New images from the Hubble Space Telescope helped researchers identify more than 250 distant galaxies, including some of the faintest, smallest galaxies in the universe.
Scientists have long wondered how the universe pierced the heavy veil of hydrogen gas that enshrouded it for millions of years after the Big Bang. This opaque layer of hydrogen was thick enough to block ultraviolet light, and the process of clearing away the hydrogen is known as re-ionization.
Yet the universe’s largest and brightest galaxies did not produce enough energy to account for re-ionization. That’s where the newly discovered, faint galaxies proved crucial to understanding this cosmic phenomenon.
A team led by Hakim Atek, a postdoctoral researcher at Yale University, found that the accumulated light from these tiny galaxies—added to the other light—would be enough to cause re-ionization.
“The most exciting part of this work was the fact that we keep unveiling fainter and fainter galaxies, and they happen to be more and more abundant,” says Atek, who conducted his research at Yale and the Ecole Polytechnique Fédérale de Lausanne, in Switzerland. “This raises the question: What are the faintest and smallest galaxies ever formed in the early universe?”
The research team looked at Hubble Frontier Fields images of three galaxy clusters. Powerful gravitational forces generated by these clusters magnify the faint light of galaxies located far behind them; this is called gravitational lensing.
“Hubble remains unrivaled in its ability to observe the most distant galaxies, and the sheer depth of the Hubble Frontier Fields data guarantees very precise understanding of the cluster magnification effect, allowing us to make discoveries like these,” says coauthor Mathilde Jauzac of Durham University in the UK and the University of KwaZulu-Natal in South Africa.
The research represents one of the largest samples of dwarf galaxies ever discovered from the early universe, just 600 to 900 million years after the Big Bang. With the new information, the researchers say, they estimate the universe became fully transparent about 700 million years after the Big Bang.
The research will appear in a forthcoming issue of the Astrophysical Journal. Other coauthors represent the Observatoire de Lyon, Aix Marseille Université, and CNRS in France; the Université de Genéve in Switzerland; the University of Hawaii and the University of Arizona in the US.
Source: Yale University