Spherical Geometry

Spherical Geometry

Presumptive Galactic Cannibal

Some clusters of galaxies have their galaxies arranged in an unambiguously spherical geometry; they are composed chiefly of ellepticals, often dominated by one giant elliptical, the presumptive galactic cannibal. Other clusters with a far more disordered geometry have, comparatively, many more spirals and irregulars. Galactic collisions distort the shape of an originally spherical cluster and may also contribute to the genesis of spirals and irregulars from ellepticals. The form and abundance of the galaxies have a story to tell us of ancient events on the largest possible scale, a story we are just beginning to read.

The development of high speed computers makes possible numerical experiments on the collective motion of thousands or tens of thousands of points, each representing a star, each under a gravitational influence of all the other points.

Presumptive galactic cannibal. Zen Dark Sky. Image: © by Megan Jorgensen (Elena)

In some cases, spiral arms form all by themselves in a galaxy that has already flattened to a disk. Occasionally, a spiral arm may be produced by the close gravitational encounter of two galaxies, each of course composed of billions of stars.

The gas and dust diffusely spread through such galaxies will collide and become warmed. But when two galaxies collide the stars pass effortlessly by one another, like bullets through a swarm of bees, because a galaxy is made mostly of nothing and the spaces between the stars are vast.

Nevertheless, the configuration between the galaxies can be distorted severely. A direct impact on one galaxy by another can send the constituent stars pouring and careening through intergalactic space, galaxy wasted.

When a small galaxy runs into a larger one face-on it can produce one of the loveliest of the rare irregulars, a ring galaxy thousands of light-years across, set against the velvet of intergalactic spac. It is a splash in the galactic pond, a temporary configuration of disrupted stars, a galaxy with a central piece turned out.