Gravity is the architect. Given enough hydrogen in one place, gravity pulls it together until the core reaches 15 million Kelvin and nuclear fusion ignites. A star is born. For millions to billions of years, the outward pressure of fusion holds gravity at bay. When the fuel runs out, gravity wins. What follows — white dwarf, neutron star, or black hole — depends entirely on how much mass was there to begin with.
This is the stars and planets layer: the astrophysics of how gravity and nuclear physics create the large structures of the universe. Stars, stellar remnants, black holes, neutron stars, galaxy-scale dynamics, and the planets and moons that form around stars. It is also the layer where specific exoplanet discoveries live — the individual worlds we have found that might, or might not, harbor life.
The core questions at this scale
- What happens to a star when it dies — and does the answer depend on its mass?
- What are black holes, really, and how do we observe something that emits no light?
- How did Earth-like conditions arise around so many different stars?
- What do gravitational waves tell us about collisions we cannot see?
- Are there planets beyond our solar system with conditions suitable for life?
Stellar remnants and extreme objects
- Types of Black Holes — stellar-mass, supermassive, and primordial
- How Black Holes Form — the stellar collapse process in detail
- Neutron Stars Explained — the densest stable objects in the universe
- Magnetars Explained — neutron stars with the strongest magnetic fields known
- White Dwarf Stars — the quiet end state of most stars
- What Is a Quasar? — supermassive black holes at their most active
- Gravitational Waves — ripples in spacetime from colliding massive objects
The Milky Way and beyond
- The Milky Way Galaxy — our home galaxy in context
- Cosmic Rays Explained — high-energy particles accelerated by extreme events
- The Oort Cloud — the distant shell of comets at the edge of our solar system
Exoplanets — specific worlds
The site covers dozens of specific exoplanet discoveries in detail — from Kepler-22b to TRAPPIST-1d to LHS 1140 b. These are at How Scientists Detect Exoplanets. The most astrobiologically significant worlds connect directly to the Life layer below.
← Layer above: Matter — the particles and forces that make stars possible → Layer below: Life — where planetary chemistry becomes biology