- 4572 - EARLIEST GALAXIES - tell us the Universe formation? The earliest galaxies formed amazingly fast after the Big Bang. Do they break the universe or change its age? The James Webb Space Telescope (JWST) is the largest and most powerful space telescope built to date. Since it was launched in December 2021 it has provided groundbreaking insights.
------------------------- 4572
- EARLIEST GALAXIES
- tell us the Universe formation?
-
- JWST is discovering the earliest and most
distant known galaxies, which existed just 300 million years after the Big
Bang. These distant objects are also
very ancient because it takes a long time for the light from these objects to
reach telescopes. JWST has now found a number of these very early galaxies.
We're effectively looking back in time at these objects, seeing them as they
looked shortly after the birth of the universe.
-
- These observations from JWST agree with our
current understanding of cosmology and of galaxy formation. But they also
reveal aspects we didn't expect. Many of these early galaxies shine much more
brightly than we would expect given that they existed just a short time after
the Big Bang.
-
- Brighter galaxies are thought to have more
stars and more mass. It was thought that much more time was needed for this
level of star formation to take place. These galaxies also have actively
growing black holes at their centers.
This is a sign that these objects matured quickly after the Big Bang.
-
- Scientists have been able to study these
early galaxies by combining JWST's detailed images with its powerful
capabilities for spectroscopy. Spectroscopy is a method for interpreting the
electromagnetic radiation that's emitted or absorbed by objects in space.
-
- Our understanding of cosmology and galaxy
formation rests on a few fundamental ideas. One of these is the cosmological
principle, which states that, on a large scale, the universe is homogeneous
(the same everywhere) and isotropic (the same in all directions). Combined with
Einstein's theory of general relativity, this principle allows us to connect
the evolution of the universe to its energy and mass content.
-
- The standard cosmological model, known as
the "Hot Big Bang" theory, includes three main components. One is the ordinary matter that we can see
with our eyes in galaxies, stars and planets. A second ingredient is cold dark
matter (CDM), slow-moving matter particles that do not emit, absorb or reflect
light.
-
- The third component is what's known the
“cosmological constant” (Λ, or lambda). This is linked to something called dark
energy and is a way of explaining the fact that the expansion of the universe
is accelerating. Together, these components form what is called the ΛCDM model
of cosmology.
-
- Dark energy makes up about 68% of the total
energy content of today's universe.
Despite not being directly observable with scientific instruments, dark
matter is thought to make up most of the matter in the cosmos and comprises
about 27% of the universe's total mass and energy content.
-
- While dark matter and dark energy remain
mysterious, the ΛCDM model of cosmology is supported by a wide range of
detailed observations. These include the measurement of the universe's
expansion, the cosmic microwave background, or CMB (the "afterglow"
of the Big Bang) and the development of galaxies and their large-scale
distribution, the way that galaxies cluster together.
-
- The ΛCDM model lays the groundwork for our
understanding of how galaxies form and evolve.
The CMB, which was emitted about 380,000 years after the Big Bang,
provides a snapshot of early fluctuations in density that occurred in the early
universe. These fluctuations, particularly in dark matter, eventually developed
into the structures we observe today, such as galaxies and stars.
-
- Galaxy formation consists of complex
processes influenced by numerous different physical phenomena. Some of these
mechanisms are not fully understood, such as what processes govern how gas in
galaxies cools and condenses to form stars.
-
- The effects of supernovae, stellar winds and
black holes that emit significant amounts of energy (active galactic nuclei, or AGN) can all heat
or expel gas from galaxies. This in turn can boost or curtail star formation
and therefore influence the growth of galaxies.
-
- The efficiency and scale of these
"feedback processes," as well as their cumulative impact over time,
are poorly understood. They are a significant source of uncertainty in
mathematical models, or simulations, of galaxy formation.
-
- One of the simpler models of galaxy
formation assumes that the rate at which stars form in a galaxy is directly
tied to gas flowing into those galaxies. This model also proposes that the star
formation rate in a galaxy is proportional to the rate at which dark matter
halos grow. It assumes a fixed efficiency at converting gas into stars,
regardless of cosmic time.
-
- This "constant star formation
efficiency" model is consistent with star formation increasing
dramatically in the first billion years after the Big Bang. The rapid growth of
dark matter halos during this period would have provided the necessary
conditions for galaxies to form stars efficiently. Despite its simplicity, this
model has successfully predicted a wide range of real observations, including
the overall rate of star formation across cosmic time.
-
- JWST has ushered in a new era of discovery.
