Diffuse Galaxies (UDG). Only about a dozen UDG's have been discovered and are about as large as the Milky Way but have 1000 times fewer stars and not much gas or dust, but that's not the strangest thing about them. UDG's were found to contain very little Dark Matter. Because they are so dim UDG are hard to observe, so some have suggested the observed lack of Dark Matter was simply due to observational inaccuracies, but on December 2 researchers reported on the most detailed observation of a UDG so far and they were unable to find any Dark Matter in it. Zero. To predict the motions of the stars in a UDG all you need is Kepler's laws of planetary motion and there would be no need to invoke Dark Matter or modify Newtonian gravity at all, much less Einsteinian gravity.
And Einstein's General Relativity doesn't seem to need a modification because it just passed with flying colors its most stringent test ever. Astronomers have been observing a double pulsar, 2 Neutron Stars orbiting each other every 147 minutes at a speed of 620,000 MPH, one neutron star rotates once every 2.8 seconds and the other rotates 44 times a second; on December 13 they reported on the results of 16 years of observations and they were compatible with the predictions made by General Relativity within the margin of error, if there was any conflict it was less than one part in 7700.
So we know more about what Dark Matter isn't but we still don't know what the hell it is. And Dark Energy is even more mysterious.
By the way, the Webb Telescope is now scheduled to be launched no earlier than Christmas Eve.
John K Clark See what's on my new list at Extropolis