Mass Extinction And The Structure Of The Milky Way

There was a 2013 paper titled "Mass Extinction and the Structure of the Milky Way" that you might find interesting: https://arxiv.org/abs/1309.4838 - I don't know if there have been any significant follow ups since it published. Basically our galaxy is a spiral galaxy with four arms, and it's rotating. The center moves slower than the outside, and our sun's orbit is near the inner rim of the Orion arm. We orbit the galaxy roughly every 240 million years and in that time we cross the dense galactic arms every so often (arms aren't symmetrical). The paper: "A correlation was found between the times at which the Sun crosses the spiral arms and six known mass extinction events."

Density wave theory [1] posits that the "arms" of a spiral galaxy are more like stellar gravitational traffic jams than persistent objects-- stars pass through and clump up in arms, but the stars in each arm change through the eons. If you plot mass extinction events against when the solar system transits through the arms, eleven extinction events in the last 500 million years occurred while going passing through one of these high density regions. [2] [1]: https://en.wikipedia.org/wiki/Density_wave_theory [2]: https://arxiv.org/abs/1309.4838

Full text: https://arxiv.org/pdf/1309.4838.pdf With what reasoning or evidence do they propose their new model of the galaxy? Is it: - extinction events, therefore new model or - astronomical data, therefor new model, and look how nicely it correlates with known extinction events

Fun fact: spiral galaxies' galactic arms are stationary waves. They don't spin like spokes on a wheel. Stars in the arms don't remain in them - every star traverses through the arms and the regions between them [1]. Indeed, correlations have been hypothesised between Earth's extinction events and our Sun's predicted passage through these arms [2]. [1] https://m.youtube.com/watch?v=c5Us-jonCLA [2] https://arxiv.org/pdf/1309.4838.pdf

It boggles the mind. All of it. The scale of space, the scale of time, our own tiny brief existence in it. The possibility that several civilization collapses occurred right here and we wouldn't know it. The possibility that life elsewhere in the universe came and went and the light informing us of it won't reach us before we possibly burn out. Meanwhile we're just a flicker from a spent flintwheel. The thing that gave me a particular "oh" moment was reading the study that correlated Earth's geologic events (mass extinctions, impacts, etc) timed to our Sun transiting through the spiral arms of our galaxy. Fun read: https://arxiv.org/pdf/1309.4838.pdf