Scientists may have discovered why the pace of star formation slowed about 11 billion years ago. It turns out that quasars may have something to do with it.
In this latest study, the researchers looked at information on 17,468 galaxies. They found a tracer of energy known as the Sunyaev-Zel'dovich Effect. This particular event occurs when high-energy electrons disturb the Cosmic Microwave Background, or CMB. The CMB is effectively a sea of microwave radiation that's left over from the birth of the universe.
The researchers analyzed thermal energy levels to see if they rise above predictions for what it would take to stop star formation. They looked at a large number of galaxies for this with the help of information gathered by the Sloan Digital Sky Survey and other telescopes. This allowed them to take faint temperature measurements that would show the Sunyaev-Zel'dovich Effect in addition to finding quasars.
So what did they find? Galaxies produced the most stars about 11 billion years ago. Then, they slowed down. Currently, the pace of star formation is about one-thirtieth as fast as when it peaked. In this case, the researchers discovered that intense radiation and galaxy-scale winds emitted by quasars heat up clouds of dust and gas. This, heat prevents the material from cooling and forming more dense clouds and, over time, stars.
"I would argue that this is the first convincing observational evidence of the presence of quasar feedback when the universe was only a quarter of its present age, when the cosmic star formation was more vigorous," said Tobias Marriage, an assistant professor at Johns Hopkins University. "It's like finding a smoking gun with fingerprints near the body, but not finding the bullet to match the gun."
By studying the Sunyaev-Zel'dovich Effect, researchers were able to see the full effect of galactic wind on the surrounding galaxy.
"Unlike all other methods that are probing small clumps within the wind, the Sunyaev-Zeldovich Effect is sensitive to the bulk of the wind, the extremely hot plasma that's filling the volume of the wind and is completely undetectable using any other technique," said Nadia L. Zakamska, one of the co-authors of the new study.
The findings reveal a bit more about the SZ Effect and also show that these cosmic winds may be behind the slower star formation in our universe. More specifically, quasars could be the ones that help slow the pace of star birth.
The findings are published in the March 2016 journal Monthly Notices of the Royal Astronomical Society.
