Eli5: so i just learned that nebula is just a lit up piles of gas, how does piles a gas exactly lit up?

Question

Like to start, how do they even produce light? Also how do they stay together?

In: 2

Answer 1

You can classify nebulae into three broad categories: Emission, reflection, and dark.

Dark nebulae are not lit up, and they block (visible light), hence why they appear dark. Reflection nebulae reflect light from stars that are in or near the nebula. Emission nebulae emit their own light, this can happen due to being ionised by the ultraviolet light of a hot star. The atoms and electrons then emit light when they recombine, and can also emit light from being so hot.

A nebula might not stay together, or it might collapse (possibly making stars). They are so huge though that any difference is on a very long timescale.