Why are white dwarf supernovae more useful for measuring cosmic distances than massive star supernovae?

White dwarf supernovae, particularly Type Ia supernovae, are crucial for measuring cosmic distances because they have a consistent true peak luminosity. This characteristic stems from the mechanism behind their explosion, which involves the thermonuclear detonation of a white dwarf that has reached the Chandrasekhar limit (approximately 1.4 times the mass of the Sun). Since this limit is consistent across all white dwarfs, the energy output at the peak of the explosion is also uniform.

This reliability allows astronomers to use white dwarf supernovae as "standard candles" for distance measurement in the universe. By comparing the known peak luminosity to the observed brightness, astronomers can calculate how far away the supernova is, allowing for precise distance estimations in the cosmos.

In contrast, massive star supernovae (such as Type II supernovae) have a more variable luminosity depending on the progenitor star's mass and other factors, making them less reliable for such measurements. Their unpredictability in terms of brightness means they do not serve as effective standard candles like white dwarf supernovae do.