Galaxies that formed in the first billions of years after the Big Bang should have lived long and healthy lives. But new observations have revealed the existence of ‘dull’ galaxies that disrupted star formation and became empty.

An international team of astronomers studied a group of six early galaxies with the ALMA and Hubble space telescopes. 

These galaxies were selected because they are known to be “quenched”, that is, with little or no star formation.

Previously, astronomers believed that some factor had intervened and stopped star formation in those galaxies. Otherwise, they would be full of stars.

“The most massive galaxies in the Universe lived fast and furious, creating their stars in a remarkably short amount of time. Gas, the fuel of star formation, should be plentiful at these early times in the Universe,” says Kate Whitaker, lead author on the study, and assistant professor of astronomy at the University of Massachusetts, Amherst.

The team found that, contrary to expectations, there was no sudden drop in the ability of galaxies to turn cold gas into stars. Rather, the stars lacked cold gas entirely.

Christina Williams, an astronomer at the University of Arizona and a co-author of the research, explains that scientists still don’t know why this happens, but possible explanations could be as follows:

• The supply of the primary gas that powers the galaxy is cut off.

• A supermassive black hole is injecting energy that keeps the gas in the galaxy hot.

“This means that the galaxies are unable to refill the fuel tank, and thus, unable to restart the engine on star production,” Williams says.

But what is it that removes cold gas from galaxies? Astronomers will have to continue their observations to find clues to this great space mystery.

“The mere fact that these massive beasts of the cosmos formed 100 billion stars within about a billion years and then suddenly shut down their star formation is a mystery we would all love to solve, and REQUIEM has provided the first clue,” the researchers concluded.

The results of the research were published in the journal Nature.

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