The mystery of how the first quasars in the universe formed—something that
has baffled scientists for nearly 20 years—has now been solved by a team of
astrophysicists whose findings are published in Nature.
The existence of more than 200 quasars powered by supermassive black holes
less than a billion years after the Big Bang had remained one of the
outstanding problems in astrophysics because it was never fully understood
how they formed so early.
The team of experts led by Dr. Daniel Whalen from the University of
Portsmouth have found that the first quasars naturally formed in the
violent, turbulent conditions of rare reservoirs of gas in the early
universe.
Dr. Whalen, from the University's Institute of Cosmology and Gravitation,
said: "This discovery is particularly exciting because it has overturned 20
years of thought on the origin of the first supermassive black holes in the
universe.
"We find supermassive black holes at the centers of most massive galaxies
today, which can be millions or billions of times the mass of the sun. But
back in 2003 we began finding quasars—highly luminous, actively-accreting
supermassive black holes that are like cosmic lighthouses in the early
universe—that existed less than a billion years after the Big Bang. And no
one understood how they formed by such early times."
A few years ago, supercomputer simulations showed that early quasars could
form at the junctions of rare, cold, powerful streams of gas. Only a dozen
of these existed in a volume of space a billion light-years across, but the
black hole had to be 100,000 solar masses at birth. Black holes today form
when massive stars run out of fuel and collapse, but they are usually only
10–100 solar masses.
Astrophysicists had long theorized that 10,000–100,000 solar-mass stars
formed in the early universe but only in exotic, finely-tuned environments
like strong ultraviolet backgrounds or supersonic flows between gas and dark
matter that had no resemblance to the turbulent clouds in which the first
quasars formed.
Dr. Whalen said: "We think of these stars as a bit like dinosaurs on earth,
they were enormous and primitive. And they had short lives, living for just
a quarter of a million years before collapsing to black holes.
"Our supercomputer models went back to very early times and found that the
cold, dense streams of gas capable of growing a billion solar-mass black
hole in just a few hundred million years created their own supermassive
stars without any need for unusual environments. The cold streams drove
turbulence in the cloud that prevented normal stars from forming until the
cloud became so massive it collapsed catastrophically under its own weight,
forming two gigantic primordial stars—one which was 30,000 solar masses and
another which was 40,000.
"Consequently, the only primordial clouds that could form a quasar just
after cosmic dawn -when the first stars in the universe formed—also
conveniently created their own massive seeds. This simple, beautiful result
not only explains the origin of the first quasars but also their
demographics—their numbers at early times.
"The first supermassive black holes were simply a natural consequence of
structure formation in cold dark matter cosmologies—children of the cosmic
web."
The paper "The Turbulent Origins of the First Quasars" is published in
Nature.
Reference:
Daniel Whalen, Turbulent cold flows gave birth to the first quasars, Nature
(2022).
DOI: 10.1038/s41586-022-04813-y
Tags:
Space & Astrophysics