Astronomical Observatory: Cool Images

Astr111 Photography Projects, Spring 2007

Messier 99 Spiral Galaxy (M99), Phil Beverly

Messier 99 is a spiral galaxy in the Coma Berenices constellation.  Galaxies are massive systems of stars (some contain up to trillions of stars!) and other interstellar objects. In 1781, Pierre Mechain discovered this galaxy, and in 1846, Messier 99 became the second galaxy to be discovered as a spiral (Kronberg).  Messier 99 is one of the brightest galaxies in the Virgo Cluster that has a spiral shape (Knapen and Szymanek).  This galaxy is "about 50 million light-years away from us...[and] has a total mass of about 50 billion suns” (Leach). 

All spiral galaxies are shaped in a disk, which includes a bright white-yellow core at the center of the galaxy, and spiral arms, which are the bluish spirals that emerge from the core. The spiral arms are blue because they are made up of younger stars that are hotter than the stars that compose the core (Kronberg). A dense wave travels through spiral galaxies, triggering the formation of the young stars that make up the blue spiral arms. These stars appearing incredibly bright for a short time, but fade very quickly as the wave moves on. Messier 99's angular size is about 4 arc minutes, and its linear size (or diameter) is approximately 60,335 light-years across. In addition to the galaxy shown at the center of the picture, the small bright orbs that are scattered around the image are stars.

References:
Knapen, Johan and Nik Szymanek. "Galaxies and Clusters of Galaxies." <http://www.ing.iac.es/PR/science/galaxies.html#m99>.

Kronberg, Christine. "Galaxies." <http://seds.lpl.arizona.edu/messier/galaxy.html>.

Kronberg, Christine. "Messier 99." <http://www.seds.org/messier/m/m099.html>.

Leach, Sid. "M99." <http://members.cox.net/~sidleach/m99.htm>.