[DexesTTP]

Not quite that, we've known about galaxies outside our own (like the Magellanic clouds or the Andromeda galaxy) for a few millenia, and the main reason black holes haven't been discovered for a while because they're black and we needed a theory to know where to look. The current theory of cosmology has overall been pretty stable for a while.

What's interesting there isn't that much the object themselves which are bog-standard as far as celestial objects go, but how red-shifted (and therefore how far away/long ago) they are, which is something the model doesn't quite exclude but does warrant some tweakings of the "initial parameters" of the universe to make it work this way compared to what we expect.

[Hemospectrum]

> we've known about galaxies outside our own (like the Magellanic clouds or the Andromeda galaxy) for a few millenia

Well, we could see them, but we weren't able to distinguish a galaxy from a nebula until after investing multiple centuries into the development of powerful telescopes.

[actionfromafar]

But did we know they were galaxies and not just some shining object?

[macintux]

Their nature wasn’t confirmed until the 20th century. Wikipedia tackles the history: https://en.wikipedia.org/wiki/Andromeda_Galaxy

[ahazred8ta]

> In 1924, Edwin Hubble established the distance to classical Cepheid variables in the Andromeda Galaxy, until then known as the "Andromeda Nebula" and showed that those variables were not members of the Milky Way. Hubble's finding settled the question raised in the "Great Debate" of whether the Milky Way represented the entire Universe