Light Beyond the Bulb: Bent Light in Space

Narrator (April Hobart, CXC): One of the most interesting characteristics of light is that the path that it travels can bend. This happens when light is moving through one medium like air, and then enters another medium like glass or water. We experience this all of the time here on Earth. Whenever we put eyeglasses on or insert contact lenses, we are taking advantage of the fact that we can bend the path of light so it can properly focus onto the retinas of our eyes. We also see examples of bent light in the slightly oval appearance of the setting Sun or when we think we see water on in the distance on a hot highway.

Light being bent is also very important when we want to learn about things in space. In fact, some of the most exciting discoveries made by the Chandra X-ray Observatory and other telescopes involve light that has been bent. Take, for example, the Bullet Cluster. This system contains two galaxy clusters that have rammed into one another at tremendous speeds. The collision was so violent that normal matter has been wrenched away from dark matter. While we can’t see the dark matter directly, we can learn where it is by light being lensed.

How does this work? When the light from very distant galaxies passes through a massive cluster of galaxies, like in the Bullet Cluster, the cluster can bend the path of the galaxy's light, in essence acting like a lens. From the vantage point of our telescopes, the distant galaxies appear distorted or elongated. Astronomers can use this information to build maps about where the dark matter is, which tells them more about this mysterious substance.

The ultimate light benders in the Universe are black holes, which can bend light rays into a closed loop so they never escape the black hole. Chandra has observed many black holes and their environments over the course of the mission. Whether they are the smaller black holes that are produced by the collapse of a giant star or the enormous supermassive black holes at the centers of galaxies, Chandra will continue to observe these objects that bend light in amazing ways across the Universe.