- 4386 - JAMES WEBB - finds oldest galaxies? James Webb telescope finds that dwarf galaxies reionized the universe. Astronomers estimate 50,000 sources of this near-infrared light has traveled through various distances to reach the telescope’s detectors, representing the vastness of space .
------------------- 4386 - JAMES WEBB - finds oldest galaxies?
- The concentration
of mass in a particular galaxy cluster is so great that the fabric of spacetime
is warped by gravity, creating a natural, super-magnifying glass called a
'gravitational lens' that astronomers can use to see very distant sources of
light beyond the cluster that would otherwise be undetectable, even to Webb.
-
- Using these
unprecedented capabilities scientists have obtained the first spectroscopic
observations of the faintest galaxies during the first billion years of the
universe. These findings help answer a longstanding question for astronomers:
What sources caused the reionization of the universe? These new results have
effectively demonstrated that small dwarf galaxies are the likely producers of
prodigious amounts of energetic radiation.
-
- The Reionization
Era was a period of darkness without any stars or galaxies. It was
filled with a dense fog of hydrogen gas until the first stars ionized
the gas around them, and light began to travel through. Astronomers have spent
decades trying to identify the sources that emitted radiation powerful enough
to gradually clear away this hydrogen fog that blanketed the early universe.
-
- “Gravitational
lensing” magnifies and distorts the appearance of distant galaxies, so they
look very different from those in the foreground. The galaxy cluster 'lens' is
so massive that it warps the fabric of space itself, so much so that light from
distant galaxies that passes through the warped space also takes on a warped
appearance.
-
- This magnification
effect allowed astronomers to study very distant sources of light beyond “Abell
2744”, revealing eight extremely faint galaxies that would otherwise be
undetectable, even to Webb. These faint
galaxies are immense producers of ionizing radiation, at levels that are four
times larger than what was previously assumed. This means that most of the
photons that reionized the universe likely came from these dwarf galaxies.
-
- This discovery
unveils the crucial role played by ultra-faint galaxies in the early universe's
evolution. They produce ionizing
photons that transform neutral hydrogen into ionized plasma during cosmic
reionization. It highlights the importance of understanding low-mass galaxies
in shaping the universe's history.
-
- These cosmic
powerhouses collectively emit more than enough energy to get the job done.
Despite their tiny size, these low-mass galaxies are prolific producers of
energetic radiation, and their abundance during this period is so substantial
that their collective influence can transform the entire state of the universe.
-
- This is the first
time scientists have robustly measured the number density of these faint
galaxies, and they have successfully confirmed that they are the most abundant
population during the epoch of reionization. This also marks the first time
that the ionizing power of these galaxies has been measured, enabling
astronomers to determine that they are producing sufficient energetic radiation
to ionize the early universe.
-
- In an upcoming
Webb observing program, termed GLIMPSE, scientists will obtain the deepest
observations ever on the sky. By targeting another galaxy cluster, named Abell
S1063, even fainter galaxies during the epoch of reionization will be
identified in order to verify whether this population is representative of the
large-scale distribution of galaxies.
-
- The GLIMPSE
observations will also help astronomers probe the period known as “Cosmic
Dawn”, when the universe was only a few million years old, to develop our
understanding of the emergence of the first galaxies.
-
- Oldest 'dead'
galaxy ever seen defies current models of the ancient universe. This galaxy appears to challenge current
models of the early universe. The newly
discovered galaxy, named “JADES-GS-z7-01-QU”, stopped forming stars more than
13 billion years ago, when the universe was only 700 million years old.
-
- Data from the JWST
Advanced Deep Survey (JADES) shows that this galaxy most likely had a quick
burst of star formation that lasted between 30 million to 90 million years, and
then stopped suddenly between 10 million and 20 million years before the point
in time observed by the JWST.
-
- Dead galaxies,
those that no longer form stars, have been observed in the early universe
before. This one is the oldest such
galaxy yet recorded at only 700 million years after the Big Bang that formed
the universe 13.8 billion years ago. It is also much smaller than other dormant
galaxies previously observed in the early universe.
-
- These recent
observations are the deepest views into the distant universe made to date by
the JWST. The rapid burst of star formation observed in the galaxy may have
exhausted the galaxy's reservoir of dust and gas from which new stars are
formed.
-
- Everything seems
to happen faster and more dramatically in the early universe, and that might
include galaxies moving from a star-forming phase to dormant or quenched. Given astronomers are still unsure why
exactly the galaxy's star formation stopped, or if the galaxy ever came back to
life, they plan to find a greater number of old galaxies to help piece together
galactic evolution in the early universe and create more accurate models of
that time period.
-
- Scientists think
that by studying a cluster of "baby quasars," they can get a better
understanding of supermassive black holes in the early universe. Quasars are extremely bright objects powered
by actively feeding supermassive black holes at the centers of galaxies. The
target quasar emitted its light approximately 13 billion years ago, less than a
billion years after the Big Bang.
-
- While these
mysterious spots had been previously recorded by the Hubble Space Telescope, it
wasn't until scientists viewed them using the far more powerful JWST that they
could finally distinguish them from normal galaxies.
