Galaxies
Exploring cosmic structures and evolution across the universe
Overview
Galaxies are vast collections of stars, gas, dust, and dark matter bound together by gravity. They represent the fundamental building blocks of the universe, containing anywhere from millions to trillions of stars. Our own Milky Way is just one of an estimated two trillion galaxies in the observable universe.
The study of galaxies encompasses their formation, evolution, structure, dynamics, and interactions. Understanding galaxies helps us unravel the history of the universe, from the first stars that formed after the Big Bang to the complex cosmic web we observe today.
Galaxy Classification
Galaxies are classified into three main types based on their shape:
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Spiral Galaxies: Characterized by rotating disks with spiral arms, containing young stars, gas, and dust. Examples include the Milky Way and Andromeda Galaxy.
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Elliptical Galaxies: Smooth, featureless ellipsoids containing mostly older stars with little gas or dust. They range from nearly spherical to highly elongated.
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Irregular Galaxies: Lacking a distinct shape, often resulting from gravitational interactions or mergers with other galaxies.
Formation & Evolution
Galaxy formation is a complex process that began shortly after the Big Bang:
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Primordial Gas Collapse: Dark matter halos provided gravitational wells for gas to collapse and form the first stars.
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Hierarchical Merging: Small galaxies merged over billions of years to form larger structures.
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Ongoing Evolution: Galaxies continue to evolve through star formation, mergers, and interactions with their environment.
Key Research Areas
Dark Matter
Galaxies are embedded in massive dark matter halos that provide most of their gravitational mass. Understanding dark matter distribution is crucial for galaxy dynamics.
Learn more →Active Galactic Nuclei
Supermassive black holes at galaxy centers can become active, emitting enormous amounts of energy and influencing galaxy evolution.
Related: Stellar Evolution →Galaxy Clusters
Galaxies group together in clusters and superclusters, forming the largest structures in the universe through gravitational interactions.
Recent Discoveries
Ultra-Diffuse Galaxies
Recent observations have revealed a population of extremely faint, diffuse galaxies that challenge our understanding of galaxy formation. These galaxies have stellar masses similar to dwarf galaxies but are spread over much larger areas.
See JWST Findings →Galaxy Rotation Curves
Observations of how stars orbit galactic centers reveal discrepancies that provide evidence for dark matter. The rotation curves of spiral galaxies show stars moving at constant speeds regardless of distance from the center.
Learn Observation Techniques →