This large, fuzzy-looking galaxy is so diffuse that astronomers call it a “see-through” galaxy because they can clearly see distant galaxies behind it. The ghostly object, catalogued as NGC 1052-DF2, doesn’t have a noticeable central region, or even spiral arms and a disk, typical features of a spiral galaxy. But it doesn’t look like an elliptical galaxy, either. Even its globular clusters are oddballs: they are twice as large as typical stellar groupings seen in other galaxies. All of these oddities pale in comparison to the weirdest aspect of this galaxy: NGC 1052-DF2 is very controversial because of its reconstructed, hotly-debated dark matter profile. MOND explains it perfectly, however. (NASA, ESA, AND P. VAN DOKKUM (YALE UNIVERSITY))

There’s A Debate Raging Over Whether Dark Matter Is Real, But One Side Is Cheating

Dark matter feels fake. MOND sounds plausible. What should you conclude?

Imagine I told you that everything you ever saw, touched, or experienced — in this world and in the Universe beyond — was just a tiny fraction of the matter that’s out there. That for every particle of normal matter that existed, there was at least five times as much, mass-wise, of a new form of invisible matter that we’ve never directly detected. And that beyond that, the Universe also contained a mysterious form of energy that caused distant galaxies to suddenly speed up and accelerate away from us some six billion years ago. When all was said and done, all the normal stuff was just 5% of the grand total.

You’d wonder if we didn’t have something fundamentally wrong. If we hadn’t goofed something fundamental, like our theory of gravity. This is the heart of the debate over the existence of dark matter. But before you pick a side, tempting though it is, let’s think about the problem.

Our galaxy is embedded in an enormous, diffuse dark matter halo, indicating that there must be dark matter flowing through the solar system. But it isn’t very much, density-wise, and that makes it extremely difficult to detect locally. (ROBERT CALDWELL & MARC KAMIONKOWSKI NATURE 458, 587–589 (2009))

When it comes to any endeavor involving the physical world, the goal is to arrive at…