It's metallicity.

The first. Going down metallicity decreases.

A 16.0 solar mass star would spend about 11.7 million years on the main sequence (depending on the metallicity). After approximately 13.0 million years it would become a 1.5 solar mass (approx.) neutron star. This was calculated using metallicity z=0.02 (solar)

Q. Daniel Wang has written:

'A2111, a z = 0.23 Butcher-Oemler cluster with a non-isothermal atmosphere and normal metallicity' -- subject(s): Astrophysics, Disk galaxies, Galactic clusters, Intergalactic media, Metallicity, Proportional counters, ROSAT mission, X rays

Astronomers can name all the designations of the 100 billion galaxies in the universe using their mass, age, and metallicity.