An international team of astrophysicists, including Professor Rennan Barkana from Tel Aviv University has managed for the first time to statistically characterize the universe’s first galaxies.
According to the study, which was published in the peer-reviewed journal, Nature Astronomy on Wednesday, the earliest galaxies were relatively small and faint — far dimmer than today’s galaxies.
“This is a very new field and a first-of-its-kind study”, said Prof. Barkana, who works at TAU’s Sackler School of Physics and Astronomy.
“We are trying to understand the epoch of the first stars in the Universe, known as the ‘cosmic dawn’, about 200 million years after the Big Bang. The James Webb Space Telescope, for example, can’t really see these stars. It might only detect a few particularly bright galaxies from a somewhat later period. Our goal is to probe the entire population of the first stars.”
Scientists generally accept that before stars began to fuse heavier elements inside their cores, the universe was nothing but a cloud of hydrogen atoms from the Big Bang. While the universe today is also filled with hydrogen, it is mostly ionized due to radiation from stars.
“Hydrogen atoms naturally emit light at a wavelength of 21cm, which falls within the spectrum of radio waves”, says Prof. Barkana. “Since stellar radiation affects the light emitted by hydrogen atoms, we use hydrogen as a detector in our search for the first stars: if we can detect the effect of stars on hydrogen, we will know when they were born, and in what types of galaxies.”
Barkana said he was among the first theorists to develop this concept 20 years ago, and now researchers around the world are “attempting to discover the 21cm signal from hydrogen in the early universe.”
He stressed that experiments are becoming more reliable and year each year.
“We expect to find stronger upper limits, giving us even better constraints on the cosmic dawn. We hope that in the near future we will have not only limits, but a precise, reliable measurement of the signal itself,” Barkana said.