Nearly 400,000 years After the Big Bang, the primordial plasma of the newborn universe cooled enough for the first atoms to recombine, creating space for the embedded radiation to soar freely. That light—the cosmic microwave background (CMB)—continues to propagate through the sky in all directions, emitting the snapshots of the early universe that are captured by specialized telescopes and even displayed as static on old cathode ray televisions.
After scientists discovered CMB radiation in 1965, they meticulously mapped its microscopic temperature variations, showing exact state of the universe when it’s just a bubbling plasma. Now, they are reusing CMB data to catalog large-scale structures that evolved over billions of years as the universe matured.
“That light has been through most of the universe’s history, and by seeing how it changes, we can learn about different ages,” said. Kimmy Ngoa cosmologist at the SLAC National Accelerator Laboratory.
During its nearly 14-billion-year journey, light from the CMB has been stretched, squeezed, and bent by all the matter in its path. Cosmologists are beginning to look beyond primary fluctuations in CMB light to secondary traces left by interactions with galaxies and other cosmic structures. From these signals, they got a sharper look at the distribution of both ordinary matter—everything made up of atomic parts—and the enigmatic dark matter. In turn, those insights are helping to solve some age-old cosmic mysteries and pose some new ones.
“We realized that the CMB doesn’t just tell us about the initial conditions of the universe. It also tells us about the galaxies themselves,” he said. Emmanuel Schaan, is also a cosmologist at SLAC. “And that turned out to be really powerful.”
A universe of darkness
Standard optical surveys, which track the light emitted by stars, ignore most of the fundamental mass of galaxies. That’s because much of the universe’s total matter content is invisible to telescopes—hidden from view as clumps of dark matter or as the diffuse ionized gas that bridges galaxies. But both dark matter and scattered gas leave detectable marks on the magnification and color of the incident CMB light.
“The universe is really a dark theater in which galaxies are the protagonists and the CMB is the backlight,” says Schaan.
Many shadow players are now feeling relieved.
When light particles, or photons, from the CMB scatter electrons in the intergalactic gas, they collide with each other to achieve higher energies. In addition, if those galaxies are moving relative to the expanding universe, then the CMB photons will receive a second energy shift, up or down, depending on the relative motion of the cluster.
This pair of effects, called the thermal and kinetic Sunyaev-Zel’dovich (SZ) effects, respectively, are first theory in the late 1960s and has been detected with increasing precision over the past decade. Together, the SZ effects leave a characteristic signature that can be separated from the CMB images, allowing scientists to map the location and temperature of all common matter in the universe. .
Finally, a third effect known as weak gravitational lensing warps the path of CMB light as it travels near massive objects, distorting the CMB as if it were viewed through the bottom of a drinking glass. alcohol. Unlike the SZ effects, the lens is sensitive to all matter—dark or not.
Taken together, these effects allow cosmologists to separate ordinary matter from dark matter. Scientists can then overlay these maps with images from galactic surveys to measure cosmic distances and even traces of star formation.
