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 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. My thanks go to many people: to all those I worked with on the Hipparcos and Gaia projects over almost 30 years, to those now dedicating huge reserves of their time, energy, and skill to the ongoing data processing, and to those who have entered into the Gaia catalogue and published the results described here. 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. In a few cases, I've recorded an interview on the subject (see science interview page).
New: As of early July 2025, 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.
As of July 2025, my essays will be monthly (on the first Monday of the month) until further notice.
This table page lists all essays, updated to the end of June 2025 (1–235 inclusive), in tabular form. It includes a simple search on the title field.
New: This Gaia Science Tree (v3.0, July 2025) presents essays 1–235 (Jan 2021–Jun 2025) 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
Please make use of this subscribe page to receive an email (usually Monday) when each new essay is published
Essays through to the end of 2023 (1–156 inclusive) also appear in a hyperlinked indexed form in the Bulletin of the American Astronomical Society (BAAS Vol. 56, Issue 1, 15 March 2024): ADS 2024BAAS...56a.008P
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213. Telescope calibration/pointing: 1
Star positions are needed to point and calibrate telescopes
Gaia is making substantial contributions to the improved calibration and pointing of ground- and space-based telescopes. Here, I look first at what is now largely consigned to history - how the first space astrometry positions from Hipparcos were applied to the calibration of photographic plates and meridian circles.
27 January 2025
212. Runaway stars in R136
Many more runaways with cosmological implications
Gaia has recently identified 55 massive runaway stars in the young cluster R136 in the LMC, increasing the known number by an order of magnitude. They fall into two groups, an isotropic sample ejected soon after the cluster's birth, and 16 ejected in a preferentially northern direction. I discuss the interpretation, and the cosmological significance.
20 January 2025
211. The end of Gaia operations
Gaia operations end on 15 January 2025, after more than 10 years
In just two days from today, on 15 January 2025, the Gaia satellite will cease its science operations. More than 10 years of spectacular astrometric (and related) observations of unprecedented accuracy, number, and magnitude range, will come to an end. I'll provide some details.
13 January 2025
210. SETI, Game Theory, and Gaia
Some clever ideas for SETI searches
The challenges in searching for extraterrestrial intelligence are compounded by the multiple dimensions of potential search space. The problem can be simplified if the task is considered of mutual interest to both parties. In that case, appeal can be made to `game theory' to establish more efficient search strategies.
6 January 2025
209. A selection of journal plaudits
Some nice recognition for those involved in space astrometry
I will end this fourth year of my weekly essays on Gaia with some of the positive words that have appeared in the scientific literature about the mission’s advances. I hope they make enjoyable reading, especially for those involved in Hipparcos or Gaia.
30 December 2024
208. Gaia science highlights to 2024
Some of the highlights of Gaia's scientific achievements to date
In my previous essay, I gave an overview of the many scientific areas being impacted by Gaia, divided into five categories: solar system; the photometry and RVS spectra; stellar physics; Galaxy structure and dynamics; and cosmology. Here, I will say more on some of the highlights to date.
23 December 2024
207. Gaia science synopsis to 2024
A very short overview of Gaia's scientific achievements to date
I give a concise ‘run through’ of the scientific areas impacted by Gaia so far. I divide this into five categories: solar system; applications of the photometry and radial velocity spectrometer (RVS) spectra; stellar physics; Galaxy structure and dynamics; and local group and cosmology.
16 December 2024
206. Alerts - and tidal disruption events
More evidence for supermassive black holes
Tidal disruption events, or TDEs, result from a star passing sufficiently close to a supermassive black hole that tidal forces overcome its self-gravity. Predicted 50 years ago, some 100 such events are now known. The Gaia science alerts system has discovered 25, and I will describe what is known about the two brightest, Gaia19bvo and Gaia19eks.
9 December 2024
205. Two unusual microlens alerts
Surprising phenomena in microlen systems
I look here at two other interesting microlens systems discovered by means of the science alerts pipeline: Gaia19dke, a long-duration single-lens event but with multiple peaks, and Gaia19bld, an event in which rotating arc-like images have been spatially resolved for the first time.
2 December 2024
204. The unique AM CVn Gaia14aae
Unique amongst a rare class of important objects
AM CVn systems are a rare class of compact interacting binaries, distinguished from other cataclysmic variables by the absence of hydrogen in their spectra, and affected by the poorly modelled process of common envelope evolution. The 5th Gaia alerts object, Gaia14aae, is only the third known eclipsing AM CVn system, and the first in which the white dwarf is fully eclipsed.
25 November 2024
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