The coldest objects in the universe are supermassive black holes. The more massive the black hole, the colder it is.
Image: Alain R. (Wikimedia)
You don’t need a very heavy black hole to reach freekin’ cold temperatures. A black hole more heavy than Earth’s moon is already colder than the cosmic microwave background.
A black hole 6 times the mass of the sun is as cold as 10 billionth of a degree above absolute zero.
The heaviest known black hole weighs in at about 60 billion times the mass of the sun. That translates into a temperature a billionth of a billionth degree above absolute zero.