I hope your Christmas day was a good one, considering…
Did you get to see the Great Conjunction on the 21st? Or did you get clouded out? We were ready, big binoculars and a telescope set up. Had a few neighbors stop by. Clouds were in the way most of the time, but managed a few peeks and that was good. But it’s not over yet. Jupiter and Saturn will be pretty close for a while, slowly separating and setting earlier as the days get longer.
Often compared with the practice of alchemy, aether, also known as quintessence, was an ancient concept for the “stuff” filling space above our terrestrial sphere. It enabled light to travel, buoyed stars and planets, and everything else in the celestial sphere. It was later poo-pooed as utter nonsense. Light can travel in a vacuum, planets and stars and everything else in space are buoyed by gravity. No need for aether/quintessence. Gravity rules! Isaac Newton figured that out.
Then came Lord Kelvin, Henri Poincare, Jacobus Kapteyn, Jan Oort, Fritz Zwicky, Horace Babcock, Vera Rubin, Kent Ford, Ken Freeman…others. They studied our and other galaxies and found a bothersome anomaly. The amount of mass for all the stars in a galaxy did not come close to the mass (gravity) needed to hold galaxies together. There was something that could not be seen keeping galaxies from flying apart. Whatever it is, it has a lot of mass too. Oh, no! Not aether again!
No, not aether and not quintessence, modern instruments disprove that. But it’s something, something massive.
Welcome back to the dark matter quest. My last update was in 2018, and dark matter still has not been identified. The search continues with ever bigger and more sophisticated instruments.
We know that dark matter does not appear to interact directly with baryonic (normal) matter. We know dark matter interacts with baryonic matter via gravity. The standard model of our universe (general relativity) stipulates that gravity is intimately associated with mass; it is “caused” by mass. Therefore, dark matter has mass because it has gravity. We just seem unable to detect this mass.
Most methods working to detect dark matter look for low energy recoils of atoms when dark matter collides with them. These detectors are huge (Olympic swimming pool), typically use a pure noble gas such as xenon and are situated in deep (miles deep) pits. Another detector design uses large, cryogenically stored pure crystals of germanium.
There are numerous dark matter “candidates”, including particles (Weakly Acting Massive Particles, Axions, Sterile Neutrinos, etc.), superfluid (Bose-Einstein Condensate), entropic gravity, even negative mass.
We don’t yet know what dark matter is. We don’t know what makes gravity work either. I think if we figure out one the other will be revealed. Happy New Year!
What’s in the Sky?
Jupiter and Saturn still appear close to each other. Go out for a few evenings at least and follow their separation progress.