If a main-sequence star suddenly started burning hydrogen at a faster rate in its core, it would become. a. larger, hotter, and more luminous. b. larger, cooler, and more luminous. c. smaller, hotter, and more luminous. d. smaller, cooler, and more luminous.

Hydrogen fusion is the process that powers main-sequence stars. This process occurs in the core of the star, where temperatures and pressures are extremely high.
During hydrogen fusion, hydrogen nuclei combine to form helium, releasing a tremendous amount of energy in the form of light and heat.
This energy then radiates outward, providing the star with its luminosity and heat. Hydrogen fusion is a delicate balance. If a star starts burning hydrogen at a faster rate, the core temperature and pressure increase, which leads to various changes in the star's structure and behavior.

Stellar luminosity is a measure of how much light a star emits. It's an important characteristic that can tell us a lot about a star's size, temperature, and energy production.
When hydrogen fusion happens at a faster rate, more energy is produced in the star's core. This increased energy output means the star becomes more luminous.
Think of it like turning up a light bulb to a higher wattage; it becomes brighter because it's using more energy. For main-sequence stars, an increase in fusion activity not only makes them hotter but also significantly increases their luminosity.
Higher luminosity affects how a star is observed from Earth, making it appear brighter in the night sky.

The core temperature of a main-sequence star is crucial for maintaining the balance between gravity and the pressure from fusion reactions. When hydrogen fusion speeds up, the temperature in the core rises.
This higher temperature increases the rate of fusion, creating even more energy and thus making the core even hotter.
The increased core temperature also impacts the surrounding layers of the star, causing them to expand and the overall size of the star to increase.
In summary, a rise in core temperature leads to a chain reaction of increased energy production, higher luminosity, and changes in the star’s size and structure.