Webb Space Telescope Shows Early Universe Crackled With Bursts of Star Formation
Equipped with a sizable mirror and the ability to detect infrared radiation, NASA’s James Webb Space Telescope (JWST) is uniquely designed for the investigation of galaxies that emerged during the early stages of the universe, a mere few hundred million years following the occurrence of the big bang.
A significant portion of Webb’s observation period, spanning slightly over one month, is dedicated to the JWST Advanced Deep Extragalactic Survey, known as JADES. JADES aims to delve deeply into the cosmos to examine some of the most remote and faint galaxies.
Initial findings from the program have unveiled the existence of hundreds of galaxies that originated when the universe was less than 600 million years old, as well as galaxies that have undergone multiple episodes of intense star formation.
Intense Star Formation Unveiled in the Early Universe
Unraveling the mystery of how the first stars and galaxies came into existence remains a fundamental pursuit in the field of astronomy. NASA’s James Webb Space Telescope has already begun shedding light on this inquiry by offering new insights.
Among the most prominent endeavors in Webb’s inaugural year of scientific operations is the JWST Advanced Deep Extragalactic Survey, also known as JADES. This extensive initiative dedicates approximately 32 days of telescope time to uncovering and characterizing remote and faint galaxies.
While the analysis of data is ongoing, JADES has already made remarkable discoveries, revealing the presence of hundreds of galaxies that originated when the universe was younger than 600 million years. Additionally, the research team has identified galaxies that sparkle with numerous young and hot stars.
Marcia Rieke, co-lead of the JADES program from the University of Arizona in Tucson, highlights the multitude of questions JADES aims to address: How did the earliest galaxies form and come together? At what rate did they generate stars? What factors contribute to some galaxies ceasing their star formation activities?
A Study on Galaxies
Under the leadership of Ryan Endsley from the University of Texas at Austin, a study was conducted on galaxies that existed between 500 and 850 million years following the occurrence of the big bang.
This particular era is recognized as the Epoch of Reionization and holds significant importance. During the initial hundreds of millions of years after the big bang, the universe was immersed in a gaseous haze that rendered it opaque to high-energy light.
However, by approximately one billion years after the big bang, this fog dissipated, and the universe transitioned into a state of transparency, a phenomenon referred to as reionization. Scientists have engaged in debates regarding the primary catalyst behind reionization, contemplating whether it was triggered by active supermassive black holes or galaxies brimming with young, hot stars.
As a component of the JADES program, Endsley and the research team examined these galaxies with the objective of identifying indications of star formation. Their findings revealed an abundance of such signatures.
Endsley remarked, “Virtually every galaxy we have discovered exhibits remarkably robust emission line characteristics that indicate recent and vigorous star formation. These early galaxies demonstrated remarkable proficiency in generating young, massive stars.”
The Role of Hot, Massive Stars in Reionization
These luminous and substantial stars emitted copious amounts of ultraviolet light, effectively transforming the neighboring gas from being opaque to becoming transparent through the process of ionization, wherein electrons were stripped away from their atomic nuclei.
Given the significant presence of these hot and massive stars in the early galaxies, they likely played a crucial role in driving the reionization process. The subsequent recombination of electrons and nuclei produced distinctively strong emission lines.
Endsley and his colleagues also uncovered evidence suggesting that these young galaxies experienced periods of rapid star formation, interspersed with quieter intervals characterized by fewer star formations.
These intermittent bursts and pauses could have arisen as galaxies captured clusters of gaseous raw materials necessary for star formation. Alternatively, due to the rapid demise of massive stars, they might have periodically injected energy into the surrounding environment, impeding the condensation of gas required for the formation of new stars.
Unveiling the Secrets of the Early Universe
Another facet of the JADES program involves the quest to identify the most ancient galaxies that emerged when the universe was younger than 400 million years old. Through the examination of these galaxies, astronomers aim to gain insights into how star formation differed during the early stages following the big bang compared to the present era.
The light emanating from galaxies situated far away undergoes a stretching effect due to the expansion of the universe, causing it to shift towards longer wavelengths and redder hues, a phenomenon referred to as redshift. By measuring the redshift of a galaxy, astronomers can ascertain its distance and, consequently, when it existed in the early universe.
Prior to the advent of the James Webb Space Telescope (Webb), only a limited number of galaxies had been observed with a redshift above 8, corresponding to when the universe was younger than 650 million years. However, the JADES initiative has now unearthed nearly a thousand of these remarkably distant galaxies.
Red-shift estimation using filter image
The primary method for determining redshift, a crucial factor in understanding the nature of galaxies, involves analyzing a galaxy’s spectrum, which measures its brightness across a range of closely spaced wavelengths. However, a reasonable approximation can be achieved by capturing images of a galaxy using filters that cover specific narrow bands of colors, allowing for a handful of brightness measurements. By employing this approach, researchers can estimate the distances of thousands of galaxies simultaneously.
Kevin Hainline and his colleagues from the University of Arizona in Tucson utilized Webb’s Near-Infrared Camera (NIRCam) instrument to obtain these measurements, known as photometric redshifts.
Their analysis resulted in the identification of over 700 potential galaxies that existed when the universe was between 370 million and 650 million years old. The abundance of these galaxies exceeded previous predictions made prior to Webb’s launch. The exceptional resolution and sensitivity of the observatory enable astronomers to obtain a clearer view of these distant galaxies than ever before.
Advancements in Determining Redshift and Unveiling Distant Galaxies
Hainline emphasizes the significance of these findings, stating, “Previously, the earliest galaxies we could observe appeared as mere indistinct smudges. However, those smudges represent millions or even billions of stars at the dawn of the universe. Now, we can perceive that some of these galaxies exhibit visible structures and extended shapes. We can witness the formation of stellar clusters occurring only a few hundred million years after the birth of time itself.”
According to Rieke, “We are discovering that star formation in the early universe is much more intricate than we previously believed.” These findings are being presented at the 242nd meeting of the American Astronomical Society held in Albuquerque, New Mexico.
As the foremost space science observatory globally, the James Webb Space Telescope is poised to unravel mysteries within our solar system, explore distant exoplanets orbiting other stars, and delve into the enigmatic structures and origins of our universe, providing insights into our cosmic existence. Webb represents an international collaboration led by NASA, in partnership with the ESA (European Space Agency) and CSA (Canadian Space Agency).
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