Some proposals were designed to explain the notorious riddle of Mercury’s perihelion shift: The longitude of the planet’s closest approach to the Sun kept advancing by the small but mysterious angle of 43 seconds of arc per century, and no known Newtonian forces could account for it. Nevertheless, no other great prediction of Einstein’s geometric theory of gravity stands today so far from triumphant exploitation.Heaviside’s work does not appear to have made much of an impression on Zenneck, who relegates it to a footnote, but Zenneck does describe the work of several other contemporaries who likewise assumed that gravitational effects propagated at the speed of light. None pushes to a higher pitch the art of detecting a small effect, and none gives more promise of providing an unsurpassable window on cataclysmic events deep inside troubled stars. Of all the workings of the grip of gravity, none is more fascinating or opens up for exploration a wider realm of ideas than a gravity wave. Energy once resident as mass in the interior of a star has radiated out to us and to all the universe. Because it can change distance, it can do work. The same reasoning applies to a gravity wave. After all, the ability of a water wave to change a distance lets itself be translated into the ability to do work. The idea of extracting energy from ocean waves is old. There is no theoretical upper limit to its mass. A black hole of three solar masses would have a "radius" of about 9 kilometers. A black hole can have a mass as small as a few times the mass of our Sun.
Strong evidence for the existence of black holes has been found, but it is not yet convincing to all astrophysicists. No one who accepts general relativity has found any way to escape the prediction that black holes must exist in our galaxy. Even light cannot escape from a black hole, whence its name.
As of 1990, nearly 500 pulsars have been identified.Ī black hole is an object created when a star collapses to a size so small that strong spacetime curvature prevents it from communicating outward with the external universe. Because of this behavior, such neutron stars are called pulsars. The periodic shock to the electrons of the plasma from the periodic arrival of this field excites those electrons to radiate periodic pulses of radio waves and visible light _ both observed on Earth. When that field is aligned at an angle relative to the axis of spin of the star las in Earth, for example), it sweeps around like a giant whisk brush through the plasma in the space around the star. A neutron star typically has an immense magnetic field. Many neutron stars spin rapidly - with a period as short as a few milliseconds.
Neutron stars were predicted in 1934 but not observed until 1968. The core that remains becomes a neutron star in some events, it is believed, in others a black hole. This explains the spectacular luminosity that is such a prominent feature of a supernova. That region thereupon acts like a spring, or explosive charge, and drives off the outer portions of the star. The Niagara Falls of infalling mass in some cases go too far and overcompress the inner region of the star. In such an event a star teetering on the edge of instability finally collapses. How often is a neutron star formed? Towards answering this still open question we have one important lead: In our own galaxy we see one supernova explosion on average about every 300 years. mirror-to-mirror distance reveals a momentary change in the three-dimensional geometry of space itself. The radius of a neutron star is approximately 10 kilometers. \), or one Earth mass per cube of edge length 400 meters.
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