Sideline Quasars Responsible For Slowing Galaxy Formation?

This artist’s impression shows how a very distant quasar called ULAS J1120+0641, may have looked just 770 million years after the Big Bang. (Courtesy: ESO/M Kornmesser)

According to a new study from astronomers at the University of Colorado, one of the brightest quasars known formed some 11 billion years ago with interesting ramifications.It may have been responsible for slowing growth in the Universe. This “sideline quasar” may have combined with another to heat the ever-present helium gas and cut down on small galaxy formation. 

CU-Boulder Professor Michael Shull and Research Associate David Syphers used the Hubble Space Telescope to observe the brilliant nucleus of an active galaxy. This highlighted source acted as a “lighthouse”, assisting the researchers in understanding what the early Universe was like. How did they do it? By observing the gases between the telescope and quasar with a ultra-violet spectrograph onboard the Hubble Space Telescope – a sensitive piece of equipment designed by a team from CU-Boulder’s Center for Astrophysics and Space Astronomy.

Scientists point back to an epoch which happened about 11 billion years ago and is referred to as the “helium reionization era”. They speculate at the time, that waves of ionizing radiation from black holes thought to be located at the heart of quasars may have stripped atoms from the beginning helium atoms – a process which may have begun 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.

According to the news release, 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.”

A new CU-Boulder study shows that distant quasars teamed up to stifle the formation of small galaxies billions of years ago. Image courtesy NASA

These new results were courtesy of the he Cosmic Origins Spectrograph – a specialty-designed piece of equipment meant specifically for observing quasars, and examining stellar, galactic and intergalactic matter evolution. 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. COS was built in an industrial partnership between CU and Ball Aerospace & Technologies Corp. of Boulder.

“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.”

Of course, we’re all aware of the Big Bang – an event which is believed to be the start-up of our Universe. It is surmised to have begun with a huge conflagration of plasma which expanded then turned into cool, neutral gas for about 380,00 years. This is described as the cosmic “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.

Enter the quasar. Radiation from huge quasars a theorized to be responsible for heating 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.”

There are many definitions to describe what a quasar is. According to the dictionary, a quasar is “A starlike object that has a large red shift and emits powerful blue light and often radio waves.

The researchers are employing the COS to examine ancient gases present in the early Universe, including a structure referred to as the “cosmic web” – long, slender filaments of galaxies and intergalactic gas which are separated by huge areas of “nothingness”. Astronomers postulate a single cosmic web filament may extend across as much as hundreds of millions of light years. The COS instrument parcels light into single layers, similar to how sunlight is refracted in a rainy sky, creating a rainbow. These different colors tell us much, such as temperature, density, velocity, distance and chemical composition of stars, galaxies and even gas clouds.

To aid their research, Shull and Syphers used four and half 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,” said Shull. “Who knows? Maybe our Milky Way used to be a quasar.”

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.

Original Story Source: University of Colorado Boulder News Release. Submitted by Tammy Plotner for “Dave Reneke’s World of Space and Astronomy News”.

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