SPACE, EXPLAINED SIMPLY
Vast stellar cities that make up the cosmic web.
01
A galaxy is a gravitationally bound system of stars, planets, gas, dust, and dark matter. The largest galaxies can contain trillions of stars and span more than a million light-years.
Most large galaxies host a supermassive black hole at their centres, but that black hole does not hold the entire galaxy together alone. The combined mass of all its components, including dark matter, shapes stellar motions.
02
The familiar galaxy types are spiral, elliptical, and irregular. Spiral galaxies have disks and arms, ellipticals usually appear smoother and rounder, and irregular galaxies lack a clear symmetric form.
Shapes change over cosmic history. Gravitational encounters and mergers can distort galaxies, trigger star formation, and alter gas motions, while the viewing angle also changes the appearance we see.
03
The Solar System lies in a spiral arm of the Milky Way, roughly between the galactic centre and the edge of its disk. Because we are inside our own galaxy, we cannot take a photograph of it from outside.
Astronomers infer its structure from the positions and motions of stars, gas clouds, and other objects. They also compare the Milky Way with other spiral galaxies that can be observed from the outside.