Cosmic Archaeology: Deciphering the Mystery of the First Light of the Universe 

Scientists are studying the kSZ effect to understand the age of reionization, when the first stars ionized the hydrogen and lit up the early universe, using data from the South Pole Telescope and advanced simulations

Scientists study the epoch of reionization (EoR), a time when the first stars and galaxies ionized the hydrogen, illuminating the early universe. Using data from the South Pole Telescope and simulations, the researchers aim to identify the faint kSZ effect, which may help understand the timing and process of reionization, although they have not yet found the signal

Imagine a journey back to the time of the early universe, to the beginning of the age of re-ionization. This is when the first stars and galaxies formed, and their energy separated the protons and electrons in the dense primordial hydrogen gas, creating bubbles of ionized gas.

In your cosmic journey, you would see many such bubbles in the dark, which gradually coalesce, ionizing all the hydrogen in the universe and illuminating the darkness, allowing the development of galaxies as we know them today.

Unfortunately, scientists cannot create time machines to take us back to the age of reionization, but they can collect terabytes of data and create simulations to understand the early universe and a process central to understanding the formation and evolution of galaxies.

According to Srinivasan Ragunathan, Ph.D., a postdoctoral research fellow in the Center for Astrophysics Surveys (CAPS) at the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign, "These first stars emitted a lot of energy, and when their ultraviolet photons interacted with atoms The neutral hydrogens, they knock an electron out of the atom, and that's actually how the universe ionized again."

Discovery of the kSZ effect

Raghunathan led a multi-institutional research team that attempted to detect the kSZ effect from temperature maps of the cosmic background radiation (CMB) using data obtained from the South Pole Telescope and the SPIRE instrument on the Herschel Space Observatory. The research findings were recently published in the journal Physical Review Letters.

The team took data from the South Pole Telescope—measured at frequencies of 90, 150, and 220 GHz in the submillimeter range—and performed a mathematical analysis that measured correlations between four points in the system to look for the non-Gaussian nature of the kSZ effect. The effect is expected to give a slight increase in the energy (measured in temperature) of the CMB as galaxies begin to form and reionization occurs throughout the universe.

A simulation of the ancient universe

To help search for the kSZ signal, the researchers developed high-resolution computer simulations of the universe, working to filter out redundant signals and gravitational lensing effects from the cosmic background radiation.

According to Raghunathan, "We are trying to build a statistical model of the age of reionization. We know that there are many galaxies, or very many bubbles, and that there must be a certain correlation between them that creates the kSZ signal. We are trying to guess how our universe underwent reionization based on the correlations these."

Although the group has not yet detected the signal, the result is considered an important step forward in the study of the early universe and in understanding the age of reionization. Placing an upper limit on the end of reionization period allows researchers a working parameter for further study of the early universe.

"The current research is a first step in the search for the signal," Ragunathan said, "and in the near future, we hope to detect it. We know it exists, and that reionization has occurred. Now we want to know why and how the whole process happened."

More of the topic in Hayadan:

• The dark ages of the universe
• The record for the most distant galaxy has been broken again