Conceptual Physics (12th Edition)

Published by Addison-Wesley
ISBN 10: 0321909100
ISBN 13: 978-0-32190-910-7

Chapter 36 - Think and Discuss: 60


We would need a radio telescope, or one sensitive to even longer wavelengths.

Work Step by Step

The energy of a photon is given by E = hf, where h is Planck's constant. The light from the astronauts climbs the gravitational well of the black hole, losing energy. If the energy of light is lowered, as in traveling upward in a gravitational field, its frequency is lowered (the light is said to be red-shifted). Light signals from the astronauts would be red-shifted to the low-frequency, long-wavelength domain of radio waves, and eventually to even longer wavelengths.
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