The Milky Way is not like other barred spiral galaxies; Instead of showing a flat disk, it makes it curved up on one side and down on the other .
Many of the stars in the Milky Way are distributed in the thin disk, the region of space occupied by the spiral arms of our galaxy. And recently, scientists discovered that the disk is slightly warped at the edges.
Now, thanks to data from ESA’s Gaia stellar mapping satellite, they have discovered that the warped disk of our galaxy, the Milky Way, wobbles, similar to the movement of a spinning top, confirming earlier indications that this deformation it is not static. They call it precession. The reason? It is the result of a collision with a smaller galaxy sometime in the Milky Way’s dark past.
Thanks to ESA’s Gaia data
Astronomers tracked the position and motion of 12 million giant stars to measure how fast the warp spins around the galaxy. They found that it changes orientation over time, wobbles like a top, and completes a full rotation much faster than expected.
“We measure the speed of the deformation by comparing the data with our models. Depending on the speed obtained, the deformation would complete a rotation around the center of the Milky Way in 600 to 700 million years “, explained Eloisa Poggio of the Astrophysical Observatory of Turin, Italy, to the journal Nature Astronomy that publishes the study.” That is much faster than we expected based on predictions from other models, such as those looking at the effects of the non-spherical halo. “As an example, the Sun orbits the galactic center every 220 million years.
Did something collide with the Milky Way?
The direction and magnitude of the precession rate of the galactic warp favor the scenario that this is the result of a recent or ongoing encounter with a satellite galaxy , rather than the relic of our galaxy’s ancient history.
What is not clear is when it was or what galaxy was involved, but it seems that such deformation could only have been caused by a relatively recent , or even ongoing , cosmic dispute with one of the Milky Way’s satellite galaxies. Astronomers believe it could be the Sagittarius dwarf spheroidal galaxy, which is in a fairly close orbit with our galaxy and has historically proven quite damaging to it. But there is no need to worry: the Milky Way will absorb Sagittarius and incorporate its globular clusters, although there is still a long way to go.
“With Gaia, for the first time, we have a large amount of data on many stars, whose movement is measured with such precision that we can try to understand the large-scale movements of the galaxy and model its formation history, ” said the associate scientist. from ESA’s Gaia project, Jos de Bruijne. “This is something unique. This is really the Gaia revolution.”
Referencia: E. Poggio et al. Evidence of a dynamically evolving Galactic warp, Nature Astronomy (2020). DOI: 10.1038/s41550-020-1017-3
