The Milky Way, as it is now conceived, is the result of several collisions between protogalaxies over the last billion years. Studies of stellar evolution indicate that all of these combinations of structures occurred long before the solar system, including Earth, formed. However, an article recently published in Monthly Notices of the Royal Astronomical Society It is estimated that the last major galactic collision occurred when our planet was half its current age.
According to the report, 2.7 billion years ago, a dwarf galaxy collided with the Milky Way in an event called the ‘Virgo Radial Merger’, adding matter to the inner halo. The Earth is approximately 4.6 billion years old, so during the supposed collision it was going through the Neoarchaic era. During this period, the planet was experiencing a process of molecular oxygenation thanks to the first bacteria that carried out photosynthesis in an accelerated manner.
The Milky Way was formed from huge “blocks” and two have just been identified: Shiva and Shakti
Scientists from the Max Planck Institute for Astronomy found two of the primordial blocks of which the galaxy is composed.
The proposal by the team led by Thomas Donlon, from the Department of Applied Physics and Astronomy at Rensselaer Polytechnic Institute in New York, contrasts significantly with another hypothesis about a probable galactic clash. According to that alternative guideline, 11 billion years ago, the Milky Way protodisk collided with a dwarf galaxy called Gaia-Sausage/Enceladus.
What do the wrinkles of the galaxy say?
The key to the research lies in the study of the stars under the folds or wrinkles that the galactic disk itself presents. Although the Milky Way is relatively “flat,” like the disk of the solar system, it has fluctuations in its topography that reveal its violent past.
According to astronomers, these wrinkles in the galactic disk are probably vestiges of past collisions. The more folds a spiral galaxy has, the more recent its collision was. If the merger scenario 11 billion years ago were accurate, the galaxy’s disk would be mostly flat. However, it is not, researchers say.
“By watching these wrinkles dissipate over time, we can track when the Milky Way experienced its last major collapse, and it turns out that this happened billions of years later than we thought,” Donlon notes.
The team of physicists studies the behavior of the Milky Way through computer simulations. By marking the starting point as two protogalaxies colliding with each other, it is possible to visualize the shape of the folds or wrinkles that a new structure will take. At some point in those simulations, the disk markings matched current data provided by the European Space Agency’s Gaia telescope.
The wrinkles of the Milky Way were previously discovered by Gaia in 2018. They confirmed that the galaxy has a topology with depressions, mountains and waves, where the stars navigate. “The history of the Milky Way is constantly being rewritten at the moment, largely thanks to new data from Gaia,” says the author.
The Milky Way’s next major collision will be with its companion, the Andromeda galaxy, in about 4.5 billion years. Both will approach and orbit as binary systems until they “collide” and combine. Astronomers explain that these types of events are generally imperceptible to the planets.
