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The Question

(Submitted July 17, 2003)

What is the best current estimate of the age of our galaxy compared to the time since the big bang?

The Answer

There was a review article in the magazine Science by Lawrence M. Krauss and Brian Chaboyer (Vol 299, page 65, 3 January 2003). If you have access to a library with a subscription to Science, you might want to read the actual article. Here is a brief summary.

There are three independent ways to infer the age of the oldest stars in our galaxy.

Radioactive dating (using Thorium 232 and Uranium 238, both radioactive elements with half-life in billions of years) gives 14.0+/-2.4 billion years for a star called CS 31082-001.

White dwarf cooling method suggests 12.7+/-0.7 billion years (observational errors only, that of the cooling model not included).

The main-sequence turn-off timescale method for oldest globular clusters gives the best estimate of 12.6 billion years and the 95% confidence range of 10.4-16 billion years.

In contrast, the time since Big Bang is estimated to be about 13.7 billion years:
http://map.gsfc.nasa.gov/m_mm/mr_age.html

Best wishes,

Koji & Scott
for "Ask an Astrophysicist"

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