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A new study by the European Space Agency (ESA) shows the lasting impact of a near collision between the Milky Way and another galaxy hundreds of millions of years ago, triggering a "ponds" effect Among the stars.
Thanks to ESA's star mapping mission, Gaia, which measures the positions and velocities of over a billion stars, researchers have been able to reconstruct the trajectories of a few million stars in the Milky Way. What the data revealed left them in awe.
A form stood out – a snail shell of stars swirling with time. The event would have occurred between 300 and 900 million years ago.
"At first, the characteristics were very strange for us," said Teresa Antoja, from the Universitat de Barcelona in Spain, who conducted the research in a version of ESA. "I was a little shocked and I thought there might be a problem with the data because the shapes are so clear.
However, after rigorous validation by other teams of researchers, their results were confirmed. In fact, what they found through modeling exists in our galaxy. And that opened a new question: why did this happen?
The answer was that the Milky Way was close to collision with another galaxy. This sets off millions of moving stars and is at the origin of the characteristic shape of the vortex at the center of the Milky Way. "It's a bit like throwing a stone into a pond, which moves water in the form of waves and waves," Antoja said.
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The Milky Way is still experiencing the effects of this vast and ancient stellar rocket, a story that is remembered in the current speeds and trajectories of the affected stars.
"Although the meeting took place about 500 million years ago, we can still see the consequences on the current orbits of stars near the Sun," said Antoja. Newsweek by email.
"The current velocities of the stars we have analyzed show unexpected motions indicating that they are still recovering from the past gravitational impact.In fact, it may take more than 1000 million years for stars to reach equilibrium. wrinkles disappearing). "
The researchers believe that the responsible system could be the dwarf galaxy of Sagittarius, which has only a few tens of millions of stars currently eaten by the Milky Way.
Amina Helmi from the University of Groningen, The Netherlands, collaborated on the project and was the second author of the research paper.
"We already knew this little galaxy, Sagittarius, but we assumed that its effect on the Milky Way would be small, perhaps negligible," said Helmi. Newsweek. "So, it was a great surprise that it had an effect on the Milky Way and near the Sun, 500 million years ago."
Helmi said such events are rarer today than in the past. "The encounters were more frequent in the past (because the universe was smaller), and we think that the Milky Way has already cannibalized several small galaxies.
"But we thought it was relatively quiet and isolated (without disruption) for eight billion years. It will merge in the future with another galaxy (magellanic clouds), but it will still take a few billion years before we feel much of the associated action. "
The new research shows that smaller galaxies have a greater impact on the Milky Way than previously thought – which means scientists need to rethink their understanding of the star system in which we live.
"This discovery implies that the disk of the galaxy is dynamically young, which means that it is very sensitive to external disturbances and that it changes sharply over time," Antoja said. Newsweek.
"Now we have to revise our galaxy dynamics models, so far we still assume that the disk is in equilibrium and that it is not suffering from external perturbations, but we now know that this is incorrect.
"We will have to examine whether other past impacts have also carved the fate of our galaxy disk and predict whether future encounters will also have similar consequences."
There are about 200 billion stars in the Milky Way, or 100,000 light-years in diameter.
ESA's Gaia satellite, launched on 19 December 2013 in Kourou, French Guiana, has at least the 3D mapping of our galaxy up to 2020.
The map shows up here the color, movement and distance of nearly 1.3 billion stars, and the position and brightness of nearly 1.7 billion.
This article has been updated to include more comments from Antoja.
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