`Sideline quasars` stifled early galaxy formation
Washington: University of Colorado Boulder astronomers have claimed that "sideline quasars" teamed up with one of the brightest quasars glowing in the universe 11 billion years ago in order to prevent small galaxy formation.
CU-Boulder Professor Michael Shull and Research Associate David Syphers used the Hubble Space Telescope to look at the quasar-the brilliant core of an active galaxy that acted as a "lighthouse" for the observations-to better understand the conditions of the early universe.
The scientists studied gaseous material between the telescope and the quasar with a 70-million-dollar ultraviolet spectrograph on Hubble designed by a team from CU-Boulder`s Center for Astrophysics and Space Astronomy.
During a time known as the "helium reionization era" some 11 billion years ago, blasts of ionizing radiation from black holes believed to be seated in the cores of quasars stripped electrons from primeval helium atoms, Shull said.
The initial ionization that charged up the helium gas in the universe is thought to have occurred sometime shortly after the Big Bang.
"We think ` sideline quasars` located out of the telescope`s view reionized intergalactic helium gas from different directions, preventing it from gravitationally collapsing and forming new generations of stars," he said.
Shull likened the early universe to a hunk of Swiss cheese, where quasars cleared out zones of neutral helium gas in the intergalactic medium that were then "pierced" by UV observations from the space telescope.
The results of the new study also indicate the helium reionization era of the universe appears to have occurred later than thought, Shull, a professor in CU-Boulder`s astrophysical and planetary sciences department said.
"We initially thought the helium reionization era took place about 12 billion years ago. But now we think it more likely occurred in the 11 to 10 billion-year range, which was a surprise," he added.
The findings are published online in the Astrophysical Journal.
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