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Astronomers have just found 83 quasars, powered by supermassive black holes dating back to the childhood of the Universe, when it was less than 10% of its current age.
This discovery reveals that such objects were more common in the mists of time than we thought and challenged our entire cosmological model.
Quasars are among the brightest objects in the universe, extremely bright galactic nuclei powered by supermassive black holes. When the material swirls around the black hole, its friction generates radiation so intense that it can be seen even at billions of light years away.
There is just a big problem. We think we know how black holes are formed: they are the collapsed nuclei of massive stars. And supermassive black holes can have billions of times the mass of the Sun.
This takes time and requires large amounts of material. So, how on earth did all these quasars appear so early in the history of the Universe?
"It is remarkable that such dense and massive objects could have formed so soon after the Big Bang," said astrophysicist Michael Strauss of Princeton University.
"Understanding how black holes can form at the beginning of the universe and how common they are is a challenge for our cosmological models."
A quasar at 13.05 billion light years. (National Astronomical Observatory of Japan)
We knew that there were quasars at the time. The oldest we've seen dates back to about 690 million years after the Big Bang, when the Universe was about 5% of its current age – and a few others were also spotted.
But these – although it remains a puzzle – were considered relatively rare. Astronomers from Japan, Taiwan and the United States have therefore expanded the search with the help of Hyper Suprime-Cam data mounted on the Subaru telescope in Hawaii.
With this instrument, they could look for quasars much weaker than those previously discovered. The oldest quasar that they found was 13.05 billion light-years, tied for the second-most distant quasar ever discovered.
It is thought that the universe is about 13.8 billion years old and the first stars – we think – only appeared about 500 million years after the Big Bang, after the reionization of the 39, neutral hydrogen from the beginning of the universe. This just leaves a few hundred million years for the quasars to form.
The team's investigation suggests that these objects were actually quite abundant at the time. They identified the candidate quasars in the HSC data, and then conducted a dedicated survey using several telescopes to obtain bright signatures, or spectra, of these objects.
(National Astronomical Observatory of Japan)
These spectra revealed the 83 new quasars of recent years. With 17 known quasars in the study area, the team calculated that there was about a quasar for each cubic light year; that is, a cube of space with a billion light-years per side.
Although this is more than previously thought, this is not enough for another hypothesis.
Just after the Big Bang, the Universe was a kind of dark and hot "primordial soup" on the cosmic scale, in full expansion.
As it expanded, it cooled, causing protons and neutrons to begin to combine into ionized hydrogen atoms; about 240,000 to 300,000 years after the Big Bang, these hydrogen atoms attracted electrons and merged into neutral hydrogen.
But it is only when gravity began to gather the first stars and galaxies in this dark void and filled with hydrogen that the light of the stars appeared … and shortly thereafter, according to the current theories, the Neutral hydrogen was excited by the ultraviolet light of the latter. nascent stars, galaxies, quasars not yet detected, or a combination of the three.
This is what is called the era of reionization, and we just do not know how it happened. But now, we know – based on this research – that there were not enough quasars to be solely responsible for this process.
The new quasar population data will help us learn more about the formation of supermassive black holes in the first universe – and the team will continue its research to see if they can find even older quasars. This could help researchers understand when the first black holes are born.
"The quasars we have discovered will be an interesting topic for future follow-up observations with current and future facilities," said Yoshiki Matsuoka astronomer of Ehime University in Japan.
"We will also study the formation and early evolution of supermassive black holes by comparing measured number density and luminance distribution with theoretical model predictions."
The findings were detailed in five documents, which you can find here, here, here, here and here.
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