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The Question
(Submitted June 12, 1997)
What would happen to Earth's orbit if the Sun became a
black hole?
The Answer
Thanks for your question about the orbit of the Earth if
the Sun became a black hole. The Sun is not massive enough to
ever evolve into a black hole; it will end its life in about 4.5
billion years as a white dwarf star. But, perhaps you are asking
what would happen to the Earth's orbit if the Sun's mass was suddenly
collapsed into a black hole (not plausible,given our understanding of
stellar evolution, but an interesting theoretical question).
If a one solar mass black hole were to suddenly
replace the Sun at the center of our solar system, the orbits
of the planets would not change. This is because the physical
laws that determine the orbital motion of the Earth depend only on
the actual mass of the Sun, and not on whether it is distributed
within a sphere (like the Sun) or at a point (like a black hole). I hope
that answers your question.
Regards,
Padi Boyd,
for the Ask a High-Energy Astronomer
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