Black Holes Heated Gas in Space Much Later than Previously Assumed

Black holes, which were the companions of early stars, heated gas in space much later than previously assumed, according to a latest study. The research shows that astronomers might have a good chance of studying the origin of universe.

According to researchers at the Tel Aviv University, these companion black holes have also "imprinted clear signals in the radio waves," which the astronomers can find and study.

"One of the exciting frontiers in astronomy is the era of the formation of the first stars," explained Prof. Rennan Barkana of TAU's School of Physics and Astronomy, an author of the study, according to a news release. "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."

Two cosmic events that occurred during the beginning of time shaped the universe that we see today; hydrogen gas was first heated and then was re-ionized or made transparent. These events occurred some 100 million years after the Big Bang, Space.com reported.  

"Previously, it was thought that these two milestones are well separated in time, and thus in observational data as well," study co-author Rennan Barkana, of Tel Aviv University, told Space.com via email.

Understanding the Cosmic 'Dark Ages'                                                           

A few thousand years after the Big Bang, the universe composed mainly of dark matter. The period is known as "cosmic dark ages" because the bright stars weren't born yet. This matter was mostly neutral hydrogen and helium.

It's this Dark Age that doesn't allow astronomers to study the beginning of the universe.

In the present study, researchers looked at early "black-hole binaries." These are star-pairs in which the larger star ends its life with a supernova explosion and leaves a black hole in its place. The companion star is then ripped apart due to gravity and gas from it is drawn towards the hole emitting high-energy X-ray radiation.

According to researchers, this radiation spread across the space and heated up gas. The study shows that this heating was much later than what other astronomers had believed.

"It was previously believed that the heating occurred very early," said Prof. Barkana in a news release, "but we 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. 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."

Seeing the Origin of Universe

The Low-Frequency Array in the Netherlands, the Precision Array for Probing the Epoch of Reionization in South Africa are two radio telescopes that look for radio signals from early universe.

Another mega radio telescope under construction is the Square Kilometer Array, which will be shared by South Africa and Australia.

Judd Bowman of Arizona State University told space.com that SKA can detect radio signals from heating up of early universe if its designers take the current research into account.

The study is published in the journal Nature.