In the 1st year of the period (Period: The length of time between two events. For a wave, this is usually the length of time it takes two successive peaks to pass a given point. This number is simply 1 divided by the Frequency of the wave.) Chih-ho, the 5th moon, the day chi-ch'ou, a guest star appeared...
Yang Wei-T'e, Imperial Astronomer of the Sung Dynasty, 1054 A.D.
Starting July 4, 1054 A.D., the people of the world were treated to an astonishing spectacle. A new star appeared in the sky. For 23 days, it was visible even during daylight. The star gradually faded following its appearance on July 4. After a little more than a year, the event was over entirely. It could no longer be seen, even at night. Its brief glory was recorded by Chinese and Korean astronomers, as well as American Indians of the Southwest United States. The witnesses to that singular event in 1054 were seeing a Supernova (Supernova: Violently exploding stars which shine very brightly for days or weeks. They occur when the fuel for nuclear reactions is used up, and a star cools. Gravity pulls all the matter down toward the star's center. If this happens quickly, nuclear reactions may suddenly begin again, detonating the star in a nuclear explosion. )})|supernovas}).
We've seen that old stars use up their fuel, cool off, and settle down into a White Dwarf (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. )})|white dwarves}), Neutron (Neutron: One of the particles in an atomic nucleus. These particles have no electric charge, but they hold together the protons (positive particles in a nucleus), and account for roughly half of the particles in the nucleus. Neutrons are fermions, and are believed to form the majority of the matter in a neutron star.) Star (Neutron Star: A type of star which is very old, having cooled off and stopped nuclear fusion reactions. When gravity pulls the star down on itself, the electrons and protons are squeezed together, leaving just neutrons. The star is then supported against gravity by "neutron degeneracy pressure" (no two neutrons can be in the same place at the same time). These are produced when a star is too heavy to be a white dwarf, but not heavy enough to turn into a Black Hole. )}), or Black Hole (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 (Black Hole: A region of spacetime 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, 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}) believed to exist are thought to be formed in the collapse of very large stars, or the collision of stars or other Black Holes. ). This usually doesn't happen very peacefully, however. The cooling is like a chair being tipped over. It is steady until it reaches the tipping point. Once it passes that point, it goes faster and faster. Soon, however, the inner layers of the star — its most dense part — will be stopped from falling by electron (Electron: A tiny particle usually found swirling around an atomic nucleus (Nucleus: The central part of an atom, which contains Neutrons and Protons. Electrons are usually found around the Nucleus. Strictly speaking, this is the only part of an atom involved in Nuclear Reactions (Fission or Fusion). )}), the electron carries the standard unit of negative charge, which balances the positive charges in a nucleus. The interaction between electrons (Electron: A tiny particle usually found swirling around an atomic nucleus, the electron carries the standard unit of negative charge, which balances the positive charges in a nucleus. The interaction between electrons and nuclei is responsible for chemistry. Electrons can become detached from the nucleus, when given enough energy, and become free. Electrons are members of the particle class called fermions (Fermion: A type of particle with "odd half-integral angular momentum" — a spin (Spin: An intrinsic property of particles. (That is, a property which does not change. Mass and electric charge are examples of intrinsic properties.) Spin is related to the usual notion of spin, though it is a little more difficult to understand. Spin comes in units of 1/2, so that a particle may have a spin of 0, 1/2, 1, 3/2, and so on. A particle's spin determines whether it is a Fermion or a Boson.) of 1/2, 3/2, etc. Spin refers to an intrinsic quality of all particles. Examples of fermions are electrons, neutrons, and protons. The other type of particle is the boson. ), and are roughly 2,000 times lighter than neutrons and protons. ) and nuclei is responsible for chemistry. Electrons can become detached from the nucleus, when given enough energy, and become free. Electrons are members of the particle class called fermions, and are roughly 2,000 times lighter than neutrons and protons. ) or neutron degeneracy pressure as the core changes into a miniature White Dwarf or Neutron Star. The falling matter from above will suddenly crash into this inner layer, and change too. The fall and crash happens in just seconds. All this sudden crashing and changing gives off enormous amounts of energy. That energy heats up the outer layers of the star and blows them out into space with fantastic speed (Speed: For a wave, the speed of a particular point (such as its crest).). At its peak, a typical supernova might shine ten billion times more brightly than our Sun! Luckily, we are usually far enough away that this isn't too bright.
With such sudden movements of matter, the intense warpage of spacetime will change drastically and quickly. It should not be surprising, then, if 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. ) are given off by a supernova. In fact, gravitational waves will only come out if the supernova has some "asymmetry" — that is, only if the supernova has bumps. This will likely happen, for example, if the original star was rotating very quickly. Fortunately, we expect most supernovae to go off in this way. Then, the gravitational waves will come out as one big — though brief — burst.
Carl Sagan said, "We are star stuff." He meant that we are made of matter that came from the stars. The Oxygen we breathe, the Carbon found in every cell in our bodies, the Calcium in our bones... all of this was formed in stars. Without supernovae to blow all this star stuff into the wide cosmos, however, it would all still be trapped deep inside of those stars. These most violent of explosions breathe life into the Universe.
Check out other sources of gravitational wavesRead about Numerical Relativity (Numerical Relativity: The branch of Relativity research which deals with simulating the development of Spacetime, using computers. This is believed to be the only possible way to understand things like the merger of two Black Holes.)