Green Pea Galaxy May Reveal More about the Big Bang

After the Big Bang, the universe expanded and then cooled down, matter progressively taking shape. Then the universe reheated and hydrogen ionized in a process called cosmic reionization. Now, scientists may have discovered proof of cosmic reionization in the form of a compact galaxy emitting a large number of ionizing photons.

Normal matter in the early universe consists mostly of gas, which forms the first galaxies. UV radiation emitted by these stars contains numerous ionizing photons. For this reason, scientists have long suspected that galaxies were responsible for the cosmic reionization. However, to make this happen, galaxies need to "eject" these photons.

In this latest study, the researchers decided to look at "green pea" galaxies, which are a rare class of galaxies in the nearby universe that are very compact and could host stellar explosions or power winds strong enough to "eject" the ionizing photons.

Using the Hubble Space Telescope, the researchers found the "green pea" galaxy J0925, located at a distance of three billion light-years. This galaxy was "ejecting" ionizing photons with unprecedented intensity. This discovery shows that galaxies of this type could explain cosmic reionization. This, in turn, may confirm the most commonly made hypothesis.

In fact, the galaxy has a peculiar signature. Its Lyman-alpha spectrum is much narrower and stronger than that of most galaxies. This confirms theoretical predictions and provide the base for an efficient new method to search for galaxies responsible for cosmic reionization 13 to 14 billion years ago.

The findings are published in the journal Nature.

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