Early universe crackled with bursts of star formation, Webb shows

Date:
June 5, 2023
Source:
NASA/Goddard Space Flight Center
Summary:
Among the most fundamental questions in astronomy is: 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. While the data is still coming in, 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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FULL STORY ========================================================================== Among the most fundamental questions in astronomy is: 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. While the data is still coming in, 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.

"With JADES, we want to answer a lot of questions, like: How did the
earliest galaxies assemble themselves? How fast did they form stars? Why
do some galaxies stop forming stars?" said Marcia Rieke of the University
of Arizona in Tucson, co-lead of the JADES program.

Star Factories Ryan Endsley of the University of Texas at Austin led
an investigation into galaxies that existed 500 to 850 million years
after the big bang. This was 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. 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 reionization.

As part of the JADES program, Endsley and his colleagues studied
these galaxies with Webb's NIRSpec (Near-Infrared Spectrograph)
instrument to look for signatures of star formation -- and found them in abundance. "Almost every single galaxy that we are finding shows these unusually strong emission line signatures indicating intense recent
star formation. These early galaxies were very good at creating hot,
massive stars," said Endsley.

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.

Endsley and his colleagues also found evidence that 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.

The Early Universe Revealed Another element of the JADES program involves
the search for the earliest galaxies that existed when the universe was
less than 400 million years old. By studying these galaxies, astronomers
can explore how star formation in the early years after the big bang was different from what is seen in current times. The light from faraway
galaxies is stretched to longer wavelengths and redder colors by the
expansion of the universe -- a phenomenon called 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.

The gold standard for determining redshift involves looking at a galaxy's spectrum, which measures its brightness at a myriad of 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.

Kevin Hainline of the University of Arizona in Tucson and his colleagues
used Webb's NIRCam (Near-Infrared Camera) instrument to obtain these measurements, called photometric redshifts, and 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.

"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," said Hainline. "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." "We're finding star formation in the
early universe is much more complicated than we thought," added Rieke.

These results are being reported at the 242nd meeting of the American Astronomical Society in Albuquerque, New Mexico.

* RELATED_TOPICS
o Space_&_Time
# Galaxies # Astrophysics # Stars # Big_Bang # Cosmology #
Extrasolar_Planets # Astronomy # Black_Holes
* RELATED_TERMS
o Hubble_Deep_Field o Supergiant o Galaxy
o Large-scale_structure_of_the_cosmos
o Galaxy_formation_and_evolution o Radio_telescope o
Edwin_Hubble o Astrophysics

========================================================================== Story Source: Materials provided by
NASA/Goddard_Space_Flight_Center. Note: Content may be edited for style
and length.


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Link to news story: https://www.sciencedaily.com/releases/2023/06/230605181111.htm

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