sentences:  By way of comparison, the Milky Way galaxy has an estimated diameter of 150-200 kly and consists of between 100 and 500 billion stars and a mass of around 1.54 trillion suns.The gap separating the two stellar populations may contain some star clusters that are almost too faint to see.Though ring galaxies are rare, another more distant ring galaxy (SDSS J151713.93+213516.8) can be seen through Hoag's Object, between the nucleus and the outer ring of the galaxy, at roughly the one o'clock position in the image shown here.