Additional material
Spiral shape in the vertical phase space
Formation of the spiral shape with time
This animation shows how a snail shell is formed with time in the graph plotting the altitude of the stars above/below the Galactic plane against their vertical velocity. At the beginning all stars are concentrated in one region of this graph. With time each star revolves in circles in the clockwise direction and the global distribution starts to curl, eventually showing a spiral shape as we see in the Gaia data. The movie is based on the toy model described in the article above.
CREDIT: Teresa Antoja (ICCUB)
Comparison of phase space from Gaia first and second data releases
This animation shows fig 1 of the article (altitude of the stars above/below the Galactic plane against their vertical velocity) comparing the Gaia data from the first data release (DR1, 2016) and the RAVE survey with data entirely from the second Gaia data release (DR2, 2018). A snail shell shape that was previously blurred by measurement errors appears now.
CREDIT: Teresa Antoja (ICCUB)
Comparison data and models
This animation shows fig 1 of the article (altitude of the stars above/below the Galactic plane against their vertical velocity) comparing a simple Galaxy model in equilibrium with the Gaia data from the second Gaia data release (DR2). A clear snail shell appears in the Gaia data that does not show up in the model.
CREDIT: Teresa Antoja (ICCUB)
The approach of the Sagittarius dwarf galaxy
SATEDGE.mpgMovie showing a generic interaction between a large galaxy and a smaller companion
CREDIT: Chris Mihos and Sean Maxwell (Case Western Research University).
The past orbit of Sagittarius computed in Helmi et al. 2018 (https://www.aanda.org/articles/aa/abs/2018/08/aa32698-18/aa32698-18.html)
CREDIT: Teresa Antoja (ICCUB), ESA/ATG medialab
Artistic images
The spiral shape of fig 1c of the article appears superposed to an image of the Milky Way built from Gaia Second Data Release. This figure from our article resembles a fossil and it can, in fact, be considered symbolically as a fossil since it has allowed us to trace back the perturbation that shook the Milky Way in the past.
CREDIT: Teresa Antoja (ICCUB), Surinye Olarte. Gaia sky in colours: ESA/Gaia/DPAC, A. Moitinho / A. F. Silva / M. Barros / C. Barata, University of Lisbon, Portugal; H. Savietto, Fork Research, Portugal.
This shows an image of the Milky Way built from Gaia Second Data Release broken as if it was a piece of glass. This symbolises the perturbation that the Milky Way suffered in the past and that we have just discovered.
CREDIT: Edmon de Haro/iStock. Gaia sky in colours: ESA/Gaia/DPAC, A. Moitinho / A. F. Silva / M. Barros / C. Barata, University of Lisbon, Portugal; H. Savietto, Fork Research, Portugal.
The spiral shape of fig 1c of our article appears inside an old watch symbolising the fact that these data has allowed us to date back the perturbation that shook the Milky Way disk. This figure shows how from the new obtained Gaia data we can know more about the past of the Galaxy.
CREDIT: Edmon de Haro/iStock