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SECTION 13.7 • Energy Considerations in Planetary and Satellite Motion 409 Figure 13.18 A binary star system consisting of an ordinary star on the left and a black hole on the right. Matter pulled from the ordinary star forms an accretion disk around the black hole, in which matter is raised to very high temperatures, resulting in the emission of x-rays. Figure 13.17 A black hole. The distance R S equals the Schwarzschild radius. Any event occurring within the boundary of radius R S , called the event horizon, is invisible to an outside observer. Black hole R S Event horizon Black Holes In Example 11.7 we briefly described a rare event called a supernova—the catastrophic An even more unusual star death may occur when the core has a mass greater than about three solar masses. The collapse may continue until the star becomes a very black hole. In effect, black holes are remains of stars that have collapsed under their own gravitational force. If an object The escape speed for a black hole is very high, due to the concentration of the mass of the star into a sphere of very small radius (see Eq. 13.23). If the escape speed S at which the escape speed is c is called the Schwarzschild radius (Fig. 13.17). The imaginary surface of a sphere of this radius surrounding the event horizon. This is the limit of how close you can approach the black hole and hope to escape. Although light from a black hole cannot escape, light from events taking place near the black hole should be visible. For example, it is possible for a binary star system to con- accretion disk around the black hole, as sug- gested in Figure 13.18. Friction among particles in the accretion disk results in transfor- |