February 6, 2014
Black Holes Heated The Early Universe Later Than Previously Believed
[ Watch the Video: Black Holes Heated Gas Later Than Believed ]
redOrbit Staff & Wire Reports - Your Universe Online
In what is being described as a landmark discovery about the origins of the universe, Tel Aviv University researchers report in the journal Nature that black holes, formed from the first-ever stars, heated the gas throughout space much later than previously believed.
In addition, study authors Professor Rennan Barkana of TAU's School of Physics and Astronomy, Dr. Anastasia Fialkov of the École Normale Supérieure in Paris and Dr. Eli Visbal of Harvard University imprinted a clear signature in radio waves that can be searched for by astronomers.
“One of the exciting frontiers in astronomy is the era of the formation of the first stars,” Barkana explained in a statement. “Since the universe was filled with hydrogen atoms at that time, the most promising method for observing the epoch of the first stars is by measuring the emission of hydrogen using radio waves.”
Just like archaeologists here on Earth, astronomers often work to explore the universe during its earliest days, only they are able to see directly into the past thanks to the length of time it takes far-off objects to reach our world. This phenomenon allows scientists to view objects as they were when the light was first emitted, the investigators explained, and can even allow them to observe the first stars as they actually were in the ancient past.
“Thus, the new finding that cosmic heating occurred later than previously thought means that observers do not have to search as far, and it will be easier to see this cosmic milestone,” TAU said. “Cosmic heating may offer a way to directly investigate the earliest black holes, since it was likely driven by star systems called ‘black-hole binaries.’”
Black-hole binaries are pairs of stars in which the larger of the two ended its lifespan with a supernova explosion that left behind a black-hole remnant, the authors said. It then pulls in gas from the surviving companion star, ripping it apart with its strong gravitational forces and emitting high-energy X-rays capable of traveling great distances. This radiation is believed to have re-heated cosmic gases cooled following the original cosmic expansion.
However, Prof. Barkana and his colleagues now report that the heating did not occur very early on, as they had previously believed. On the basis of their research, they discovered that “this standard picture delicately depends on the precise energy with which the X-rays come out.”
“Taking into account up-to-date observations of nearby black-hole binaries changes the expectations for the history of cosmic heating,” he added. “It results in a new prediction of an early time (when the universe was only 400 million years old) at which the sky was uniformly filled with radio waves emitted by the hydrogen gas.”
These discoveries contradict the common view that cosmic heating took place too early to be visible – an assumption upon which modern radio telescope arrays were constructed. Those instruments were designed to detect radio waves given off by hydrogen resulting from later cosmic events. However, the study authors claim that their findings indicate that these telescopes could also be used to locate cosmic heating from the earliest black holes.