Correct Option
The correct option is 1 and 3 only.
Explanation
A galaxy is a massive gravitationally bound system consisting of stars, stellar remnants, interstellar gas, dust, and dark matter. The formation of stars is a fundamental process within the evolution of galaxies, originating from vast clouds of gas and dust known as nebulae.
Statement-wise Analysis
- Statement 1 is Correct: Galaxies are immense structures spread over vast distances. Their sizes are typically measured in thousands to hundreds of thousands of light-years. For instance, the Milky Way galaxy has a diameter of approximately 100,000 light-years.
- Statement 2 is Incorrect: A galaxy does not contain a small number of stars; rather, it contains a huge number of stars, ranging from hundreds of millions in dwarf galaxies to one hundred trillion in giant elliptical galaxies. The Milky Way alone is estimated to contain between 100 to 400 billion stars.
- Statement 3 is Correct: Star formation begins within a nebula. Under the influence of gravity, a growing nebula develops localized clumps of gas. These clumps get progressively denser and hotter, eventually forming gaseous bodies that ignite nuclear fusion to become stars.
Key Takeaway: Galaxies are vast systems containing billions of stars held together by gravity. Stars are born from the gravitational collapse of dense clumps of gas within nebulae.