Galaxies, like so many other astronomical objects, are surprisingly difficult to define. Here’s a hand-wavy attempt: a galaxy is a collection of stars, gas, dust and dark matter all held together by ...
A surprisingly mature spiral galaxy named Alaknanda has been spotted just 1.5 billion years after the Big Bang—far earlier than astronomers believed such well-structured galaxies could form. With ...
Tiny galaxies orbiting the Milky Way may hold clues to one of cosmology’s biggest mysteries. Ultra-faint dwarf galaxies are among the smallest known galaxies orbiting the Milky Way. Astronomers have ...