- 4131 - JAMES WEBB TELESCOPE - early galaxy discoveries? Why is James Webb Telescope seeing in the infrared wavelengths? Why is this powerful infrared observatory key to seeing the first stars and galaxies that formed in the universe? Why do we even want to see the first stars and galaxies that formed?
------- 4131 - JAMES WEBB TELESCOPE - early galaxy discoveries?
- The microwave COBE and WMAP satellites saw
the heat signature left by the Big Bang about 380,000 years after it occurred.
But at that point there were no stars and galaxies. In fact the universe was a
dark place.
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- After the Big Bang, the universe was like a
hot soup of particles, protons, neutrons, and electrons. When the universe
started cooling, the protons and neutrons began combining into ionized atoms of
hydrogen and eventually some helium. These ionized atoms of hydrogen and helium
attracted electrons, turning them into neutral atoms which allowed light to
travel freely for the first time, since this light was no longer scattering off
free electrons.
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- The universe was no longer opaque! However,
it would still be up to a few hundred million years post-Big Bang before the
first sources of light would start to form, ending the cosmic dark ages.
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- Exactly what the universe's first light
when stars that fused the existing hydrogen atoms into more helium. When these first stars formed is not known.
These are some of the questions Webb was designed to help us to answer.
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- Imagine light leaving the first stars and
galaxies nearly 13.6 billion years ago and traveling through space and time to
reach our telescopes. We're essentially seeing these objects as they were when
the light first left them 13.6 billion years ago. By the time this light reaches
us, its color or wavelength has been shifted towards the red, we call a
"redshift."
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- The expansion of the universe means it is
the space between objects that actually stretches, causing objects (galaxies)
to move away from each other. Furthermore, any light in that space will also
stretch, shifting that light's wavelength to longer wavelengths. This can make
distant objects very dim (or invisible) at visible wavelengths of light,
because that light reaches us as infrared light.
-
- Webb is able to see back to about 100
million to 250 million years after the Big Bang. Redshift means that light that is emitted by
these first stars and galaxies as visible or ultraviolet light, actually gets
shifted to redder wavelengths by the time we see it here and now. For very high
redshifts, the farthest objects from us, that visible light is generally
shifted into the near- and mid-infrared part of the electromagnetic spectrum.
-
-
Webb is
addressing several key questions to help us unravel the story of the formation
of structures in the Universe such as:
-
----------------------------- When and how did reionization occur?
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----------------------------- What sources caused reionization?
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----------------------------- What are the first galaxies?
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- To find the first galaxies, Webb will make
ultra-deep near-infrared surveys of the Universe, and follow up with
low-resolution spectroscopy and mid-infrared photometry , the measurement of
the intensity of an astronomical object's electromagnetic radiation. -
- To study reionization, high resolution
near-infrared spectroscopy is needed.
-
- After the Big Bang, the universe was like a
hot soup of particles (i.e. protons, neutrons, and electrons). When the
universe started cooling, the protons and neutrons began combining into ionized
atoms of hydrogen and deuterium. Deuterium further fused into helium-4. These
ionized atoms of hydrogen and helium attracted electrons turning them into
neutral atoms. Ultimately the composition of the universe at this point was 3
times more hydrogen than helium with just trace amounts of other light
elements.
-
- This process of particles pairing up is
called "Recombination" and it occurred approximately 240,000 to
300,000 years after the Big Bang. The Universe went from being opaque to
transparent at this point. Light had formerly been stopped from traveling
freely because it would frequently scatter off the free electrons. Now that the
free electrons were bound to protons, light was no longer being impeded.
-
- The “era of recombination" is the
earliest point in our cosmic history to which we can look back with any form of
light. This is what we see as the Cosmic Microwave Background today with
satellites like the Cosmic Microwave Background Explorer (COBE) and the
Wilkinson Microwave Anisotropy Probe (WMAP). -
-
- Following this are the “cosmic dark ages” ,
a period of time after the Universe became transparent but before the first
stars formed. When the first stars formed, it ended the dark ages, and started
the next epoch in our universe.
