“Dark matter or invisible element?
You decide.” -Toba Beta
The dark matter wars rage on and on, with both sides — those in favor of modifying gravity and those in favor of adding an additional mass component to the Universe — claiming victories for their own side and defeat for the other. But one piece of evidence, hitherto elusive, might finally hold the key to distinguishing one from the other: early, young, less-evolved galaxies. Billions of years ago, not as much dark matter had fallen into the inner portions of galaxies, meaning that the outer portions of rotating spirals should display less dark matter in the past than they do today.
Instead of flat rotation curves, the galaxies in the distant Universe should exhibit falling rotation curves. In a series of new papers, a team was able to observe 101 distant galaxies at relatively high redshifts, and what they found presented compelling evidence for exactly this phenomenon. As always, more and better data is needed, as it’s only a three-sigma effect so far.