William Butler Yeats had different beasts in mind, when he first penned the below — after WWI. That much is certain.

But consider that entirely dark galaxies are out there — and should you be unlucky enough to miss the gravitational waves, it might just swallow you… whole. But fret not — this one is over 600 million light-years out, in Perseus. We won’t fall in — by anyone’s accident or inattention.

“…Things fall apart; the centre cannot hold;
Mere anarchy is loosed upon the world,
The blood-dimmed tide is loosed, and everywhere….

A gaze blank and pitiless as the sun,

Is moving its slow thighs, while all about it

Reel shadows of the indignant desert birds.

The darkness drops again; but now I know

That [six million] centuries of stony sleep
Were vexed to nightmare by a rocking cradle,

And what rough beast, its hour come round at last,

Slouches towards [Perseus] to be born?“

— William Butler Yeats (1919)

Hah! [Pretty… dark, and foreboding — like our current moment.] Yet, in any event, here’s the far more cheerful latest-, and a video- explainer, from NASA (on these stealthy enigmas):

…NASA’s Hubble Space Telescope has revealed an exceptional discovery in the Perseus galaxy cluster: CDG-2, an ultra-low surface brightness galaxy composed of 99% dark matter.

This elusive galaxy remained hidden until astronomers detected a slight increase in globular cluster density, suggesting the presence of an underlying galactic structure.

Observations from Hubble, ESA’s Euclid observatory, and the Subaru Telescope confirmed a faint halo of diffuse light surrounding these ancient star clusters.

Analysis indicates CDG-2 has the luminosity of approximately six million Sun-like stars, with the clusters comprising about 16% of its visible matter. The galaxy’s normal matter was likely stripped away through gravitational interactions within the Perseus cluster….

नमस्ते