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

Objects ~60x Jupiter’s mass are big enough to start fusing and become stars. (See J0523)

So we have to limit “supermassive” to objects less than 60 Jupiters or they emit light.

Exoplanets can fit that bill but until recently our instruments weren’t sensitive enough or been observing long enough to catch planets with long years which means they were all close to their stars = hot.

Black holes and nebulas are objects that are very massive and very dark. They’re detected by their gravitational effect on other visible objects or how they block or scatter the light of objects behind them.