For more than 30 years, researchers have assumed that the Milky Way’s bar – the center of the Milky Way where billions of stars are located – is slowing down. Now researchers from Oxford University and University College London (UCL) They finally have the test.
In the new study, Posted in Monthly notifications of the Royal Astronomical Society, The researchers used the European Space Agency (ESA) Gaia telescope to observe a large group of stars known as the Hercules Stream, which orbit the core of the Milky Way at the same speed as the galactic bar. If the bar speed slows down, the stars move away.
Stars are gravitationally trapped by the rotating band, just like the asteroids in the asteroid belt that follow the orbit of Jupiter. Experts have discovered that stars bear a “chemical fingerprint”. This element comes in the form of heavier metals, which indicates that the stars are moving away from the center of the galaxy, as stars and gases contain richer elements.
Using this data, the team concluded that the ribbon – made up of billions of stars and trillions of solar masses – has slowed its rotation by at least 24% since its formation.
A new kind of dark matter measurement
The researchers say it provides a new kind of insight into the nature of dark matter, which acts as a counterweight that slows spin.
Study co-author Dr. Ralph Schönreich said: “The counterweight slowing this spin must be dark matter. Until now, we could only infer dark matter by mapping the gravitational potentials of galaxies and subtracting the contribution of visible matter.” “Our research provides a new kind of measurement of dark matter: not its gravitational energy, but its inertial mass (dynamic response), which slows down the rotation of the rod,” he added.
The Milky Way, like other galaxies, is believed to be engulfed in a “halo” of dark matter that extends well beyond its visible edge, according to a UCL press release. Dark matter is invisible and its nature unknown, but its existence is inferred from galaxies that behave as if surrounded by a mass much greater than we can see. It is believed that there is about five times more dark matter in the universe than normal visible matter.
Alternative theories of gravity, such as modified Newtonian dynamics, reject the idea of dark matter and attempt to explain the contradictions by modifying Einstein’s general theory of relativity.
FEW (UCL, Monthly notifications of the Royal Astronomical Society, New Scientist)