-
- Analyzing these
tiny dots, which are tinged red by clouds of dust obscuring their light, required JWST's powerful infrared camera. By
studying the different wavelengths of light emitted by the dots, the
researchers determined that each one appeared to be a "very small gas
cloud that moves extremely rapidly and orbits something very massive young
quasar.
-
- The dots don't seem
out of place in the early universe. Yhey
are "problematic quasars", ultra-monstrous black holes that appear
too massive to exist at such early epochs of the universe.
-
- If we consider that
quasars originate from the explosions of massive stars, and that we know their
maximum growth rate from the general laws of physics, some of them look like
they have grown faster than is possible.
-
- The researchers
hope further study of these newly discovered "baby quasars" could
help reveal how these problematic black holes grow so big, so fast. Astronomers have used the JWST and an effect predicted by Albert Einstein
over 100 years ago to discover that small galaxies in the early cosmos packed a
massive punch, shaping the entire universe when it was less than 1 billion
years old.
-
- They found galaxies
which resemble dwarf galaxies that exist today.
They played a vital role during a crucial stage of cosmic evolution that
occurred between 500 and 900 million years after the Big Bang. These small
galaxies also vastly outnumbered larger galaxies in the infant universe, adding
that it's likely the realms supplied most of the energy needed for a process
called cosmic reionization.
-
- The main surprise is
that these small, faint galaxies had so much power, their cumulative radiation
could transform the entire universe.
Prior to around 380 million years after the Big Bang happened, during a
period called the “epoch of recombination”, the now 13.8 billion-year-old
universe had been opaque and dark. This was because, in its dense and ultra-hot
state, free electrons endlessly bounced around particles of light, photons.
-
- Later, during the
“epoch of recombination”, the universe
had expanded and cooled enough to allow electrons to bond with protons and
create the first atoms of hydrogen, the lightest and simplest element in the
cosmos. This disappearance of free electrons meant photons were suddenly free
to travel, and as a result, the "dark age" of the universe ended.
-
- The cosmos
suddenly became transparent to light. This "first light" can be seen
today in the form of a cosmic fossil that uniformly fills the universe called
the "cosmic microwave background" or "CMB."
-
- Because electrons
and protons have equal but opposite electric charges, these first atoms were
electrically neutral, but they would soon undergo yet another transformation.
-
- After 400 million
years, the first stars and galaxies formed.
Then, during the era of reionization, neutral hydrogen, the predominant
element in the universe, was transformed into charged particles. These
particles are called “ions”. Ionization
is caused by electrons absorbing photons and increasing their energy, breaking
free from atoms. Until now, scientists weren't sure where this ionizing
radiation came from.
-
- Suspects for the
radiation source behind reionization had included supermassive black holes
feeding on gas from accretion disks surrounding them, causing these regions to
eject high-energy radiation, large galaxies with masses in excess of 1 billion
suns, and smaller galaxies with masses less than this.
-
- Astronomers didn't
think small galaxies would be so efficient at producing ionizing radiation.
It's four times higher than what they expected, even for normal-sized galaxies.
-
- JWST has
spectroscopic capabilities in the infrared to understand what happened during
the epoch of reionization. Even with the
impressive infrared observing power of the JWST, spotting these dwarf galaxies
wouldn't have been possible without the help of Albert Einstein ,without the
help of his 1915 theory of general relativity, and an effect on light it
predicts.
-
- General relativity
suggests all objects of mass warp the very fabric of space and time, which are,
in truth, united as a single entity called "space-time." Our
perception of gravity, the theory says, arises as a result of that curvature.
The greater the mass of an object, the more "extreme" the curvature
of space-time is. Thus, the stronger its gravitational effects are.
-
- Not only does this
curvature tell planets how to move in orbits around stars and, in turn, tell
those stellar bodies how to orbit the supermassive black holes at the centers
of their home galaxies, but it also changes paths of light coming from the
stars.
-
- Light from a
background source can take different paths around a foreground object as it
travels toward Earth, and the closer that path is to an object of great mass,
the more it gets "bent." Thus, light from the same object can arrive
to Earth at different times as a result of the foreground, or
"lensing," object.
-
- This lensing can
shift the location of the background object in the sky, or it can cause the
background object to appear in multiple places in the same image of the sky.
Other times, light from the background object is amplified, and thus that
object is magnified in the sky.
-
- This effect is
known as "gravitational lensing," and the JWST has been using it to
great effect to observe ancient galaxies near the dawn of time, which it would
otherwise have had no chance of seeing.
-
- To observe the
newly studied distant and early dwarf galaxies, and analyze the light they
emit, the JWST used a galaxy cluster
“Abell 2744” as a gravitational lens.
Even for the JWST, these small galaxies are very faint, we needed to add
gravitational lensing to amplify the flux of from them.
-
- Astronomers want to
understand the formation of the first galaxies,and they really need to understand
the formation of tiny, low-mass galaxies. And this is what we will be trying to
do with this program.
-
-
March 13, 2024 JAMES
WEBB - finds oldest galaxies? 4386
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