Almost 400,000 years after the Big Bang, the primordial plasma of the infant universe cooled enough for the primary atoms to fuse, creating space for the released embedded radiation. This light – the cosmic microwave background (CMB) – continues to stream across the sky in all directions, emitting a snapshot of the early universe that has been recorded by dedicated telescopes and even revealed in static on old cathode ray televisions.
After the invention of CMB radiation by scientists in 1965, its slight variations in temperature were meticulously mapped, showing exact state of the cosmos when it was just plain foaming plasma. Now they’re reusing CMB data to catalog large-scale structures which have evolved over billions of years because the universe matures.
“This light has experienced a lot of the history of the universe, and by watching the way it has modified, we will find out about different epochs,” he said. Kimmy Wucosmologist on the SLAC National Accelerator Laboratory.
Throughout its nearly 14-billion-year journey, light from the CMB has been stretched, compressed, and warped by all matter in its path. Cosmologists are starting to look beyond the CMB’s primary light fluctuations to secondary traces left by interactions with galaxies and other cosmic structures. These signals give them a clearer picture of the distribution of each abnormal matter – anything made from atomic parts – and the mysterious dark matter. In turn, these insights help to settle some long-standing cosmological mysteries and pose some latest ones.
“We realize that the CMB tells us greater than just the initial conditions of the universe. It also tells us in regards to the galaxies themselves,” he said Emmanuel Schaan, also a cosmologist at SLAC. “And that seems to be really powerful.”
A universe of shadows
Standard optical surveys that track the sunshine emitted by stars miss a lot of the mass of galaxies. This is since the overwhelming majority of the universe’s total matter content is invisible to telescopes – hidden out of sight either as clusters of dark matter or as diffuse ionized gas that connects galaxies. But each dark matter and diffuse gas leave detectable marks on the magnification and color of the incoming CMB light.
“The universe is basically a shadow theater where the galaxies are the protagonists and the CMB is the backlight,” Schaan said.
Many shadow players are beginning to feel relieved now.
When light particles or photons from the CMB scatter electrons within the gas between galaxies, they’re collided with higher energies. Also, if these galaxies are moving relative to the expanding universe, the CMB photons get a second energy shift, either up or down, depending on the relative motion of the cluster.
This pair of effects, known respectively because the Sunyaev-Zel’dovich (SZ) thermal and kinematic effect, was theorize first within the late Nineteen Sixties and have been detected with increasing precision within the last decade. Together, the SZ effects leave a particular signature that could be extracted from CMB images, allowing scientists to map the placement and temperature of all abnormal matter within the universe.
Finally, a 3rd effect, often called weak gravitational lensing, warps the trail of CMB light because it travels near massive objects, distorting the CMB as if seen through the bottom of a wine glass. Unlike SZ effects, lensing is sensitive to any matter, dark or otherwise.
Taken together, these effects allow cosmologists to separate abnormal matter from dark matter. Then scientists can overlay these maps with images from galaxy surveys to measure cosmic distances and even trace star formation.
