An extremely primitive star in the Galactic halo

摘要

The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium; almost all other elements were subsequently created in stars and supernovae. The mass fraction of elements more massive than helium, Z, is known as 'metallicity'.%出于理论上的原因，也由于低金属性(所渭金属性，指比氦重的元素的含量)的恒星明显不存在，所以人们曾提出，低质量恒星在星际介质富集到金属性的一个临界值Z之上之前是无法形成的，而这个Z值估计在1 5×10~(-8)和15×10~(-6)之间。