Monday, February 26

James Webb Telescope Reveals Bursts of Star Formation Illuminating Early Universe

The quest to understand the origins of the first stars and galaxies has always been at the forefront of astronomical inquiries. NASA’s James Webb Space Telescope has recently made significant strides in shedding light on this profound question. One of the telescope’s most extensive research initiatives during its inaugural year of scientific operations is the JWST Advanced Deep Extragalactic Survey, affectionately known as JADES. This program is dedicated to studying and characterizing faint, distant galaxies and will allocate around 32 days of precious telescope time to achieve its objectives. Although the data is still being collected, JADES has already made noteworthy discoveries, unearthing hundreds of galaxies that existed when the universe was younger than 600 million years. Furthermore, the team has identified galaxies brimming with youthful, hot stars.

Marcia Rieke from the University of Arizona in Tucson, one of the co-leads of the JADES program, expressed the team’s ambitious goals: “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?”

A Stellar Production Line

Ryan Endsley, leading a study from the University of Texas at Austin, focused on galaxies that emerged between 500 and 850 million years after the Big Bang—an era crucially known as the Epoch of Reionization. During this period, which lasted for hundreds of millions of years after the Big Bang, the universe was enshrouded in a gaseous fog that rendered it opaque to energetic light. However, by the time one billion years had passed, the fog dissipated, rendering the universe transparent in a process called reionization. Scientists have long debated whether active, supermassive black holes or galaxies teeming with young, hot stars were primarily responsible for this reionization process.

Within the framework of the JADES program, Endsley and his colleagues employed the Webb telescope’s NIRSpec (Near-Infrared Spectrograph) instrument to search for signs of star formation. Their efforts yielded a profusion of positive results. Endsley noted, “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.”

These brilliant, massive stars radiated copious amounts of ultraviolet light, which ionized the surrounding gas, transforming it from opaque to transparent and removing electrons from atomic nuclei. Since these early galaxies possessed a significant population of hot, massive stars, they may have been the principal drivers of the reionization process. The subsequent reunion of electrons and nuclei produces distinctively strong emission lines.

Endsley and his team also identified evidence suggesting that these young galaxies underwent periods of rapid star formation interspersed with quieter phases in which fewer stars formed. These fluctuations may have occurred as galaxies captured clusters of gaseous raw materials required for star formation. Alternatively, the explosive demise of massive stars might have intermittently injected energy into the surrounding environment, hindering the condensation of gas necessary for the birth of new stars.

Revealing the Early Universe

Another facet 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 gain insights into how star formation in the early universe differed from what is observed in the present era. The light emitted by galaxies located far away from us is stretched by the expanding universe, resulting in longer wavelengths and redder colors—an effect known as redshift. By measuring the redshift of a galaxy, astronomers can determine its distance and, consequently, its age in the early universe. Prior to the Webb telescope’s launch, only a handful of galaxies had been observed with a redshift greater than 8, corresponding to a universe younger than 650 million years. However, JADES has now revealed nearly a thousand of these exceptionally distant galaxies.

Determining redshift typically involves examining a galaxy’s spectrum, which measures its brightness at numerous closely spaced wavelengths. Yet, a rough approximation can be obtained by capturing photographs of a galaxy using filters that cover narrow bands of colors, yielding a few brightness measurements. This method allows researchers to estimate the distances of thousands of galaxies simultaneously.

Kevin Hainline from the University of Arizona in Tucson, along with his colleagues, utilized Webb’s NIRCam (Near-Infrared Camera) instrument to obtain these measurements, known as photometric redshifts, and identified over 700 potential galaxies that existed between 370 million and 650 million years after the Big Bang. The sheer number of these galaxies far surpassed previous predictions based on pre-Webb observations. Thanks to the telescope’s exceptional resolution and sensitivity, astronomers now have an unprecedented view of these distant galaxies.

Hainline remarked, “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.”

Rieke added, “We’re finding that star formation in the early universe is much more complicated than we thought.”

These remarkable findings are being presented at the 242nd meeting of the American Astronomical Society in Albuquerque, New Mexico.

Source: NASA / Image: NASA, ESA, CSA, Brant Robertson (UC Santa Cruz), Ben Johnson (CfA), Sandro Tacchella (Cambridge), Marcia Rieke (University of Arizona), Daniel Eisenstein (CfA).