- 4491 - WEBB TELESCOPE - new discoveries? - How did the first stars and galaxies form? NASA's James Webb Space Telescope is already providing new insights into this question. One of the largest programs in Webb's first year of science is the JWST Advanced Deep Extragalactic Survey, or JADES, which will devote about 32 days of telescope time to uncover and characterize faint, distant galaxies.
------------------------------------- 4491 - WEBB TELESCOPE - new discoveries?
- JADES already has discovered hundreds of
galaxies that existed when the universe was less than 600 million years old.
The team also has identified galaxies sparkling with a multitude of young, hot
stars.
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- How did the earliest galaxies assemble
themselves? How fast did they form stars? Why do some galaxies stop forming
stars?.
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- Galaxies that existed 500 to 850 million
years after the Big Bang was during a crucial time known as the “Epoch of
Reionization”. 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.
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- 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 this
reionization.
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- Almost every single galaxy that they find
shows these unusually strong emission line signatures indicating intense recent
star formation. These early galaxies were very good at creating hot, massive
stars.
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- 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.
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- 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.
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- The light from faraway galaxies is stretched
to longer wavelengths and redder colors by the expansion of the univers,
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.
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- The gold standard for 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.
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- These “photometric redshifts” identified
more than 700 candidate galaxies that 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.
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- Previously, the earliest galaxies we could
see just looked like little smudges. And yet those smudges represent millions
or even billions of stars at the beginning of the universe. Now, we can see that some of them are
actually extended objects with visible structure. We can see groupings of stars
being born only a few hundred million years after the beginning of time.
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- 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.
-
- The Webb telescope has unleashed a torrent
of scientific discovery since becoming operational last year, peering farther
than ever before into the universe's distant reaches, looking back in time. 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.
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- 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.
These 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.
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- That is the greatest distance ever observed
by astronomers. The Webb telescope
also 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.
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- 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. But the galaxies are "very active in
star formation in proportion to their mass.
Those stars were forming at around the same rate as the Milky Way.
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- 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.
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- However in February, 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. If confirmed, the standard model could need
updating.
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June 7, 2024 WEBB
TELESCOPE - new discoveries? 4491
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--------------------- --- Friday, June 7, 2024
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