The Big Bang’s Afterglow Reveals Invisible Cosmic Structures

The cosmic microwave background (CMB) radiation, first discovered in 1965, is being repurposed to uncover how the universe was formed. The CMB is the first light that was emitted after the Big Bang, and its tiny temperature variations give scientists a glimpse of what the universe was like at its creation almost 14 billion years ago. Now, cosmologists are focusing on the secondary imprints that the CMB has picked up from the interactions with galaxies and other structures. They are using this data to create a clearer view of the distribution of ordinary matter, which is everything composed of atomic parts, and dark matter, which is still a mystery, but is believed to make up to around 85% of total matter.

Unlike standard optical surveys, which track the light emitted by stars, the magnification and color of the incoming CMB light allow for a view of galaxies’ underlying mass, including that which is invisible to telescopes. The vast majority of the universe’s total matter content is hidden, including as the clumps of dark matter or as the diffuse ionized gas between galaxies. By tracking the shadows or imprints that the dark matter leaves, cosmologists can create an accurate representation of the universe that has evolved over billions of years.

The SZ effects, known as the thermal and kinematic Sunyaev-Zel’dovich effects, and weak gravitational lensing mark the location and temperature of all the ordinary matter in the universe. However, only lensing is sensitive to all matter, including dark matter. Cosmologists can create detailed maps of the universe’s structure by using these effects to separate the ordinary matter from the dark matter. Images from galaxy surveys can then be overlaid to measure cosmic distances and trace star formation.

In using the CMB to analyze the secondary imprints left by interactions with cosmic structures, cosmologists are gaining insights into the universe’s development and settling some long-standing cosmological mysteries, as well as uncovering new ones. By seeing how the CMB has changed, from the initial conditions of the universe through its history, cosmologists can track how galaxies formed and have changed over time, providing a more detailed understanding of the universe’s evolution.



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