Very Old Stars

The determination of the age of the universe

"The spectra obtained of this comparatively faint star are absolutely superb - indeed of a quality which until recently was reserved for naked-eye stars only. Despite its faintness, the uranium line can therefore be measured with very good accuracy."

Roger Cayrel, Paris Observatory
ESO Observations

Astronomers have used the Very Large Telescope to perform a unique measurement that paves the way for an independent determination of the age of the Universe. They measured for the first time the amount of the radioactive isotope uranium-238 in a star that was born when the Milky Way, the galaxy in which we live, was still forming. See ESO Press Release eso0106.

Like carbon-dating in archaeology, but over much longer timescales, this uranium 'clock' measures the age of the star. It shows that the star is 12.5 billion years old. Since the star cannot be older than the Universe itself, the Universe must be even older than this. This agrees with what we know from cosmology, which gives an age of the Universe of 13.7 billion years. The star, and our Galaxy, must have formed very soon after the Big Bang.

Another result pushes astronomical technology to its limits, and throws new light on the earliest times in the Milky Way. Astronomers made the first ever measurement of the beryllium content in two stars in a globular cluster. With this, they studied the early phase between the formation of the very first stars in the Milky Way and those of this stellar cluster. They found that the first generation of stars in the Milky Way galaxy must have formed soon after the end of the ~200 million-year long 'Dark Ages' that followed the Big Bang. See ESO Press Release eso0425.