We finally know what causes the Milky Way’s mysterious “ripples.”

These waves come from the impact of a massive object, such as a rock thrown into a pond.

Looking at galaxies in photographs brought back by various space agencies, we can easily believe that structures of these astronomical proportions are relatively stable; But just because they are made of much larger material with a much longer lifespan than humans doesn’t mean they are formless.

Far away from there; Although these phenomena are difficult to detect at our scale, they are highly energetic objects. There is a completeness between the gravitational forces that develop in different planets, the chemical reactions that occur there, and the influence of other objects in space. Many external factors It disturbs the peace of these great things.

Our good old Milky Way is no exception. It even presents a curious phenomenon. In photos, it traditionally looks like a nice flat and disc, but the reality is very different. In fact, the core is constantly being rocked by large waves – like a bit A large stone abandoned pond.


A crash between cosmic giants

This analogy was not chosen at random. This is surprisingly consistent with a new theory by an international team of researchers; Its members explain that they succeeded in determining the origin of these oscillations, which until now remained a mystery. They suggest that the only scenario in which these ripples can be achieved involves the passage of a massive object – except here, “ Bear The question is about 400 million times heavier than the Sun!

To arrive at this hypothesis, the researchers started from studies that focused on the most popular hypothesis among experts. In fact, most cosmological models accept the fact that our galaxy is set in motion. Consecutive passages of the second dwarf constellation, baptized Sagittarius. By traversing the Milky Way from side to side at full speed, the latter would have behaved like the famous rock described above; These impacts would have created ripples that are still observed today.

A promising hypothesis, but there was a catch: If cosmological models had this dwarf galaxy passing through us this way, These vibrations can be extended to its limits. However, this phenomenon has not yet been directly observed.

A representation of the ballet involving Sagittarius and the Milky Way. © ESA

High-flying constellation seismicity

The researchers relied on readings from the Gaia satellite, an ESA machine that records the motion of millions of celestial bodies relative to the center of the Milky Way. Thus he seeks to create a grand catalog of the universe. More recently, these data have already helped astronomers find the closest black hole to Earth (see our Article)

In this particular case, they compared the motions of about 20 million stars distributed throughout the Milky Way, paying particular attention to those located at the periphery. And it turns out that they did Those famous ripples have been seen all the way to the edge of our galaxy. ” We see these stars moving up and down at different speeds says Paul McMillan, an emeritus astronomer affiliated with Sweden’s prestigious Lund University.

They tried to confirm that their observations actually corresponded with the passage of Sagittarius. To do this, they engaged in an exercise they describe. Interstellar Seismic “. This is not an official or common term in the scientific literature, but it has the advantage of being more obvious.

They worked like geophysicists studying the wave profile associated with earthquakes, but on an astronomical scale; Here, astronomers have constructed a Extensive computer simulation This refers to current ripples as they have observed them through Gaia. They extrapolated from this data to see how the phenomenon might have evolved over time.

This approach has proven successful; According to their model, the current position of the ripple coincided with the path of Sagittarius several hundred million years ago, when the now-dying galaxy was massive.

For researchers, this confirmation is very interesting because it lays a very solid foundation, which helps to enrich and strengthen many works interested in the interactions between celestial bodies and the global dynamics of the universe.

Direct science For example recalls a study It was released in 2020 thanks to Gaia; Its authors suggest that collisions between the Milky Way and Sagittarius would have produced enormous growth. Baby boomers » StarThat means an incredible number of stars were born in a very short time near the point of impact.

This kind of work is crucial to understanding what mechanisms have made it possible to define the current architecture of the universe, so it will be very interesting to follow the fallout from it.

The text of the study is available Here.

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