Dating the Milky Way's Discsu201707 | www.cfa.harvard.edu/
https://www.cfa.harvard.edu/news/su201707
When a star like our sun gets to be very old, after another seven billion years or so, it will no longer be able to sustain burning its nuclear fuel.
With only about half of its mass remaining, it will shrink to a fraction of its radius and become a white dwarf star. White dwarfs are common, the most
famous one being the companion to the brightest star in the sky, Sirius. As remnants of some of the oldest stars in the galaxy, white dwarfs offer
an independent means of dating the lifetimes of different galactic populations.
A globular cluster is a roughly spherical ensemble of stars (as many as several million) that are gravitationally bound together and typically located
in the outer regions of galaxies. The white dwarf stars in the Milly Way's globular clusters reveal an age spread of between eleven and thirteen billion
years. By contrast, the thick disk of the galaxy is thought to be older than ten billion years but that figure is not very well constrained. White dwarfs
in the disc can be used to refine those age estimates and, since they are closer and brighter to us than those in globular clusters, they can provide
more detailed information. However, they are not located in well-defined regions like clusters and so they are also harder to spot.