Age of universe fixed at 12bn years
The universe is a ripe 12 billion years old, according to an international team of scientists which has, for the past eight years, been studying the age of the cosmos using the Hubble space telescope. Nailing down the elusive "Hubble constant", used to approximate the age of the universe, was one of three major goals set when the telescope was launched in 1990.
The instrument and the constant are both named after Edwin Hubble, who discovered 70 years ago that galaxies were rushing away from each other, a consequence of the Big Bang. The constant is based on the fact that the galaxies are moving at a rate proportional to their distance from us, the farther away the faster the recession.
The expansion rate is measured in kilometres per second per megaparsec distance, a megaparsec being 3.26 million light years. Research estimates varied wildly, however, from 50km per second per megaparsec to 100km per second per megaparsec.
This led to serious problems. Scientists had decided that the oldest stars yet found were probably aged about 12 billion years, but this conflicted with some calculations which suggested that the universe was younger than this at a fresh-faced 10 or 11 billion years.
Variability continues, but now most astronomers can at least present data which prove that the universe is at least as old as the oldest stars. The Hubble team is amongst these, measuring the constant at 70km per second per megaparsec with an uncertainty of 10 per cent.
This sets the age of the cosmos at 12 billion years.