Archive for August 27, 2020

08/27/2020 – Ephemeris – Unsolved mysteries: Dark Matter

August 27, 2020 Comments off

This is Ephemeris for Thursday, August 27th. Today the Sun will be up for 13 hours and 27 minutes, setting at 8:27, and it will rise tomorrow at 7:01. The Moon, 2 days past first quarter, will set at 1:58 tomorrow morning.

It was in the 1930s that some astronomer concluded by measuring the velocities of individual galaxies that galaxy clusters contain more mass that can be explained by the size and brightness of the galaxies within. Fritz Zwicky coined the term dark matter for it after his study in 1933. Vera Rubin and others discovered the effect of dark matter on the rotation rates of galaxies in the 1960s and 70s. Nobody knows what dark matter is. There are two leading theories that they are made of particles coined WIMPs and objects called MACHOs that don’t interact with normal matter except gravitationally. Astronomers do have fun with their acronyms. Dark matter is detected by their gravity and how it distorts the light from the galaxies behind it.

The event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


Bullet Cluster showing what happened to the dark matter

This is called the Bullet Cluster. It’s two galaxy clusters that collided. The pink is hot gas visible in x-rays. The blue is added to show where dark matter resides. It is detected by studying the far distant galaxies beyond for distortion caused by the gravitational lensing of the dark matter. Most of the mass of the galaxy clusters is dark matter, which also contain hot gas and, of course the galaxies. When galaxy clusters collide the gas of the two clusters interact and are stripped out and the dark matter and galaxies go merrily on. Image Credit: NASA, ESA, CXC, M. Bradac (University of California, Santa Barbara), and S. Allen (Stanford University)

FYI: WIMPs = Weakly Interacting Massive Particles, MACHOs = MAssive Compact Halo Objects.