Guest Author - Lea Terry

Until 1924, we didn’t even know there were galaxies besides our own, the Milky Way. Since then, we’ve discovered several more, but there’s much about galaxies we don’t understand--including their evolution. However, recent observations made of the Comet Galaxy, located 3.2 billion light-years from Earth, may help us better understand how galaxies transform.

What does it mean?

So what’s so important about these new observations? The Comet Galaxy is doing something unusual: being ripped apart by its own tidal forces. Gas and stars within the galaxy are being pulled away by these tidal forces; the damage is compounded by the pressure of the gas plasma of the cluster the galaxy is situated in, Abell 2667. This force is known as ram pressure stripping. The combination of these forces is stripping young stars away from the galaxy, which will leave it an empty, gas-poor galaxy with mainly old stars. The Comet Galaxy’s behavior may help explain the formation of elliptical galaxies, which usually have little gas or dust, and primarily old stars. They are usually found in the middle of crowded galaxy clusters. Scientists have been unable to explain the high number of elliptical galaxies, because when the universe was half its current age, only one in five galaxies were elliptical. Astronomers had suspected elliptical galaxies were formed out of other types of galaxies, but because such a process takes billions of years, there was no visual evidence. The Comet Galaxy is about 200 million years into this process, allowing astronomers to see this evolution for the first time. The observations were made through the use of the Hubble Space Telescope and various ground- and space-based telescopes.

A note about elliptical galaxies...

Elliptical galaxies can be circles or ovals, and are either spherical or flat. Containing mostly older stars, elliptical galaxies look like fuzzy blots of light when photographed, and their size, mass, and brightness varies widely. An estimated 20 percent of the brightest galaxies are elliptical, and giant ellipticals are the brightest of the known galaxies. An elliptical galaxy is brightest at the center, with its light fading toward the edges, where it’s the dimmest. An elliptical galaxy also becomes emptier toward its edges, eventually merging with the space around it. This makes it difficult to determine its exact boundaries.