Something Keeps Stealing Dark Matter From the Same Neighborhood

Astronomers just found a third galaxy in a row that appears to have almost no dark matter, the invisible stuff thought to hold most galaxies together. The galaxy, called DF9, sits in the same faint cosmic chain as two earlier oddballs, DF2 and DF4, both already famous among astronomers for the same missing ingredient.

DF9 is fainter and harder to spot than its neighbors, which is likely why it took this long to notice. Researchers used the Keck Cosmic Web Imager to track the motion of its stars and estimate its mass. The dark matter that should have shown up in that measurement mostly didn't.

The leading theory is that these galaxies are wreckage from ancient, high-speed collisions between much bigger galaxies, violent enough to strip ordinary matter away from dark matter. That theory works fine for one galaxy. It gets shakier when the same wreckage keeps turning up in the same exact neighborhood.

Read the full story at Scientific American, June 17, 2026

Hot Take: Losing your dark matter once is bad luck. Losing it three times in the same cosmic block means the collision story is covering for a gap nobody's found yet.