Hypothetical astronomical object

Various unknown astronomical objects have been hypothesized throughout recorded history.

For example, in the 5th century BCE, the philosopher Philolaus defined a hypothetical astronomical object which he called the "Central Fire", around which he proposed other celestial bodies (including the Sun) moved.

[1] Hypothetical astronomical objects have been speculated to exist both inside and outside of the Solar System, and speculation has included different kinds of stars, planets, and other astronomical objects.

Hypothetical types of extrasolar planets include:

Artist's concept of Earth, orbited by a hypothetical second moon
31 Crateris , a possible eclipsing binary initially mistaken for a moon of Mercury
Artist's concept of a carbon planet . The surface is dark and reddish from hydrocarbon deposits.
Artist's conception of HD 209458 b , a possible Chthonian planet , transiting its star