This week, the world will see one of the biggest dumps of astronomical data, ever. Launched in 2013, the ESA’s Gaia spacecraft is meant to do so-called astrometry, or space measurement, taking a 3D snapshot of more than a billion objects making up the Milky Way. On September 14, the team will release its first galaxy map, comprising more than two million stars and other objects, and with it a full 19 papers by Gaia astronomers. Suffice to say, the prospect is exciting to those who study this subject, as the brand new tool is set to revolutionize our understanding of not just this galaxy, but all of them.
Remember that Gaia’s main job is to map the galaxy, delivering the sort of data that could be used to create a walk-through VR version of the galaxy with accurate positions for stars. To deliver this information, Gaia is using one of the oldest techniques in astronomy: parallax, or the extent to which an object seems to move as your position changes. This is much the same technique used by astronomers hundreds of years ago to study the distances to the first distant astronomical objects, but without the confounding effects of an atmosphere. Gaia will orbit in the Earth’s “L2” Lagrangian point, so the space between its two furthest measurements will be a bit larger than the diameter of the Earth’s orbit.
These positions will be measured over the course of Gaia’s five-year mission in concert with the Radial Velocity Spectrometer, which will allow Gaia to derive the motion of each object. This motion will allow scientists to look into the period immediately before and after the measurements themselves by running a complex simulation of the galaxy. This should reveal quite a bit about how the galaxy has been evolving — and also, what forces exist to direct that movement. These days, that should immediately remind you of one thing, that hottest of topics in astrophysics: dark matter.
By looking at how the universe moves, and comparing that to how it ought to move based on what matter we can see, astronomers can derive how much other mass must be were, to explain the observed motion. This large-scale look at the distribution and motion of matter, and thus of the distribution and motion of dark matter, will deliver unprecedented insight into how this mysterious substance has directed the evolution of our galaxy.
Astronomers are about to understand this iconic spiral structure a lot more accurately.
Just a few weeks ago, astronomers announced a galaxy that seems to be made of mostly dark matter, which ought not to be possible by existing theories of how galaxies form. This sort of study will hopefully allow astronomers to make sense of such findings, and the role dark matter plays in galactic formation. Gaia will provide the most abundant and precise data ever used for this sort of galactic archaeology.
But these precise position measurements can be used for even more! I said that dark matter is the hottest topic in astrophysics, but in astronomy the big thing is probably exoplanets — and Gaia’s got something to add to that, too. The positions of stars over time can be used to detect exoplanets by looking for characteristic, tiny changes in their paths due to the gravitational pull of large planets.
Twenty rocky, temperate exoplanets like Proxima b were singled out for further study using equipment like the Kepler telescope and TESS, which we use to hunt exoplanets using the transit method. Image: NASA
This is distinct from the most popular method of detecting exoplanets now, which involves watching the luminosity of a star drip in response to a planet “transiting” in front of our view. The transit method has its advantages, mostly its historical contribution of the vast majority of confirmed exoplanets, but Gaia’s method has an extra advantage in that it directly measures the mass of the planet by looking at the magnitude of the perturbation in the star’s path.
In addition to its simple range-finder, Gaia comes equipped with an instrument for measuring luminosity and the components of the light being emitted by a star. Gaia can not only find a star and pinpoint its location, track its movement and where it’s likely to be in the future, it can also directly measure the makeup of the star itself.
There are so-called “Gaia sprints” being planned to try to take advantage of this glut of information in a timely fashion — sort of like a game jam but for space scientists. What’s exciting is that this level of enthusiasm is shared across the astronomical community; everybody seems confident Gaia’s data will let us see something totally new, simply by measuring something we’ve already measured many times before.