Gravitational waves / Elementary Tour: Conclusion

Gravitational waves promise a glimpse into regions of our cosmos that are inaccessible to regular astronomical observation. In the past, whenever astronomers have opened a new window to the universe (for example, at the beginning of radio astronomy or X-ray astronomy), this has brought about new, and often unexpected, results for astrophysics. With gravitational waves, researchers hope for a similar leap forward.

With the first direct detection of gravitational waves in 2015, the gateway to gravitational wave astronomy was opened. Now an exciting time begins for astrophysics in which the new window to the cosmos can be explored in practice.

Elementary Einstein continues with a look at some compact objects that make promising sources for gravitational waves:

Next chapter: Black holes & Co.

Readers who would like to learn a bit more about gravitational waves first might want to check out the category Gravitational waves of our Spotlights on relativity.

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Definitioner

X-ray astronomy

Branch of physics devoted to the observation of X-rays reaching us from the depths of space. Such radiation is typically produced as the thermal radiation of matter at extremely high temperatures. An important example are the hot gases in the accretion disc of a black hole.

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.

waves (wave)

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

time

It is a fact of life that not all events in our universe happen concurrently - instead, there is a certain order. Defining a time coordinate or defining time, the way physicists do it, is to define a prescription to associate with each event a number so as to reflect that order - if event B happens after event A, then the number associated with B should be larger than that associated with A. The first step of this definition is to construct a clock: Choose a simple process that repeats regularly. (What is "regular"? Luckily, in our universe, all elementary processes such as a swinging pendulum, the oscillations of atoms or of electronic circuits lead to the same concept of regularity.) As a second step, install a counter: A mechanism that, with every repetition of the chosen process, raises the count by one. With this definition, one can at least assign a time (the numerical value of the counter) to events happening at location of the clock. For events at different locations, an additional definition is necessary: One needs to define simultaneity. After all, the statement that some far-away event A happens at 12 o'clock is the same as saying that event A and "our clock counter shows 12:00:00" are simultaneous. The how and why of defining simultaneity - a centre-piece of Einstein's special theory of relativity - are described in the spotlight topic Defining "now". With all these preparations, physicists can, in principle, assign a time coordinate value ("a time") to any possible events, and describes how fast or how slow processes happen, compared to that time coordinate.

radio astronomy

Branch of astronomy dedicated to the detection and evaluation of radio waves from outer space. Such observations have led to the discoveries of radio galaxies, quasars and pulsars.

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.

gravitational wave astronomy

Discipline of astronomy which aims at using gravitational waves to gain information about cosmic objects or the cosmos as a whole – for instance about what's happening in the core region of a supernova, about neutron star or about the heated past of our universe. Since 2015, scientists have been detecting gravitational waves using highly sophisticated gravitational wave detectors, so that the time of gravitational astronomy has now begun for real.

Gravitational waves / Elementary Tour: Conclusion

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