eli5 why we never hear about supermassive objects which aren’t hot/bright

Question

For example, some giant “planet” the size of our sun which has a surface like the moon, floating through space in darkness.

Tangentially, how are we sure that black holes aren’t these? Are we misinterpreting absence of light as black holes when instead they could just be large dark objects?

In: 9

Answer 1

How would we see a massive dark object? With our giant space flashlight that can shine light across thousands of light years? Unless a dark object crosses in front of a bright object or disturbs it’s path through the sky (via gravity) we have no way of knowing it’s there.