M94

M94 is approximately 17 million light years distant and contains both inner and outer rings.  Star formation occurs in both rings but is mainly concentrated in the inner ring which is also known as a starburst ring, within this region, the rate of star formation is occurring so fast that it will exhaust the available interstellar gas supply well before the death of the galaxy.  The extensive outer ring contains about 20% of the galaxies mass and consists of spiral arms when viewed in IR/UV,  however, in  visible light it appears as a halo.  Exactly how the outer ring formed is subject to debate.  Past theories include gravitation interaction with a nearby star system or accretion of a satellite galaxy, however, problems have been identified with each of these theories.  It is also strange that in 2008 a study indicated that M94 also seems to have little or no dark matter, which is very odd since it is inconsistent with current galaxy formation models.  So, all in all, a very mysterious object.