What is the structure and composition of galaxies?

Introduction

Galaxies are complex, massive systems composed of stars, stellar remnants, gas, dust, and dark matter. Understanding their structure and composition is crucial for comprehending the broader universe. This synthesis explores the structural components and composition of galaxies, drawing insights from multiple research papers.

Key Insights

Hierarchical Structure of the Universe:
- Galaxies are massive, gravitationally bound systems consisting of stars, stellar remnants, gas, dust, and dark matter. They form clusters and superclusters, creating a nonuniform distribution known as the Cosmic Web.
Components of Disc Galaxies:
- Disc galaxies typically have a centrally concentrated spheroid, a thin disc with stars in nearly circular orbits, and a thick disc with properties intermediate between the thin disc and the spheroid. The spheroid is composed mainly of old, metal-poor, and α-enhanced stars, while the thin disc is younger and more metal-rich.
Spiral Structure of the Milky Way:
- The Milky Way is a disk-shaped galaxy with four spiral arms, two of which are large and two smaller. These arms are regions of active star formation, dominated by young stars, dust, and gas. The galaxy also contains an extensive dark halo, which exerts gravitational pull on visible matter .

Conclusion

Galaxies are intricate systems with a hierarchical structure, forming part of the larger Cosmic Web. Disc galaxies feature a spheroid, thin disc, and thick disc, each with distinct characteristics. The Milky Way, a disk-shaped galaxy, has a well-defined spiral structure with regions of active star formation and an extensive dark halo. Understanding these components provides valuable insights into the composition and evolution of galaxies.

What is the structure and composition of galaxies?

Summary

Introduction

Key Insights

Conclusion

Sources and full results

Formation of galaxies in Λcold dark matter cosmologies – I. The fine structure of disc galaxies

In a cold dark matter scenario, disc galaxies have a slowly rotating central spheroid, two disc components, and a thick disc with intermediate properties, possibly resulting from merger-driven processes and long-lived internal perturbations.

The Structure of the Universe

The universe is organized into hierarchical structures, with galaxies, stellar associations, and superclusters of galaxies forming the Cosmic Web, a nonuniform structure composed of walls and voids.

The Spiral Structure of the Milky Way Galaxy from Radio Observations

The Milky Way galaxy is a disk-shaped galaxy with four spiral arms, dominated by young stars, dust, and gas, and a dark halo void of luminous stars.

On the spiral structure of the Milky Way Galaxy

The Milky Way Galaxy has a four-arm spiral pattern in the inner region, with asymmetric multi-arm spiral arms in quadrants III and IV, and a regular magnetic field in the Carina and Cygnus arms.

Density Wave Theory of Spiral Structure of Galaxies

The density-wave theory of spiral structure in galaxies explains the gravitational instability of galactic disks and offers a general framework for future research in continuum mechanics.

Galaxies appear simpler than expected

The structure of galaxies, as observed through neutral hydrogen radio-frequency emission, appears to be controlled by a single parameter, contradicting the hierarchical galaxy formation theory.

Constraints on galaxy structure and evolution from the light of nearby systems

Nearby galaxy light can constrain galaxy structure and evolution, revealing shapes, stellar motions, compositional clues, and dark matter content, impacting the current theory of hierarchical galaxy formation.

The structures of distant galaxies - V. The evolution of galaxy structure in stellar mass at z < 1

Starlight mass maps reveal clear separations between early- and late-type galaxy morphologies, but cannot easily distinguish between star formation and dynamically disturbed systems.

What shapes a galaxy? – unraveling the role of mass, environment, and star formation in forming galactic structure

Distance from the star forming main sequence and stellar mass are more predictive of galaxy structure than global star formation rate or environmental metric.

The structure of galaxy clusters in various cosmologies

Galaxy clusters have a higher proportion of disordered clusters in critical-density universes, but their structure is similar in both high-resolution N-body simulations and low-resolution ones.

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