Scientists Say Quasars |May Stunt Stellar Birth

     
     (CN) — Quasars may be the answer to a long-standing mystery of why star formation has slowed drastically over the past 11 billion years, according to evidence presented in a recent study.
     Astronomers estimate galaxies are creating stars at a pace that is roughly 30 times slower than their peak 11 billion years, which may be due to massive radiation and intense winds that are emitted by the brightest objects in the universe: quasars, the sites where stars are born.
     Quasars emit radiation and galactic winds that heat clouds of dust and gas, preventing them from cooling to the point of forming dense clouds, which are the precursors to stars.
     “Galactic winds are thought to limit the maximal mass of galaxies in the universe. Without them, all the available gas turns into stars and you would get enormous galaxies,” said Dr. Nadia Zakamska, an assistant astronomy professor at Johns Hopkins University and co-author of the study published in the Oxford Journals’ Monthly Notices of the Royal Astronomical Society.
     Zakamska said that scientists believe that gas is falling into the galaxy, which makes new stars before falling into a black hole. As the gas falls into the black hole, it produces a significant amount of radiation — which is referred to as the quasar phase of black hole growth. This feedback process regulates the creation of stars.
     “This radiation powers the wind, which blows up the rest of the gas, shutting down star formation,” Zakamska said.
     The researchers reviewed 17,468 galaxies and found a tracer of energy known as the Sunyaev-Zel’dovich Effect – a phenomenon named for two Russian physicists who predicted it in the 1960s — which appears when the Cosmic Microwave Background is disturbed by high-energy electrons. The Cosmic Microwave Background is thermal radiation left over from the universe’s superheated formation roughly 13.7 billion years ago.
     Thermal energy levels were analyzed to determine if they were above the predictions of the threshold necessary to stop star formation.
     “The Sunyaev-Zel’dovich Effect is very subtle. It just changes the properties of the Cosmic Microwave Background a little bit, and that’s what we measured,” Zakamska said. “It’s a symptom of an extremely powerful process, which is invisible otherwise. So the Sunyaev-Zel’dovich Effect is the method that we used to detect the powerful winds.”
     Study co-author Dr. Tobias Marriage added that “the Sunyaev-Zel’dovich Effect is proportional to the energy in the galaxy — the more energy in the galaxy the bigger the transfer to the Cosmic Microwave Background.”
     The group of researchers used two ground-based telescopes and a receiver mounted on a space telescope to take the temperature measurements necessary to demonstrate the Sunyaev-Zel’dovich Effect.
     An optical telescope at the Apache Point Observatory in New Mexico was used to find the quasars, while the thermal energy and evidence of the Sunyaev-Zel’dovich Effect were found using the Atacama Cosmology Telescope in Chile, which is designed to study the Cosmic Microwave Background.
     Using instruments with varying strengths in order to measure the Sunyaev-Zel’dovich Effect is relatively new.
     “The Atacama Cosmology Telescope data were collected for the study of the Cosmic Microwave Background. It was an unusual and interesting idea on our part to use it for studies of galactic winds,” Zakamska said. “I think this type of research will now become much more common, with several groups now pursuing similar methods to ours for all kinds of work.”
     Marriage and Zakamska are collaborating with scientists who create massive computer simulations of the universe containing different prescriptions for energy feedback from galactic winds and other physical mechanisms that affect galaxy formation, along with pursuing other research related to the Sunyaev-Zel’dovich Effect.
     “One of the extremely exciting things we think we will be able to do in the next few months is obtain images of the extreme winds at the peak galaxy-formation epoch, when the winds are blowing gas out of the galaxy at extreme velocities, thousands of miles per second,” Zakamska said.

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