Difference between galaxy and universe
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Difference Between Galaxy and Universe
Understanding the Galaxy: Definition and Structure
A galaxy is a massive, gravitationally bound system that includes stars, stellar remnants, an interstellar medium of gas and dust, and dark matter. Galaxies are the fundamental building blocks of the universe and come in various shapes and sizes, from spiral to elliptical forms 2. Each galaxy contains millions to billions of stars, along with their planetary systems, and can also include star clusters and nebulae 3.
Galaxies are not isolated; they often form clusters and superclusters, which are large groupings of galaxies bound together by gravity. These clusters and superclusters are part of a larger structure known as the Cosmic Web, which consists of walls and voids formed by the nonuniform distribution of galaxies in the universe 2.
The Universe: A Vast and Expanding Entity
The universe encompasses everything that exists, including all galaxies, stars, planets, and the cosmic structures that bind them together. It is a vast, expanding space that originated from the Big Bang, an event that occurred approximately 13.8 billion years ago 5. The universe contains billions of galaxies, each with its own unique properties and structures 3.
The universe is not just a collection of galaxies; it also includes intergalactic space, which is filled with gas, dark matter, and cosmic radiation. The average density of the universe is close to the critical value needed to halt its expansion, with only about 3 percent of this density contained within galaxies. The rest is primarily intergalactic gas and dark matter 5.
Key Differences Between Galaxy and Universe
Scale and Composition
- Scale: A galaxy is a single, gravitationally bound system, whereas the universe includes all galaxies and the space between them. The universe is incomprehensibly larger than any individual galaxy 12.
- Composition: Galaxies are composed of stars, gas, dust, and dark matter, while the universe contains all of these components plus intergalactic space and cosmic radiation 25.
Structure and Organization
- Structure: Galaxies have a defined structure, often categorized into types such as spiral, elliptical, and irregular. The universe, on the other hand, has a hierarchical structure that includes galaxies, clusters, superclusters, and the Cosmic Web 2.
- Organization: Galaxies are organized into clusters and superclusters, which are part of the larger Cosmic Web. The universe itself is the overarching entity that contains all these structures 25.
Observational Differences
- Observational Scope: Studying a galaxy involves examining its stars, planetary systems, and interstellar medium. Studying the universe involves understanding the large-scale structure, cosmic background radiation, and the overall dynamics of cosmic expansion 25.
- Tools and Techniques: Observations of galaxies often focus on their individual properties and interactions, while observations of the universe require understanding cosmological phenomena such as the Big Bang and cosmic microwave background radiation 5.
Conclusion
In summary, while a galaxy is a massive, gravitationally bound system of stars, gas, and dark matter, the universe is the all-encompassing space that includes all galaxies and the cosmic structures that connect them. The universe is vastly larger and more complex, containing not only galaxies but also intergalactic space, dark matter, and cosmic radiation. Understanding the differences between these two entities helps us appreciate the scale and complexity of the cosmos.
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