Here's why:
* Massive Stars: Stars with more mass than our Sun have a much stronger gravitational pull, which leads to higher core temperatures and pressures. This causes them to burn through their nuclear fuel much faster.
* Evolution: As massive stars age, they exhaust their hydrogen fuel and begin fusing heavier elements in their core. This process expands the star's outer layers, making it significantly larger and cooler.
* Surface Temperature: The expansion of the star's surface area leads to a lower surface temperature, even though the core remains extremely hot.
Key Points:
* Red giants are significantly larger than our Sun, sometimes even swallowing nearby planets.
* They are cooler, giving them a reddish hue.
* They are in a later stage of stellar evolution.
Example: Betelgeuse, a bright red supergiant star in the constellation Orion, is much more massive than our Sun, but its surface temperature is significantly lower.
