BULL'S-EYE. Hoag’s Object, a galaxy 600 million light-years away, has a familiar yellow core and a normal outer region of young blue stars, but the rest of it is missing. It’s unique in the cosmos except for a similar ring galaxy within it.
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.
