Dying Galaxies — The Real Tragedy Is How

Unfortunately, everything must come to an end. No less our beautiful, massive dying galaxies. However, the big question is how? Galaxies don’t just dissipate and then cease to exist. Dying galaxies are strangled to death. It’s really the cut off of a material that is needed to make stars. Without this material, and without the stars, our galaxies are choking. A galaxy is only as living as the stars within them.

For a long time, researchers wondered why and how dying galaxies happen. A team from the University of Cambridge and the Royal Observatory Edinburgh has found the difference between living and dying galaxies. Galaxies are basically split off into two groups. One group is the land of the living, while the other is a choking, strangled pit of death. The ones that are alive are the galaxies that are still producing stars, while the dead ones have no stars and no star formation.

Theories On Dying Galaxies

The study of the change in galaxies from being active to passive has been at the forefront of many researchers’ minds. There have been two main theories that explain what happens when galaxies die off. One theory is that when a sudden ejection of gas, either internal or external, pushes the gas out of the galaxy. The other theory consists of being strangled. When a galaxy is strangled, the supply of cold gas comes to a complete halt, which is the cause of strangulation. This halt is stopping the galaxy from getting the material needed to make new stars.

Living galaxies, much like our own Milky Way, have enough gas such as hydrogen, so that stars can be created. The dead galaxies have just run out of gas, or the gas has been ejected out of reach. The main mystery is no longer how galaxies die off, but why. Where does the gas go that causes the strangulation of these galaxies? Again, there are two main theories to answer this question.

One theory is that the gas has been sucked away from the galaxy at such a speed that is seems to halt. The good news is the gravitational pull of the passing galaxy leads to a quick death. The other theory is that the supplies of gas are blocked in some way, causing the slow tragic death by strangulation.

Clues to Solving the Puzzle

Researchers want to know how dying galaxies die so they turned to the Sloan Digital Sky to look at the metallic levels of about 26,000 galaxies. Metals and star formation go together like bread and butter. The more stars there are in a galaxy, the more metal it has. Looking at the content of the metal in the dead galaxies gave researchers clues as to how they died. If the galaxies died due to the sudden pull of cold gas, resulting in a quick death, then the metal content should be the same because the formation of stars should have come to an abrupt stop. However, if the dying galaxies are a result of strangulation, the metal content should keep rising, but then after some time, come to a stop. The formation would continue until the cold gas has completely run out.