请教GWD-4-Q35 一句话的理解

everydayhappy

Baryons--subatomic particles that are generally protons or neutrons--are the source of setllar, and therefore galactic, luminosity, and so their numbers can be estimated based on how luminous galaxies are.

在这句话中, galactic 是形容词,怎么和 luminosity 并列呢? 实在看不懂. 请高人指点.

dayuyunhai

Baryons--subatomic particles that are generally protons or neutrons--are the source of setlar, and therefore galactic, luminosity; 【Baryons粒子导致了乳白色和光亮度；】
and so their numbers can be estimated based on how luminous galaxies are.【所以Baryons粒子的数量可以根据星系的亮度来估计】
●形容词可以当名词用，它后面的名词省略了。比如：“红的放这边，绿的放那边”。