'Sideline quasars' prevented early galaxy formation
Washington, March 22 : Astronomers targeting one of the brightest quasars glowing in the universe some 11 billion years ago say "sideline quasars" likely teamed up with it to heat abundant helium gas billions of years ago, preventing small galaxy formation.
University of Colorado 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, said Shull.
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, said Shull, a professor in CU-Boulder's astrophysical and planetary sciences department.
"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," said Shull.
The Cosmic Origins Spectrograph used for the quasar observations aboard Hubble was designed to probe the evolution of galaxies, stars and intergalactic matter.
For the study, Shull and Syphers used 4.5 hours of data from Hubble observations of the quasar, which has a catalog name of HS1700+6416.
While some astronomers define quasars as feeding black holes, "We don't know if these objects feed once, or feed several times," Shull said.
They are thought to survive only a few million years or perhaps a few hundred million years, a brief blink in time compared to the age of the universe, he said.
The first quasar, short for "quasi-stellar radio source," was discovered 50 years ago this month by Caltech astronomer Maarten Schmidt.
The quasar he observed, 3C 273, is located roughly 2 billion light-years from Earth and is 40 times more luminous than an entire galaxy of 100 billion stars.
That quasar is receding from Earth at 15 percent of the speed of light, with related winds blowing millions of miles per hour, said Shull.
A paper on the subject by Shull and Syphers was published online this week in the Astrophysical Journal.