Far out cosmology: the Milky Way neighborhood (Introduction)

by David Turell , Saturday, January 28, 2023, 16:09 (453 days ago) @ David Turell

The local sheet makes us special:

https://www.universetoday.com/159754/according-to-simulations-the-milky-way-is-one-in-a...

"...the Illustris TNG simulation shows that the Milky Way is special.

"Illustris TNG is an ongoing series of large-scale simulations. The goal is to understand the mechanisms behind galaxy formation and evolution. The effort is a “series of large, cosmological magnetohydrodynamical simulations,” according to the Illustris TNG website. So far, the project has produced three primary runs, each one larger and higher resolution than the previous one: TNG 50, TNG 100, and TNG 300. Each run also focuses on various aspects of galaxy formation. TNG 300 is the largest, simulating a region of almost 300 million megaparsecs, over a billion light-years across, and containing millions of galaxies.

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"New research based on Illustris TNG shows that the Milky Way is special. But it’s not special purely for its intrinsic qualities. It’s special in relation to its surroundings.

"The findings are in a new paper based on Illustris TNG 300 published in the Monthly Notices of the Royal Astronomical Society. The title is “The unusual Milky Way-local sheet system: implications for spin strength and alignment.” The lead researcher is Miguel Aragón, a computational cosmologist and assistant professor at the National Astronomical Observatory, Universidad Nacional Autonoma de Mexico.

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"Cosmological walls are made up of galaxies. They’re a subtype of filaments, but they’re flattened and have voids on either side. The voids seem to squash the walls into their flattened shape. The cosmological wall nearest the Milky Way is called the Local Wall or Local Sheet.

"The Local Sheet influences how the Milky Way and other nearby galaxies rotate on their axes. The Milky Way takes about 250,000,000 years to rotate, and the study shows that the rotation is more organized than if the galaxy wasn’t near the Local Sheet.

"The study also shows that the Milky Way is special. While typical galaxies tend to be much smaller in relation to walls, the Milky Way is surprisingly massive in relation to the Local Wall. According to the research, this is a rare cosmic occurrence.

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"Specifically, the Local Sheet affects the spin of the Milky Way. “… there are particularly strong alignments between the sheet and galaxy spins,” they explain, adding that in the simulation, the galaxies near walls have low spin parameters.

"This all affects how galaxies grow and merge over time, they think. It leads to lower-mass galaxies in these types of cosmic neighbourhoods. That’s why the Milky Way, with its high mass, is so unusual and why the simulation found only one like it in up to 200 cubic megaparsecs of space.

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“'The Milky Way doesn’t have a particularly special mass or type. There are lots of spiral galaxies that look roughly like it,” Joe Silk, another of the researchers, said. “But it is rare if you take into account its surroundings. If you could see the nearest dozen or so large galaxies easily in the sky, you would see that they all nearly lie on a ring embedded in the Local Sheet. That’s a little bit special in itself. What we newly found is that other walls of galaxies in the Universe like the Local Sheet very seldom seem to have a galaxy inside them that’s as massive as the Milky Way.”

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“"You do have to be careful, though, choosing properties that qualify as ‘special,’” Dr. Mark Neyrinck, another member of the team, said. “If we added a ridiculously restrictive condition on a galaxy, such as that it must contain the paper we wrote about this, we would certainly be the only galaxy in the observable Universe like that. But we think this ‘too big for its wall’ property is physically meaningful and observationally relevant enough to call out as really being special.'”

Comment: life appeared after many astronomical contingencies which created our special neighborhood and the Milky Way specialness. Luck or design? Take your preference, you know
mine.