Black Holes Help (page 3)

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By — McGraw-Hill Professional
Updated on Sep 17, 2011

Do Black Holes Really Exist?

There are plenty of stars that are more than three times the mass of the Sun. Astronomers agree that many of these stars have long since blown up, gone through their white dwarf phases, and presumably also gone through the collapsing process. This suggests that black holes comprise a significant proportion of the matter in the Universe.

As long as we can’t see them, we do not have a good way to find out if black holes exist. Fortunately, however, real black holes are not as black as theory implies. According to the research of the well-known cosmologist Stephen Hawking, black holes gradually lose their mass by emitting energy. This need not necessarily all be in the form of EM radiation; energy also can be lost as gravitational waves .

The idea of a gravitational wave was first made plausible when Einstein developed his general theory of relativity. Figure 14-8 is a simplified depiction of a gravitational wave as it leaves a black hole and travels through the space-time continuum. Just as a pebble, when dropped into a still pond, produces concentric, expanding, circular ripples in the two-dimensional surface of the water, so does the black hole produce concentric, expanding, spherical ripples in the three-dimensional continuum of space. Ripples are also produced in time—as hard as this might be to imagine!

Extreme Objects in Our Galaxy Matter And
Antimatter Do Black Holes Really Exist?

Figure 14-8. Some black holes should be expected to emit gravitational waves.

Gravitational-wave detectors have been built in an effort to detect ripples in space and time as they pass. Because they involve the very fabric of the Cosmos, such waves can penetrate anything with no difficulty whatsoever. A gravitational disturbance coming from the nadir (straight down as you see it while standing upright) would be every bit as detectable as one coming from overhead.

As of this writing, no conclusive evidence of gravitational waves has been found. However, astronomers are reasonably confident that they exist. The challenge is nothing more (or less) than continuing to refine the detection strategy until ripples in space and time are discovered and can be attributed to some real, however bizarre, celestial object.

When we expand our scope of observation to an intergalactic scale, there is other evidence for the existence of black holes.

Practice problems of this concept can be found at: Extreme Objects in Our Galaxy Practice Problems

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