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What was little more than a point of light for the Hubble Space Telescope has been revealed to be one of the oldest galaxies ever discovered, and the discovery is thanks to none other than Hubble’s little brother: the James Webb Space Telescope.
The James Webb Space Telescope’s international “Glass” collaboration made detailed observations of the galaxy, called Gz9p3, seen as it was just 510 million years after the Big Bang. That’s during the relative infancy of the universe, which is now 13.8 billion years old.
The team found that, like other early galaxies seen by JWST, Gz9p3 is much more massive and mature than expected for a galaxy in the infant universe. During the ancient period in which it was discovered, it already appears to contain several billion stars.
When it comes to the cosmic puzzle of how the first galaxies grew so massive so quickly, Gz9p3 could be a real puzzle. Not only is it more massive than expected, but it is about 10 times more massive than other galaxies that JWST has seen at similar times in the history of the universe.
Related: The James Webb Space Telescope complicates the paradox of the expanding universe by verifying the work of Hubble
“Just a couple of years ago, Gz9p3 appeared as a single point of light through the Hubble Space Telescope,” team member Kit Boyett, a scientist at the University of Melbourne, wrote for the institute’s report. Chase Post. “But using JWST we were able to observe this object as it was 510 million years after the Big Bang, about 13 billion years ago.”
Gz9p3 is simply extraordinary. In addition to its size and maturity, its shape also reveals clues about its creation.
Was Gz9p3 created by an early galaxy merger?
Using JWST and direct imaging, the team was able to determine that Gz9p3 has a complex shape with two bright spots revealing its two dense nuclei. This indicates that Gz9p3 was likely created when two early galaxies collided in the infant universe. It is possible that this collision was still ongoing during the time astronomers noticed Gz9p3 with the JWST.
“The JWST images of the galaxy show a morphology typically associated with two interacting galaxies. And the merger is not over because we still see two components,” Boyett explained. “When two massive objects come together in this way, they effectively discard some matter in the process. Therefore, this discarded matter suggests that what we observe is one of the most distant mergers ever seen.”
In addition to determining the age, mass, and shape of this ancient galaxy, Boyett and his colleagues were able to probe deeper within Gz9p3 to examine the stellar population of these colliding galaxies. Because young stars are brighter than their older counterparts, they typically dominate images of galaxies, especially those that are so distant that their light has been traveling to Earth for billions of years.
“For example, a bright, young population caused by galaxy mergers, less than a few million years old, dwarfs an older population that is already more than 100 million years old,” Boyett continued.
The Glass collaboration solved this problem by performing spectroscopic observations of Gz9p3 and taking advantage of direct imaging. Spectroscopy can be used to determine the elements that make up stars; Because young and old stars have different compositions, this allowed the researchers to separate the two categories in this early galaxy.
Older stars have worked their way through supplying hydrogen in their cores, having fused it all into helium and then fusing this helium to create even heavier elements, which astronomers call “metals.” This means that older stars are richer in metals than younger ones, which are still dominated by hydrogen and some helium.
The study team used JWST to detect specific elements in the population of older Gz9p3 stars. These target elements included silicon, carbon and iron, the latter of which is the heaviest element that stars can synthesize. This means that these stars, when they died in supernova explosions, would have enriched the early universe with metals. Much of this metal content would have become the building blocks of the next generation of stars.
Additionally, the team discovered that the population of ancient stars in Gz9p3 was much larger than previously suspected. This means that while astronomers have been aware of this cycle of stellar life and death and the increasing metal enrichment of subsequent generations of stars, observations of Gz9p3 indicate that galaxies may have become “chemically mature” faster than what had been previously suspected.
“These observations provide evidence for a rapid and efficient accretion of stars and metals immediately after the Big Bang, linked to ongoing galaxy mergers, demonstrating that massive galaxies with several billion stars existed earlier than expected,” he wrote. Boyett.
A history of violence
Galaxies that are isolated from their galactic counterparts form stars, but the process is slow and ends when that galaxy exhausts its reserve of gas and dust, the materials that make up stars.
In the case of galaxies close to each other, the star formation process can be accelerated and even reactivated once stopped. This is because when these galaxies come together due to a mutual gravitational attraction, they collide. The merger then triggers an influx of fresh gas that starts a period of rapid star birth called a “starburst,” meaning that mergers provide a great way for galaxies to rapidly grow their stellar populations.
Most large galaxies in the universe have grown in this way; Our own galaxy, the Milky Way, shows a history of mergers. For example, it has been involved in the cannibalization of smaller satellite galaxies that once orbited it. Currently, the Milky Way forms stars at a slow rate, but this will change when it collides with our neighboring galaxy, Andromeda, in about 4.5 billion years. This will cause an influx of gas that will start a new starburst.
Thanks to observations of Gz9p3, astronomers are getting the message that this channel of rapid mass accumulation and star birth was a more important factor in the early universe than anticipated.
“These observations of Gz9p3 show that galaxies were able to rapidly accumulate mass in the early universe through mergers, with star formation efficiencies higher than we expected,” Boyett explained. “This and other observations using JWST are causing astrophysicists to adjust their models of the early years of the universe.
“Our cosmology is not necessarily wrong, but our understanding of how quickly galaxies formed probably is, because they are more massive than we ever thought possible.”
The team’s research was published March 7 in the journal Nature Astronomy.