Why is the adjective capitalized?

Question

I have the following sentence where the adjective is capitalized, although there is a noun next to it:

Unser Kühlschrank ist wie ein Schwarzes Loch.

Is this correct or am I missing something here?

Answer 1

A "Schwarzes Loch" refers exclusively to the space phenomenon of high mass.
It's used here metaphorical: Their fridge swallows objects.

A "schwarzes Loch", however, is any very dark hole.