Here's why:

* Electromagnetic Radiation: Thermal radiation is a form of electromagnetic radiation. This means it consists of oscillating electric and magnetic fields that propagate through space.

* Speed of Light: The speed of light in a vacuum is a fundamental constant, approximately 299,792,458 meters per second (approximately 186,282 miles per second).

* No Medium Required: Electromagnetic radiation, including thermal radiation, does not require a medium to travel. It can propagate through the vacuum of space.

Important Note: While thermal radiation travels at the speed of light, the intensity of the radiation depends on the temperature of the object emitting it. Hotter objects emit more thermal radiation and at higher frequencies (like infrared or visible light).