Using the James Webb Space Telescope (JWST), astronomers have discovered star clusters in the arc of “cosmic gems” that existed just 460 million years after the Big Bang. It is the first discovery of star clusters in a nascent galaxy, such as it was when the 13.8 billion-year-old universe was less than 500 million years old.
The Cosmic Gems Arc, originally discovered by the Hubble Space Telescope and officially designated SPT0615-JD1, is a gravitationally lensed infant galaxy located approximately 13.3 billion light-years from Earth. This means that light from this galaxy, as seen by JWST, has traveled toward Earth for about 97% of the life of the universe.
The international team of astronomers behind this discovery discovered five young massive star clusters in the Cosmic Gems Arc. These clusters existed at a time when young galaxies were undergoing intense bursts of star formation and emitting enormous amounts of ultraviolet light. This radiation could be responsible for triggering one of the two major phases in the evolution of the universe: the epoch of cosmic reionization.
The study of these clusters of five stars could teach astronomers a lot about this first period of the cosmos.
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“The surprise and amazement was incredible when we opened the JWST images for the first time,” said Angela Adamo, of Stockholm University and the Oskar Klein Center in Sweden, and team leader, in a communicated. “We saw a small chain of bright points reflecting from one side to the other: these cosmic jewels are star clusters! Without the JWST, we would not have known that we were observing star clusters in such a young galaxy!”
The newly detected star clusters in the Cosmic Gems arc are notable due to their massive and dense nature. The density of clusters of five stars is considerably higher than that of nearby star clusters.
A helping hand from Einstein
The epoch of reionization is so important because it was when the cosmos’ first sources of light—the first galaxies, stars, and supermassive quasars powered by black holes—provided the energy that separated electrons from the neutral hydrogen that filled the universe. .
The newly discovered star clusters are located in a very small region of their galaxy but are responsible for the majority of the ultraviolet light coming from that galaxy, meaning that clusters like these could have been the main drivers of the reionization.
By studying reionization, scientists can learn more about the processes that formed large-scale structures in the universe. This may reveal how the remarkably smooth distribution of matter in early cosmic times gave way to the highly structured universe of galaxies (and galaxy clusters) that astronomers see in later epochs of the universe.
Specifically, these first five star clusters can show where stars formed and how they were distributed during the infancy of the cosmos. This provides a unique opportunity to study star formation as well as the inner workings of nascent galaxies from an unprecedented distance, according to the study team.
“The incredible sensitivity and angular resolution of JWST in near-infrared wavelengths, combined with the gravitational lensing provided by the massive galaxy cluster in the foreground, made this discovery possible,” said researcher Larry Bradley. principal of the observing program which captured these data, in the press release. . “No other telescope could have made this discovery.”
To see such distant objects as they existed in the early universe, JWST uses a principle from Einstein’s 1915 theory of gravity: general relativity.
General relativity suggests that objects with mass cause the very fabric of space and time to warp, united into a four-dimensional entity called “space-time.” The more mass an object has, the more it causes space-time to distort.
When light from background sources exceeds this distortion, its path becomes curved. The closer the light gets to the distorted object, the more its trajectory curves. As a result, light from a single object can arrive at an observer, like the JWST, more than once and at different times.
This means that light sources can appear in multiple locations in the same image, have their positions shifted to apparent positions, or, more usefully, have their light amplified. The latter phenomenon is called “gravitational lensing”, with the body between a distant background object and the Earth being called a “lensing object”.
In this case, the lensing object is a lensing galaxy cluster called SPT-CL J0615−5746, and the background objects are the cosmic gems, their star clusters, and two distant lensing galaxies.
“The special thing about the Cosmic Gems arc is that thanks to gravitational lensing, we can actually resolve the galaxy on a parsec scale!” Adamo said.
How are globular clusters formed?
A promising follow-up study from this JWST observation of early star clusters concerns how arrangements of stars, called “globular clusters,” form. As seen in our galaxy, the Milky Way, globular clusters are ancient relics of intense bursts of star formation in the early universe.
Scientists aren’t sure exactly how these spherical conglomerates of tightly packed, gravitationally bound stars come together, but it could be key that massive, dense young star clusters in the arc of the cosmic gems could well be the early stages of the formation of globular clusters. This means they could provide an incredibly useful window into the early stages of globular cluster birth.
These five star clusters could also help understand other aspects of cosmic evolution.
“The high stellar densities found in the clusters provide us with the first indication of the processes taking place inside their clusters, thus giving new insights into the possible formation of very massive stars and black hole seeds, which are both important for the evolution of galaxies,” Adamo said. said.
The study of the Cosmic Gems arc will continue, with the team behind this research already planning to observe this first galaxy with the Near Infrared Spectrograph (NIRSpec) and Mid Infrared Instrument (MIRI) instruments. of the JWST during Cycle 3 of the $10 billion Space Telescope operations. .
“The NIRSpec observations will allow us to confirm the redshift of the galaxy and study the ultraviolet emission from star clusters, which will be used to study their physical properties in more detail,” Bradley said. “The MIRI observations will allow us to study the properties of ionized gas.”
These spectroscopic observations should reveal the intensity of star formation in active sites of this nascent galaxy.
The astronomers behind this study also intend to study other galaxies to look for star clusters similar to these five.
“I am convinced that there are other systems like this waiting to be discovered in the early universe, which will allow us to deepen our understanding of the first galaxies,” said Eros Vanzella, member of the team from the National Institute of Astrophysics (INAF).
The team’s research was published Monday June 24 in the journal Nature.