A planetary nebula in Sagittarius, 3000 light-years away, features waves 100 billion kilometres high, caused by supersonic shocks from a hot star's stellar winds. Hubble's image of the Carina Nebula ...
Galaxies like the Milky Way grow by merging with smaller galaxies over billions of years, unlike dwarf galaxies, which have long been thought to lack the heft to attract mass and grow in the same way.