Astr110 Photography Projects, Spring 2006

Galaxy M100, Karianne N. Pasma

This is the galaxy M100, a large spiral galaxy, similar to our own galaxy, the Milky Way. It contains over 100 billion stars, which is also roughly the same as in our own galaxy. Spiral galaxies are the most common types of galaxies, with more than half of all observed galaxies being spiral. The reason for spiral shapes is uncertain, but one of the theories is that the spirals are caused by manifestations of spiral density waves. Stars will not always remain in the position that they are now in, but will pass through the arms as they travel in their orbits. The active star-forming regions found within these galaxies helps make them the most visible galaxies. Spiral galaxies have high concentrations of gas and dust, which is what makes them so interesting to look at.

M100 was discovered in 1781 by P. Mechain, and is over 50 million light years away. It is estimated to have a diameter of 160 000 light years, in good agreement with this photo from which the diameter measures closer to 157 000 light years, based on the 4 arcminutes of the photo it takes up. It has a total mass of roughly 160 billion suns. M100 is in the Virgo Cluster, which is part of our intergalactic neighbourhood. The Virgo Cluster is the physical centre of our Local Supercluster, and has gravitational effect on all the other galaxies and galaxy groups because of its large mass. M100 has two prominent arms, with many young, high temperature giant stars, and several fainter arms. There have been five supernovae discovered in it since its original discovery in 1781. M100 is tilted nearly face-on when seen from earth, which also helps make it interesting to look at.

References:
APOD June 26, 1995, Galaxy M100

Number of Stars In The Milky Way

Spiral Galaxies

The Virgo Cluster of Galaxies

M100 Coma Berenices

Spiral Galaxy M100

Wikipedia - Spiral Galaxy