Using the James Webb Space Telescope (JWST), astronomers have discovered clusters of stars in the “Cosmic Gem” arc that existed just 460 million years after the Big Bang. This marks the first discovery of star clusters in an infant galaxy, seen as it was when the 13.8-billion-year-old universe was less than 500 million years old.
The Cosmic Gems Arc, first discovered by the Hubble Space Telescope and officially named SPT0615-JD1, is a gravitationally lensed infant galaxy about 13.3 billion light-years from Earth. This means that the light from this galaxy, seen by JWST, has been traveling to Earth for about 97% of the universe’s lifetime.
The international team of astronomers following this discovery found five new massive star clusters in the Cosmic Gem Arc. These clusters existed during a period when young galaxies were undergoing intense bursts of star formation and were emitting large amounts of ultraviolet light. This radiation may be responsible for triggering one of two major phases in the evolution of the universe: the cosmic reionization era.
Studying these five star clusters can teach astronomers a lot about this early period in the cosmos.
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“The surprise and amazement was incredible when we opened the JWST images for the first time,” team leader Angela Adamo of Stockholm University and the Oskar Klein Center in Sweden said in a statement. “We saw a tiny chain of bright points mirrored from side to side—these cosmic gems are star clusters! Without JWST, we wouldn’t know we were looking at star clusters in such a young galaxy!”
The newly discovered star clusters in the Cosmic Gem arc are remarkable because of their massive and dense nature. The density of five star clusters is significantly greater than that of nearby star clusters.
A helping hand from Einstein
The age of reionization is so important because this was the stage in which the first light sources in the cosmos—early galaxies, stars, and supermassive black hole-powered quasars—supplied 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 most of the ultraviolet light coming from that galaxy, meaning that clusters like these may have been the main drivers of reionization .
By studying reionization, scientists can learn more about the processes that formed large-scale structures in the universe. This may reveal how the extremely smooth distribution of matter during the early cosmic times gave way to the highly structured universe of galaxies (and galaxy clusters) that astronomers see in the later ages of the universe.
More specifically, these five early 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 infant galaxies at an unprecedented distance, the research team says.
“JWST’s exceptional sensitivity and angular resolution at near-infrared wavelengths, combined with gravitational lensing provided by the massive foreground galaxy cluster, made this discovery possible,” Larry Bradley, the program’s principal investigator, said in a statement. observation that captured this data. . “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, united as a four-dimensional entity called “space-time,” to distort. The more mass an object has, the greater the space-time distortion it causes.
When light from background sources passes this warp, its path becomes curved. The closer the light passes to the warping object, the more curved its path. As a result, light from a single object can reach an observer, such as JWST, more than once and at different times.
This means that light sources can appear in multiple places in the same image, have their positions moved to visible positions, or, more usefully, have their light amplified. The latter phenomenon is called “gravitational lensing”, with the body between a distant background object and Earth being called a “lensing object”.
In this case, the lensed object is a lensed galaxy cluster called SPT-CL J0615−5746, and the background objects are the Cosmic Gems, their star clusters, and two distant lensed galaxies.
“What’s special about the Cosmic Gem Arc is that thanks to gravitational lensing, we can resolve the galaxy down to the order of a parsec!” said Adamo.
How are globular clusters joined?
A promising follow-up study to come from this JWST observation of early star clusters relates to how arrangements of stars, called “globular clusters,” form. As seen in our own galaxy, the Milky Way, globular clusters are ancient relics of intense bursts of star formation in the early universe.
Scientists aren’t quite sure how these tightly packed, gravitationally bound spherical conglomerates of stars come together, but it may be the key that new massive and dense clusters of stars in the Cosmic Gem Arc may be the first stages of the formation of globular clusters. This means they can provide an incredibly useful window into the early stages of the birth of globular clusters.
These five star clusters can also help in understanding other aspects of cosmic evolution.
“The high stellar densities found in the clusters give us the first indication of the processes taking place in their interior, providing new insights into the possible formation of very massive stars and black hole seeds, both of which are important on the evolution of galaxies,” Adamo. said.
The study of the Cosmic Gemstone Arc will continue with the team behind the search already planning to observe this early galaxy with the Near Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI) instruments of JWST during Cycle 3 of the $10 billion space telescope’s operations. .
“The NIRSpec observations will allow us to confirm the galaxy’s redshift and study the ultraviolet emission of the star clusters, which will be used to study their physical properties in more detail,” said Bradley. “The MIRI observations will allow us to study the properties of ionized gas.”
These spectroscopic observations should reveal how intense star formation was in the active sites of this young galaxy.
The astronomers behind this study also now intend to study other galaxies to hunt 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, enabling us to improve our understanding of early galaxies,” said team member Eros Vanzella from the National Institute for Astrophysics (INAF).
The team’s research was published Monday (June 24) in the journal Nature.