Thursday, October 12, 2017

The Cosmic Web: Galactic Communities and Voids

In the December 2016 issue of Discover magazine is an article entitled “Why Nothing Really Matters”— Gaping cosmic voids might hold the answers to dark matter, dark energy and the very foundations of the universe:

“Between here and the moon, about a quarter-million miles away, there’s virtually nothing — just stray hydrogen, helium and the odd dust particle. On far grander scales, this barrenness becomes unimaginably vast. A desolate, virtually starless, 2.5 million light-year gulf — that’s nearly 15 quintillion miles — separates our home galaxy, the Milky Way, from its nearest sizable neighbor, the Andromeda Galaxy.”

“Yet compared to cosmic scales, the Milky Way and Andromeda are right next door. Like neighbors awkwardly catching glances of each other through the windows, we can see Andromeda with the naked eye as a glowing smudge. The vast majority of the universe’s galaxies similarly huddle together. They gather into the equivalent of neighborhoods, cities and interconnected megalopolises known in astro-jargon as groups, clusters and filaments. Here in our Local Group, for instance, some 50-odd galaxies nestle within a dumbbell-shaped space 10 million light-years long.”

“In contrast to such typically close-knit galactic communities, enormous zones called voids are the ‘boonies’. For example, only several dozen small galaxies dot the Bo├Âtes Void, a spherical, bucolic region that spans a whopping 250 million light-years. (A more urban part of space might pack 10,000 galaxies into such a volume.) Void galaxies are the loneliest galaxies...”

“Cosmic voids, not galactic metropolises, are actually the cosmic norm. Voids occupy most of the universe....”

“The cosmos is akin to Swiss cheese or foam, with galaxies clumping by the hundreds of thousands around colossal cavities.”

“The Cosmic Web, to use the preferred nomenclature, emerged from fluctuations in the primordial cosmos that arose 13.8 billion years ago in the Big Bang. Dark matter — the mysterious, invisible substance reckoned to comprise 80 percent of the universe’s matter — clumped here and there, gravitationally drawing regular matter toward it. As the universe expanded and matured, these overdense regions of matter gelled into galaxy clusters, leaving underdense voids to grow emptier.”

“Then the Sloan Digital Sky Survey, the biggest redshift survey to date, bagged thousands upon thousands of voids...
Looking at them as a whole, we're gleaning that they're typically oval-shaped and span 50 million to 150 million light-years in the modern, nearby universe. A few billion years ago, though, voids tended to be smaller. That suggests they're growing, joining together in places, squeezing and concentrating dark and luminous matter between them. Voids evolve in a hierarchical way. They build up into bigger soap suds, like in your kitchen sink, where you see the suds merging into larger bubbles."

“As voids grow, they become ever emptier. Such underdense areas have lower gravitational attraction than the surrounding overdense, galaxy-laced regions, and mass keeps on attracting mass. As the universe expands, voids have, in effect, acted repulsively, losing matter toward their more massive, galaxy-lined edges...”

Note: There is much that I’ve edited out and there’s yet more after where I left off. You can read the article by clicking on the following link:

Note: To what degree do you suppose the Cosmic Web is cosmologically related to Cosmic Law and Akasha?

More articles by Adam Hadhazy: