Shadows in the Big Bang afterglow reveal invisible cosmic structures

By | March 18, 2023

Zack Savitsky writes:

Nearly 400,000 years after the Big Bang, the primordial plasma of the infant universe cooled enough for the first atoms to coalesce, making space for the embedded radiation to soar free. That light — the cosmic microwave background (CMB) — continues to stream through the sky in all directions, broadcasting a snapshot of the early universe that’s picked up by dedicated telescopes and even revealed in the static on old cathode-ray televisions.

After scientists discovered the CMB radiation in 1965, they meticulously mapped its tiny temperature variations, which displayed the exact state of the cosmos when it was a mere frothing plasma. Now they’re repurposing CMB data to catalog the large-scale structures that developed over billions of years as the universe matured.

“That light experienced a bulk of the history of the universe, and by seeing how it’s changed, we can learn about different epochs,” said Kimmy Wu, a cosmologist at SLAC National Accelerator Laboratory.

Over the course of its nearly 14-billion-year journey, the light from the CMB has been stretched, squeezed and warped by all the matter in its way. Cosmologists are beginning to look beyond the primary fluctuations in the CMB light to the secondary imprints left by interactions with galaxies and other cosmic structures. From these signals, they’re gaining a crisper view of the distribution of both ordinary matter — everything that’s composed of atomic parts — and the mysterious dark matter. In turn, those insights are helping to settle some long-standing cosmological mysteries and pose some new ones.

“We’re realizing that the CMB does not only tell us about the initial conditions of the universe. It also tells us about the galaxies themselves,” said Emmanuel Schaan, also a cosmologist at SLAC. “And that turns out to be really powerful.” [Continue reading…]

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