Galaxies are the largest things in the universe. Happily for us, they come in only a few varieties, making them easier to identify and theorize about. Nearly all are either elliptical (ball-shaped), irregular, or else spirals of various kinds. But a handful of oddballs fit none of these categories, and one galaxy stands all by itself.

In 1950, astronomer Arthur Hoag came upon a tiny, faint, 16th-magnitude ring surrounding a ball-like center, and reasonably assumed it was a planetary nebula — a nearby puff of gas expelled from a single old-aged star. He also proposed an alternative and far more exotic explanation that this was an “Einstein Ring” from a faraway quasar. In this scenario, the quasar’s light is distorted into a halo by space-warping caused by a massive foreground spherical galaxy that it seems to surround. But later spectroscopic studies rejected this because the golden central ball and the blue ring have exactly the same redshift, indicating a whopping rush-away speed of 7,916 miles (12,740 kilometers) per second, which proves they’re both located exactly the same distance from us.

Hoag also thought it possible that this was some sort of peculiar galaxy. And — as if to prove that if you make enough guesses, you increase your chance of success — his last surmise was right.

In 2002, the ultra-sharp optics of the Hubble Space Telescope revealed Hoag’s Object, as it is now called, as a perfect blue ring of stars, dust, and gas, complete with knotty clumps that are unresolved star clusters. In other words, yes, this is a galaxy. The problem, of course, is that Hoag’s Object does not assume the familiar spiral pattern, with arms wending their way inward to the older, yellower stars that make up nearly every galaxy’s nucleus. Instead, the nucleus sits all by itself in space. A whopping 70,000 light-years away from it, separated by near-nothingness, hovers that ring of billions of stars, planets, and who-knows what else.

Hoag’s Object lies 600 million light-years away from us in the constellation Serpens Caput, the rear half of the writhing snake held by Ophiuchus the Serpent Bearer. Its inner yellow core is 24,000 light-years across, almost the same as the core of our Milky Way. The outer ring of Hoag’s Object, with a width of 120,000 light-years, is similar in size to our galaxy’s diameter. It’s almost as if some malevolent alien starship vacuumed up the middle sections of a galaxy but bewilderingly spared both the center and the outermost regions.