Also known as NGC 4736, is a spiral galaxy in the constellation Canes Venatici, about 17.0 ± 1.4 million light-years from Earth. It was discovered by Pierre Méchain in 1781, and catalogued by Charles Messier two days later. Although some references describe M94 as a barred spiral galaxy, the “bar” structure appears to be more oval-shaped. M94 is one of the brightest galaxies within the M94 Group, a group of galaxies that contains between 16 and 24 galaxies. This group is one of many that lie within the Virgo Supercluster. Although a large number of galaxies may be associated with M94, only a few galaxies near it appear to form a gravitationally bound system. Most of the other nearby galaxies appear to be moving with the expansion of the universe.
M94 is also notable in that it has two ring structures; contains both an inner ring with a diameter of 70″ (secs) and an outer ring with a diameter of 600″. 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 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, containing 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. There are several possible external events that could have led to the origin of M94’s outer disk including the accretion of a satellite galaxy or the gravitational interaction with a nearby star system. However, further research found problems with each of these scenarios. Therefore, the report concludes that the inner disk of M94 is an oval distortion, which led to the creation of this galaxy’s peripheral disk.
The latest image from the Hubble Space Telescope peers into the heart of one of the most beautiful galaxies in the Messier catalog. M94 itself may be a little on the small size, spanning just 50,000 light-years across (our own galaxy is at least twice its size), but its central core is among the brightest. Of course, that is far from the most beautiful feature; that honour goes to its intricate series of rings, which seamlessly blend into its sweeping spiral arms.
Within Messier 94’s brightest and most prominent ring, new stars are born at a fervent rate. Called a starburst ring, the feature suggests M94 was recently involved in some collision or merger, most likely with a satellite galaxy, or a similarly small companion. “The cause of this peculiarly shaped star-forming region is likely a pressure wave going outwards from the galactic centre, compressing the gas and dust in the outer region,” the ESA explains. “The compression of material means the gas starts to collapse into denser clouds. Inside these dense clouds, gravity pulls the gas and dust together until temperature and pressure are high enough for stars to be born.”
Credits: NASA, Wikipedia.