In research that could help solve a longstanding mystery about the evolution of the universe, a team of University of Geneva researchers believe they have discovered why the period of post-Big Bang cooling ended after about one billion years and things began to heat up again.
After the Big Bang first caused the universe to heat up, atoms started forming and the universe began to expand. As it cooled down, matter condensed, forming stars and galaxies over the next several hundred thousand years. At one point, however, things started to once again heat up, and the element hydrogen returned to an ionized state, as it was shortly after the Big Bang.
This took place in a period known as “cosmic reionization”, and according to Gizmodo, it has long puzzled scientists. What could have caused it to happen? How was this transformation even possible? Now, as they reported in a recently-published Nature study, the Geneva team believes it has found the answer: a class of high-energy galaxies known as “green pea galaxies”.
First discovered in 2007, green pea galaxies are extremely compact, but for years experts have suspected that they emitted enough energy to re-ionize hydrogen, the website explained. In an attempt to determine whether or not this was the case, the study authors analyzed data pertaining to green pea galaxies and found one actively ejecting ionized hydrogen.
Anomalies detected at galaxy J0925 could solve the mystery
The astronomers, led by Yuri Izotov of the Ukraine’s National Academy of Sciences, located the galaxy in question, J0925, using the Hubble Space Telescope. The galaxy, which is roughly three billion light-years away, was found to be intensely “ejecting” ionizing photons, the research team said, thus demonstrating that these galaxies may explain cosmic reionization.
In a statement, the scientists noted that J0925 also has an unusual signal: one of the spectral lines of hydrogen it emits (its Lyman-alpha spectrum) is far stronger and more narrow than most other galaxies, which will enable them to search for other galaxies that may have been responsible for the cosmic reionization and the reheating of the universe some 13 to 14 billion years ago.
These observations could be a big step forward in the research of the early universe, according to the researchers. They plan to conduct further observations using the Hubble telescope to confirm their findings, and to help better understand the unusual photon ejection mechanisms responsible for cosmic reionization.
More detailed analysis should be possible once the NASA James Webb Space Telescope is launched in 2018. That instrument will “allow astronomers to discover and study in detail the first galaxies and sources of cosmic reionization,” the university added. “Largely unknown so far, the early Universe starts to be revealed.”
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Feature Image: Ivana Orlitová, Astronomical Institute, Czech Academy of Sciences (Prague)
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