And there was light: How the universe came out of a cosmic dark age

Scientists may have solved the mystery behind how our universe emerged from the cosmic dark ages to a clearer, light-filled state that we see today.

Researchers at the University of Iowa (UI) in the US propose that black holes within galaxies produce winds strong enough to fling out matter that punctures holes in galaxies, allowing light to escape.

Soon after the Big Bang, the universe went completely dark. The intense, seminal event that created the cosmos churned up so much hot, a thick gas that light was completely trapped.

As many as one billion years after the Big Bang, the universe expanded, became more transparent, and eventually filled up with galaxies, planets, stars, and other objects that give off visible light.

According to a new study, black holes that dwell in the centre of galaxies fling out matter so violently that the ejected material pierces its cloudy surroundings, allowing light to escape.

The researchers arrived at their theory after observing a nearby galaxy from which ultraviolet light is escaping.

"The observations show the presence of very bright X-ray sources that are likely accreting black holes," said Philip Kaaret, professor in the UI Department of Physics and Astronomy.

"It is possible the black hole is creating winds that help the ionising radiation from the stars escape. Thus, black holes may have helped make the universe transparent," said Kaaret, corresponding author of the study published in the journal Monthly Notices of the Royal Astronomical Society.

The team focused on a galaxy called Tol 1247-232, located some 600 million light years from Earth, one of only three nearby galaxies from which ultraviolet light has been found to escape.

In 2016, using an Earth-orbiting telescope called Chandra, the researchers saw a single X-ray source whose brightness waxed and waned and was located within a vigorous star-forming region of Tol 1247-232.

The team determined it was something other than a star.

"Stars don't have changes in brightness. Our Sun is a good example of that," Kaaret said.

No one knows for sure how a black hole, whose intense gravitational pull sucks in everything around it, also ejects matter, researchers said.

Black holes are hard to study, in part because their immense gravitational pull allows no light to escape and because they're embedded deep within galaxies.

Recently, however, astronomers have offered an explanation: The jets of escaping matter are tapping into the accelerated rotational energy of the black hole itself, researchers said.

As gravity pulls matter inward toward a black hole, the black hole likewise spins faster. As the black hole's gravitational pull increases, the speed also creates energy, they said.

"As matter falls into a black hole, it starts to spin and the rapid rotation pushes some fraction of the matter out," Kaaret said.

"They are producing these strong winds that could be opening an escape route for ultraviolet light. That could be what happened with the early galaxies," he added.