The cosmic web: how gravity weaves the universe's architecture
In short: Galaxies are not isolated islands; they are the building blocks of a vast, interconnected cosmic web. From tiny dwarf systems to giants spanning millions of light-years, these massive structures of stars and gas are bound by gravity into a complex network of clusters and superclusters.
Gravity binds together massive clouds of dust and gas, along with planets and stars, to form a galaxy. These structures vary wildly in scale: the smallest can contain just a few thousand stars and span a few hundred light-years, while the largest can house trillions of stars and stretch across more than a million light-years. While many galaxies aged 10 billion to 13.6 billion years, others emerged nearly 13.8 billion years ago, shortly after the universe's birth.
The diversity of galaxies is driven by their evolutionary history. Astronomers classify them primarily by shape into spirals, ellipticals, and irregular forms. Some are vibrant hubs of activity, featuring glowing gas and molecular complexes where new stars are vigorously forming. Others are quiescent, having long ago ceased star production. At the heart of many large galaxies lies a supermassive black hole, some with masses billions of times that of our Sun. These objects are so luminous in the distant past that they appear as quasars.
On a larger scale, galaxies organize into groups of about 100 or fewer members, which further aggregate into clusters containing thousands of galaxies. These clusters can reach dimensions of hundreds of millions of light-years. These structures are arranged into superclusters, which are separated by nearly empty voids. This arrangement creates a cosmic web—a network of sheets, chains, and walls of matter that defines the large-scale structure of the universe.
Our home, the Milky Way, is a spiral galaxy with a disk spanning more than 100,000 light-years. Earth sits along one of its spiral arms, roughly halfway from the center. Our solar system completes one orbit around the Milky Way every 240 million years. We reside in the Local Group, a neighborhood of over 50 galaxies, which sits off the edge of the Virgo cluster and belongs to the Laniakea supercluster.
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Sources
- Summary by Intellect · source: What is a Galaxy?
- Also: Galaxies - NASA Science
- Also: Galaxy | Definition, Formation, Types, Properties, & Facts | Britannica
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