Question

The mass of three clouds of gas and dust (nebulae) are provided below. Imagine that each cloud will collapse to form a single star. Use this information to complete the following and explain your reasoning. \- Cloud A is 60 times the mass of the Sun. Cloud \(\mathrm{B}\) is 7 times the mass of the Sun. Cloud \(\mathrm{C}\) is 2 times the mass of the Sun. a. Which cloud or clouds, if any, will evolve into a red main-sequence star? b. Which of the stars that will form from these clouds, if any, will reach the giant stage? c. Which of the stars that will form from these clouds, if any, will go through the supernova stage?

Short answer

None will become red main-sequence stars; all can become giants; only Cloud A will become a supernova.

Step-by-step solution

Assess Star Formation for Main-sequence Type

A red main-sequence star is typically a lower-mass star. Typically, stars with masses less than about 0.3 to 0.5 times the mass of the sun are considered red dwarfs. Given the masses: Cloud A (60 solar masses), Cloud B (7 solar masses), and Cloud C (2 solar masses), none of these clouds will form into red main-sequence stars because they all are above this threshold.

Determine Star Reaching the Giant Stage

Stars will reach the giant stage if they have enough mass to undergo significant nuclear fusion stages after the main sequence. Generally, stars with masses greater than about 0.3 times the solar mass evolve into the giant phase. Therefore, all three clouds (A, B, and C) are likely to evolve into the giant stage since they all exceed this mass limit.

Evaluate Star for Supernova Potential

A star will likely go through a supernova explosion if it has a mass greater than approximately 8 times that of the sun. From the given clouds, only Cloud A, with 60 solar masses, exceeds this threshold and can evolve into a supernova, while Clouds B and C, with 7 and 2 solar masses respectively, will not undergo supernova events.

Key concepts

Nebulae

Nebulae are vast clouds composed of gas and dust floating throughout space. They may appear as beautiful swirls and patterns, and can be seen in spectacular colors when viewed through telescopes. These cosmic cradles serve as the birthplace for stars. When conditions are right, parts of a nebula may contract under their own gravity. As the gas and dust pull together, the temperature and pressure inside increase. Eventually, this process can lead to the creation of new stars. There are different types of nebulae, including:

• Emission Nebulae: Gas within these nebulae is energized by nearby stars, causing it to glow.
• Reflection Nebulae: These do not create their own light but reflect the light of nearby stars.
• Dark Nebulae: Dense clouds of gas and dust that blot out light from stars and other nebulae behind them.

Understanding nebulae is crucial, as they are the starting point for star formation.

Main-sequence Star

A main-sequence star is one that is in a stable period of its lifecycle, where it fuses hydrogen into helium in its core. This process releases energy that balances the force of gravity pulling the star inward, maintaining its structure. Most of the stars in our universe, including the Sun, are in this stage, which can last billions of years. Main-sequence stars vary greatly in size and brightness, classified as:

• Dwarf stars, like red dwarfs, are typically cooler and composed of lower mass, shining faintly for potentially trillions of years.
• Giant stars, more massive than the Sun, burn hotter and brightly, consuming fuel rapidly.
• Intermediate-mass stars like our Sun, provide a moderate balance of brightness and longevity.

This stage is crucial in a star's lifecycle, as it sets the stage for further evolution into more complex stages.

Giant Stage

The giant stage marks a period in a star's life when it exhausts its hydrogen core. As hydrogen dwindles, the core contracts while the outer layers expand, leading to a significant increase in size and a cooling of the star's surface. Stars generally transition to this stage after their main-sequence phase, particularly when they have a sufficient mass to sustain nuclear fusion beyond hydrogen. In this stage, the star can become:

• Red Giant: Typically lower-mass stars, expanding dramatically.
• Supergiant: Stars with significantly higher mass, growing extremely large.

The giant stage is a transformative time, often leading a star towards its final fate, whether as a white dwarf, neutron star, or black hole.

Supernova

A supernova is a spectacular explosion occurring at the end of a massive star's life. When a star with a mass greater than about 8 times that of the Sun can no longer support itself against gravitational collapse, it leads to this explosive event. The explosion disperses the star's elements into space, often outshining entire galaxies for a short period. This occurrence is crucial for the creation of heavy elements, like iron, necessary for planet formation and life. The types of supernovae include:

• Type I: Occurs in binary systems due to the explosion of a white dwarf.
• Type II: Results from the collapse of a single, massive star's core.

Supernovae are pivotal cosmic events that recycle elements throughout the universe, contributing to the formation of new stars and worlds.