A lower limit of 9.5 Gyr on the age of the Galactic disk from the oldest white dwarf stars
Abstract
WHITE dwarf stars represent the final evolutionary state for most main-sequence stars. They cool slowly enough that even the oldest white dwarfs are still observable in sufficiently deep surveys and they therefore provide a record of the age and star-formation history of the local disk of the Milky Way1-7-and hence a useful constraint on the age of the Galaxy itself. Here we report the initial results of a very deep survey of white dwarfs, that avoids many of the problems associated with the incompleteness of earlier surveys. We use model age-luminosity relations to interpret the luminosity function of our sample of stars, and thus obtain a minimum age for the local Galactic disk of ~9.5 Gyr. Our results lend weight to an emerging picture of the evolutionary history of the Milky Way, in which the halo formed ~14-17 Gyr ago8,9, followed by the bulge globular clusters ~12-14 Gyr ago10, with a modest hiatus before the onset of star formation in the local disk ~10 Gyr ago.
- Publication:
-
Nature
- Pub Date:
- August 1996
- DOI:
- 10.1038/382692a0
- Bibcode:
- 1996Natur.382..692O