- 4620 -
REIONIZATION - in the early Universe? -
The James Webb telescope observations has shed new light on “Cosmic
Reionization”. The “Epoch of
Reionization” was a critical period for cosmic evolution and has always fascinated
and mystified astronomers. During this epoch, the first stars and galaxies
formed and reionized the clouds of neutral hydrogen that permeated the
Universe.
------------------------------------- 4620 - REIONIZATION - in the early Universe?
- This reionization epoch ended the “Cosmic
Dark Ages” and led to the Universe becoming “transparent,” what astronomers
refer to as “Cosmic Dawn.” According to our current cosmological models,
reionization lasted from 380,000 to 1 billion years after the Big Bang. This is
based on indirect evidence since astronomers have been unable to view the Epoch
of Reionization directly.
-
- Investigating this period was one of the
main reasons for developing the James Webb Space Telescope (JWST), which can
pierce the veil of the “dark ages” using its powerful infrared optics. However,
observations provided by Webb revealed that far more galaxies existed in the
early Universe than previously expected.
-
- According to a recent study, this suggests
that reionization may have happened more rapidly and ended at least 350 million
years earlier than our models predict. Once again, the ability to peer into the
early Universe has produced tensions with prevailing cosmological theories.
-
- According to current cosmological models,
the Universe was filled with a hot, dense plasma of protons and electrons for
the first 380,000 years after the Big Bang. Eventually, the Universe cooled
enough for protons and electrons to come together and form neutral hydrogen. By
ca.100 million years after the Big Bang, the first stars (Population III) began
to form, which were extremely massive and hot. These stars came together to
create the first galaxies, and their ultraviolet light caused neutral hydrogen
to once again split into protons and electrons ( became ionized).
-
- Once most of the hydrogen in the Universe
became ionized (ca. 1 billion years after the Big Bang), the Epoch of
Reionization ended. At this point, the Universe was transparent, and light from
this period is visible to optical telescopes today. Reionization played a major role in how the
Universe evolved. The process heated
and ionized gas in the Universe, which regulated how fast galaxies grew and
evolved. These early stars established
the overall structure of galaxies in the Universe.
-
- Before the deployment of the JWST,
scientists relied on measurements of the Cosmic Microwave Background (CMB), the
relic radiation from the Big Bang, and the Lyman-alpha Forest which is the
wavelength of light associated with hydrogen reionization. From this,
astronomers have gained a sense of how much energy was available for
reionization to occur (a “photon
budget”) and how long it lasted.
-
- Reionization is the last major change to
happen. You went from neutral and cold and boring to ionized and hot. And this
isn’t something that only happened to one or two galaxies. It happened to the
whole Universe. It’s an accounting game. We know that all hydrogen was neutral
before reionization. From there, you need enough extreme ultraviolet to split
each atom. So you can do the math to figure out when reionization ended.
-
- However, observations made with the JWST
have revealed things that challenge accepted models. This includes a greater
abundance of galaxies, which produce more UV radiation than previously
anticipated. These findings suggest that reionization should have ended 550 to
650 million years after the Big Bang rather than 1 billion years.
-
- But if this were true, the CMB and
Lyman-alpha Forest would look different.
There is a tension between these measurements and Webb‘s observations.
-
- Much like the “Hubble Tension”, these
findings suggest something could be missing from our current cosmological
models. One possibility that the team explored is recombination, where ionized
protons and electrons come together again to form neutral hydrogen. This is
precisely what happened 380,000 years after the Big Bang, known as the “Era of
Recombination.”
-
- If this process happened more often than
our models suggest, it could increase the amount of extreme-UV light needed to
reionize the Universe. Follow-up observations are needed to confirm this
theory. We need more detailed and deeper
observation.
-
-
November 24, 2024 REIONIZATION - in
the early Universe? 4620
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--- to:
------
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------ “Jim Detrick” -----------
--------------------- --- Monday, November 25,
2024
---------------------------------
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