The universe entered a cosmic dark age after the Big Bang because it was still too hot for atoms to form. Without atoms, none of the stars would also be formed. The first atoms that eventually emerged were positively charged hydrogen atoms. As the universe cooled down, the hydrogen atoms reunited with electrons to form neutral atoms.

About 377,000 years after the Big Bang, atoms started clumping together and the universe emerged from the cosmic dark age, forming the first stars and galaxies. This period is called the Epoch of Reionization (EoR), a pivotal yet least understood event in cosmic history.

In a new study soon to be published in The Astrophysical Journal, researchers described using the Murchison Widefield Array (MWA) in Western Australia to find signals of neutral hydrogen from the dark ages, before the first stars and galaxies emerged. To do this, the MWA had to be configured to improve its sensitivity to neutral hydrogen signals, and its tiles were doubled from 128 to 256.

Since the universe expanded, the radiation neutral hydrogen emits has expanded its wavelength from 21 centimeters to about 2 meters, which is what the researchers are looking for. The problem was that other sources such as digital televisions, signals from the Milky Way and even radio signals also emit the same wavelength. So, researchers eliminated potential contaminations by using multiple processing techniques.

Through the researchers’ analysis of the data fed into a supercomputer called Correlation as well as data from the telescope itself, the researchers were able to set a new possible limit for the neutral hydrogen’s signal strength. In fact, it is the second consecutive “best limit to date” analysis from the MWA.

This means that, because of the researchers’ work, we may one day be able to find neutral hydrogen signals from when the universe was first forming and see how it changed during EoR. Should astronomers find the signal one day, it will not only gives us an idea of when the cosmic dawn really occurred. However, it will also help us understand the pivotal moment in cosmic history.

“We can say with confidence that if the neutral hydrogen signal was any stronger than the limit we set in the paper, then the telescope would have detected it,” corresponding author Jonathan Pober of Brown University said. “These findings can help us to further constrain the timing of when the cosmic dark ages ended and the first stars emerged.”

This artist's impression of the formation of a galaxy cluster in the early universe was released in 2014 as a handout by the European Southern Observatory
This artist's impression of the formation of a galaxy cluster in the early universe was released in 2014 as a handout by the European Southern Observatory EUROPEAN SOUTHERN OBSERVATORY / M. KORNMESSER
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