What is difference between galaxy and universe
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Difference Between Galaxy and Universe
Understanding the difference between a galaxy and the universe is fundamental in the field of astronomy. These terms, while often used interchangeably in casual conversation, refer to vastly different scales and structures within the cosmos.
Definition of a Galaxy
Gravitationally Bound Systems
A galaxy is a massive, gravitationally bound system that consists of stars, stellar remnants, an interstellar medium of gas and dust, and dark matter. Galaxies are the primary building blocks of the universe and come in various shapes and sizes, including spiral, elliptical, and irregular forms .
Star Clusters and Stellar Associations
Within galaxies, stars are grouped into clusters and associations. These include open clusters, which are loosely bound groups of a few thousand stars, and globular clusters, which are tightly bound groups of up to hundreds of thousands of stars. These clusters are significant regions of star formation and evolution.
Classification Challenges
The classification of galaxies can be complex, especially with the discovery of low luminosity and low surface brightness objects. These objects challenge traditional definitions, leading to new criteria based on gravitational binding and the inability to explain their properties solely through baryons and Newton's laws of gravity.
Definition of the Universe
Vast and Inclusive
The universe encompasses everything that exists, including all matter, energy, planets, stars, galaxies, and even the very fabric of space and time. It is a vast, incomprehensible expanse that includes countless galaxies, each containing millions or even billions of stars.
Hierarchical Structure
The universe is structured hierarchically. Galaxies form clusters, which in turn form larger superclusters. These superclusters are not uniformly distributed but form a complex structure known as the Cosmic Web. This web consists of walls and voids, remnants of fluctuations in matter from the early universe, post-Big Bang.
Beyond the Observable
While our galaxy, the Milky Way, is just one of many within the universe, the term "universe" refers to the totality of all these galaxies and the space they inhabit. The universe extends far beyond what we can observe with current technology, containing regions and phenomena that remain beyond our comprehension.
Conclusion
In summary, a galaxy is a specific, gravitationally bound system of stars, gas, dust, and dark matter, while the universe is the all-encompassing expanse that includes all galaxies and everything else in existence. Understanding this distinction helps clarify the scale and structure of the cosmos, from the relatively small and comprehensible galaxies to the vast and mysterious universe.
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