Simulations find ghostly whirls of dark matter trailing galaxy arms
Galaxies are far more than the sum of their stars. Long before stars even formed, dark matter clumped up and drew regular matter together with its gravity, providing the invisible scaffolding upon which stars and galaxies eventually grew.
Today, nearly all galaxies are still embedded in giant “halos” of dark matter that extend far beyond their visible borders and hold them together, anchoring stars that move so quickly they would otherwise break out of their galaxy’s gravitational grip and spend their lives adrift in intergalactic space.
The way dark matter and stars interact influences how galaxies change over time. But until recently, scientists had mainly only examined one side of that relationship, exploring the way dark matter pulls on normal matter.