A Type Ia supernova is a powerful explosion that occurs in a binary star system, where one star is a white dwarf. This white dwarf accumulates material from its companion star, eventually reaching a critical mass. When this mass limit is exceeded, the white dwarf undergoes a thermonuclear explosion, resulting in a brilliant burst of light. These supernovae are important for astronomers because they have a consistent peak brightness. This allows scientists to use them as standard candles to measure distances in the universe, helping to understand its expansion and the presence of dark energy.