Long Ago, In a Galaxy Far, Far Away

The ghostly galaxy NGC 1052-DF2 is exceedingly diffuse.

 See the distant galaxies behind it? The galaxy is missing

 most, if not all, of its dark matter. 

There was not enough Dark Matter to keep it together? It must be "The Force": Astronomers find the 'impossible': a galaxy without dark matter

Stupefied astronomers on Wednesday unveiled the first and only known galaxy without dark matter, the invisible and poorly-understood substance thought to make up a quarter of the Universe.

The discovery could revise or even upend theories of how galaxies are formed, they reported in the journal Nature.

"This is really bizarre," said co-author Roberto Abraham, an astronomer at the University of Toronto. "For a galaxy this size, it should have 30 times as much dark matter as regular matter," he told AFP by phone. "What we found is that there is no dark matter at all." "That shouldn't be possible," he added.

There are 200 billion observable galaxies, perhaps more, astronomers estimate. Some 65 million light-years from Earth, NGC1052-DF2 -- "DF2" for short -- is about the same size as our Milky Way, but has 100 to 1,000 times fewer stars.

Dark matter's existence is inferred from the motion of objects affected by its gravitational pull.

"It is conventionally believed to be an integral part of all galaxies, the glue that holds them together and the underlying scaffolding on which they are built," said co-author Allison Merritt from the Max Planck Institute for Astronomy, in Germany.

I can remember when "dark matter" was just an accounting trick to account for missing mass in the universe. Wait a minute. It's still just an accounting trick. It's never been directly detected.

Theories? Maybe it's the remnant of a galactic collision, where a group of stars were flung out and away from the colliding galaxies without the dark matter, which would pass through largely unaffected.

Linked "above the line" at Pirate's Cove in the weekly "Sorta Blogless Sunday Pinup" and links.