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PSR1913+16

A specific binary system consisting of two orbiting neutron stars, one of which is a pulsar from which we here on Earth receive regularly spaced radio pulses. From the point of view of general relativity, the system is interesting not only because, using the pulses, one can measure effects such as Shapiro delay with impressive precision, but because it has given us the first indirect proof for the existence of gravitational waves: the orbital period of the two stars becomes slightly shorter with each orbit, exactly in the way predicted by general relativity due to the energy the system radiates away in the form of gravitational waves.

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waves (wave)

In a general sense: any travelling pattern, whether or not it involves matter being transported as well. Simple examples are water-waves - wave crests and troughs travelling over a water surface, and a Mexican wave in a football stadium, with fans alternately standing up and sitting down - the pattern moves throught the stadium, not the fans themselves.

An especially simple form for a wave is a sinus wave, a regular pattern of wave crests and troughs.

gravitational waves

Distortions of space geometry that propagate through space with the speed of light, analogous to ripples on the surface of a pond propagating as water waves. For more informations about gravitational waves, please consult the chapter Gravitational waves of Elementary Einstein. Selected aspects of gravitational wave physics are described in the category Gravitational waves of our Spotlights on relativity.

energy

Physical quantity with the special property that, in physical processes, energy is neither destroyed nor created, simply transformed from one form of energy to another. Some of the different forms of energy that are defined separately are kinetic energy, thermal energy and the energy carried by electromagnetic radiation. Processes that transform one form of energy into another take place in all machines we use in everyday life, from the engine of a subway train (electrical energy into kinetic energy of the train) to an electric blanket (electrical energy into thermal energy). One important consequence of special relativity is that energy and mass are completely equivalent - two different ways to define what is, on closer inspection, one and the same physical quantity. See the keyword equivalence between mass and energy.

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PSR1913+16

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