- 4510
- WEBB TELESCOPE'S
- new discoveries? When the James Webb Space Telescope was
launched at the end of 2021, we expected stunning images and illuminating
scientific results. So far, the powerful space telescope has lived up to our
expectations. The JWST has shown us things about the early universe we never
anticipated.
-
------------------------------- 4510
- WEBB TELESCOPE'S
- new discoveries?
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- JADES-GS-z14-0 is not like the types of
galaxies that have been predicted by theoretical models and computer
simulations to exist in the very early universe. 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- Young stars were the primary light source
for the reionization. They created expanding bubblesof ionized hydrogen that
overlapped one another. Eventually, the bubbles expanded until the entire
universe was ionized.
-
- 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.
-0
- We know that hydrogen reionization
happened, but exactly when and how it happened has been a major missing piece
in our understanding of the first billion years. 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.
-
- 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.
JWST results also show that accreting black holes and their AGN likely
contributed no more than 25% of the UV light that caused reionization.
-
- There is still significant debate about the
primary sources of reionization, in particular, the contribution of faint
galaxies. Even though the JWST is extraordinarily powerful, some distant, faint
objects are beyond its reach.
-
- 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. There's
definitely much more to come. Who knows what the sum total of its contributions
will be?
-
- Among the most fundamental questions in astronomy
is: How did the first stars and galaxies form? 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.
-
- Almost every single galaxy that we are
finding shows these unusually strong emission line signatures indicating
intense recent star formation. These early galaxies were very good at creating
hot, massive stars.
-
- These 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.
-
- 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.
-
- The light from faraway galaxies is
stretched to longer wavelengths and redder colors by the expansion of the
universe—a phenomenon 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.
-
- 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.
-
- More than 700 candidate galaxies 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. The observatory's exquisite resolution and sensitivity
are allowing astronomers to get a better view of these distant galaxies than
ever before.
-
- James Webb Space Telescope has discovered
the four most distant galaxies ever observed, one of which formed just 320
million years after the Big Bang when the universe was still in its infancy.
-
- 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..
-
- The galaxies date from 300 to 500 million
years after the Big Bang more than 13 billion years ago, when the universe was
just two percent of its current age.
That means the galaxies are from what is called "the epoch of
reionisation," a period when the first stars are believed to have emerged.
The epoch came directly after the cosmic dark ages brought about by the Big
Bang.
-
- The Webb telescope confirmed the existence
of JADES-GS-z10-0, which dates from 450 million years after the Big Bang and
had previously been spotted by the Hubble Space Telescope. All four galaxies are "very low in
mass," weighing roughly a hundred million solar masses. The Milky Way, in
comparison, weighs 1.5 trillion solar masses by some estimations.
-
- The galaxies are very active in star
formation in proportion to their mass.
The galaxies were also "very poor in metals. 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.
-
- However, the discovery of six massive
galaxies from 500-700 million years after the Big Bang led some astronomers to
question the standard model. Those
galaxies, also observed by the Webb telescope, were bigger than thought
possible so soon after the birth of the universe.
-
-
June 23, 2024 4511
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------ “Jim Detrick” -----------
--------------------- --- Sunday, June 23, 2024
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