Astronomers Grapple with JWST’s Discovery of Early Galaxies

Astronomers Grapple with JWST’s Discovery of Early Galaxies

Astronomers are still trying to figure out the origins of the stars and galaxies that illuminate the cosmos. However, they are getting closer to enlightenment each day.

That’s the almost inescapable conclusion from initial observations by the James Webb Space Telescope (JWST), the $10-billion observatory that began science operations in July. JWST was designed to see the faint infrared glows of the universe’s earliest luminous object. Its vision extends back into the first few hundred millions years after the big bang to provide more and better data than any other facility. However, its galactic “baby photos” have proven to be more valuable than most researchers could imagine. Simply put, candidate galaxies are appearing in the early universe in numbers that defy predictions. dozens have been found .. This excess could require significant revisions to the prevailing cosmological model. These changes could result in the first galaxies becoming earlier, their stars shining brighter, or perhaps the nature of dark energy or dark matter being more complex and mysterious.

Now, two of JWST’s most intriguing candidate early galaxies have been examined more closely. This confirms scientists’ suspicions about the state of our cosmic history knowledge. Dating back to 350 million and 450 million years after the big bang, at the time of their discovery, both galaxies were older than any others known before. Two teams independently discovered them, one led now by Rohan Naidu , at the Massachusetts Institute of Technology and other led now by Marco Castellano of Italy’s Astronomical Observatory of Rome. Initially posted on the preprint server arXiv.org, the two discovery papers have now cleared the key hurdle of peer-reviewed publication, each appearing in the Astrophysical Journal Letters in late November and October, respectively. This is more than a symbolic milestone. early calibration issues with JWST’s instruments had fueled concerns by astronomers that such findings could have miscalculated their true distance to these galaxies. They were therefore more modern imposters, only appearing to be part the early cosmic coterie. Castellano states that after careful peer review, “we are able to say with very high confidence that calibration is not an problem for these galaxies.” They are very strong candidates. “We have now put to rest the issues of calibration.” However, follow-up observations will still be required to confirm their record-breaking distances.

Astronomers have meanwhile since found several other early galaxy candidates, some seemingly as far back as 200 million years post-big bang. Prior to the launch of JWST, no one knew if galaxies could even form so early in the universe’s 13.8-billion-year history, at a time when matter was thought to still be sedately coalescing into the gravitationally bound clumps required to give birth to large groups of stars. “And so, we’re asking, ‘Does anyone really understand the early stages of the formation of these galaxy?'” Garth Illingworth, an Astronomer at the University of California Santa Cruz, said at a press conference, held by NASA to announce peer-reviewed validation of two candidates. “This has raised many questions for the theorists

Chief is the one who explains how dark matter influenced the emergence galaxies. The cosmos was so hot for the first few hundred thousands years after the big bang that gravity couldn’t pull normal matter together to form large progalactic clusters. Jorge Penarrubia from the University of Edinburgh, Scotland, says that this was not an issue for dark material. Instead, gravity is the master of this invisible substance. This means that just a few moments after the big bang, primordial chaos was overthrown, gravity began to glomming together dark matters into large clumps called halos. These dark matter halos are thought to have been gravitational sinks for normal material, which in turn seeded the formation of galaxies at the beginning of the universe. Their endurance is still evident in the telltale motions of stars they shepherd. Such halos still surround galaxies like our own, majestic-but-invisible sculptors of the modern cosmos.

JWST’s rapid discovery and analysis of early galaxies “might have been straining our current understanding about how these early dark matter structure forms,” says Rachel Somerville (astrophysicist at Flatiron Institute in New York City). Scientists have shown that simple treatments of dark material, which interacts only with itself and normal matter via gravitation, can accurately reproduce large-scale cosmic structures. Nature is not perfect. In reality, dark matter could interact directly with itself via an unknown force, possibly via a particle not included in the current Standard Model of Physics. Somerville states that dark matter could interact with itself to change how it clumps up in the early times. “And so, you might actually form larger dark matter halos within the early universe,” which could explain how fast large, bright galaxies were possible to emerge.

This unusual situation could lead to faster star formation in the early universe. Perhaps dark matter halos pull in more matter more quickly to fuel such growth. Today our galaxy produces roughly one new star per year, but Castellano’s paper suggests that star-formation rates must have been at least 20 times higher in his and Naidu’s two candidate galaxies. Another JWST-derived preprint paper posits that Milky Way-sized galaxies could have arisen just a half-billion years after the big bang–a scenario that would demand star-formation rates 10 times higher still than Castellano’s estimates. Michael Boylan-Kolchin is a University of Texas cosmologist. He believes that such high rates of star formation pushes the limits of what is physically possible. He says that if these values are correct, then you would need [galaxies] converting all their mass into stars and creating stars as fast as possible.

