Far out cosmology: how spirals form (Introduction)

by David Turell , Friday, August 18, 2023, 19:05 (253 days ago) @ David Turell

Finally unraveled:

https://www.livescience.com/space/cosmology/the-milky-way-wasnt-always-a-spiral-and-ast...

"A 100-year-old mystery surrounding the "shape-shifting" nature of some galaxies has been solved, revealing in the process that our Milky Way galaxy did not always possess its familiar spiral appearance.

"Astronomer Alister Graham used old and new observations to show how the evolution of galaxies from one shape to another takes place  — a process known as galactic speciation . The research shows that clashes and subsequent mergers between galaxies are a form of "natural selection" that drives the process of cosmic evolution.

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"Galaxies come in an array of shapes. Some, like the Milky Way, are composed of arms of well-ordered stars revolving in a spiral shape around a central concentration or "bulge" of stellar bodies. Other galaxies like Messier 87 (M87) are composed of an ellipse of billions of stars chaotically buzzing around a disordered central concentration.

"Since the 1920s, astronomers have classified galaxies based on a sequence of varying galaxy anatomy called the "Hubble sequence." Spiral galaxies like ours sit at one end of this sequence, while elliptical galaxies like M87 sit at the other. Bridging the gap between the two are elongated sphere-shaped galaxies, lacking spiral arms, called lenticular galaxies.

"But what this widely-used system has lacked until now were the evolutionary paths that link one galaxy shape to another.

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"This [study] revealed the existence of two different types of bridging lenticular galaxies: One version that is old and lacks dust, and the other that is young and rich in dust.

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"When dust-poor galaxies accrete gas, dust, and other matter, the disk that surrounds their central region is disrupted, with said disruption creating a spiral pattern radiating out from their hearts. This creates spiral arms, which are over-dense rotating regions that create gas clumps as they turn, triggering collapse and star formation.

"The dust-rich lenticular galaxies, on the other hand, are created when spiral galaxies collide and merge. This is indicated by the fact that spiral galaxies have a small central spheroid with extending spiral arms of stars, gas and dust. Young and dusty lenticular galaxies have notably more prominent spheroids and black holes than spiral galaxies and dust-poor lenticular galaxies.

"The surprising upshot of this is the conclusion that spiral galaxies like the Milky Way actually lie between dust-rich and dust-poor lenticular galaxies on the Hubble sequence.

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"The history of the Milky Way is believed to be punctuated with a series of "cannibalistic" events in which it devoured smaller surrounding satellite galaxies to grow.

"This research indicates that in addition to this, our galaxy's cosmic "acquisitions" also included it accreting other material and gradually transforming from a dust-poor lenticular galaxy to the spiral galaxy we know today.

"Our galaxy is set for a dramatic merger with its closest large galactic neighbor, the Andromeda galaxy, in between 4 billion and 6 billion years. This collision and merger will see the spiral arm pattern of both galaxies erased and the new research indicates that the daughter galaxy created by this union is likely to be a dust-rich lenticular galaxy still possessing a disk, albeit without a spiral structure carved through it."

Comment: we live in a giant spiral galaxy safely halfway out the second spiral arm far from the very active center with its giant black hole. Not to worry about Andromeda colliding. Our sun will be dying at that point, and we won't survive the explosion, if we still exist. My view of God's role is monitoring the Milky Way's development placing the Earth properly for our safety.