Ask Ethan: Why doesn’t darkish matter collapse attributable to gravity? | by Ethan Siegel | Begins With A Bang! | Feb, 2025
Right here in our Universe, each regular and darkish matter may be measured astrophysically. However solely regular matter can collapse. Why is that?
Right here in our Universe, it might be the traditional matter that we will instantly detect, measure, manipulate, experiment with, and observe, however it’s the darkish matter that represents many of the mass within the Universe. Whereas all of the “stuff” that the planets, stars, gasoline, plasma, and dirt are composed of represents about 4.9% of the whole power within the Universe, the mysterious darkish matter — whose nature is unknown however for which the observational astrophysical proof is overwhelming — makes up a whopping 27% of the cosmic power funds. Solely darkish power, making up 68% of the Universe, is extra necessary from an power density perspective.
And but, darkish matter is simply ever present in diffuse halos, by no means in collapsed clumps like regular matter. Why is that? That’s the topic of this week’s query, coming all the way in which from Barry Lewis in New Zealand, who needs to know:
“How does darkish matter, whereas being gravitational, not collapse? I can’t consider any dialogue I’ve come throughout that addresses this obvious want for it to expertise some kind of mutual repulsive drive.”
