- 4500 - WEBB DISCOVERIES - giving new science? The James Webb Space Telescope was launched at the end of 2021. New evidence arrive at the speed the JWST is delivering it tells us the early universe are in need of a significant update.
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- WEBB DISCOVERIES
- giving new science?
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- The early universe is one of the JWST's
primary scientific targets. Its infrared capabilities allow it to see the light
from ancient galaxies with greater acuity than any other telescope. The
telescope was designed to directly address confounding questions about the
high-redshift universe.
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- The early universe and its transformations
are fundamental to our understanding of the universe around us today. Galaxies
were in their infancy, stars were forming, and black holes were forming and
becoming more massive.
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- The Hubble Space Telescope was limited to
observations at about z=11. The JWST current high-redshift observations have
reached z=14.32. Astronomers think that the JWST will eventually observe
galaxies at z=20.
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- The first few hundred million years after
the Big Bang is called the “Cosmic Dawn”. JWST showed us that ancient galaxies
during the Cosmic Dawn were much more luminous and, therefore, larger than we
expected. The galaxy the telescope found at z=14.32, called “JADES-GS-z14-0”, has several hundred
million solar masses.
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- This raises the question: How can nature
make such a bright, massive, and large galaxy in less than 300 million
years?" They were differently
shaped, that they contained more dust than expected, and that oxygen was
present. The presence of oxygen indicates that generations of stars had already
lived and died. The presence of oxygen
so early in the life of this galaxy is a surprise and suggests that multiple
generations of very massive stars had already lived their lives before we
observed the galaxy.
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- Active galactic nuclei (AGN) are
supermassive black holes (SMBHs) that are actively accreting material and
emitting jets and winds. “Quasars” are
a sub-type of AGN that are extremely luminous and distant, and quasar
observations show that SMBHs were present in the centers of galaxies as early
as 700 million years after the Big Bang. But their origins were a mystery.
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- Astrophysicists think that these early
SMBHs were created from black hole "seeds" that were either
"light" or "heavy." Light seeds had about 10 to 100 solar
masses and were stellar remnants. Heavy seeds had 10 to 105 solar masses and
came from the direct collapse of gas clouds.
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- The JWST's ability to effectively look back
in time has allowed it to spot an ancient black hole at about z=10.3 that
contains between 107 to 108 solar masses. The Hubble Space Telescope didn't
allow astronomers to measure the stellar mass of entire galaxies the way that
the JWST does.
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- Thanks to the JWST's power, astronomers know
that the black hole at z=10.3 has about the same mass as the stellar mass of
its entire galaxy. This is in stark contrast to modern galaxies, where the mass
of the black hole is only about 0.1% of the entire stellar mass.
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- Such a massive black hole existing only
about 500 million years after the Big Bang is proof that early black holes
originated from heavy seeds. This is actually in line with theoretical
predictions.
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- We know that in the early universe,
hydrogen became ionized during the “Epoch of Reionization” (EoR). Light from
the first stars, accreting black holes, and galaxies heated and reionized the
hydrogen gas in the intergalactic medium (IGM), removing the dense, hot,
primordial fog that suffused the early universe.
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- Young stars were the primary light source
for the reionization. They created expanding bubbles of ionized hydrogen that
overlapped one another. Eventually, the bubbles expanded until the entire
universe was ionized.
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- This was a critical phase in the
development of the universe. It allowed future galaxies, especially dwarf
galaxies, to cool their gas and form stars. But scientists aren't certain how
black holes, stars, and galaxies contributed to the reionization or the exact
time frame in which it took place.
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- Astronomers knew that reionization ended
about 1 billion years after the Big Bang, at about redshift z=5-6. But before
the JWST, it was difficult to measure the properties of the UV light that
caused it. With the JWST's advanced spectroscopic capabilities, astronomers
have narrowed down the parameters of reionization.
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- We have found spectroscopically confirmed
galaxies up to z = 13.2, implying reionization may have started just a few
hundred million years after the Big Bang.
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- JWST results also show that accreting black
holes and their AGN likely contributed no more than 25% of the UV light that
caused reionization.
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- There is still significant debate about the
primary sources of reionization, in particular, the contribution of faint
galaxies. The JWST is not even halfway
through its mission and has already transformed our understanding of the
universe's first one billion years. It was built to address questions around
the Epoch of Reionization, the first black holes, and the first galaxies and
stars.
