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: This table page lists all essays, updated to the end of December 2024 (1–209 inclusive), in tabular form
New: This Gaia Science Tree (v2.0, Jan 2025) presents essays 1–209 (Jan 2021–Dec 2024) 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
218. Red supergiants: the biggest stars
Puzzling stars whose photospheres would extend beyond the orbit of Jupiter
The biggest stars have radii some 1500 times that of the Sun. Although extremely luminous, their detection poses a number of challenges, and their large distances make them difficult to characterise. I explain their importance for understanding stellar evolution, and the ways in which Gaia is contributing.
3 March 2025
217. Zero-point of the Gaia parallaxes
An explanation of why the offset arises, and how it's characterised
I explain how a global offset of the Gaia parallaxes arises. And I describe the investigations carried out to identify and characterise the nature of such a `zero-point' offset, both for Gaia DR2 and (E)DR3. In practice, the offset is a non-trivial function of magnitude, colour, and sky coordinate.
24 February 2025
216. Star and exoplanet radii: an update
Huge numbers of new star and exoplanet radii
Compared to the few hundred stellar diameters directly measured with an accuracy of 1-2 percent, Gaia's distances and stellar parameters are providing diameters, of somewhat lower accuracy, for some 500 million stars. One consequence is for the improved radius estimates for several thousand transiting exoplanets.
17 February 2025
215. Black holes and Gaia: an update
New results on nearby black holes in binary systems
I review Gaia's contribution to supermassive and intermediate-mass black holes, and focus on the latest discoveries of black holes in wide, non-interacting binary systems, through the astrometric motion of their companion star. The three systems Gaia~BH1, BH2, and BH3 provide some deep insights into their formation and evolution.
10 February 2025
214. Telescope calibration/pointing: 2
How Gaia contributes to the operation of other space missions and ground-based telescopes
I continue the theme of my previous essay, and look how Gaia is contributing to the calibration and pointing of the Hubble and James Webb Space Telescopes, and ESA's satellite missions operated at ESOC. I look also at just a few examples from ground-based telescopes, including SAAO, SDSS, and WHT.
3 February 2025
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
