We live through the twentieth, 223-250 million year old orbit of our solar system of the Milky Way near the inner edge of the ephemeral spiral function known as the Orion Arm or, less poetically, the Local Arm. The ghostly spiral arm is a concentration of gas and dust where stars are formed, produced by disturbances within the Milky Way, or on occasion by an external shock, such as a supernova. Life-threatening asteroids and comets occur more frequently when a planetary system crosses one of the spiral arms of the galaxy, where potentially deadly, dusty gas clouds converge, piling up in the equivalent of a hydrostatic leap.
The Galactic Bar Paradox
We also happen to live in a time when the central beam and the spiral of the Milky Way are connected, giving the illusion of a large and slow beam. Embedded in the center of the spiral arms of the Milky Way, the beam is 27,000 light-years long and cuts across the heart of the central region where the supermassive black hole resides.
However, the motion of the stars by the sun remains governed by the true, much smaller nature of the bar, and so these observations seem contradictory. “” Says Ivan Minchev of the Leibniz Institute for Astrophysics Potsdam (AIP), about new research that sheds light on a mysterious and long-standing mystery at the heart of our galaxy, the so-called “Galactic bar paradox”, which various observations contradict. producing the movement of the central regions of the Milky Way ..
The image below of a Milky Way galaxy simulation shows the bar in the center and the spiral arms are thought to rotate at different speeds. If the beam (horizontally in yellow and white) is in the shorter phase on the left, a few spiral arms can be seen nearby, but not quite firmly connected to the beam. Meanwhile, when the beam is at its longest on the right side, two stronger spiral arms pass this time. These are more clearly attached to each end of the bar, effectively pulling it out and slowing it down
The beam size and rotational speed of the Milky Way have been strongly contested over the last 5 years; while studies of the movements of stars near the sun find a bar that is both fast and small, direct observations of the galactic central region agree on one that is significantly slower and larger. The majority of spiral galaxies have a large bar-like structure of stars at their center. Knowledge of actual bar size and rotational speed is crucial for understanding how galaxies form and evolve, as well as how they form similar bars throughout the universe.
The illusion
The new study, led by an international team of scientists led by Tariq Hilmi of the University of Surrey and Minchev, provides a solution to this discrepancy. Analyzing modern simulations of the Milky Way galaxy formation, they show that both the size of the beam and its rotational speed fluctuate rapidly over time, causing the illusion of the bar to appear up to twice as long and 20 percent faster turns. at certain times.
“Milky Way Orbit 19” – Extinction by Spiral-Arm Apocalypse
Spiral weapons create a cosmic dance of 80 million years
The pulsations of the beams, reports the Royal Astronomical Society, are the result of their regular encounters with the galactic spiral arms, in what might be described as a “cosmic dance.” As the beam and the spiral arm approach each other, their mutual attraction due to gravity slows the beam and makes the spiral faster. Once connected, the two structures move as one and the beam appears much longer and slower than it actually is. When the dancers split apart, the bar moved faster, while the spiral slowed down.
Recent observations have confirmed that the inner Milky Way spiral arm is currently connected to the bar, which is estimated to occur about once every 80 million years. Data from the upcoming 3rd Gaia mission data release could further test this model, and future missions will be discovered as the dance continues in other galaxies across the entire universe.
Source: T Hilmi et al. Fluctuations in galactic rod parameters by bar-spiral interaction, Monthly Notices of the Royal Astronomical Society (2020). DOI: 10.1093 / mnras / staa1934
The Daily Galaxy, Sam Cabot, via University of Surrey and Royal Astronomical Society
