Sources of Gravitational Waves

Stirring Up the Ripples

Gravitational waves (Gravitational Wave: A gravitational disturbance that travels through space like a wave. This type of wave is analogous to an Electromagnetic Wave. Gravitational waves are given off by most movements of anything with mass. Usually, however, they are quite difficult to detect. Physicists are currently working hard to directly detect gravitational waves. Experiments like LIGO and LISA are designed for this purpose. ), like the ones shown distorting the boat on the last page, pass through the Earth constantly. Every ship that ever plied the ocean has run into both water waves and gravitational waves. The only difference is that gravitational waves are typically so extraordinarily small in amplitude (Amplitude: The height of the peak of a wave, measured relative to its center. Equivalently, the depth of the trough of a wave.) that it is nearly impossible to notice them.

One reason that the effects of gravitational waves are so small is that they get smaller the farther we are from their source. This is the same thing that we see with light. It's nearly impossible to look into a light bulb up close (and not recommended, unless you're trying to dodge a draft). But the light has to spread out over a much greater area when it shines far away, so its intensity must go down. From across the room, the light is much less bright and not painful at all. In just the same way, gravitational waves spread out when we are far away from them, and their amplitude goes down.

It turns out that nothing in the Solar System is good at creating big gravitational waves. No matter how close to the Earth-Sun "paddle" we get — even on it — we wouldn't notice the astoundingly miniscule waves coming out. There are two reasons for this. First, the curvature in the Solar System is never very large because gravity really isn't all that strong in our neighborhood. This means that the curvature can't change by much. Second, it doesn't change very quickly when things move on time scales like a month or a year. To produce gravitational waves with large amplitudes, an object must produce a lot of quickly-changing curvature. Everything in the Solar System is too soft, too weak, and too slow to do this. Astrophysicists have, however, discovered other things in the distant Universe capable of giving off gravitational waves intense enough to be measured on Earth.

Take a look through the below links to learn more about sources of gravitational waves, like white dwarfs (White Dwarf: A type of star which is very old, having cooled off and stopped nuclear fusion reactions. A white dwarf is supported by "electron degeneracy pressure" (no two electrons can be in the same place at the same time). These are produced when a star is not heavy enough to turn into a Neutron Star or a Black Hole. )}), black holes (Black Hole: A region of spacetime (Spacetime: A concept in physics which merges our usual notion of space with our usual notion of time.) where the warpage of both space and time (gravity) is so intense that nothing — even light — can ever escape. Objects may fall in to the Black Hole, but once they pass the Event Horizon (Event Horizon: A surface — like the one surrounding a Black Hole — enclosing a region of space from which nothing (even light) can ever escape.), they can never escape again. Most Black Holes believed to exist are thought to be formed in the collapse of very large stars, or the collision of stars or other Black Holes. )})|blackholes}), and even the Big Bang (Big Bang: An astrophysical theory of the beginning of the Universe. It suggests that the Universe began in a very tiny region of space, and exploded outward. Astrophysicists believe that this occurred roughly 14 billion years ago. Other astrophysical theories for the beginning of the Universe — like the Braneworld theory — exist, though none is as thoroughly studied and supported by the data as the Big Bang model. Scientists have no idea what came before the Big Bang.).