Gaia: science essays

40. The distance of Omega Centauri

Globular clusters are amongst the oldest Galactic populations, and their origin remains unclear. But they are too distant for direct estimates of their parallaxes and ages to have been made in the past. Determination of the distance of Omega Centauri with Gaia represents a new milestone of distance measurements in astronomy.

4 October 2021

39. The Galactic anti-centre

Observations towards the Galactic centre probe its densest and most complex regions, with multiple populations superimposed: the thin and thick disks, star clusters, spiral arms, a bar, and the central bulge. In the anti-centre direction, star densities and interstellar extinction are lower, and the disk and halo can be more easily resolved.

27 September 2021

38. The Magellanic Clouds

The Magellanic Clouds are two 'nearby' irregular dwarf galaxies, visible to the unaided eye in the dark skies of the southern hemisphere. They may be orbital companions to our Milky Way, or on a 'first approach' at the start of a grand galactic merger event. Hipparcos observed less than 50 stars in both systems. Gaia is observing more than 10 million.

20 September 2021

37. Ultra-wide binaries

Gaia is identifying tens of thousands of very wide and ultra-wide binaries from their highly accurate space motions. The resulting discoveries, and their space motions, are allowing great progress in understanding their formation, evolution, and the various processes that contribute to their eventual disruption.

13 September 2021

36. Science alerts

Gaia monitors the precise magnitudes of every star a few hundred times throughout its lifetime. From these measurements, the mission is discovering enormous numbers of variable stars. Amongst them are novae and supernovae, as well as even more exotic variables. A powerful 'alerts' system is discovering many that deserve a closer look.

6 September 2021

35. Stellar flybys

Although interstellar space is very empty, noticeable effects due to nearby star passages can occur. A predicted consequence of a close approach is that the gravitational pull of the passing star can perturb the delicate equilibrium of the Oort cloud comets, with the possibility of an increased impact hazard on Earth.

30 August 2021

34. Perspective acceleration

For a fixed space velocity, a star's proper motion varies inversely with its distance. However, the tangential velocity changes due to the varying angle between the line-of-sight and its space velocity. The two effects result in a changing proper motion and, for a few nearby stars, an apparent acceleration of the star's motion on the sky.

23 August 2021

33. Nearby stars

Surveys of our solar neighbourhood provide the foundations for defining our Galaxy's stellar luminosity and velocity distributions, the occurrence of binary stars, and the nature of many other types of objects, including brown dwarfs, white dwarfs, and exoplanets. Gaia is revolutionising this knowledge [gif courtesy: galaxymap.org].

16 August 2021

32. Aberration and Galactic rotation

As the Earth orbits the Sun, star positions change due to the combination of the Earth's velocity, and the speed of light arriving from the star. The effect is already at levels imperceptible to the human eye. But a million times more sensitive still, Gaia has recently detected a similar effect due to the Sun's 250 million year orbit around the Galaxy.

9 August 2021

31. The motion of dwarfs spheroidals

Dwarf spheroidal galaxies are small, low-luminosity galaxies comprising old stellar populations. By the late 1990s, their rarity seemed to be in conflict with the 'Lambda cold dark matter' cosmological model, which predicted that massive galaxies like the Milky Way should be surrounded by many dark matter dominated halos.

2 August 2021