Beyond the Solar System
From the nearest stars to the edge of the observable universe — the objects, processes and distances that shape the cosmos.
Cosmic distance scale
Our planet, about 12,742 km across.
Our galaxy is a barred spiral about 100,000 light-years across, containing a few hundred billion stars, gas and dust, all embedded in a much larger halo of dark matter. The Sun lies about 26,000 light-years from the centre and takes roughly 230 million years to complete one orbit.
At the centre sits Sagittarius A*, a supermassive black hole of about 4.3 million solar masses, imaged by the Event Horizon Telescope in 2022. ESA's Gaia mission measured positions and motions for nearly two billion of the galaxy's stars, revealing ancient mergers in its history.
| Star | Type | Distance (ly) |
|---|---|---|
| Proxima Centauri | M5.5 V red dwarf | 4.2465 |
| Alpha Centauri A & B | G2 V + K1 V | 4.37 |
| Barnard's Star | M4 V red dwarf | 5.96 |
| Wolf 359 | M6 V red dwarf | 7.86 |
| Lalande 21185 | M2 V red dwarf | 8.31 |
| Sirius A & B | A1 V + white dwarf | 8.6 |
| Epsilon Eridani | K2 V | 10.47 |
| Tau Ceti | G8 V | 11.9 |
Distances from parallax measurements (rounded). Proxima Centauri hosts at least one confirmed planet, Proxima b.
Star classification
Class G
Yellow dwarfs like our Sun.
Approximate main-sequence ranges; boundaries vary slightly between sources. Shares are for stars in the solar neighbourhood.
Clouds of gas and dust. Emission nebulae such as the Orion Nebula glow where young hot stars ionise hydrogen; planetary nebulae are the shed outer layers of dying Sun-like stars; supernova remnants such as the Crab Nebula expand from stellar explosions.
Spirals, ellipticals and irregulars hold millions to trillions of stars. The Milky Way and Andromeda are approaching each other and are expected to interact in several billion years. Deep surveys suggest the observable universe holds hundreds of billions of galaxies or more.
Regions where gravity prevents anything escaping from within the event horizon. Stellar black holes form from collapsing massive stars; supermassive black holes of millions to billions of solar masses sit at galactic centres. Merging black holes emit gravitational waves, first detected by LIGO in 2015.
Collapsed stellar cores about 20 km across with more mass than the Sun, made largely of neutrons. Rapidly spinning, magnetised neutron stars appear as pulsars. Merging neutron stars forge heavy elements such as gold, as seen in the 2017 event GW170817.
Core-collapse supernovae end the lives of massive stars; Type Ia supernovae destroy white dwarfs that exceed their mass limit. Type Ia events are 'standard candles' that revealed the accelerating expansion of the universe in 1998.
Light has had about 13.8 billion years to reach us, but because space has expanded meanwhile, the most distant regions we can see are now about 46.5 billion light-years away. The cosmic microwave background marks the limit of what light can show us.
Calculate a black hole's event horizon with the Schwarzschild radius calculator, or explore relativity with the time dilation calculator.