The Milky Way has a 'broken' arm that could reveal its galactic history

rod

Oct 22, 2019
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A number of reports out now on this find in our galaxy. Astronomers find a 'break' in one of the Milky Way's spiral arms, https://phys.org/news/2021-08-astronomers-milky-spiral-arms.html

My observation. This was refreshing to read here. "Astronomers don't yet fully understand what causes spiral arms to form in galaxies like ours." Maintaining spiral arms is difficult too, especially when using long ages like the age of the universe or 10 billion year time scales. Other reports indicate spiral arms live only about 80 to 200 million years if that long and must then be regenerated to explain the population of spiral galaxies seen in the universe today. This high pitch angle structure reported is clearly young composed of various YSO and said to be some 950 pc long. The high pitch angle structure origin is difficult to explain too. Reference paper, A high pitch angle structure in the Sagittarius Arm, https://www.aanda.org/articles/aa/full_html/2021/07/aa41198-21/aa41198-21.html, 21-July-2021. “Abstract Context. In spiral galaxies, star formation tends to trace features of the spiral pattern, including arms, spurs, feathers, and branches."

There are many reports out now discussing spiral arms in galaxies too. On the Milky Way spiral arms from open clusters in Gaia EDR3, https://ui.adsabs.harvard.edu/abs/2021arXiv210504590C/abstract

"Context. The physical processes driving the formation of Galactic spiral arms are still under debate. Studies using open clusters favour the description of the Milky Way spiral arms as long-lived structures following the classical density wave theory. Current studies comparing the Gaia DR2 field stars kinematic information of the Solar neighbourhood to simulations, find a better agreement with short-lived arms with a transient behaviour."

Spiral galaxies with their arms are all young features compared to the BB model age for the universe, globular cluster ages, or age of the solar system accepted today, some 4.6 billion years old.
 
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Catastrophe

"There never was a good war, or a bad peace."
"Scientists have spotted a previously unrecognized feature of our Milky Way galaxy: A contingent of young stars and star-forming gas clouds is sticking out of one of the Milky Way's spiral arms like a splinter poking out from a plank of wood. Stretching some 3,000 light-years, this is the first major structure identified with an orientation so dramatically different than the arm's." My emphasis.

Excellent comment on this by rod
 
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