Astronomers have identified distant gas-rich galaxies that probably caused the Universe's rate of star formation to peak some 10 billion years ago.

Several teams used the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile to probe a well-studied patch of sky called the 'Hubble Ultra Deep Field', which offers the deepest view into the early Universe. Roberto Decarli at the Max Planck Institute for Astronomy in Heidelberg, Germany, and his colleagues found galaxies rich in carbon monoxide gas, which fuels star formation. The farther back in space and time the scientists looked, the more gas there was — corresponding to the burst of new stars that began about 3 billion years after the Big Bang.

The work is the first to reveal these long-expected, but never before seen, clumps of cool gas in the early Universe.

Astrophys. J. in the press. Preprints at http://arxiv.org/abs/1607.06770; http://arxiv.org/abs/1607.06771 (2016)