Galactic orbits

A galaxy is a chaotic place. Sure, they may look silent and motionless, suspended in space, but a galaxy is in constant motion. Hundreds of billions of stars, swirling around at hundreds of meters per second, gravitationally fixed in place by the pull of a supermassive black hole [1]

But there’s more than one way to orbit a galaxy. Spiral galaxies like the Milky Way where we live actually have several distinct populations of stars. The youngest stars lie in the galaxy’s disk along with us. These stars undulate and wobble up and down as they orbit the centre of the galaxy, staying loosely in a single plane. A big stellar pancake, if you will.

Then you have the halo stars. These have much larger orbits which carry them up far from the galaxy’s disk. A galactic halo is essentially a diffuse cloud of stars in a loosely spheroid shape around the galaxy. Not many new stars form out in orbits like these. Halo stars are old. Some of them very old indeed.

Finally, you have the bulge orbits. The galactic bulge is the bright patch surrounding the core of the galaxy, also roughly spheroidal in shape. This region is packed full of dense interstellar clouds, held fast by the supermassive black hole’s gravity. Along with those clouds are an assortment of stars in fast and chaotic orbits. Some of these stars are young and bright, freshly squeezed from interstellar clouds by galactic tidal forces. Others are as old as the galaxy itself and have spent their entire lives living in the gravitational strangehold of the galactic centre. It is these Halo stars, Pulsars and Quasars that are the basis of Astronavigation and are anchor points for Navigation purposes. The Astrographical Society (Union Astrographical Society ) issues a yearly update on the positions of these Halo stars along with a Universal time reference and spatial reference to Pluribus Unum. (The same organization also maintains the Galactic Ping )