type-ia-supernovae

When the Sun dies, it will leave behind a white dwarf — a city-sized object containing half the Sun's mass, supported not by nuclear fusion but by quantum mechanics. White dwarfs are already the most common stellar remnants in the galaxy, and every star you see in the night sky under 8 solar masses will eventually become one. Some will detonate as the universe's most reliable distance markers. Others will crystallize into diamond-like spheres and cool for trillions of years.

In 1998, two teams studying distant Type Ia supernovae found that cosmic expansion is speeding up. The cause, dark energy, makes up about 68% of the universe's energy budget, and nobody knows what it is.

The Chandrasekhar limit, about 1.44 solar masses, is the heaviest a white dwarf can be before electron degeneracy pressure fails. It shapes Type Ia supernovae, cosmic distance measurements, and which stellar remnants become white dwarfs, neutron stars, or black holes.

From parallax to supernovae, astronomers chain overlapping methods together to measure distances from the nearest stars to galaxies billions of light-years away. Here is how each rung of the cosmic distance ladder works, and why its top rung is now in dispute.