With its advanced instruments, the space telescope can capture both detailed
images and high resolution spectra charts showing the intensity of
electromagnetic radiation emitted or absorbed by objects in the sky. For JWST,
these spectra are in the near infrared region of the electromagnetic spectrum.
-
- Studying this region is crucial for
observing early galaxies whose optical light has turned into near infrared (or
"redshifted") as the universe has expanded. Redshift describes how the wavelengths of
light from galaxies become stretched as they travel. The more distant a galaxy
is, the greater its redshift.
-
- Over the past two years, JWST has identified
and characterized galaxies at redshifts with values of between ten and 15.
These galaxies, which formed around 200–500 million years after the Big Bang,
are relatively small for galaxies (about 100 parsecs, or 3 quadrillion
kilometers, across). They each consist of around 100 million stars, and form
new stars at a rate of about one sun-like star per year.
-
- While this does not sound very impressive,
it implies that these systems double their content of stars within only 100
million years. For comparison, our own Milky Way galaxy takes about 25 billion
years to double its stellar mass.
-
- The surprising findings from JWST of bright
galaxies at high redshifts, or distances, could imply that these galaxies
matured faster than expected after the Big Bang. This is important because it
would challenge existing models of galaxy formation. The constant
star-formation efficiency model described above, while effective at explaining
much of what we see, struggles to account for the large number of bright and
distant galaxies observed with a redshift of more than ten with a redshift of
more than ten.
-
- To address this, scientists are exploring
various possibilities. These include changes to their theories of how
efficiently gas is converted into stars over time. They are also reconsidering
the relative importance of the feedback processes and how phenomena such as
supernovae and black holes also help regulate star formation.
-
- Some theories suggest that star formation
in the early universe may have been more intense or "bursty" than
previously thought, leading to the rapid growth of these early galaxies and
their apparent brightness.
-
- Others propose that different factors, such
as lower amounts of galactic dust, a top-heavy distribution of star masses, or
contributions from phenomena such as active black holes, could be responsible
for the unexpected brightness of these early galaxies.
-
- These explanations invoke changes to galaxy
formation physics in order to explain JWST's findings. But scientists have also
been considering modifications to broad cosmological theories. For example, the
abundance of early, bright galaxies could be partly explained by a change to
something called the “matter power spectrum”. This is a way to describe density
differences in the universe.
-
- One possible mechanism for achieving this
change in the “matter power spectrum” is a theoretical phenomenon called
"early dark energy". This is the idea that a new cosmological energy
source with similarities to dark energy may have existed at early times, at a
redshift of 3,000. This is before the CMB was emitted and just 380,000 years
after the Big Bang.
-
- This early dark energy would have decayed
rapidly after the stage of the universe's evolution known as “recombination”.
Intriguingly, early dark energy could also alleviate the Hubble tension which
is a discrepancy between different estimates of the universe's age.
-
- The galaxy findings from JWST required
scientists to stretch the age of the universe by several billion years. However, other phenomena could account for
the bright galaxies.
-
- The current record holder for the most
distant galaxy is called “JADES-GS-z14-0”. The data gathered so far indicate
that these galaxies have a large diversity of different properties. Some galaxies show signs of hosting black
holes that are emitting energy, while others seem to be consistent with hosting
young, dust-free populations of stars.
-
- Because these galaxies are faint and
observing them is expensive (it takes exposure times of many hours), only 20
galaxies for which the redshift is more than ten have been observed with
spectroscopy to date, and it will take years to build a statistical sample.
-
- A different angle of attack could be
observations of galaxies at later cosmic times, when the universe was 1 billion
to 2 billion years old (redshifts of between three and nine).
-
- In the first year of JWST's operation, it
was claimed that some of the earliest galaxies had extremely high stellar
masses (the masses of stars contained within them) and a change in cosmology
was needed to accommodate bright galaxies that existed in the very early
universe.
-
- Soon after, it was clear that these
galaxies do not break the universe, but their properties can be explained by a
range of different phenomena. Better observational data showed that the
distances to some of the objects were overestimated which led to an
overestimation of their stellar masses.
-
- The emission of light from these galaxies
can be powered by sources other than stars, such as accreting black holes.
Assumptions in models or simulations can also lead to biases in the total mass
of stars in these galaxies.
-
- As JWST continues its mission, it will help
scientists refine their models and answer some of the most fundamental
questions about our cosmic origins. It should unlock even more secrets about
the universe's earliest days, including the puzzle of these bright, distant
galaxies.
-
-
October 9, 2024 EARLIEST
GALAXIES - tell us the Universe formation? 4572
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--------------------- --- Tuesday, October 8,
2024
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