Astronomers use Type Ia supernovae as "standard candles" to measure distances across the universe.

Type Ia supernovae occur in binary star systems where a white dwarf orbits a companion star. Over time, the white dwarf's gravity pulls material from its partner, steadily increasing its mass until it reaches the Chandrasekhar limit—approximately 1.44 times the mass of our Sun. At this critical threshold, the star becomes unstable and undergoes a catastrophic thermonuclear explosion.Because these stars always explode at the same mass, they release a consistent amount of energy and light. This uniformity allows astronomers to treat them as "standard candles," much like knowing the wattage of a distant light bulb helps you judge how far away it is. By measuring the observed peak luminosity, researchers can determine the distance to the host galaxy with remarkable precision.This technique proved revolutionary in 1998 when two independent teams—the Supernova Cosmology Project and the High-Z Supernova Search Team—observed distant Type Ia supernovae. Their observations revealed that these explosions were dimmer than expected, indicating they were farther away than a decelerating universe model would predict. This discovery provided the first direct evidence for dark energy and the accelerating expansion of the universe.The leaders of these teams, Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess, were awarded the 2011 Nobel Prize in Physics for this groundbreaking achievement. Today, Type Ia supernovae remain among the most reliable tools for mapping the cosmos and studying dark energy's effects across billions of years.