Dark matter slows the rotation of the Milky Way’s rods

news/tmb/2021/dark-matter-is-slowing.jpg" data-src="https://scx2.b-cdn.net/gfx/news/2021/dark-matter-is-slowing.jpg" data-sub-html="An artist’s conception of the Milky Way. Credit: Pablo Carlos Budassi/Wikimedia Commons">

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The rotation of the Milky Way galaxy’s trunk, made up of billions of cluster stars, has slowed by about a quarter since it formed, according to a new study by researchers at University College London (UCL) and the University of Oxford.

For 30 years, astrophysicists have predicted such a slowdown, but this is the first time such a slowdown has been measured.

The researchers say it provides a new kind of insight into the nature of dark matter, which acts as a counterbalance that slows the spin.

In a study published in Monthly Notices of the Royal Astronomical SocietyResearchers analyzed observations of the Gaia space telescope from a large group star, the Herculean current, which is aligned with the band – that is, it orbits the galaxy at the same rotational speed of the band.

These stars are gravitationally trapped by the spinning rods. The same phenomenon occurs with the Trojan and Greek asteroid Jupiter, which orbit around Jupiter’s Lagrangian points (ahead and behind Jupiter). If the rotation of the band slows down, these stars are expected to move further into the galaxy, keeping their orbital period identical to that of the band’s rotation.

The researchers found that the stars in the river have chemical traces – they are richer in heavier elements (called metals in astronomy), proving that they have moved away from the galactic center, where stars and star-forming gas are about 10 times as dense. rich. in minerals than in outer galaxies.

Using this data, the team concluded that the line was made up of billions of stars and trillions solar massThe spin has slowed by at least 24% since it first formed.

Co-author Dr Ralph Schönrich (UCL Physics & Astronomy) said: “Astrophysicists have long suspected that the axis at the center of our galaxy is slowing down, but we have found the first evidence that this is happening.

“The counterbalance that slows this spin must be dark matter. Until now, we could only infer dark matter by mapping the gravitational potential of galaxies and subtracting the contribution from visible matter.”

“Our research provides a new type of measurement of dark matter — not for its gravitational energy, but for its inertial mass (dynamic response), which slows the rotation of the rods.”

Co-author and PhD. Student Rimbe Chiba, from the University of Oxford, said, “Our findings offer an interesting perspective on the limiting nature of dark matter, as different models will alter this inertial tension on the galactic blade.

“Our findings also pose a major problem for alternative theories of gravity — because they lack dark matter in the corona, they predict no bands or very little hysteresis.”

The Milky Way, like other galaxies, is believed to be embedded in a dark matter “halo” that extends beyond the visible edge.

Dark matter is invisible and its properties are unknown, but its existence can be inferred galaxy It behaves as if it were covered with a much larger mass than we can see. It is believed that there is about five times the amount of dark matter in the universe that ordinary matter and visible matter contain.

Alternative theories of gravity such as Modified Newtonian Dynamics reject the idea dark matter, instead attempted to explain the contradiction by modifying Einstein’s general theory of relativity.

The Milky Way is a barred spiral galaxy, with a thick band of stars in the center and spiral arms extending across the disk outwards from the band. The bar rotates in the same direction as the galaxy.

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