Everything emits light with intensity directly proportional to how hot it is. Even you, or a loaf of bread. The phenomenon is called black body radiation, and it is why metals “glow” when they are super hot. Cold objects don’t emit very much light, and it is lower intensity. But it takes energy to create light. Everything is slowly losing energy by this process. Since light can travel through a vacuum, stuff still loses energy in space.
Side note: Objects in orbit with the sun hitting them will be heated to 120C. Heat is generally bad for electronics, so a lot of thought is put into cooling stuff in space. The solution is basically a heat sink that operates using black body radiation instead of air cooling. You can dump a significant amount of energy with a big enough surface area pointing away from any heat sources.
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