Three in a Row: The Ghost Galaxies That Lost 85% of Their Mass

Sixty-seven million light-years away, a dozen small galaxies hang in a narrow line like beads on a wire. Three of them have almost no dark matter, which should be basically impossible.

Dark matter is the universe's structural skeleton. It makes up roughly 85% of all matter in the cosmos, forming the invisible "halos" in which galaxies coalesce and hold their shape. Without it, a galaxy shouldn't really work. And yet a dwarf galaxy called DF9, newly studied by a Yale-led team using the Keck Observatory in Hawaii, weighs in at just 100 million solar masses, almost exactly what its visible stars account for and nothing more. A typical galaxy its size should clock in at over 10 billion solar masses, mostly from that invisible halo.

What makes DF9 extraordinary isn't the missing mass alone. It's the company it keeps. Two of its neighbors along the same galactic string, DF2 and DF4, were already confirmed to lack dark matter, first in 2018, then 2019. Now there's a third. All three sit on the same narrow trail. All three formed together. All three are ghostly, diffuse and structurally impossible by the standard playbook.

The leading explanation is a "bullet dwarf" collision: two ancient dwarf galaxies crashed into each other at high speed, shearing the visible matter from the dark matter the way a car wreck separates cargo from a truck. The stars passed through mostly unharmed; the dark matter kept going. What got left behind was these pale, hollowed-out dwarfs.

Nine galaxies in that string still haven't been measured. Nobody knows what they'll find.

Read the full story at Live Science, July 28, 2026

Hot Take: Three galaxies on the same trail with the same impossible condition move this from anomaly to pattern. The universe apparently runs a second set of books, and astronomers are only now finding the ledger.