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The heart of the Milky Way is slowing down

The heart of the Milky Way is slowing down

What astronomers have suspected for decades has been confirmed by observations of the Gaia space telescope by British scientists: the giant bar of stars in the center of the Milky Way is spinning slower and slower. This insight provides new evidence for the existence of dark matter. is over Scientists in Monthly Notices of the Royal Astronomical Society.

The Milky Way is a barred spiral galaxy: spiral arms extend from a bar in the center. About 100,000 light-years away and 6,000 light-years thick, the Milky Way looks like a giant pancake. The system is home to hundreds of billions of stars, including our star, the Sun. Earth is about 25,000 light-years away from the center, somewhere on a side street called the Orion Arm: a small branch of one of the Great Arms.

The star bar in the center of the Milky Way galaxy consists of billions of stars fairly close to each other and rotating around its axis. The strip is about a third of the distance between the Sun and the center of the Milky Way.

Astronomers suspected for some time that the speed with which this beam rotates on its axis must decrease. It was rubbed with dark matter. These are virtual particles that make up about 25% of the universe. Scientists have not yet found them, because these particles do not give out or absorb light, but they can explain the missing mass in the universe.


British astronomers Rembe Sheba of the University of Oxford and Ralph Schönrich of University College London found that if the band at the center of the Milky Way slowed down, they could determine the region of the stars of Hercules surrounding it. This is a stream of stars moving in a special way. Like other stars in the Milky Way, they rotate around the center, but the speed at which they do so corresponds to the speed of the beam’s rotation. Astronomers call this long-term relationship an echo. The region in which the stars of Hercules are located and which have such a relationship with the beam, they call the region of resonance. The slower the rotation of the beam, the larger the circumference of the resonance region becomes and the more distant stars become trapped in it.

To see if the resonance region is indeed increasing, astronomers analyzed the iron content of stars in that region using the European Space Agency’s Gaia space telescope. It follows from computer simulations that if the beam was always rotating at the same speed, and the buzzing region was always the same size, then the region would consist of only one type of star; the same amount of iron.

Annual episodes

Indeed, astronomers have seen that the region consists of all kinds of rings with different types of stars: with different iron content – just like the annual rings of a tree. The oldest ring is in the center and consists of stars with a high iron content – the newest ring is on the edge and consists of stars with a low iron content. Based on the iron content, astronomers estimate that the spin of the beam has decreased by more than 24 percent since its inception. It’s still too early to say that the beam will stop completely. The researchers believe that more complex models are needed to determine exactly how the streak evolved.

“By itself, the ribbon in the center of the Milky Way was expected to rotate more and more slowly,” says Amina Helmy, an astronomer at the University of Groningen and not involved in the study. “But it’s really surprising that astronomers have been able to measure such a complex system.”

According to astronomers, this provides further evidence for the existence of dark matter. My dream agrees. “Astronomers have shown that this part of the Milky Way behaves as you would expect in a dark matter universe. It is now up to other scientists working on alternatives to dark matter to explain the beam delay with their theory.”

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