A team of astronomers has discovered 250 tiny galaxies that existed 600 to 900 million years after the Big Bang. Observations by the NASA/ESA Hubble Space Telescope have taken advantage of gravitational lensing to reveal the largest sample of the faintest and earliest known galaxies in the Universe.
Some of these galaxies formed just 600 million years after the Big Bang and are fainter than any other galaxy yet uncovered by Hubble. The team has determined, for the first time, with some confidence that these small galaxies were vital to creating the Universe that we see today.
The international team, led by Hakim Atek of the Ecole Polytechnique Federale de Lausanne, Switzerland, has discovered one of the largest samples of dwarf galaxies yet to be discovered at these epochs. The light from these galaxies took over 12 billion years to reach the telescope, allowing the astronomers to look back in time when the universe was still very young.
Although impressive, the number of galaxies found at this early epoch is not the team’s only remarkable breakthrough, as Johan Richard points out, “The faintest galaxies detected in these Hubble observations are fainter than any other yet uncovered in the deepest Hubble observations.”
By looking at the light coming from the galaxies, the team discovered that the accumulated light emitted by these galaxies could have played a major role in one of the most mysterious periods of the Universe’s early history — the epoch of reionisation. Reionisation started when the thick fog of hydrogen gas that cloaked the early Universe began to clear. Ultraviolet light was now able to travel over larger distances without being blocked and the Universe became transparent to ultraviolet light.
Lead author Atek explained, “If we took into account only the contributions from bright and massive galaxies, we found that these were insufficient to reionise the Universe. We also needed to add in the contribution of a more abundant population of faint dwarf galaxies.”
These results highlight the impressive possibilities of the Frontier Fields programme with more galaxies, at even earlier time, likely to be revealed when Hubble peers at three more of these galaxy clusters in the near future.