A galaxy is a gravitationally bound system of stars, gas, dust, and dark matter, ranging from dwarfs of a few million stars to giants holding a hundred trillion. Astronomers sort them broadly into spiral, elliptical, and irregular shapes, and most harbor a supermassive black hole at the center. Galaxies are not scattered at random: they gather into groups, clusters, and superclusters strung along the filaments of the cosmic web. Estimates of how many fill the observable universe range from a few hundred billion to two trillion, depending on how faint the counting goes.
Cosmology · Early Universe · Black Holes
When JWST looked deep into the early universe, it found a swarm of tiny, intensely red points of light. The leading answer would mean black holes appe...
Astrophysics · Milky Way · Stars
The Sun was not born alone. It formed in a cluster with thousands of sibling stars that long ago scattered across the galaxy. Using a spacecraft that ...
Cosmology · Search for Life · SETI
In 1961, a young astronomer wrote seven terms on a blackboard to organize a single impossible question: how many civilizations in our galaxy might we ...
Astrophysics · Milky Way · Galactic Center
In 2010, a space telescope revealed two colossal balloons of energy tens of thousands of light-years above and below the center of our galaxy, the sca...
Cosmology · Cosmic Distances · Expansion
You cannot lay a tape measure to a galaxy. Astronomers built a ladder instead, each rung a different method calibrated by the one below, reaching from...
Astrophysics · Milky Way · Star Clusters
Scattered around every large galaxy are dense spheres of hundreds of thousands of stars, among the oldest things in the universe. They once revealed o...