Vacuums, such as the vacuum of space, contain no matter of any type. Usually, one thinks of the vacuum as having no atmosphere (essentially negligible pressure) but there's a lack of solids or liquids as well. The vacuum does however often contain photons. This doesn't stop it from being a vacuum, because photons do not contain matter—just energy. This is how the vacuum can still exist at some temperature above absolute zero: the photons allow it to have that thermal energy without having matter. See Figure 1 to see the vacuum of space.
For Further Reading
- Law and R. Rennie, A dictionary of physics. Oxford: Oxford University Press, 2015.
- NASA, accessed: https://earthobservatory.nasa.gov/images/44267 on August 26th, 2018.