Answer: It can travel through empty space
Step-by-step explanation:
Let's begin by explaining that there are three ways in which the thermal transfer occurs:
1. By Conduction, when the transmission is by the direct contact.
2. By Convection, heat transfer in fluids (like water or the air, for example).
3. By Radiation, by the electromagnetic waves (they can travel through any medium and in vacumm) .
Hence, both conduction and convection need matter to transfer thermal energy, but by radiation there is no need of matter for the heat transfer.
So, since outter space is vacuum (sometimes called "empty" or "empty space"), energy cannot be transmitted by convection, nor conduction. Therfore, it must be transmitted by electromagnetic waves that are able to travel with or without a medium (by radiation).