Hi DA,
Very interesting. What strikes me the most about this article is the amount of telescope time used - a whopping 1000 hours on the Hubble. (I believe a good chunck was the director's discretionary time.)
Fritz Zwicky (1898-1974) who was one of the most original and productive astronomers of the 20th century and was the discoverer of dark matter. (Also, he was one of the most anti-social as well as eccentric. But this was just toward students and colleagues. He did have his good side. He help rebuild scientific libraries destroyed during the WWII and assisted in setting up a foundation to aid war orphans.)
He noticed that most galaxies tend to occur in clusters of several thousand galaxies each. He made spectroscopic studies of the Virgo and Coma Berenices clusters, in 1933 to obtain more detailed information.
He calculated that the distribution of galaxies in the Coma Berenices cluster was statistically similar to the distribution of molecules in a gas when it is at equilibrium.
This suggested to him that the virial theorem might be useful.
This theorem is now widely used in astrophysics, but had its start in thermodynamics and mechanics.
The virial theorem is a relation between the average value of the kinetic and potential energies of a system in a steady state or a quasi-steady state.
In astrophysics the virial theorem, as Zwicky showed, is very useful.
It might be stated as: for a stable, self-gravitating, spherical distribution of equal mass objects, e.g., galaxies in a cluster, the total kinetic energy is equal to minus 1/2 times the total gravitational potential energy.
If there is not, then something is wrong. Well it turns out that the something was what we now call dark matter.
Well "back in the day" getting telescope time was not easy to get, especially for low priority stuff like galaxy surveys. (Astronomers still have to scramble for scope time.)
So what did Zwicky do? Well he and Walter Baade (1893-1960) set up the first Schmidt telescope (18 inchs) on Palomar in 1935. This kind of telescope, with its wide field, is ideal for surveys. (Baade and Zwicky were the astronomical "odd couple." Stories still circulate!)
Subsequent investigations has shown that 99% of the matter in the known unverse is dark. This much of the universe rates plenty of telescope time.
Well I'll just leave it at that, but 1000 hours of scope time!!!
Dr. R.
