In space, heat can be lost through a process called thermal radiation. While it is true that space is a vacuum and lacks particles for conduction or convection to occur, thermal radiation allows the transfer of heat energy in the form of electromagnetic waves, specifically infrared radiation.
Thermal radiation occurs due to the temperature of an object. Any object with a temperature above absolute zero (0 Kelvin or -273.15 degrees Celsius) emits thermal radiation. The amount and wavelength of radiation emitted depend on the object's temperature and its emissivity, which is a measure of how efficiently the object emits radiation.
When an object in space, such as a spacecraft or an astronaut, is exposed to the vacuum, it radiates thermal energy away in the form of infrared radiation. This radiation travels through space until it encounters another object, such as another spacecraft or celestial body. The heat energy is then either absorbed or reflected by that object.
It's important to note that in the absence of a medium like air or water, the rate of heat loss through radiation can be relatively slow compared to the rate at which heat is transferred in a conductive or convective environment. Nevertheless, over extended periods, thermal radiation is the primary method for heat dissipation in the vacuum of space. This is why spacecraft and satellites are designed with specialized thermal control systems to manage heat buildup and prevent equipment from overheating or freezing in extreme temperatures.