top of page

Gaia: science essays

In these short 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 are not necessarily the most important. They do not follow any specific sequence. They are not a complete review of a given topic. Many will be quickly superseded by new results. But 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, 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: a subscribe page: to receive an email (usually Monday morning) when each new essay is published

New: a table page which lists all essays through to the end of 2023 (1–156 inclusive) in tabular form

164. Sub-subgiants and (tiny) black holes

A new class of star, and a link with primordial black holes

I look at some recent advances in the numbers of blue stragglers identified by Gaia, and Gaia's contribution to the identification and understanding of the new class of sub-subgiant star. I discuss whether these offer a particularly interesting search sample for stars hosting primordial black holes in their centres.

19 February 2024


163. Dual active galactic nuclei

A remarkable contribution to Lambda CDM cosmology

Dual active galactic nuclei, we now know, provide an important probe of the physical processes that drive the in-spiralling of supermassive black hole pairs inside a single merged galaxy. Difficult to detect and characterise, Gaia is making a significant contribution to their discovery.

12 February 2024


162. Cosmology with Gaia's quasars

Two topical tests of Lambda CDM cosmology

The large number of quasars measured by Gaia contributes fundamentally to the determination of the quasi-inertial reference frame. Today, Gaia's quasar survey is also being applied to two topical observational questions in Lambda CDM cosmology: the kinematic dipole anomaly, and the S8 tension.

5 February 2024


161. Strongly lensed quasars

A new search for gravitational lenses in the Gaia data

In this last of five essays on ESA's October 2023 'Focused Product Release' topics, I look at a new search for strongly lensed quasars in the data interval used for Data Release 3. Exploiting Gaia's 0.18 arcsec angular resolution, this new analysis found 450 previously known systems but with 86 newly detected components, and 381 new lensed candidates.

29 January 2024


160. More on diffuse interstellar bands

Spatial distribution of these absorption features out to 4000 parsec

In this fourth of five essays on ESA's October 2023 'Focused Product Release' topics, I look at improved modelling of the two diffuse interstellar bands (DIBs) present within the wavelength range of Gaia's Radial Velocity Spectrometer instrument (845-872 nm). Six million RVS spectra have been used to map their spatial distribution out to 4000 parsec.

22 January 2024


159. Improved solar system astrometry

A dramatic improvement in orbits for 157,000 asteroids

In this third of five essays on ESA's October 2023 'Focused Product Release' topics, I look at the significant improvements in orbit determination for the 157,000 asteroids provided in DR3, but now exploiting the 66-month time interval that will form the basis of Data Release 4 in 2025. This is mainly due to the observations now extending beyond a typical orbital period.

15 January 2024


158. Radial velocity time-series of LPVs

New insights into long period variables and ellipsoidal variables

In this second of five essays on ESA's October 2023 'Focused Product Release' topics, I look at the application of the newly available radial velocity time-series measurements (from Gaia itself) to the class of long-period variables. The time series data provide a powerful complement to the epoch photometry in identifying and characterising LPVs.

8 January 2024


157. Many more Gaia sources in Omega Cen

More than half a million new sources in this globular cluster

In essay 40 I described the first Gaia-based estimates of the distance to the globular cluster Omega Cen. Gaia DR3 contained 321,698 cluster sources. A series of special observations, and part of ESA's October 2023 'Focused Product Release', results in a further 526,587 sources in its core region. I also summarise other results on Omega Cen to date.

1 January 2024


156. Update on stellar streams

Nearly 100 stellar streams now know in the Galaxy halo

A growing number of accreted stellar 'streams' are being identified in our Galaxy's halo, from 20 in 2016 to nearly a hundred today, now mostly coming from Gaia. Some are attributed to captured dwarf galaxies, others to disrupted globular clusters. I described some of the early discoveries in essays 15 and 71, and bring the subject more up-to-date here.

25 December 2023


155. Gaia satellite operations

An insight into the complexities involved

Ten years on from the launch of Gaia, on 19 December 2013, I provide a picture of the tasks involved in the operations of the Gaia satellite. I will start with a brief background to some of the top-level requirements that influenced the operational design and implementation, and continue with a first-hand account by the Gaia spacecraft operations manager, David Milligan.

18 December 2023

bottom of page