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Artist’s impression of the gas surrounding a young galaxy in the distant
universe. The gas, shown as red streams on the left, is actually
invisible, and the starlight from the galaxy is too faint for
astronomers to see directly. Instead, the gas is seen in silhouette
against a bright, background quasar. Molecules in the gas imprint a
shadow, or absorption line, onto the quasar light at a very specific
color, as seen on the right, and astronomers can detect this shadow. Image credits: ESO/L. Calçada/ESA/AOES Medialab, Swinburne Astronomy Productions - Hi-res image5.10 MB JPEG
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.
Without starlight to see them directly, the team, which includes Dr. Regina Jorgenson of the Institute for Astronomy at the University of Hawaii at Manoa—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 10 of the 90 young galaxies we observed, but we
just one case,” said Associate Professor Michael Murphy from Swinburne
University of Technology in
Australia. He co-led the study with
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,” 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,” 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.
It was conducted by researchers from the
University of Hawaii at Manoa, Swinburne University of Technology, the
University of Cambridge and the University of Arizona.