With the help of two Harvard researchers, one of the great mysteries of the cosmos is closer to being solved.

Earlier this week, members of the Hubble Space Telescope (HST) research team announced a new estimate for the universe's age, in one of the team's greatest achievements since the telescope's launch nine years ago.

The team, including Professor of Astronomy John P. Huchra, combined information from the telescope and measurements of the universe's acceleration, compiled in part by Professor of Astronomy Robert P. Kirshner '70, for the new estimate.

Their estimate of 12 billion years for the universe's age is much more accurate than previous estimates, given at somewhere between 10 and 20 billion years.

"We used to disagree by a factor of two...[that's] like being unsure if you have one foot or two," Kirshner said.

The HST Key Project Team, which includes Huchra, made independent measurements of the relative distance of different galaxies as well as the speed at which they are moving away from the Earth.

The relation between an object's distance and the speed at which it is receding is represented by what astronomers call the Hubble constant. Discovery of the constant would lead to an estimate of the age of the universe.

While astronomers earlier had a less accurate estimate of the Hubble constant, the team's work has provided a narrower estimate--and thus a better estimate of the universe's age.

Research

To complete their research, the team focused on the principle that an object

appears dimmer when it is farther away.

The researchers relied on Cepheid variable stars, whose brightness is constant and measured, as an indicator of distance of the remote galaxies.

In addition, they measured the stars' "red shift," which indicate the speed at which the stars are receding. Together, the speed and velocity measurements helped the researchers to target the Hubble constant.

Researchers previously believed that the Hubble constant was between 50 and 100. The new research of Cepheids gives an estimate of 70 for the constant, with a 10 percent margin of error.

Finding the Hubble constant was "a driving force" behind the design of the Hubble telescope, and the primary goal of the Hubble telescope mission, said Ed Weiler, NASA associate administrator for space science.

Combined with the best current measurements of the universe's density, the Hubble constant led scientists to their estimate of 12 billion years for the universe's age.