Galaxy found missing crucial ingredient: Dark Matter

Some stories in astronomy just keep getting rewritten, and you can actually tell how up-to-date people are but what they think the universe is up to.

Take galaxies. Once upon a time, admittedly before I was born, folks believed everything in our universe was made of the kinds of atoms and particles that we regularly work with on Earth and experience as parts of our furniture and as unstable interlopers in our experiments.

But when researchers Vera Rubin and Fritz Zwicky studied the motions of rotating galaxies and galaxies in clusters in their separate research, they discovered the motions they saw didn’t match what was seen: The observed stars, gas, and dust just didn’t have enough mass to account for all the motions.

Rotation curve of spiral galaxy Messier 33. The dashed line shows how fast things were expected to move based on what can be seen. The solid line is the observed motions, and dark matter is required to explain these faster rotation rates.

And thus, over years, astronomers came to accept that our universe is largely constructed of material we can’t observe through light; stuff that makes up a larger portion of our universe than regular (baryonic) matter. This weird stuff was given the unfortunate name Dark Matter, and we have been struggling to understand it ever since.

When I was in grad school, we were taught that the bulk of most galaxies is dark matter, and we even learned how to fit dark matter halos to light distributions to get at the ratio of normal to dark matter for different kinds of…