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Until the late 1990s, astronomers expected the expansion of the universe to be slowing down, because gravity between all the matter in the universe pulls it back.
In 1998, two teams measured the distances to very distant galaxies using type 1a supernovae. These are exploding white dwarfs that all reach almost the same peak luminosity, so they act as 'standard candles': measuring how bright one appears from the Earth gives its distance. Comparing these distances with the galaxies' red shifts showed that the distant supernovae were fainter, and so further away, than expected. The expansion of the universe is accelerating.
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Key terms in this lesson
- dark matter
- Matter that does not emit or absorb electromagnetic radiation, detected only through its gravitational effects, making up much of the universe's mass.
More in Astrophysics and Cosmology
- The Cosmological Principle
- The Doppler Effect and Red Shift
- Hubble's Law
- The Big Bang Theory
- Cosmic Microwave Background Radiation
- The Age of the Universe
- Evolution of the Universe
- Dark Matter
All 24 lessons in Astrophysics and Cosmology · All OCR A-level Physics topics