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Unit 7: Astrophysics Page 50
detect large, dark objects like black If you toss a ball up in the air, it
holes and pulsars. The light from does indeed come back down. If
the distant objects they observe you toss it up higher, it does return
gets bent and distorted to form back to you. What if you toss it so
streaks and double-images on the high that it breaks free of the
camera. Earth’s gravitational pull and
escapes?
We call this special threshold speed
the “escape speed”. For the Earth,
it’s about 7 miles per second. For
the sun, it’s around 400 miles per
second.
This means you need to throw a
ball with a speed of 7 miles per
second in order for it never to
come back down. If you throw it
harder than this, it will not only
Gravitational Waves
escape but have enough speed to
An exciting area of science are
spare.
trying to figure out how to detect
gravitational waves. We did this with the Voyager
missions (which have just passed
General relativity predicts that
the heliosphere and are no longer
ripples in the fabric of spacetime
under the influence of the sun).
should travel at the speed of light.
Scientists named this effect What if we squeezed the Earth
gravitational waves. As of yet, we down to half its size? We still stand
have not been able to detect any. on the surface, but the Earth is
much more tightly packed
Scientists have been able to detect
together, and now you try to toss
that a gravitational wave was
the ball up in the air. What
present, but they have not been
happens to its required escape
able to find the wave itself.
speed? Did it increase or decrease?
Black Holes Since the mass of the Earth did not
True or false? “What goes up must change, the escape speed actually
come down.” increased. Now we need a much
faster speed to escape the pull of
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