Isophoric News · Tuesday, October 27, 2026
Study of Gaia star ages supports a model in which the Milky Way's thick disk formed first and later stars formed in ever-thinner layers
A study in The Astrophysical Journal Letters, led by David Mirabal of the Instituto de Astrofisica de Canarias, used Gaia data to work out precise ages for stars in the Sun's neighborhood and found that older stars sit in thicker layers of the Milky Way's disk, according to the paper's abstract and a Universe Today article carried by Phys.org. The authors report that the disk's vertical scale height fell steeply, from over 1.26 to about 0.5 kiloparsecs, in roughly two billion years, and then thinned only gradually, to about 0.1 kiloparsecs for the youngest populations. They say this points to an "upside-down" formation in which the oldest stars were born in a thick disk, not scattered into it later, and that it "strongly support[s]" a two-phase history; Mirabal said in a press release, as quoted by Universe Today, that it is the first clear observational evidence favoring one of two competing models. The work is observational and rests on stars in the solar neighborhood, which the abstract states as its sample, so it does not by itself describe the whole galaxy. The authors say their results support one scenario over the other; they do not call the question closed. Universe Today puts the change in thinning rate at about 10.8 billion years ago; the quoted passage of the paper gives about 10.85.
