- 4520
- BLACKHOLES - at the Universe beginning? - The
feeding supermassive black hole, which powers a quasar at the heart of the
galaxy J1120+0641, was seen as it was when the universe was just around 5% of
its current age. It also has a mass that is over a billion times that of the
sun.
-
------------------------------------ 4520 - BLACKHOLES - at the Universe beginning?
- Using the James Webb Space Telescope
(JWST), astronomers have spotted this supermassive black hole at "cosmic
dawn" that seems to be impossibly massive. The confusion comes from the
fact that it doesn't seem like this giant void was feasting on much surrounding
matter during that time, but, in order to reach its immense size, one would
expect it to have been ravenous when time began.
-
- While it is relatively easy to explain how
closer, and thus more recent, supermassive black holes have grown to have
billions of solar masses, the merger and feeding processes that facilitate this
growth are expected to take something like a billion years. That means finding
such supermassive black holes existing before the 13.8 billion-year-old
universe was a billion years old is a real dilemma.
-
- The new observations only add to the
mystery: Early quasars were shockingly normal.
No matter in which wavelengths we observe them, quasars are nearly
identical at all epochs of the universe.
-
- Finding supermassive black holes billions of
years after the Big Bang is expected, but discovering them around the time the
first stars formed is more surprising.
In the last 13.8 billion
years of cosmic history, galaxies have grown in size by acquiring mass either
by taking in surrounding gas and dust, by cannibalizing smaller galaxies, or by
merging with larger galaxies.
-
- Around 20 years ago, before the JWST and
other telescopes began finding troubling supermassive black holes in the early
universe, astronomers had assumed that the supermassive black holes at the
hearts of galaxies grew gradually in lockstep with the processes that led to
galactic growth.
-
- Because of the conservation of angular
momentum, matter can't fall directly into a black hole. Instead, a flattened
cloud of matter called an accretion disk is formed around the black hole.
-
- The immense gravity of the central black
hole gives rise to powerful tidal forces that create turbulent conditions in
the accretion disk, heating it and causing it to emit light across the
electromagnetic spectrum. These emissions are so bright they often outshine the
combined light of every star in the surrounding galaxy. The regions in which
all this happens are called “quasars”, and they represent some of the brightest
celestial objects.
-
- This brightness has another function.
Despite not having mass, light does exert pressure. That means that the light
emitted by quasars pushes on surrounding matter. The faster the black hole
powering the quasar feeds, the greater the radiation pressure and the more
likely the black hole is to cut off its own food supply and stop growing. The
point at which black holes, or any other accretor, starve themselves by pushing
away surrounding matter is known as the "Eddington limit."
-
- That means supermassive black holes can't
just feed and grow as fast as they like. Thus, finding supermassive black holes
with masses as great as 10 billion suns in the early universe, especially less
than a billion years after the Big Bang, is a real problem.
-
- Astronomers need to know more about early
quasars to determine whether early supermassive black holes were able to
overcome the Eddington limit and become so-called "super-Eddington
accretors."
-
- To do this, in January 2023, astronomers
focused the JWST's Mid-Infrared Instrument (MIRI) on the quasar at the heart of
J1120+0641, located 13 billion light-years away and seen as it was just 770
million years after the Big Bang. The investigation constitutes the first
mid-infrared study of a quasar that existed at the cosmic dawn.
-
- The spectrum of light from this early
supermassive black hole revealed the properties of the large, ring-shaped
"torus" of gas and dust that circles the accretion disk. This torus
helps guide matter to the accretion disk, from where it is gradually fed to the
supermassive black hole.
-
- MIRI observations of this quasar showed
that the cosmic supply chain functions similarly to that of "modern"
quasars closer to Earth that therefore exist in later epochs of the universe.
That's bad news for proponents of the theory that an enhanced feeding mechanism
led to the quick growth of early black holes.
-
- The JWST observations of this quasar did
reveal one major difference between it and its modern counterparts. The dust in
the torus around the accretion disk had a temperature of around 2,060 degrees
Fahrenheit, which is around 100 degrees hotter than the dust rings around
supermassive black hole-powered quasars seen closer to Earth.
-
- The research favors another method of early
supermassive black hole growth that suggests these cosmic titans got a head
start in the early universe, forming from black hole "seeds" that
were already massive These heavy seeds would have had masses at least a hundred
thousand times that of the sun, forming directly via the collapse of early and
massive clouds of gas
-
- Gravity is the oldest known, but the least
understood force in nature. Black holes
play important roles in galaxies, perhaps even in the large-scale behavior of
the universe and more. The other thing to note about black holes is that they
are very ‘simple’ especially when compared to stars and other astrophysical
objects. This is a consequence of the so-called ‘no hair’ theorem that states
that black holes can be fully characterized by only 3 attributes — their mass,
charge and spin.
-
- Einstein’s theory of general relativity
predicted both the existence of black holes and gravitational waves, both of
which continued to be scrutinized throughout the 20th century, which includes
what’s called the “golden age of general relativity” during the 1960s and
1970s. -
- The first object accepted by the scientific
community as a black hole, called Cygnus X-1, which was discovered in 1964.
However, it took another 52 years for the existence of gravitational waves to
be confirmed through a black hole merger, which was accomplished by the LIGO
Scientific Collaboration.
-
- Studying black holes offers insight on the
nature of gravity, space and time at the most fundamental levels. As
physicists, we are yet to develop a complete understanding of the quantum
nature of gravity, and black holes are the key to unlocking that mystery.
-
- Black holes can only be observed
indirectly. Unlike stars, since they don’t emit radiation themselves, it is
difficult for astronomers to collect data on them. At best, we can observe
their influence on their environment (like gas, stars, etc.) and infer their
properties and behavior.
-
- While it took over 100 years between
Einstein introducing his theory of general relativity in 1915 and the
confirmation of gravitational waves in 2016, it only took another three years
for astronomers to publish the first direct image of a black hole at the center
of the Messier 87 galaxy.
-
- While Messier 87 is located approximately 53
million light-years from Earth, the closest hypothesized black hole, Gaia BH1,
is located approximately 1,560 light-years from Earth. In 2022, astronomers published a direct
image of Sagittarius A*, which is the supermassive black hole at the center of
our Milky Way Galaxy.
-
- Scientists hypothesize the number of black
holes in our Milky Way Galaxy is in the hundreds of millions, despite only a
few dozen known black holes having been confirmed, thus far.
-
- Researchers use mathematical calculations
and computer models to simulate what black holes might look like, and then have
used powerful ground-based telescopes like EHT to obtain the few direct images
of black holes. These direct images
don’t capture the black hole itself, but the gases that are encircling the
black hole’s event horizon, or the unofficial boundary where light can’t escape
the black hole.
-
- How will black holes help us better
understand our place in the universe in the coming years and decades? Only time
will tell, and this is why we science!
-
-
July 5, 2024 BLACKHOLES - at
the Universe beginning? 4520
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--------------------- --- Saturday, July 6, 2024
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