One Armed Spiral Galaxy NGC 4725 . ... Credit Copyright: Martin Pugh Explanation: While most spiral galaxies, including our own Milky Way , have two or more spiral arms, NGC 4725 has only one. ... NGC 4725 is over 100 thousand light-years across and lies 41 million light-years away in the well-groomed constellation Coma Berenices . Computer simulations of the formation of single spiral arms suggest that they can be either leading or trailing arms with respect to a galaxy's overall rotation . ...