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- Among the most fundamental questions in
astronomy is: How did the first stars and galaxies form? NASA's James Webb
Space Telescope is already providing new insights into this question. The JWST
Advanced Deep Extragalactic Survey, or JADES will devote about 32 days of
telescope time to uncover and characterize faint, distant galaxies. While the
data is still coming in, JADES already has discovered hundreds of galaxies that
existed when the universe was less than 600 million years.
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- For hundreds of millions of years after
the Big Bang, the universe was filled with a gaseous fog that made it opaque to
energetic light. By one billion years after the Big Bang, the fog had cleared
and the universe became transparent, a process known as reionization.
Scientists have debated whether active, supermassive black holes or galaxies
full of hot, young stars were the primary cause of reionization.
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- These early bright, massive stars pumped
out torrents of ultraviolet light, which transformed surrounding gas from
opaque to transparent by ionizing the atoms, removing electrons from their
nuclei. Since these early galaxies had such a large population of hot, massive
stars, they may have been the main driver of the reionization process. The
later reuniting of the electrons and nuclei produces the distinctively strong
emission lines.
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- These young galaxies underwent periods of
rapid star formation interspersed with quiet periods where fewer stars formed.
These fits and starts may have occurred as galaxies captured clumps of the
gaseous raw materials needed to form stars. Alternatively, since massive stars
quickly explode, they may have injected energy into the surrounding environment
periodically, preventing gas from condensing to form new stars.
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- Another element of the JADES program
involves the search for the earliest galaxies that existed when the universe
was less than 400 million years old. By studying these galaxies, astronomers
can explore how star formation in the early years after the Big Bang was
different from what is seen in current times.
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- The light from faraway galaxies is
stretched to longer wavelengths and redder colors by the expansion of the
universe, called “redshift”. By measuring a galaxy's redshift, astronomers can
learn how far away it is, and therefore, when it existed in the early universe.
Before Webb, there were only a few dozen galaxies observed above a redshift of
8, when the universe was younger than 650 million years old, but JADES has now
uncovered nearly a thousand of these extremely distant galaxies.
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- The gold standard for determining redshift
involves looking at a galaxy's spectrum, which measures its brightness at
myriad closely spaced wavelengths. But a good approximation can be determined
by taking photos of a galaxy using filters that each cover a narrow band of
colors to get a handful of brightness measurements. In this way, researchers
can determine estimates for the distances of many thousands of galaxies at
once.
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- Webb's NIRCam (Near-Infrared Camera)
instrument obtained these measurements, called “photometric redshifts”, and
identified more than 700 candidate galaxies that existed when the universe was
between 370 million and 650 million years old. The sheer number of these
galaxies was far beyond predictions from observations made before Webb's
launch.
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- Previously, the earliest galaxies we could
see just looked like little smudges. And yet those smudges represent millions
or even billions of stars at the beginning of the universe. Now, we can see that some of them are
actually extended objects with visible structure. We can see groupings of stars
being born only a few hundred million years after the beginning of time.
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- We're finding star formation in the early
universe is much more complicated than we thought.
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- By the time light from the most distant
galaxies reaches Earth, it has been stretched by the expansion of the universe
and shifted to the infrared region of the light spectrum. The Webb telescope's NIRCam instrument has an
unprecedented ability to detect this infrared light, allowing it to quickly
spot a range of never-before-seen galaxies.
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- The galaxies are very active in star
formation in proportion to their mass.
Those stars were forming at around the same rate as the Milky Way, a
speed that was surprising so early in the Universe. The galaxies were also very poor in metals.
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- This is consistent with the standard model
of cosmology, science's best understanding of how the universe works, which
says that the closer to the Big Bang, the less time there is for such metals to
form.
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- Those galaxies, observed by the Webb
telescope, were bigger than thought possible so soon after the birth of the
universe, if confirmed, the standard model could need updating. The frontier is moving almost every
month. There was now "only 300
million years of unexplored history of the universe between these galaxies and
the Big Bang.
-
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June 18, 2024 WEBB
DISCOVERIES - giving new science? 4500
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--------------------- --- Wednesday, June 19,
2024
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