In 1998, two groups of astronomers announced that
the expansion of the universe is actually accelerating!
Astronomers had to find something brighter than Cepheid variable stars to measure
the distances to the very distant galaxies.
Type Ia supernovae all have the same peak luminosity, and are much brighter than
Movie of a supernova in Centaurus A (SN
1986G, Type Ia)
Type Ia supernovae were used to measure the distances to remote galaxies.
Observations of the most distant Type Ia supernovae (out to 7 billion light years)
showed that they appear dimmer than expected from the Hubble
law v = H0 r.
This implies that they are farther away than expected
and that therefore the expansion of the universe is accelerating.
? ? ? ? ? ? ? ? ? ?
But gravity can only act to slow the expansion by pulling everything in the
universe back together.
What is overpowering gravity and causing
the outward acceleration of the universe?
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