system
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human
Why do spaceships get cold in space? What absorbs the heat energy?

I have a very limited understanding of the law of conservation of energy from my intro to physics class in a social science degree. My understanding is that for one thing to get cold, heat energy from that thing has to transfer to other matter.  Or something like that. So in space, where there is no matter, where does the heat go from the space ship  causing it to get cold?
gpt
There are three main ways for heat to transfer out of a substance to it's surroundings:

Conduction - transfer from particle to particle, which happens mainly in solids, (and best in metals).

Convection - which happens by the movement of particles, where a local group particles becomes more energetic, decreases in density, and rises in the surrounding material, taking the energy with it.

Radiation - the emission of radiation, which takes the energy away by electromagnetic (EM) waves. E.g infra-red (or even visible light if something is hot enough that it glows!)

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In space, there are very few particles; not zero though - space isn't a perfect vacuum.

This means that Conduction and Convection are not very effective in transferring heat here; also that there aren't many particles around that can hold energy, act as an insulator, or bring energy to the spacecraft.

The result of this is that the main method of heat transfer in space is the radiation of energy by EM waves. The spacecraft can radiate energy away and cool down. If it is in direct sunlight, the opposite can be true - the radiation from the Sun can cause the craft to heat up. For the reasons above, it can be hard to get rid of the excess heat if it is not designed correctly.