A Universe of X-rays (Light Facts #7)
X-rays are useful in doctor and dentist offices – and also for studying black holes and dark matter.
Dental X-rays are useful for detecting cavities. Credit: Wikimedia Commons/Dmitry G Most of us encounter X-rays when we have an unfortunate experience with a broken bone or cavity. The concept medical or dental X-rays is pretty simple. Place the thing you want to see inside of (bone, tooth, etc.) between two things: a machine that produces X-rays and then film or an instrument that can detect them. Where more X-rays pass through, you likely have a fracture or a cavity.
Centaurus A, an active galaxy about 12 million light years from Earth, shown in X-ray light collected by NASA's Chandra X-ray Observatory. Credit: NASA/CXC/U.Birmingham/M.Burke et al.
Far away from the doctor’s office, we find X-rays coming from other places that don’t involve machines. It turns out that many, many things in outer space generate X-rays by themselves. Objects in the Universe glow in X-ray light when they either have a lot of energy or are really hot, as in millions of degrees. In order to study the X-rays from space, scientists have to put their telescopes above the Earth’s atmosphere, which, thankfully, blocks this potentially-damaging light from ever reaching us here on the surface. Astronomers use X-ray telescopes to look at everything from material in its death spiral around a black hole to the blistering hot remains of an exploded star. Heck, even things like comets and planets can give off or reflect X-rays. Just think of that the next time you’re strapped into the dentist’s chair.