| Description | William Herschel (who else?) discovered this globular cluster on December 31, 1788. It's dimmer than most other GC's and averages about 300,000 ly from both our solar system and the galactic center, taking about 3 billion years to complete a single orbit around the Milky Way. As the current best-estimate of the Milky Way is about 100,000 ly in diameter, the orbit takes it well outside the nominal boundaries of our galaxy. Originally astronomers thought it might be an intergalactic wanderer, but the current best theory is that it isn't. That said, the cluster seems to combine two populations of stars, one more helium-rich than the other, raising questions about how it actually did form. |
