A team of astronomers from Germany, the United Kingdom, the United States, France and Japan may have solved the so-called ‘Galactic bar paradox’, in which various observations produce conflicting estimates of the motion of the central regions of our Milky Way galaxy.
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 both ends of the beam, pulling it out effectively and slowing it down. Image credit: Hilmi and others, doi: 10.1093 / mnras / staa1934.
The majority of spiral stars, such as the Milky Way, have a large bar-like structure of stars at their center.
Knowledge of the actual rod size and rotational speed is crucial for understanding how galaxies form and evolve, as well as how they form through very similar beams.
However, the size and rotational speed of the Milky Way beam have been strongly contested over the last five years.
While studies on the motions of stars in 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 new study suggests an insightful solution to this difference.
Analyzing simple simulations of the Milky Way of the Milk System Formation, they show that both the size of the beam and the rotational speed fluctuate rapidly over time, causing the beam to appear up to twice as long and at certain times 20 % faster running. ,
The pulsations of the beams are the result of their regular encounters with the spiral arms of the galaxy, in what may 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.
“The controversy over the galactic bar can then simply be resolved if we happen to live in a time when the beam and spiral are connected, giving the illusion of a large and slow beam,” said co-lead author Dr. Ivan Minchev, an astronomer at the Leibniz Institute for Astrophysics Potsdam.
“However, the movement of stars in the sun remains regulated by the true, much smaller nature of the bar, and so these observations seem contradictory,” added co-lead author Tariq Hilmi, a postgraduate research student at the Astrophysics Research Group at the University of Surrey and the Leibniz Institute for Astrophysics Potsdam.
The study was published in the Monthly announcements from the Royal Astronomical Society.
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T. Hilmi and others. 2020. Fluctuations in galactic beam parameters due to bar-spiral interaction. MNRAS 497 (1): 933-955; doi: 10.1093 / mnras / staa1934
