A Type Ia supernova is a powerful explosion that occurs in a binary star system, where one star is a white dwarf. The white dwarf accumulates material from its companion star until it reaches a critical mass, leading to a runaway nuclear reaction. This explosion results in a brilliant burst of light, often outshining entire galaxies. Type Ia 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 the expansion of the universe and the effects of dark energy.