-
- Another change occurred after the first
stars started to form. Theory predicts that the first stars were 30 to 300
times as massive as our Sun and millions of times as bright, burning for only a
few million years before exploding as supernovae. The energetic ultraviolet
light from these first stars was capable of splitting hydrogen atoms back into
electrons and protons (or ionizing them).
-
- This era, from the end of the “dark ages”
to when the universe was around a billion years old, is known as "the
epoch of reionization." It refers to the point when most of the neutral
hydrogen was reionized by the increasing radiation from the first massive
stars.
-
- Reionization is an important phenomenon in
our universe's history as it presents one of the few means by which we can
(indirectly) study these earliest stars. But scientists do not know exactly
when the first stars formed and when this reionization process started to
occur.
-
- Hubble Deep Field is the first significant
look back to the era of the universe when early galaxies were forming. The
image is a long exposure of a very small area of the sky, which revealed a
large number of very faint, and previously unseen, objects. These objects are
some of the oldest and most distant galaxies and allowed us to glimpse the
first steps of galaxy formation more than 10 billion years ago.
-
- The emergence of these first stars marks
the end of the "Dark Ages" in cosmic history, a period characterized
by the absence of discrete sources of light.
These first sources is critical, since they greatly influenced the
formation of later objects such as galaxies. The first sources of light act as
seeds for the later formation of larger objects.
-
- The first stars that exploded as supernovae
might have collapsed further to form black holes. The black holes started to
swallow gas and other stars to become objects known as
"mini-quasars," which grew and merged to become the huge black holes
now found at the centers of nearly all massive galaxies.
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- JWST spies more
black holes than astronomers predicted.
JWST’s unprecedented power has allowed it to discover a huge range of
these blackholes from many faint, distant black holes to a handful of bright
ones raging even farther away.
-
- Black holes come
in several sizes, but the ones JWST has been detecting are massive ones that
weigh millions to billions times as much as the Sun. Astronomers aren’t sure
how these black holes form, but it might involve massive stars or gas clouds
collapsing and then beginning to draw in nearby gas and dust. In this scenario,
these black-hole ‘seeds’ would grow rapidly, until they become gravitational
maws that lurk at the heart of most galaxies.
-
- Black holes are
not themselves visible, their immense gravitational pull means that not even
light can escape from them, but they can
be spotted by searching for the superheated gas that spirals around them like
water going down a drain.
-
- Before JWST,
astronomers studied black holes using a range of space and ground based
telescopes. But these could spot only the brightest black holes, including
those that are relatively close to Earth. JWST is designed to see light coming
from the distant Universe and can see black holes lying farther away including
ones that astronomers thought would be too dim to detect.
-
- Distance in the
Universe can be measured by a quantity known as redshift; the -higher an
object’s redshift, the more distant it is and the earlier it appears in the
Universe’s history. Many of JWST’s newfound black holes lie at redshifts of
between 4 and 6, which corresponds to a time when the Universe was about 1
billion to 1.5 billion years old.
-
- So far, JWST has
discovered roughly ten times as many faint black holes at these intermediate
redshifts than would be expected on the basis of the number of black holes
previously known.
-
- JWST has also
found several of the most distant black holes ever seen. The confirmed record
holder of the bunch8 sits at the heart of a well-studied galaxy, called GN-z11,
which has a redshift of 10.6. This suggests that as early as 400 million years
after the Big Bang, the seeds for black holes had already formed and were able
to create a supermassive object.
-
- To JWST, distant
black holes look like blobs detected because of the gas and other matter
whirling around them. The black hole at the center of the CEERS 1019 galaxy
lies more than 13 billion light-years from Earth.
-
- Such distant JWST
discoveries fit with recent simulations of the birth of early black
holes13. Astronomers have found that big
black holes can form in the early Universe if they gobble gas at incredibly
high rates in their early stages.
-
-
August 28, 2023 JAMES WEBB TELESCOPE
- early galaxy discoveries? 4131
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