Gaia: science essays

260. Sub-halos and the Milky Way disk

In addition to the use of stellar streams to detect dark matter sub-halos of intermediate mass, recent studies have shown that the motions of these predicted sub-halos will leave a kinematic imprint on the velocity field of nearby disk stars. They may explain part of the well-known Gaia phase-space spiral, or `Gaia snail'.

21 September 2026

259. More on streams and sub-halos

Our Galaxy halo is believed to be highly clumpy, with large numbers of high-velocity dark-matter sub-halos orbiting within it. They act as gravitational `bullets' that can punch through the relatively static stellar streams now known to exist within it, resulting in gaps along the stream's length. Searches and characterisation of these gaps are ongoing.

7 September 2026

258. The Raritan and Passaic streams

Using a new search method, borrowed from the field of high-energy particle physics, another unsupervised machine-learning algorithm for anomaly detection has discovered many more stellar streams. Amongst them are two complex clusters of streams, each covering some 30-40 degrees on the sky. Their nature is currently unknown.

24 August 2026

257. More globular cluster stellar streams

More than 100 stellar streams have been discovered in our Galaxy's halo, mostly with Gaia. They are remnants of globular clusters or dwarf galaxies captured by our own over its multi-billion year history. A new study, using an interesting `spray model', has found 34 streams associated with the 156 known globular clusters of the Milky Way.

10 August 2026

256. The edge of our star-forming disk

An important feature of spiral galaxies is the form of the light profiles in their outer disks, and how this compares with cosmological predictions in view of radial migration driven by bars or transient spiral arms. Gaia is contributing to an understanding of these effects in our own Galaxy, with interesting implications for the stellar age profile beyond the solar circle.

27 July 2026

255. The tidal tails of open clusters

The first hints of extended tidal tails associated with open clusters pre-dated Gaia. But their occurrence, extent, and complexity has only become evident with the Gaia data. With more than 50 now known within 500 pc, their shapes encode a wealth of information about the clusters and their Galactic environment.

13 July 2026

254. Planet engulfment - and the Sun

Binary systems offer an important testing ground of the idea that some stars may have engulfed one of their orbiting planets. Specifically, if one component is unusually rich in refractory elements, this might point to a past planetary engulfment. Gaia is making a number of contributions to this debate.

29 June 2026

253. The oldest stars

For a handful of stars, current models of stellar structure and evolution provide age estimates which sit uncomfortably close to our estimate of the age of the Universe itself. Larger statistical samples constructed from the accurate and homogeneous Gaia data are providing a more robust `cosmic clock'.

15 June 2026

252. The Great Wave

The Galaxy disk is no longer thought of as simply `flat'. In the 1950s it was shown to be warped. Gaia has revealed other dynamical and morphological structures, including the `phase-space spiral' and the Radcliffe Wave. Recent studies have revealed a much vaster distortion, the Great Wave.

1 June 2026

251. Binary open clusters

The first hints that open clusters are sometimes found in pairs emerged in the 1970s. Today, binary clusters provide insights into cluster formation, star formation, and tidal interactions. New discoveries and detailed kinematic studies with Gaia DR3 are consolidating this picture.

18 May 2026