Messier 94 (also known as NGC 4736) is a
spiral galaxy in the constellation Canes Venatici. Although some
references describe M94 as a barred spiral galaxy, the "bar"
structure appears to be more oval-shaped. The galaxy is also
notable in that it has two ring structures, M94 contains both an
inner ring with a diameter of 70" and an outer ring with a
diameter of 600". These rings appear to form at resonance
locations within the disk of the galaxy. The inner ring is the
site of strong star formation activity and is sometimes referred
to as a starburst ring. This star formation is fueled by gas
that is dynamically driven into the ring by the inner
oval-shaped bar-like structure. A 2009 study conducted by an
international team of astrophysicists revealed that the outer
ring of M94 is not a closed stellar ring, as historically
attributed in the literature, but a complex structure of spiral
arms when viewed in mid-IR and UV. The study found that the
outer disk of this galaxy is active. It contains approximately
23% of the galaxy's total stellar mass and contributes about 10%
of the galaxy's new stars. In fact, the star formation rate of
the outer disk is approximately two times greater than the inner
disk because it is more efficient per unit of stellar mass.
