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Early Galaxies Reveal Few Seeds for New Stars

An international team of astronomers has discovered that gas around young galaxies is almost barren, devoid of the hydrogen needed to seed new stars.

Without starlight to see them directly, the team observed the young galaxies’ outskirts in silhouette. They searched for telltale signs of hydrogen molecules absorbing the light from background objects called quasars – supermassive black holes sucking in surrounding material – that glow very brightly.

“Previous experiments led us to expect molecules in about ten of the 90 young galaxies we observed, but we found just one case,” said A/Prof Michael Murphy of Swinburne University.

Astronomers believe that stars begin to form in cold gas that is rich in molecules. The team observed galaxies at a time when the Universe was most actively forming stars, about 12 billion years ago.

“This is when most stars are born, and we think this gas forms stars eventually, but it lacks the key ingredient – molecules – to do so,” Murphy said.

The team believes that location and time are the key. “The gas we observe in silhouette probably lies too far from the galaxies to form stars,” said Dr Regina Jorgenson of the University of Hawaii at Manoa. “It’s got lots of potential, but it hasn’t had time to fall into the richer, denser parts of the galaxies which might be better stellar nurseries.”

The researchers made new observations of more than 50 quasars for this study using the 6.5-metre diameter Magellan telescopes in Chile, and published the results in the Monthly Notices of the Royal Astronomical Society.