We had been convinced for years that we had seen the birth of stars. What we saw was a telescope error

“And God said: Let there be light; and there was light.” And 13.6 billion years ago, in 2018, a team of researchers from Arizona State University stood before international public opinion and claimed to have detected signs of the first stars that appeared in the universe. “It was a revolutionary observation because thanks to the faint trace left by the glow of the oldest stars we will be able to find new and unexpected evidence about dark matter” and the early universe.

Four years later, radio astronomer Ravi Subrahmanyan and his collaborators tried to replicate the observation, but could not find it. It was the first time anyone had seriously tried to do it. Therefore, the question was obvious, had we heard the “dawn of the universe” or was it simply a mistake of the original team?

the original experiment

Let’s be clear, we cannot see the light of the first stars. For this to happen, that light would have to have traveled more than 13 billion years and still be strong enough for our optical telescopes to capture it. It is not like this. In order to identify the signs, Judd Bowman’s team looked in interstellar hydrogen for certain particular wavelengths. Hydrogen is essentially transparent, but the ultraviolet light from these stars would have given it a certain opacity at specific points in the electromagnetic spectrum.

Although the company was very difficult (that small firm they were looking for is “covered” by tens of billions of different signals, like when a radio is not well tuned and you can listen to several channels at the same time), the results were exceptionally good. Too. “The dip in the spectrum was deeper and wider than cosmological theories had predicted,” and that made the researchers spend more than two years checking that their numbers were right.

The results were so strange that theoretical physicists had to juggle trying to explain the problem and, even so, they did not achieve it satisfactorily. Therefore, many people began to doubt the results. That’s where the search for answers began.

The lakes of India

The main difficulty of the experiment is that the researchers have to gain insight into how the instrument environment interacts with waves coming from space. That’s why the original experiment was a table-shaped pot in the middle of the desert, and that’s why Ravi Subrahmanyan’s team searched for months for a lake with the exact level of salinity they needed for the signal to be clear.

When they found it they designed a new device and were able to listen to the sky. The signal was not. Everything seems to indicate that the results of 2018 are due to “an error of the radio telescope used”, they concluded. And indeed, considering how challenging the original measurements were, it makes the most sense right now: the new data does add up. However, the last word has not yet been said. There are three more experiments (one in South Africa, another in the Canadian Arctic and the last in the Chilean Andes) that are trying to replicate the work of 2018. We will have to wait, then; but it is better to get used to the idea that the origin of the stars is still a great mystery.

Image | Joel Filippo