Shortly after the Big Bang, the universe became completely dark. This powerful, key event in the history of our world, as a result of which the cosmos was formed, led to the emergence of so much hot, dense gas that light could not break through it. Much later - perhaps about one billion years after the Big Bang - the universe expanded, becoming more transparent, and finally filled with galaxies, planets, stars and other objects that emit or reflect light in the visible range. This is how we know the universe today.
But how exactly did the mysterious transition from the cosmic "dark age" to the "bright state" of the Universe take place?
To answer this question in a new study, a team of scientists led by Philip Kaaret, a professor in the Department of Physics and Astronomy at the University of Iowa, USA, investigated the behavior of a black hole located in a nearby galaxy and found out that this black hole - and also, probably other black holes - capable of ejecting a part of the matter falling on it so intensely as to pierce the layer of gas surrounding the galaxy and give an outlet for ultraviolet radiation from the galaxy.
Kaareth and his team observed a galaxy called Tol 1247-232, located about 600 light-years from Earth. This galaxy is known to astronomers for being one of three nearby galaxies that emit in ultraviolet light - in other words, ultraviolet radiation has the ability to "get out" of these galaxies. In May 2016, the team found a bright and very compact X-ray source in this galaxy using NASA's Chandra space observatory, whose variable nature indicated that the source was most likely not a star, but a black hole. The discovery of this source led Kaaret to the assumption that black holes could take part in the ionization of the Universe, "breaking through" layers of gas around galaxies with their jets.
Kaaret plans further observations of the galaxy Tol 1247-232, as well as searches for other nearby ultraviolet-emitting galaxies, which may help confirm his hypothesis.
The study was published in the Monthly Notices of the Royal Astronomical Society.