NGC 3109
NGC 3109 is classified as a Magellanic type irregular galaxy, but it may in fact be a small spiral galaxy. If it is a spiral galaxy, it would be the smallest in the Local Group. NGC 3109 has a mass of about 2.3×109 times the mass of the Sun, of which 20% of the mass is in the form of neutral hydrogen. It is oriented edge-on from our point of view, and may contain a disk and a halo. The disk appears to be composed of stars of all ages, whereas the halo contains only very old and metal-poor stars. NGC 3109 does not appear to possess a galactic nucleus.