Enlarge / The European Southern Observatory’s Very Large Telescope, based in Chile. (credit: ESO)
One of the earliest indications of the existence of dark matter came from an examination of the rotation of nearby galaxies.

The study showed that stars orbit the galaxy at speeds that indicate there’s more mass there than the visible matter would indicate. Now, researchers have taken this analysis back in time, to a period when the Universe was only a couple billion years old, and the ancestors of today’s large galaxies were forming stars at a rapid clip.
Oddly, the researchers find no need for dark matter to explain the rotation of these early galaxies. While there are a number of plausible explanations for dark matter’s absence at this early stage of galaxy formation, it does suggest our models of the early Universe could use some refining.
The measurements at issue here are what are called the “galaxy rotation curves.” These curves track the speed at which stars rotate as a function of their distance from the center of the galaxy.
If regular matter were all that was present, it would be easy to predict what we’d see.

Close to the galaxy’s center, stars would only feel a portion of the total galactic mass, so they would orbit at a relatively sedate speed.

Any faster, and their orbits would shift outward.
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