From one serendipitously fortunate system, we gain a new window into the expanding Universe’s biggest conundrum.
We’ve known our Universe is expanding for ~90 years, yet unsolved mysteries persist.
Theoretically, everything composing the Universe — matter, dark matter, dark energy, radiation and more — determines the expansion rate.
Only direct observations competently measure the actual rate, but different methods disagree.
Methods based on early signals imprinted in the cosmic microwave background and on the Universe’s large-scale structure indicate one value: 67 km/s/Mpc.
However, methods relying on precise measurements to distant objects deliver a conflicting value: 74 km/s/Mpc.
With overall errors of just 1–2% apiece, this 9% difference is significant and robust.
Each new measurement has the opportunity to either validate or refute this growing tension.
In 2017, astronomers discovered a new system: DES J0408–5354.
Originally misidentified as a single, quadruply-lensed quasar, it’s actually two independent doubly-lensed systems.
With both systems at mutually different distances, more information can be extracted than for any comparable single-lens.
Through time-delays between features in the multiple images, astronomers derived distances and redshifts for both systems.
The resultant expansion rate matches the other distance ladder values: 74.2 km/s/Mpc, with a 3.9% uncertainty.
With novel methods continually increasing this cosmic tension, new physics, not an error, provides the likeliest resolution.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.