It is assumed that primordial black holes formed shortly after the Big Bang.
Shutterstock/Mohd. Afuza
An unusually massive black hole in the very early Universe may be of some sort exotic, starless Black hole was first theorized Stephen Hawking.
In August Boyuan Liu from the University of Cambridge and his colleagues discovered a strange galaxy that formed 13 billion years ago, called Abell 2744-QSO1, using the James Webb Space Telescope (JWST). The galaxy appeared to contain a huge black hole, about 50 million times the mass of the Sun, but it was almost completely devoid of stars.
“It's a mystery because the traditional theory is that stars form first, or together with black holes,” Liu says. Black holes are generally thought to form from very massive stars when they run out of fuel and collapse.
Liu and his team ran basic simulations that showed that QSO1 could instead have started out as primordial black holean exotic object first proposed by physicists Stephen Hawking and Bernard Carr in 1974. These objects were formed not from a star, but from fluctuations in the density of the Universe shortly after the Big Bang.
The primordial black holes should have largely evaporated and disappeared by the time we could come back to life with JWST, but there is a chance that some of them survived and evolved into much larger black holes like QSO1.
Although Liu and his team's calculations roughly matched their observations, they were simple and did not take into account the complex interactions between primordial black holes, gas clouds and stars.
Now Liu and his team have carried out more detailed simulations of how primordial black holes might have grown in the first hundreds of millions of years of the Universe's existence. They calculated how the gas would rotate around the small initial black hole, as well as how newly formed stars and dying stars would interact with it.
Their predictions for the final mass of the black hole and heavier elements in it match what they observed for QSO1.
“It's not critical, but it's an interesting and kind of important opportunity,” Liu says. “With these new observations that are normal [black hole formation] theories struggle to reproduce, the possibility of massive primordial black holes in the early Universe is becoming more plausible.”
Simulations show that primordial black holes may actually be a viable source of QSO1, he says. Roberto Maiolino from the University of Cambridge, who was part of the team that originally discovered the black hole. “The fact that they manage to match the properties of QSO1 both in terms of black hole mass, stellar mass and chemical enrichment is very interesting and encouraging.”
However, the largest supermassive black holes in standard models of primordial black holes typically have a mass of about 1 million solar masses, says Maiolino. “Here we are 50 times more massive,” he says. “However, it is true that these primordial black holes are expected to be highly clustered, and so it is possible that they managed to merge and quickly become much more massive.”
Another problem is that primordial black holes require an explosion of high-energy radiation to initially collapse and form, such as when a nearby star explodes, but we don't see any potential sources anywhere near QSO1, says Maiolino.
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