In the beginning, everything was dark. Then, after hundreds of millions of years, the light of primitive suns began to spread freely throughout the Universe. But what caused the lifting of this dark veil to give way to light? For scientists, it remains a mystery. However, a team of astronomers has developed a new hypothesis that explains how that primitive fog was pushed aside, allowing the light of massive stars to illuminate the entire cosmos.
According to experts from the department of physics and astronomy at the University of Iowa (USA) and the Harvard-Smithsonian Center for Astrophysics , the idea came to them thanks to observations of a rather unusual galaxy located just 600 million light-years away. away from the Earth from which ultraviolet light escapes.
The beggining
The intense event that created the cosmos produced so much hot, thick gas that the light was completely trapped. Much later, perhaps up to 1 billion years after the Big Bang, the universe expanded, became more transparent, and eventually filled with galaxies, planets, stars, and other objects that emit visible light.
What brought about the change
Black holes in the center of galaxies spew matter so violently that the ejected material passes through their cloudy surroundings , allowing light to escape (as in the case of this peculiar galaxy).
“The observations show the presence of very bright X-ray sources that are likely to accrete black holes. It is possible that the black hole is creating winds that help ionizing radiation from the stars to escape, so the black holes may have helped that the universe is transparent “, says Philip Kaaret, leader of the work.
The galaxy in question is Tol 1247-232 , one of the three nearby galaxies that emit light in the UV spectrum (another one is Haro 11). In May 2016, using the Chandra observatory, the researchers viewed a single X-ray source whose brightness increased and decreased, located within a vigorous star-forming region of Tol 1247-232.
If the stars do not have changes in their brightness (our Sun is a good example of this), then what is?
The team determined that it was more than just a star . “To change in brightness, you have to be a small object, and that really reduces everything to a black hole,” Kaaret clarifies.
But how is it possible that a black hole, whose intense gravitational pull absorbs everything around it, is also capable of expelling matter?
The quick answer is that no one knows for sure. Black holes, after all, are difficult to study, in part because their immense gravitational pull does not allow any light to escape – they are like cosmic dust sprays and not a galactic leaf blower – and because they are at the heart of the galaxies.
Is it possible that their rotation has something to do with it?
As its immense gravity pulls the material closer, the black hole’s spin increases in speed, increasing the amount of kinetic energy in the swirl of matter sliding its gravitational horizon. “As matter falls into a black hole, it begins to spin and the rapid rotation pushes a fraction of the matter out. They are producing strong winds that could open an escape route or ultraviolet light,” explains Kaaret.
It is possible that the first large black holes in the early universe could have played a key role in clearing the way for ionizing radiation to glow throughout space.
Referencia: P. Kaaret et al, Resolving the X-ray emission from the Lyman-continuum emitting galaxy Tol 1247-232, Monthly Notices of the Royal Astronomical Society (2017). DOI: 10.1093/mnras/stx1945
