Passage: Unlike most spiral galaxies, NGC 4625 has a single spiral arm, which gives the galaxy an asymmetric appearance.  It has been hypothesized that this galaxy's asymmetric structure may be the result of a gravitational interaction with NGC 4618.  Such asymmetric structure is commonly seen among many interacting galaxies.  However, observations of neutral hydrogen gas in NGC 4618 and NGC 4625 show that NGC 4625 does not appear to have been affected by the gravitational interaction.  This indicates that the single-arm structure seen in NGC 4625 may be created through intrinsic processes.

Question: What is NGC 4625 galaxy's uniqueness?
single spiral arm