Occam’s Razor Cuts Out Low Mass Stars

Primary author: Guy Worthey
Co-author(s): Xiang Shi; Islam Khan

Primary college/unit: Arts and Sciences
Campus: Pullman


A galaxy’s light is a composite of the various stars that make it up. Both giant stars and dwarf stars contribute to the total light output. The giants are cool, luminous, about one solar mass, and rare. The dwarfs are cool, faint, about 0.1 solar masses, and numerous. Most of the stellar mass of a galaxy is in these dwarf stars.

Some features in the red optical spectrum respond to dwarf/giant status in stars. Comparison of galaxy spectra to plausible mixtures of dwarf and giant light leads to the conclusion that the hugest galaxies have more dwarfs than galaxies like the Milky Way. The current picture is that these huge galaxies were formed from mergers of smaller galaxies. This leads to a paradox. If a huge galaxy is the sum of several smaller ones, why is the stellar content different?

We posit that the apparent enhancement in the number of dwarf stars in huge galaxies is an illusion. The increased heavy element content in huge galaxies causes in turn a decrease in the number of viable giant stars. The decrease in number of giants has been misinterpreted as an increase in the number of dwarfs. The trend we see in the spectrum is therefore naturally explained without generating new puzzles.