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The latest observations used the European Southern Observatory’s Very Large Telescope to map out the light emitted by hydrogen irradiated by the galaxies within a distant galactic cluster, called SSA22.

In one notable achievement, Chandra found a cloud of hot gas that extended throughout a galactic cluster several million light-years across, with temperatures as high as 40 million degrees.

Forget thanking their lucky stars: This discovery required the fortuitous alignment of a massive galactic cluster.

But not even a galactic cluster exerts enough gravity to bend light so severely unless you postulate that most of its mass consists of hypothetical dark matter.

“Penelope Saunders has one. Dwayne Simmons. Lottie McPhee. Denny Barden ... well, Denny Barden's only got a galactic cluster, but Denny's mum's been out of work these past two years. And —”