If quasar groups and gamma ray bursts have enough energy to outshine entire galaxies, how come the universe isn’t permanently bright?

Question

idgi

In: 3

Answer 1

Because entire galaxies simply are not that bright relative to how spread out they are. (And because GRBs are very brief events, not long-lasting glows.)

The Andromeda galaxy shines in the night sky for half the year, and it’s *much* closer to us than quasars. It isn’t quite as intrinsically bright, but it’s so much closer to us that it’s much brighter in the sky – but even then, it’s barely bright enough to make out with the naked eye. It’s not small in the sky: if you could see the whole thing, it’d be much larger than the Moon. If it were brighter, it [would look like this in the sky](https://pbs.twimg.com/media/BrkegNLCEAApc6K.jpg) – it just isn’t.