Another possibility is that early stars were more efficient at accumulating matter in the universe. This would result in brighter, bulkier stars, which would increase the visibility of early galaxies to JWST. Stephen Wilkins, an English astronomer, says, “Maybe you just make a whole lot of very, very large stars.” These stars could be the so-called Population III stars. They are the first stars hypothesized to exist in the universe. Although astronomers have yet not been able to observe such stars in the real world, there is plenty of evidence that they exist. Population III stars, which emerged from primordial hydrogen and helium gas, would be devoid of heavier elements. This would allow them to reach enormous sizes, many times larger than our sun. These stars would be like the brightest, shortest candles. Their lifetime would be limited to a few million years, so it would be difficult to detect them today.

It’s possible that some of the distant galaxies discovered by JWST, and those that are even older, could contain evidence for Population III star formation. These stars could be responsible for the brightness of these galaxies, which are brighter and hotter than any subsequent Population II stars or Population I stars. Daniel Whalen, a University of Portsmouth cosmologist, says that it is possible. JWST will need spectroscopic follow up of these distant candidates. This is a time-consuming process that gathers a rainbow-like spectrum from a galaxy to determine which chemical elements are in its constituent stars. One clear signature of Population III stars, Whalen says, could be a specific spectral feature of helium that could only arise within stars that are hotter than about 100,000 degrees Celsius. He says that this would be evidence of a large Population III star.

These follow-up observations will begin immediately. Jeyhan Kartaltepe of the Rochester Institute of Technology is part of a team that has been approved time on JWST to follow up a handful of early galaxy candidates found in the Cosmic Evolution Early Release Science (CEERS) Survey, for which Kartaltepe is a leading investigator. These candidates are distinguished by their high Redshifts, which is a stretching of the wavelengths their light due to the expansion of the universe over cosmic time. This makes Kartaltepe’s spectroscopic analysis not only an important probe into the galaxies’ stellar populations, but also a “reality check” of their cosmic age. Kartaltepe hopes that the measurements will enable astronomers “understand star formation rates and age of the stars.” The program will take eight hours of JWST to obtain spectra from three target galaxies. It is expected to start in late December. There are many more programs like this in the future.

Other more interesting ideas are available. If JWST finds that the apparent early burst of massive galaxy formation suddenly ebbed in subsequent cosmic epochs, this could suggest the universe was expanding faster than expected back then–perhaps twice as fast as predicted by current consensus estimates, says Nicola Menci, an astronomer at the Astronomical Observatory of Rome. This could be due to the mysterious and mysterious influence of a specific type of dark energy. So-called phantom models of dark energy allow its potency to fluctuate across cosmic time. These models, if they are valid, suggest that dark energy’s impact on the universe’s expansion may have been much greater than it is today. Initial results from JWST “seem in contradiction with most logical models that we have considered so far,” Menci said. Menci referred to Lambda Cold Dark Matter, Lambda-CDM, which is the theoretical model that incorporates cosmologists’ best estimates of the properties and effects of dark matter and dark energie on cosmic evolution.

These ideas, although seeming far-fetched at first glance, are not impossible to rule out as astronomers continue their investigation into the existence of galaxy candidates in early universe. Many of these galaxies will turn out to be mirages. They are much closer galaxies that masquerade as distant ones. Their light is redshifted by large amounts dust. Yet initial follow-up of one of Castellano’s and Naidu’s galaxies using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile suggested little evidence for such high dust content. Castellano states that, despite the ALMA results being intriguing, JWST can only give definitive answers about these galaxies.

Additional follow-up observations of galaxies like these may be conducted in JWST’s first year of science, Cycle 1, which runs until June 2023. More interesting results may occur in its second year of science, Cycle 2, for which astronomers can now propose programs by a deadline of January 27, 2023. Illingworth states that spectroscopic follow-up with JWST will be essential for the requests on distant galaxies in cycle 2. “We have a problem. It’s real. They were not in the storybook. We really have to understand what’s going on here.”

ABOUT THE AUTHOR(S)

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    Jonathan O’Callaghan is a freelance journalist covering commercial spaceflight, space exploration and astrophysics. Follow him on Twitter @Astro_Jonny

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