- 4496 - WEBB - REWRITING ASTRONOMY? - 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 shown us things about the early universe we never anticipated.
------------------------------- 4496 - WEBB - REWRITING ASTRONOMY?
- Some of those results are forcing a rewrite
of astronomy textbooks. Textbooks are
regularly updated as new evidence works its way through the scientific process.
But seldom does new evidence arrive at the speed the JWST is delivering it.
Chapters on the early universe are in need of a significant changes.
-
- 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.
-
- What are the physical properties of the
earliest galaxies? 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, “JADES-GS-z14-0”, has several hundred million
solar masses.
-
- This raises the question: How can nature
make such a bright, massive, and large galaxy in less than 300 million
years? It also showed us that 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.
-
- All of these observations, together, tell
us that 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.
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.
-
- 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 bubbles of 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.
-
- 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 to 6.
-
- JWST has found spectroscopically confirmed
galaxies up to z = 13.2, implying reionization may have started just a few
hundred million years after the Big Bang.
This also show that accreting black holes and their AGN likely
contributed no more than 25% of the UV light that caused reionization.
-
- 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?
-
-
June 8, 2024 WEBB
- REWRITING ASTRONOMY? 4496
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--------------------- --- Sunday, June 9, 2024
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