Green valley galaxies

[Tom Mazanec]

The August issue of Scientific American had an article on supermassive black holes in galaxies. If I understand it correctly, one of the reasons the Milky Way seems good for life is because the small central black hole makes the MW a "green valley" galaxy, intermittant between "blue" galaxies with high star formation and "red" galaxies with low star formation.
Any other "green valley" galaxies that you could list?

[Romanus]

Probably the vast majority of galaxies with sufficient metals, that aren't in starburst, or have AGN. In my op, a galaxy's central black hole is unimportant for the prospects of life, and not a predictor; a galaxy without one could still have plenty of stars with planets, while a galaxy with one could have plenty of present (or past) star formation. Case in point: Messier 104, the Sombrero Galaxy, has a 1 billion solar-mass CBH, along with an active star-forming disk. Even an old, massive, but metal-rich elliptical galaxy presumably has a population of planets from the galaxies that merged to create i, as will happen when M 31 and the Milky Way merge in the distant future.

[TaylorS]

The article said that the black hole may have been active as recently as 300 years ago.