Gaia: science essays

114. Our Galaxy's spiral arms

While it is well established that our Milky Way is a barred spiral galaxy, the detailed structure of its spiral arms is difficult to establish since our vantage point lies deep within the disk. Despite the ubiquity of spiral galaxies, even the driving mechanism of spiral arms remains unclear. The millions of stars with accurate astrometry in Gaia DR3 is casting new light on this long-standing question.

6 March 2023

113. Gravitational redshift

General relativity predicts that light escaping from a gravitational potential well, such as the surface of a star, will be redshifted, by some 636 km/s in the case of our Sun. The effect is most pronounced for white dwarfs. Gaia astrometry is furthering these studies, and allowing the effects to be characterised for main sequence stars in open clusters and wide binaries.

27 February 2023

112. Our Galaxy's central bar

While it has long been suspected that our own spiral Milky Way galaxy has a central bar, its structure, its orientation, and its pattern speed, are still subject to much debate. Gaia is helping to pin down all of these properties. Remarkably, Gaia's vast compilation of accurate stellar orbits provides a measure of the bar's deceleration!

20 February 2023

111. The distance to the Galactic centre

The distance to the Galactic centre is arguably the most fundamental distance entering treatments of our Galaxy's structure and dynamics, but it has been notoriously difficult to measure. A novel method, based on the kinematics of the bar region at the centre of the Milky Way, brings a new and fundamental approach to determining this important quantity.

13 February 2023

110. Variation of the gravitational constant

According to our present understanding of the laws of Nature, the gravitational constant (G) does not vary, neither across space, nor time. Measuring any variation over cosmological time would be important in confirming or challenging our present understanding. Measuring such changes is possible, and I explain how Gaia may contribute.

6 February 2023

109. The tidal tails of Palomar 5

Palomar 5 is a faint globular cluster 20 kpc from the Sun. Its two tidal tails, evidence that the cluster is experiencing heavy mass loss, have been known since 2001. With the form of the tails being sensitive to the shape of the Galactic halo, and with longer tails being more constraining, Gaia is contributing to their understanding.

30 January 2023

108. White dwarf physics

Continuing on the subject of white dwarfs, I look at two other aspects that Gaia is helping to characterise. The white dwarf sequence in the colour-magnitude diagram reveals new insights into their composition and mass, and also into the physical processes accompanying their cooling over cosmological time scales.

23 January 2023

107. The white dwarf mass-radius relation

Theories of white dwarf interiors predict a relation between mass and radius that depends on their core composition and temperature. But accurate empirical confirmation is challenging. Results from Gaia DR2 show good agreement with predictions, confirming stellar degeneracy, while raising new questions.

16 January 2023

106. The remarkable cluster Westerlund 1

At a distance of about 4 kpc, the young compact star cluster Westerlund 1 contains many rare, evolved, high-mass stars, including red supergiants, yellow hypergiants, one of the largest known stars, and 24 Wolf-Rayet stars. Gaia is pinpointing its distance and its members, and resolving the puzzling question of its age.

9 January 2023

105. Wolf–Rayet stars

Wolf-Rayet stars are the final He-burning phase in the evolution of massive O stars, the last observable stage before core collapse. They are rare, but have an enormous influence on their environment. Distances were only poorly constrained before Gaia, which is now having a significant impact on their detailed understanding.

2 January 2023