I have just read that on Sunday 2016-12-25, at the age of 88, Vera Rubin passed away.
She was a rather special discoverer.
She was the astronomer-scientist and later a women's advocate, whose 1970 published research observations identified, quite by chance (i.e., it was not central to the research project), that there was a minor and inexplicable anomaly in the orbital velocities of stars about a galactic centre - their orbital velocities were not quite what was mathematically predictable according to known laws of physics.
Her further research observations published in 1980 pinpointed the likely cause as being an unknown - some kind of matter was postulated - that interacted via gravity but not
via the spectrum of electro-magnetic forces - - it was "invisible" across the spectrum, and cast no electro-magnetic shadow.)
So, though it had previously been thought a set of cardinal rules in physics that:
- Everything interacts via gravity.
- Everything interacts via electromagnetic forces.
- here was something unknown that did not
seem to obey the latter rule.
The name eventually given to this unknown was "dark matter" (arguably a bit of a misnomer), but it is still theoretical and an unknown. However, what subsequent research has established is that, theoretically, the universe is (must be) filled with this matter, with a ratio of 5-10 times more of it than the ordinary and more sparsely distributed matter
. Ordinary matter is what makes up stars, planets, gas and the flora and fauna of earth, for example.