Gaia: science essays
In these short (mostly 2-page, weekly) 'essays', I have picked out some of the scientific highlights of the Gaia mission as they are emerging, or as they caught my attention. They offer a somewhat chronological snapshot of some of the discoveries that Gaia is making across all of astronomy. I've also included some essays on related topics, including the history of astrometry, and some more technical, managerial, or developmental aspects of both the Hipparcos and Gaia missions. In each, I have included a footnote DR1, DR2, EDR3, DR3, etc to indicate which of the (latest) data releases the essay refers to (described in essays #10 and #76), with DR0 signifying technical or historical material not connected with any specific data release. Who are they written for? Anyone who might have a general interest in science and astronomy, including amateur astronomers, young scientists starting out on their careers, mid-career scientists looking in on Gaia for the first time to get a feeling of what is possible, and specialists looking in from different areas of astronomy, or physics more generally. Click on the access PDF icon to access the file. Only a few references are included, and these are 'discreetly' hyperlinked for those who want to read more... where references appear in the form (Einstein 1908) or www.gaia.com, clicking on the text (even though generally not highlighted!) should lead to the relevant online article. Essays 1-236 were published weekly, 237-241 monthly, and 242 onwards every two weeks. In a few cases, I've recorded an interview on the subject (see science interview page).
New: This table page lists all essays, updated to the end of June 2026 (1–235 inclusive), in tabular form. It includes a simple search on the title field.
New: These annual compilations are in both pdf and 'flipbook' form (open in new page; larger files as a download):
pdf:
flipbook:
New: The material in essays 1–239 is broadly included in my review "Space astrometry with Gaia: Advances in understanding our Galaxy" published in Physics Reports, Volume 1150, pp. 1–229 (January 2026): available here
New: This Gaia Science Tree (v4.0, June 2026) presents essays 1–235 (Jan 2021–Jun 2026) as a hyperlinked "mind map"
* all end-nodes are hyperlinked to the given essay number (links are to "legacy" copies at the CERN-Zenodo site)
* catalogue content topics are at top right, background material at bottom left, otherwise moving "outwards" clockwise in the diagram
* I have prepared this as a didactic tool. Please feel free to make use of it as you wish
I have converted Essays 1–130 into audio "discussion-type" podcasts, entirely using generative AI. They are available at my Gaia Essay YouTube channel, and I describe their construction in Essay 227.
Please make use of this subscribe page to receive an email (usually Monday) when each new essay is published
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124. Planetary nebulae
Known distances have gone from 40 to 2000
Planetary nebulae are the dust and gas shells ejected during the late asymptotic giant branch phase for intermediate mass stars, the ejecta being ionised by the radiation from the hot, evolving central star. Their modelling has been constrained by poor knowledge of their distances. With Gaia DR3, the number with good distances has gone from some 40, to around 2000.
15 May 2023
123. Using ADS citations in a Latex file
Do you struggle managing your citations?
I am deviating from my usual topic of scientific results from Gaia, and offer some suggestions about one aspect of using the ADS (Astrophysics Data System) bibliography in Latex documents. Whether to use, for citations, the 19-character code created by ADS, or your own ad hoc code. If you struggle with the management of citations, do read!
8 May 2023
122. The cosmic distance ladder
The big picture of where we stand at the moment
I give a big picture of where we are in establishing the cosmic distance scale, noting the `tension' that exists between the `early' and `late Universe' estimates of the Hubble constant. This, in turn, seems to imply that there is a problem with the late Universe distance `ladder'. I point to the areas where we are expecting Gaia to contribute in the future.
1 May 2023
121. Modelling stellar evolution
How Gaia is helping to improve our models
I will look briefly at the big picture involved in modelling stellar structure and evolution. I will point to some of the areas of stellar physics where Gaia is providing new constraints, and which are contributing to a number of ongoing model refinements. Playing their part are advances in software infrastructure, computer processing power, and data storage.
24 April 2023
120. Solar analogues – and our Sun
What these stars tell us about our Sun
Solar analogues are loosely defined as stars that are `very similar' to the Sun. Their identification provides the basis for a number of important applications across astronomy, including their value in determining the colours of our own Sun. Compared with some 100 candidates previously known, more than 5000 have already been identified in Gaia DR3.
17 April 2023
119. Brown dwarfs with Gaia
What can Gaia say about these faint objects?
Brown dwarfs are objects with masses below the hydrogen-burning limit. They are faint in the optical, with most isolated objects, even the nearest, close to Gaia's survey limit. Those in binary systems can be detected through the orbital motion of the brighter component. Many new brown dwarfs have already been discovered in Data Release 3.
10 April 2023
118. The `plane of satellites' problem
Gaia resolves one of the conflicts with the Lambda CDM cosmology
Since the emergence of the Lambda CDM parameterisation of the standard `big bang' cosmological model in the late 1990s, various difficulties emerged in reconciling numerical simulations with observations at galaxy scales. Here I describe the `plane of satellites' problem, and how Gaia EDR3 data has been used to resolve it.
3 April 2023
117. The Gaia phase-space spiral
Who wants to know about the phase-space spiral?
I have previously looked at some of the kinematic features that have been revealed, using the Gaia data, in the local stellar population. An important Gaia discovery has been rich structure particular prominent in plots of the vertical location in the solar neighbourhood versus the vertical velocity. I explain the nature of this `phase-space spiral', and theories as to its origin.
27 March 2023
116. The Arcturus and HR 1614 streams
Probing two more of the local kinematic groups
Following my previous essay, I look at two more of the two dozen or so kinematic groups known to exist in the solar neighbourhood: the Arcturus group and the HR 1614 group. Data in Gaia DR2 allow an unprecedented view of the local kinematic structure, and detailed studies suggest that both are `phase-space waves' that could have been cause by an ancient merger.
20 March 2023
115. The Hercules stream
Gaia provides convincing evidence for its origin
Stars in the local solar neighbourhood do not move at random, but instead include groups or streams of stars sharing a common bulk motion around the Galaxy. Their reality long debated, Gaia spectacularly confirms their existence. For the Hercules stream, accurate distances and motions confirm that it results from resonant motions driven by our Galaxy's rotating bar.
13 March 2023
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