The brightest quasars glowing in the universe some 11 billion years
ago 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
ultraviolet spectrograph on Hubble designed by a team from CU-Boulder's
Center for Astrophysics and Space Astronomy. 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. "Our own Milky Way
has a dormant black hole in its center. Who knows? Maybe our Milky Way
used to be a quasar."
"While there are likely hundreds of millions of quasars in the universe,
there are only a handful you can use for a study like this," said
Shull. Quasars are nuclei in the center of active galaxies that have
"gone haywire" because of supermassive black holes that gorged
themselves in the cores, he said. "For our purposes, they are just a
really bright background light that allows us to see to the edge of the
universe, like a headlight shining through fog."
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," said Shull. "But now we think it more
likely occurred in the 11 to 10 billion-year range, which was a
surprise."
The Cosmic Origins Spectrograph used for the quasar observations
aboard Hubble was designed to probe the evolution of galaxies, stars and
intergalactic matter. The COS team is led by CU Professor James Green
of CASA and was installed on Hubble by astronauts during its final
servicing mission in 2009.
The universe is thought to have begun with the Big Bang that
triggered a fireball of searing plasma that expanded and then become
cool neutral gas at about 380,000 years, bringing on the "dark ages"
when there was no light from stars or galaxies, said Shull. The dark
ages were followed by a period of hydrogen reionization, then the
formation of the first galaxies beginning about 13.5 billion years ago.
The first galaxies era was followed by the rise of quasars some 2
billion years later, which led to the helium reionization era, he said.
The radiation from the huge quasars heated the gas to 20,000 to
40,000 degrees Fahrenheit in intergalactic realms of the early universe,
said Shull. "It is important to understand that if the helium gas is
heated during the epoch of galaxy formation, it makes it harder for
proto-galaxies to hang on to the bulk of their gas. In a sense, it's
like intergalactic global warming."
The team is using COS to probe the "fossil record" of gases in the universe, including a structure known as the "cosmic web" believed to be made of long, narrow filaments of galaxies and intergalactic gas
separated by enormous voids. Scientists theorize that a single cosmic
web filament may stretch for hundreds of millions of light years, an
eye-popping number considering that a single light-year is about 5.9
trillion miles.
COS breaks light into its individual components -- similar to the way
raindrops break sunlight into the colors of the rainbow -- and reveals
information about the temperature, density, velocity, distance and
chemical composition of galaxies, stars and gas clouds.
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 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.
Image credit: Credit: NASA/JPL-Caltech
Source: The Daily Galaxy via University of Colorado
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