A very large collection of stars together with dust and gas held by their mutual gravitational attraction is known as which of the following?

Introduction / Context:
In astronomy, stars are not randomly scattered in space. They are organised into enormous systems that also include gas, dust, and dark matter. These systems are bound together by gravity and can contain millions or even billions of stars. This question asks for the term used to describe such a very large collection of stars and interstellar material held together by their mutual gravitational attraction.

Given Data / Assumptions:

• The system described includes stars, dust, and gas.
• It is held together by gravitational attraction.
• The options are cluster, atmosphere, galaxy, and Sun Family.
• We assume standard astronomical definitions found in school and competitive exam material.

Concept / Approach:
A galaxy is defined as a massive system of stars, stellar remnants, gas, dust, and dark matter arranged in a gravitationally bound structure. Our own Milky Way is a galaxy. A star cluster is a smaller grouping of stars, usually within a galaxy. Atmosphere refers to gas surrounding a planet or star. Sun Family is an informal way of referring to the solar system, which includes the Sun and its planets, not a whole galaxy. The approach is to match the described huge collection with the correct term, galaxy.

Step-by-Step Solution:
Step 1: Recognise that the description mentions a very large collection of stars, along with dust and gas, in a gravitationally bound system. Step 2: Compare with the definition of a galaxy, which fits this description exactly, with examples like the Milky Way, Andromeda, and other galaxies observed in deep space. Step 3: A cluster, such as an open cluster or globular cluster, is a smaller group of stars within a galaxy and does not usually include the huge mass of gas and dust associated with entire galaxies. Step 4: Atmosphere pertains to the gaseous envelope around planets or stars, not to an entire system of stars and gas in space. Step 5: Sun Family or solar system refers to the Sun and objects gravitationally bound to it, such as planets, asteroids, and comets, which is much smaller than a galaxy. Step 6: Therefore, the correct term for the structure described in the question is galaxy.

Verification / Alternative check:
Introductory astronomy resources describe galaxies as the basic large scale units of the universe, containing from millions to trillions of stars. They show images of spiral, elliptical, and irregular galaxies, all consisting of stars, dust, and gas in gravitational equilibrium. The solar system is described separately as a single star with its planets. Clusters are presented as subsets of stars inside galaxies. This classification confirms that the term that matches the description given is galaxy.

Why Other Options Are Wrong:

• Cluster: A cluster is a smaller grouping within a galaxy, not the very large full system of stars, gas, and dust that the question points to.
• Atmosphere: Refers to gas around a single planetary body or star, not to a whole star system with dust and gas.
• Sun Family: Informally describes the solar system, which is much smaller than a galaxy and only one part of a galaxy.

Common Pitfalls:
Some learners may confuse clusters with galaxies because both contain stars. The key difference is scale. A galaxy can contain many clusters, but a cluster cannot contain a full galaxy. Another pitfall is to misinterpret Sun Family as a bigger structure because it sounds large. Remember that the term galaxy is widely used in everyday language as well, for example in the name Milky Way galaxy, which should immediately bring to mind a huge collection of stars and interstellar material.

Final Answer:
A very large collection of stars, dust, and gas held together by gravity is called a galaxy.