Silhouettes of 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 seeds from which new stars are thought to form—molecules of hydrogen. The study will be published in the Monthly Notices of the Royal Astronomical Society and is available online.
Without starlight to see them directly, the team, which includes Regina Jorgenson of the Institute for Astronomy at the University of Hawaiʻi at Mānoa, 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.
“Previous experiments led us to expect molecules in about 10 of the 90 young galaxies we observed, but we found just one case,” said Associate Professor Michael Murphy from Swinburne University of Technology in Australia. He co-led the study with Jorgenson.
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 a little mystery. 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,” said Murphy.
The team believes that location and time are key.
“The gas we observe in silhouette probably lies too far from the galaxies to form stars,” Jorgenson said. “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-meter Magellan telescopes in Chile.
The study was conducted by researchers from UH Mānoa, Swinburne University of Technology, the University of Cambridge and the University of Arizona.
Read the UH Mānoa news release for more.