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EI2GYB > ASTRO 21.12.23 18:39l 110 Lines 6280 Bytes #999 (0) @ WW
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Subj: JWST Reveals Distant "Galaxy" Is Six-way Galactic Crash
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JWST Reveals Distant "Galaxy" Is Six-way Galactic Crash
By: Chiara Villanueva December 20, 2023
Peering deep into the past, the James Webb Space Telescope's keen detectors are
revealing unprecedented details of some of the oldest structures in the
universe. Formerly fuzzy images become sharp at the telescope's highest
resolution. One such re-examination of an energetic primordial galaxy has left
many astronomers starstruck: Webb reveals the single galactic unit is actually
six galaxies, crashing together to create a deluge of fresh stars.
In 2013 astronomers using data from the Herschel Space Observatory discovered
the earliest star-forming galaxy yet seen. Bursting at the seams with new stars
when the universe was only about 850 million years old, the existence of the
object, christened HFLS3, defied accepted scenarios for how quickly galaxies
could grow. The colossal stellar factory ignited new stars at a rate about
2,000 times greater than our Milky Way, despite having roughly the same mass.
In the universe's infancy, astronomers had believed, galaxies should not nearly
be this big with such a high birth rate. Several teams attempted to image the
galaxy again using the Hubble Space Telescope and several ground-based
telescopes. Yet the photos only hinted at the rough signatures of other nearby
sources-with the potential influence of gravitational lensing, in which massive
objects closer to us warp and magnify the light rays from distant objects
behind them.
Now with new data, scientists have proposed that HFLS3 is not a single giant
starburst galaxy after all. "This galaxy was actually an interacting system of
galaxies in the early universe," says team lead Gareth Jones (University of
Oxford), "which are still very bright and starbursting, but as a system rather
than a single source."
The new observation was part of a JWST program called Galaxy Assembly with
NIRSpec Integral Field Spectroscopy. This collaboration is targeting 40 of the
most distant and massive galaxies to resolve even the smallest pockets of space
around them in great detail. The spectrograph's Integral Field Unit cast its
eye on HFLS3's radiant neighborhood in September 2022.
The team led by Jones produced a set of images that displayed brightness across
different wavelengths and fields of view. They then analyzed the motions and
heating of the gases in the galaxy, and modeled how much gravitational lensing
could have affected the perceived light. In doing so, they reconstructed a more
accurate image of HFLS3.
Jones had expected to see the typical rotational movement of gas seen in
similar early galaxies. "But instead of a single rotating [galaxy], we just had
lots of little galaxies," he says.
Based on the analysis, the bulk of HFLS3 is composed of three pairs of small,
closely interacting galaxies. Just one of those pairs is magnified by two
separate foreground galaxies. Given the incredibly dense field, scientists
suggest that the sextuplet system is colliding, triggering a surge of new stars.
Follow-up observations nearly a decade ago had shown prominently bright
emissions around HFLS3. This made Dominik Riechers (University of Cologne,
Germany), who led the 2013 discovery at a lower resolution with Herschel,
consider the possibility of neighboring mergers. However, he recognized that
the telescopes available at the time did not yet have the capability to expose
the true nature of those interactions.
"We speculated that these could be galaxies associated with starburst, but JWST
shows this beyond any doubt by measuring precise distances and sizes of these
'companion' systems," says Riechers, who was not involved in the new study.
Riechers also commends Jones and his team for verifying that we see only a weak
gravitational lensing of the cluster. This proves HFLS3 is indeed massive and
chock full of bright new stars, not just a smaller magnified system, he
explains.
Scientists can now view HFLS3 as a chaotic jumble of galaxies entangled in webs
of star formation. This reassures Kenneth Duncan (University of Edinburgh, UK),
who wasn't involved in the study, that the results actually align with current
galaxy formation theories. Had HFLS3 been one gargantuan galaxy, Duncan notes,
astronomers would have had to modify that framework. "With these observations
confirming that it is in fact a group of galaxies undergoing a series of
mergers, it supports our picture of mergers playing a critical role in the
build-up of galaxies," writes Duncan. But still, the images are striking, he
remarks: "What is surprising is really just how messy and complex the system
turns out to be."
Chiara Villanueva (@chiiavilla) is a graduate student in the Science
Communication M.S. Program at the University of California, Santa Cruz. They
have a background in astrophysics and are interested in covering stories about
the universe.
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