Abstract

I provide a synopsis of many of the scientific advances made by Gaia, through to the end of 2023, by means of a hyperlinked index to weekly essays that I been writing since the start of 2021.

Introduction

Since the launch of Gaia in 2013, there have been four data releases: DR1 (Sep 2016), DR2 (Apr 2018), EDR3 (Dec 2020), and DR3 (Jun 2022). Together, these have resulted in some 6000 refereed papers (with Gaia in the title or abstract), and a similar number of non-refereed publications. Impacting many areas of astronomy, the rapid growth of new publications makes any sort of orientation or global scientific review challenging.

This article adopts a pragmatic approach to the challenge. Since January 2021, I have posted weekly 2-page essays on the advances being made by Gaia at my own www site, michaelperryman.co.uk, with legacy copies also hosted by CERN’s Zenodo archive. These 156 essays, through to the end of 2023, together provide an evolving synopsis of many of Gaia’s scientific advances, albeit incomplete and progressively superseded.

Here, I provide hyperlinks to the (Zenodo-hosted) essays, organised by topic. Links are given in the form [nnn], where nnn is the sequential number. An indication of the essay date (and therefore the latest data release on which it was based) is given by its number: numbers 1–52 were written in 2021, 53–104 in 2022, and 105–156 in 2023.

The essays themselves provide references in standard bibliographic notation. While these are (mostly) hyperlinked to the ADS bibliographic page, I have generally suppressed an explicit hyperlink text colour in order to aid readability. More up-to-date treatments of each topic can be traced from the ADS citation records in the usual way.

I have identified about 30 topics with an asterisk. This is a subjective attempt to indicate some of the most important new results enabled by Gaia so far. A handful of essays, marked $^+$, are more loosely connected.

1. Background

1.1. History, design, and technology

Angular measurements: how and why [1]
Galactic tracers, by design [6]
GDP and Gaia [9]
German DIVA project+ [50]
Hipparcos: from concept to launch (13pp) [154]
Hipparcos: push to space (7pp) [4]
History of astrometry (24pp) [3]
Input catalogue versus on-board detection [5]
Interferometer or monolith? [56]
L2 orbit [67]
Latex files: using ADS citations+ [123]
On-board detection [7]
Photometry: overview [68]
Radial velocities: their acquisition [86]
Radial velocities: wavelength vs science goals [85]
Radial velocities: why measure them? [8]
Satellite operations and commissioning (6pp) [155]
Scientific case for Gaia in 2000 [53]
Scientific project management [60]
Star positions: why measured [2]
Technology preparation [57]

1.2. Data processing and data releases

Celestial reference frame: quasars and ICRF [27]
Classification and parameterisation [89]
Data releases: DR1, DR2, EDR3 [10]
Data releases: DR3 [76]
Iterative solution: formulation [46]
Iterative solution: implementation [47]
Science alerts: transients, lensing, supernovae [36]
Validation of catalogues [63]
Videos and visualisations: part 1 [54]
Videos and visualisations: part 2 [147]

2. Stars and stellar systems

2.1. Physical phenomena and effects

Aberration, Galactic rotation, and acceleration* [32]
Astrometric microlensing; event prediction [11]
Axions: halo streams; ultra-faint dwarf galaxies [142]
Axions: modified white dwarf cooling curves [110]
Benford’s law: parallax and distance distributions [146]
Fundamental constants [110]
Gravitational redshift: binaries; Galaxy rotation [113]
Gravitational waves [136]
Hypervelocity stars: Galactic centre and LMC* [22]
Microlensing: astrometric event prediction [11]
Microlensing: photometric events in DR3 [84]
Modified gravity (MOND) and ultra-wide binaries [14]
Perspective acceleration [34]
Radial velocities: in DR3 [87]
Relativistic light deflection: by Sun and Jupiter [104]
Variation of $G$; white dwarfs [110]

