The Coma Cluster (Abell 1656 with NGC 4889/Caldwell 35)

This is certainly one of the most spectacular galaxy clusters an amateur astrophotographer can go after. The Coma Cluster in the Coma Berenices constellation spans more than 20 million light years and is more than 300 million light years away.

It contains more than 1,000 galaxies and is thought to be the fourth most massive known galaxy cluster behind the Pheonix Cluster, El Gordo, and the Bullet Cluster—and just ahead of the Virgo Cluster.

Elliptical galaxies dominate the cluster—especially near the center. The largest of them, from our viewpoint, is NGC 4889, also catalogued as Caldwell 35. Spiral galaxies tend to be away from the center of the cluster. This makes intuitive sense because mass is pulled toward the center, making it a more dense galactic neighborhood and increasing the likelihood of galactic collisions and interactions that turn flat spiral galaxys into ellisoidal blobs.

Caldwell 35 is about 2.5 times the size of our Milky Way Galaxy and contains a supermassive black hole that is 21 million times as weighty as the sun.

The Coma Cluster also has a significant history in scientific lore. The history of astronomy contains many notable characters, but few are more fascinating and engaging than Fritz Zwicky. Born in Bulgaria in 1898, the son of a Swiss merchant, and raised in Switzerland, he moved to the United States in 1925 and worked at Caltech for 47 years.

Zwicky made contributions to a number of aspects of astrophysics including the study of gaseous ionization, supernovas (he actually coined that term), the nature of cosmic rays, neutron stars (he came up with that name as well), and cosmic rays—and he even worked on developing some of the first jet engines. But he is best known for his work on galaxies and galaxy clusters.

He had a reputation for eccentricity and thorniness, and many of his ideas were initially rejected, although he was often vindicated later. He is quoted as saying, “Astronomers are spherical bastards. No matter how you look at them they are just bastards.”

One of his most astonishing ideas came from studying the Coma Cluster. In 1933, he examined the speeds of galaxies in the cluster and determined that the cluster did not have enough apparent mass to hold together. In fact, he calculated that the cluster would have to have ten times its apparent mass to stay together. Since the source of the extra mass could not be detected at the time (and still hasn’t been), he referred to it as “dark matter.” The legendary astronomer Vera Rubin later corroborated the idea by studying individual galaxies—also concluding that given the speeds of the stars in galactic orbits, galaxies would fly apart unless they were imbued with ten times the mass of the stars and gas inside them.

He also proposed the idea of using the presence of this dark matter to see galaxies much farther away than we could normally detect with our telescopes. He referred to this as “gravitational lensing.” Most astronomers dismissed this idea, and unfortunately, it wasn’t shown to be a reality until 1979—five years after he died.

Zwicky’s combative personality resulted in him being far less well known that he might have been had he been more congenial. But over time, it has become clear that he was a genius of exceptional ability and made enormous contributions to astrophysics and cosmology.