The Milky Way in the night sky over South Africa. Below her is a very special radio telescope: The Hydrogen Epoch of Reionization Array (HERA) is one of the most sensitive radio telescopes in the world. It is used to explore the early days of the universe. The facility is located in a radio silent region, in the middle of the Karoo desert. Radios, cell phones, and even gasoline-powered cars are banned here because they could interfere with research.
350 radio dishes stand side by side, pointing upwards. These are designed to capture emissions from the reionization epoch of the universe. For the first 380,000 years after the Big Bang, the universe was a hot, ionized plasma. This gradually cooled down so that protons and electrons could combine to form atoms. As the universe expanded, matter produced galaxies and stars that produced electromagnetic radiation. As a result, matter began to ionize again. Electrically neutral atoms lost one or more electrons and became positively charged ions. This process marked the beginning of the reionization epoch.
In order to be able to capture radio emissions from this period, the HERA team doubled the sensitivity of the radio telescope again. The scientists’ search was still unsuccessful, but they were able to gain initial insights. The data collected so far confirms that the composition of stars and galaxies in the earlier universe was different: in contrast to today, they contained hardly any heavier elements, but consisted almost exclusively of hydrogen and helium. “In particular, their X-ray properties must have changed. Otherwise we would have already detected the radiation,” explains Aaron Parsons, Principal Investigator at HERA.
However, the radio telescope can only be used again between April and September, when the Milky Way is below the horizon. Because our galaxy produces a lot of radio emission, which interferes with the detection of the weak emissions from the reionization epoch. Meanwhile, the HERA team continues to work on improving the calibration of the radio telescope and the data analysis. “This is the pathway to a potentially revolutionary technique in cosmology,” says Joshua Dillon, lead author of the study. “Once you got the sensitivity you needed, there was an incredible amount of information in the data.”