2.2. Hertzsprung–Russell diagram

AGB stars: cerium [91]
AGB stars: interstellar medium [90]
AGB stars: s-process elements [121]
Asteroseismology: distance comparisons [51], [108]
Asteroseismology: g-modes, period changes [108]
Asteroseismology: gravito-inertial effects [149]
Binary stars: see separate section
Brown dwarfs: isolated; ultracool; overmassive [119]
Carbon stars [90]
Convection, overshooting, mixing length [150]
Convective kissing instability [150], [152]
DR2 results: 212 000 stars within 100 pc [42]
FGKM stars [90]
Gravito-inertial asteroseismology [149]
Hyades: main sequence [151]
Initial mass function: metallicity and age [130]
Jao gap* [152]
M dwarfs: radiative-convective boundary* [42], [152]
Nearby stars [129]
OBA stars [90]
Planetary nebulae: distance estimates [124]
Planetary nebulae: link to ultra-wide binaries [37]
r- and s-process elements [91]
Radiative-convective boundary [150]
Rotation: 3 million stars* [103]
Stellar evolution models [121]
Ultra-cool dwarfs [90]
Variable stars: see separate section
White dwarfs: see separate section
Wolf–Rayet stars: in DR2 [105]

2.3. Open clusters and associations

Coma Ber [33]
Gravitational redshift [113]
Hyades: distance, structure, tidal tails* [20]
Hyades: main sequence [151]
Hyades: white dwarfs, brown dwarfs [20]
OB associations: origins [18]
Open clusters: in EDR3 [74]
Open clusters: in DR3 [144]
Pleiades: distance controversy; tidal tails* [13]
Stellar rotation [103]
Westerlund 1 [106]
Wolf–Rayet stars [105]

2.4. Double and multiple systems

Cataclysmic variables: period gap, space density [140]
Ellipsoidal variables [133]
Non-single stars: masses; ellipsoidal variables [79]
Quadruple systems: discoveries, orbits, mergers* [139]
Resolved binaries: within 1000 pc [134]
Spectroscopic binaries: tidal circularisation [145]
Triple systems: Kozai–Lidov resonances [135]
Twin binaries: implications for star formation* [138]
Ultra-wide binaries: eccentricity distribution [37]
Ultra-wide binaries: modified gravity (MOND) [14]

2.5. Variable stars

Cepheid variables: period–luminosity relation [43]
Citizen Science [132]
Ellipsoidal variables [133]
Identification of variability: numbers from DR2 [61]
Non-radial pulsators: SPB and $\gamma$ Dor [148]
RR Lyrae variables: 140 000 in DR2 [45]
Science alerts: transients, lensing, supernovae [36]
Variability across the HR diagram* [62]

2.6. White dwarfs

Asteroseismology: g-modes, period changes [108]
Asteroseismology: versus astrometric distances [108]
Atmospheric pollution by exoplanet debris [73]
Bifurcation (DA/DB) in the HR diagram* [29], [108]
Binary systems [42]
Chronometers for the Galactic disk [108]
Cooling: in the quadruple system HD 190412 [139]
Cooling: mechanisms [108]
Cores: C-O mixture [107]
Cores: suggestions of Fe [107]
Crystallisation* [42]
Crystallisation: specific objects [108], [139]
Double degenerate binaries: unresolved [108]
Double white dwarf mergers [131]
Gaseous disks, rarity of [73]
Halo population members [29]
Low-mass objects [29]
Mass of LAWD 37 from astrometric microlensing [107]
Mass–radius relation [107]
Massive objects: uncertain origin [29]
Numbers: in DR2* [29]
Numbers: pre-Gaia [29]
Resolved binaries: occurrence in [134]
Space density [29]
Ultra-massive dwarfs [108]
White dwarf pulsars: AR Sco and J1912–4410 [141]

2.7. Neutron stars and black holes

Black holes: companions to ellipsoidal variables [133]
Black holes: distance to Cyg X-1 [101]
Black holes: microlensing detections [101]
Black holes: nearby binaries, Gaia BH1* [101]
Neutron stars and pulsars [80]
Sgr A*: distance to Galactic centre [111]
Sgr A*: Sun’s height above disk mid-plane [126]

