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You don’t notice it, but as you read this article, the Milky Way that contains the Earth rotates at 210 km per second.
Although now, a team of scientists from the University of Oxford and University College London (UCL, for its acronym in English), affirm that this speed is diminishing.
According to the research of these astronomers, our galaxy is now rotating 24% slower than it was when it formed, almost 14,000 million years.
You probably don’t notice this change in speed either, but the finding helps us better understand how works and evolves our galaxy.
In addition, it reveals key clues about one of the most mysterious components in the universe: the dark matter.
Spiral with bar
Let’s first review what the structure of the galaxy that serves as our neighborhood looks like.
The Milky Way is a spiral-shaped galaxy that is 100,000 light-years across.
Astronomers classify it as a “barred spiral galaxy”, because at its center it has a column made up of billions of stars and solar masses.
That central bar is in rotation, and from it they come off two arms that, driven by that rotation, rotate and form the spiral.
From these arms, in turn, some “spurs” or smaller arms. One of them is the arm of Orion, where our Solar System is.
For decades, astrophysicists suspected that the Milky Way might be spinning slower, but only now have they confirmed this.
To achieve this, with the help of the Gaia space telescope, they observed a gigantic group of stars known as the Hercules stream.
This stream of stars revolves around the Milky Way, synchronized to the same speed and in the same sense as the central bar of the galaxy.
The Hercules current is trapped by gravity exerted by the rotating rod, so if the rod were to rotate slower, the current would move away from the rod to maintain synchronization of the orbits.
In this research, astronomers analyzed the chemical composition from the stars of the stream, and concluded that they were indeed moving away from the central bar.
Stars in the galactic center are about 10 times richer in metals compared to those found in the outermost parts of the galaxy.
The stars of the Hercules stream are rich in heavy elements, which suggests that they formed in the galactic center.
But, as they are now further away from the center, the researchers concluded that the current reached that area because it has been away from the center bar.
The reason for this departure, according to the study authors, is that the bar is spinning slower.
According to his calculations, the galactic bar is now rotating at about 160 km per second.
And why is the bar spinning slower?
Researchers believe that the culprit is dark matter.
“Dark matter acts as a counterweight that slows down the turn [de la barra]”Ralph Schoenrich, a UCL researcher and study co-author, says in a statement.
The deceleration of the bar suggests that the gravitational force exerted by dark matter is acting on it.
Experts know very little about dark matter, but they believe that the Milky Way, like other galaxies, is wrapped in this “halo” of matter that, although not seen, does exert an influence on ordinary matter.
The existence of dark matter is inferred from the behavior of galaxies, which act as if they have a lot of more mass from which you can see.
Scientists estimate that there is five times more dark matter in the universe than ordinary matter.
For Schönrich, his finding is a sign that dark matter exists, and he believes it could be a key to begin to understand What is it made of.
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Eddie is an Australian news reporter with over 9 years in the industry and has published on Forbes and tech crunch.