Bending Under Pressure: What Lies Beyond a Galaxy

Cosmology tells us that roughly only 5% of matter in the universe is made up of normal atoms and matter that we’re familiar with. However, when astronomers try to take account of the matter they can see inside of galaxies, they find something puzzling – some of it is missing! So, where could it possibly be? It turns out there’s a good chance that it’s not inside of galaxies at all, but completely outside of them in a hard-to-observe gaseous state. When there are thousands of galaxies clustered together, this gaseous medium gets hot enough for us to see it at X-ray wavelengths, but in smaller groups of galaxies (typically 10s of galaxies), it is still difficult to observe and account for...