3. Galaxy structure

3.1. Galaxy disk

Aberration and Galactic rotation* [32]
Age of Milky Way; ancient merger history [41]
Anti-centre: content and features [39]
Arcturus and HR 1614 streams [116]
Bar: distance to the Galactic centre [111]
Bar: origin and resonances [112]
Besançon Galaxy model [125]
Cerium abundances, and Galaxy infall history [91]
Diffuse interstellar bands (DIBs)* [92]
Disk components: thin and thick disks [125]
Distance to Galactic centre: dynamical* [111]
Gould’s Belt and the Radcliffe Wave* [127]
Hercules stream, Eggen’s moving groups* [115]
Local Bubble morphology [70]
Maps of Milky Way: motions, ages, etc [143]
Mass density: $K_z$; dark matter [75]
Mass of Milky Way: timing; halo tracers [93]
Nearby stars: CNS5 (within 25 pc)* [129]
Nearby stars: GCNS (within 100 pc)* [33]
Oldest structural features* [102]
Oort constants [153]
Phase-space spiral* [117]
Rotation curve: acceleration and radial migration [113]
Rotation curve: from DR2, virial mass [49]
Sgr A*: distance to Galactic centre [111]
Solar motion [153]
Spiral arms: mapping to 4–5 kpc [114]
Sun’s height above disk mid-plane [126]
Warp: ancient relic or recent merger [72]

3.2. Galaxy halo

Bar: deceleration due to dark matter halo* [112]
Escape velocity: Milky Way mass [77]
Globular clusters: $\omega$ Cen, RGB tip* [40]
Globular clusters: motions; orbit anisotropy* [30]
Globular clusters: Palomar 5 tidal tails* [109]
Halo streams: compilation* [156]
Halo streams: defining solar motion [153]
Halo streams: Enceladus, and thick disk* [15]
Halo streams: in EDR3* [71]
Solar motion [153]
Tumbling disk [95]
Virgo Stellar Stream/Overdensity, VSS/VOD [95], [156]

3.3. Galaxy interactions

Antlia II [128]
Large Magellanic Cloud [95]
Phase-space spiral [114]
Radcliffe Wave [127]

4. Local Group

$\Lambda$CDM: plane-of-satellites problem* [118]
Andromeda (M31): photometric survey [83]
Antlia II (dwarf galaxy): dark matter properties [128]
Dwarf spheroidals: motions and orbit orientations* [31]
Local Group: mass via timing method [94]
Magellanic Clouds: bulk motions* [38]
Magellanic Clouds: distance scale [122]
Magellanic Clouds: Hubble flow [93]
Magellanic Clouds: LMC [95]

5. Cosmology

5.1. Baryonic matter

$\Lambda$CDM: core–cusp problem* [128]
$\Lambda$CDM: plane-of-satellites problem* [118]
Ages: stars older than 13.8 Gyr [69]
Cepheid distances: Hubble constant* [44]
Distance scale: LMC and beyond [122]
Galaxy survey [82]
Modified gravity (MOND): ultra-wide binaries [14]
Quasars: gravitational lensing, Einstein crosses [58]
Quasars: gravitationally lensed systems [16]
Supernovae remnants: stellar mass black holes [81]
Supernovae: distances, progenitors [59]

5.2. Dark matter

Antlia II, anomalous composition [128]
Disk–halo dynamics [95]
Escape velocity: solar neighbourhood [77]
Galactic rotation [49]
Halo streams [71]
Mass density: solar neighbourhood [75]
Mass of Milky Way [93]
Palomar 5: tidal tails [109]
Satellite halos [31]
Solar activity: speculative link [28]

6. Solar system

Asteroid impact risk$^+$ [48]
Earth’s polar motion$^+$ [26]
Flat Earth: a message for educators$^+$ [96]
Interplanetary navigation: imaging of Arrokoth [52]
Interstellar vagabonds: origin of Oumuamua* [25]
Light deflection: by Jupiter* [104]
Light deflection: by Sun [104]
Maunder minimum$^+$ [23]
Occultations: Europa and Triton* [24]
Occultations: stellar diameters [137]
Solar activity and dark matter$^+$ [28]
Solar analogues [120]
Solar siblings [17]
Solar system objects: in DR2* [64]
Stellar flybys* [35]

7. Exoplanets

Astrometry: detections/discoveries [78]
Boyajian-type stars: distances and clumping [98]
Dyson spheres [99]
Fermi paradox$^+$ [100]
Habitability: TESS-Gaia samples [66]
Hot Jupiters: star clustering, Galactic orbits [65]
Life on other worlds$^+$ [97]
Mandalas (multi-planet orbits)$^+$ [12]
Numbers predicted from astrometry$^+$ [19]
Pinpointing exoplanets for direct imaging [88]
Radii: from trigonometric distances [21]
SETI: Boyajiian’s star(s); 1977 Wow event [55]
Transit photometry: detections/discoveries [78]