Universe Doesn't Look a Day Over 12 Billion Years Old
(From the July/August 1999 issue of StarDate magazine)
The universe is about 12 billion years old, according to an international team of astronomers that studied the motions of distant galaxies for the past eight years. The figure agrees fairly well with estimates of the ages of the oldest stars in the universe.
The team of 27 astronomers used Hubble Space Telescope (HST) to obtain a more accurate measurement of the expansion rate of the universe, called the Hubble constant.
Modern cosmology says the universe was created in the Big Bang, a single instant of birth for matter, energy, space, and time, and has been expanding ever since. The gravity of all the matter in the universe acts like a brake, slowing the expansion. The Hubble constant provides an exact measurement of how quickly the expansion rate has slowed. That number, combined with an estimate of the total mass of the universe, allows astronomers to measure the age of the universe. In recent decades, various measurements of the Hubble constant yielded an age range of less than 10 billion years to about 20 billion years.
The HST team observed 18 galaxies up to 65 million light-years from Earth. It found about 800 pulsating stars, called Cepheid variables, in these galaxies. By precisely measuring a Cepheid's pulsation rate, astronomers can accurately determine its distance. This allowed the HST team to calibrate different techniques used to measure the distances to even more remote galaxies.
After eight years of work, the team concluded that the Hubble constant is 70 kilometers per second per megaparsec of space. In other words, a galaxy appears to be moving about 160,000 mph faster for every 3.3 million light-years distance from Earth. The team also assumed that there is not enough mass in the universe to cause it to eventually stop expanding. The two factors combined yield an age of 12 billion years, with an accuracy of 10 percent, the astronomers say. -- — Damond Benningfield
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