Messier 100, NGC 4321

Messier 100 is a beautiful spiral galaxy, and one of the brightest in the Coma-Virgo Cluster.

Like M 98 and M 99, Messier 100 was first seen by Pierre Mechain in 1781. Mechain's observations confirmed later that year by Charles Messier, who added it as the 100th object in his catalog. The galaxy's spiral structure was first detected by Lord Rosse with his six-foot reflector in 1850, and was listed as one of the 14 "spiral nebulae" known up to that time.

Appearance

With a visual magnitude of 9.3, Messier 100 is one of the brightest members of the Virgo Cluster of galaxies. It is located in the spring constellation Coma Berenices, and can be seen through a moderate-sized amateur telescope. Even good binoculars can show the central regions of this galaxy, as a faint elliptical patch of uneven texture. Messier 100 has a bright, small core embedded in a 7' x 6' oval halo. The halo is generally smooth and its edges diffuse, but some variation in brightness can be seen around the core. Under good observing conditions, suggestions of the inner spiral arms can be glimpsed in telescopes starting at 4" aperture.

Photos reveal the "grand design" spiral structure of M 100. It is a spiral galaxy, like our Milky Way, and tilted nearly face-on as seen from Earth. The galaxy has two prominent arms of bright blue stars, and several fainter arms. The blue stars in the arms are massive, hot, young stars which formed from density perturbations caused by interactions with neighboring galaxies. Deep photographs of M 100 have revealed that M 100 is actually much larger than it appears, and that a significant part of the its mass may lie in the faint outer regions.

Properties

M 100 has been imaged extensively by the Hubble Space Telescope, which has led to the discovery of over 20 Cepheid variables (as well as one nova). This, in turn, provided the first reliable distance determination for M 100: 56 million light years. M 100 is probably the largest spiral in the Virgo-Coma Galaxy Group, with a diameter over 130,000 light-years. M 100 seems to be exceptionally luminous, its apparent magnitude implying an absolute magnitude of -22.5, a luminosity of 83 billion suns. It is receding from us at about 960 miles per second.

Intense star formation activity is taking place in a ring of starburst activity along the periphery of M 100's innermost spiral arms. There have been several supernovae observed in this galaxy: 1901B, 1914A, 1959E, 1979C, and 2006X. Messier 100 has one satellite galaxy, NGC 4323.