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How does a star’s luminosity affect the location of its habitable zone?

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Habitable zone The habitable zones (green) for stars that are like the Sun (middle), hotter than the Sun (top), and cooler than the Sun (bottom). The red areas are those in which liquid surface water would be lost as a result of a runaway greenhouse effect, and the blue areas are those in which liquid surface water would be completely frozen.

The location of a star’s habitable zone—the orbital region where an Earth-like planet can maintain liquid water on its surface—is directly dependent on the star’s luminosity.

Because luminosity determines the amount of energy reaching a planet, it dictates the distance required to maintain temperatures suitable for liquid water. A more luminous star will have its habitable zone located further away, while a less luminous star will have a habitable zone located closer to it.

Furthermore, a star’s luminosity is not static; it typically increases over time. As a star becomes brighter, both the inner and outer boundaries of its habitable zone shift outward. Consequently, a planet that resides within the habitable zone during a star's youth may eventually become too hot as the zone moves past its orbit. Conversely, planets that are initially too cold may enter the habitable zone as the star’s luminosity increases over time.1