The Life of a Star: From Gaia observations to astrophysical properties

ESA Gaia based HR diagram animation extended with astrophysical properties and sun-like path of life…

This animation uses the Golden Sample of FGKM stars from Gaia Collaboration, Creevey et al. 2022 A&A to illustrate how the physical characteristics of the stars – temperature and luminosity – are derived from Gaia observations. Deriving these physical parameters in general is not an easy task as it requires precise knowledge of the distances and interstellar characterisation, and the ability to disentangle these and other properties from the Gaia spectra.

The Golden Sample of FGKM stars makes a selection of about 3 million stars based on the highest quality of Gaia data products, and results in a very clean temperature – luminosity diagram.

In the animation show the distribution of the FGKM sample on the sky. Then we organise the stars by using their Gaia observations of observed magnitude (phot_g_mean_mag) and colour (bp_rp, see Note). Then, the distance information is used (parallax) to transform the observed magnitude into the standard absolute system used in astronomy i.e. the brightness that an object would have if it were placed 10 parsecs away. The colour information is then corrected for the colour excess e(bp – rp) due to dust between us and the stars, and the intrinsic luminosity (lum_flame) is then derived by also considering the interstellar medium dust and the contribution to the full energy distribution that is not observed by Gaia – this latter is known as the bolometric correction. Finally the intrinsic colour is transformed to temperature (teff_gspphot).

A selection of 1-solar-mass stars with the same chemical composition of the Sun is then highlighted in orange. This sequence describes most of the lifetime of a star that is almost identical to the Sun. We call this its ‘evolution track’. We illustrate where the Sun would be placed if it were observed by Gaia at 4.57 billion years of age. We then show how the stars’ temperatures and luminosities vary depending on their age. Our Sun will reach a maximum temperature at approximately 8 billion years of age, then it will cool down and move right along this diagram while also slowly increasing in size. It reaches the base of the red giant branch, an almost vertical sequence, at around 10-11 billion years of age, and then rapidly moves up this vertical sequence while also increasing significantly in size. The end of the life of the Sun happens shortly after leaving the giant branch, where it will eventually finish as a cool dim white dwarf.

An interactive version of the animation is available at

Note. bp_rp is obtained from phot_bp_mean_mag – phot_rp_mean_mag

Acknowledgements: This animation was produced by Laurent Rohrbasser (Univ. of Geneva, Geneva, Switzerland), Krzysztof Nienartowicz (Sednai, Geneva, Switzerland), in collaboration with Orlagh Creevey (OCA, Nice, France), Laurent Eyer (Univ. of Geneva, Geneva, Switzerland), Celine Reyle (UTINAM, CNRS, Besancon, France)

Credit: ESA/Gaia/DPAC – CC BY-SA 3.0 IGO.

License: ESA/Gaia/DPAC videos are released under the Creative Commons license: CC BY-SA 3.0 IGO (



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