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Fundamentals of Physics by David Halliday, Robert Resnick, Jearl Walker

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How can we tell what monster lies at the center of M87?

The answer is in this chapter.

A jet 5000 light-years long streams from the center of galaxy M87 (the bright spot at the upper left end of the jet), which is 5 × 107 light-years from us. The jet is formed by electrons moving at nearly the speed of light. Something very strange must be occurring at the center of M87 in order for the electrons to be ejected from it at such high speed. Is there some type of monster there? Unfortunately, M87 is too distant for us to see any object at its center.

  37-1   What Is Physics?

One principal subject of physics is relativity, the field of study that measures events (things that happen): where and when they happen, and by how much any two events are separated in space and in time. In addition, relativity has to do with transforming such measurements between reference frames that move relative to each other. (Hence the name relativity.)

Transformations and moving reference frames, such as those we discussed in Sections 4-8 and 4-9, were well understood and quite routine to physicists in 1905. Then Albert Einstein (Fig. 37-1) published his special theory of relativity. The adjective special means that the theory deals only with inertial reference frames, which are frames in which Newton’s ...

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