Using the James Webb Space Telescope (JWST), astronomers have discovered star clusters in the ‘Cosmic Gems’ arc that existed just 460 million years after the Big Bang. This marks the first discovery of star clusters in a young galaxy, as it was when the 13.8 billion-year-old universe was less than 500 million years old.
The Cosmic Gems arc, initially discovered by the Hubble Space Telescope and officially named SPT0615-JD1, is a gravitationally lensed baby galaxy located about 13.3 billion light-years from Earth. That means the light from this galaxy, as seen by the JWST, has traveled to Earth for about 97% of the universe’s lifetime.
The international team of astronomers behind this discovery found five young massive star clusters in the Cosmic Gemstone Arc. These clusters existed during a period when young galaxies were undergoing intense bursts of star formation and emitting enormous amounts of ultraviolet light. This radiation may be responsible for initiating one of the two most important phases in the evolution of the universe: the epoch of cosmic reionization.
Studying these five-star clusters could 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,” Angela Adamo of Stockholm University and the Oskar Klein Center in Sweden, and team leader, said in a statement. “We saw a small chain of bright dots mirrored from one side to the other – these cosmic gems are star clusters! Without the JWST we would not have known we were looking at star clusters in such a young galaxy!”
The newly detected star clusters in the Cosmic Gemstone Arc are notable for their massive and dense nature. The density of the 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 it was the stage when the first sources of light in the cosmos – early galaxies, stars and feeding supermassive quasars powered by black holes – provided the energy that split 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. This means that clusters like these may have been the main cause 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 during early cosmic times gave way to the highly structured universe of galaxies (and clusters of galaxies) that astronomers see in the universe’s later epochs.
More specifically, these five early star clusters can show where stars formed and how they were distributed during the infancy of the cosmos. This offers a unique opportunity to study star formation and the inner workings of young galaxies at an unprecedented distance, the research team says.
“The JWST’s incredible sensitivity and angular resolution at near-infrared wavelengths, combined with gravitational lensing from the massive cluster of galaxies in the foreground, made this discovery possible,” said Larry Bradley, the principal investigator of the observing program that captured these data, in the statement. . “No other telescope could have made this discovery.”
To see such distant objects as they existed in the early universe, the JWST uses a principle from Einstein’s 1915 theory of gravity: general relativity.
General relativity suggests that objects with mass cause the fabric of space and time, unified as a four-dimensional entity called “spacetime,” to warp. The more mass an object has, the greater the curvature of spacetime it causes.
When light from background sources passes through this curvature, its path is bent. The closer the light gets to the warping object, the more curved its path becomes. As a result, light from a single object can arrive at an observer, such as the JWST, more than once and at different times.
This means that light sources can appear in multiple places in the same image, shift their positions to apparent positions, or, most usefully, amplify their light. The latter phenomenon is called “gravitational lensing”, where the body between a distant background object and the Earth is called a “lensing object”.
In this case, the lensing object is a cluster of galaxies called SPT-CL J0615−5746, and the background objects are the Cosmic Gems, their star clusters, and two distant lensing galaxies.
“What’s special about the Cosmic Gems arc is that thanks to gravitational lensing we can actually resolve the galaxy down to parsec scale!” Adamo said.
How do globular clusters come together?
A promising follow-up study emerging from this JWST observation of early star clusters concerns how the arrangements of stars, so-called ‘globular clusters’, are formed. As we see in our galaxy, the Milky Way, globular star clusters are ancient remnants of intense bursts of star formation in the early universe.
Scientists aren’t entirely sure how these globular conglomerates of tightly packed, gravitationally bound stars come together, but it could be crucial that the massive and dense young star clusters in the Cosmic Gems arc could be the initial stages of globular cluster formation. can be. 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 star densities in the clusters give us the first indication of the processes taking place in their interiors, and provide new insights into the possible formation of very massive stars and black hole seeds, both of which are important for the evolution of galaxies,” says Adamo. said.
Study of the Cosmic Gems arc will continue, with the team behind this research already planning to observe this early galaxy with the JWST’s Near Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI) instruments during cycle 3 of the operations of the $10 billion space telescope. .
“The NIRSpec observations will allow us to confirm the galaxy’s redshift and study the ultraviolet emission from the 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 how intense star formation was in the active sites of this young galaxy.
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The astronomers behind this study now plan to study other galaxies to look for star clusters similar to these five.
“I am convinced that there are more systems like this in the early universe that need to be discovered, which will further our knowledge of early galaxies,” said team member Eros Vanzella of the National Institute for Astrophysics (INAF).
The team’s research was published Monday (June 24) in the journal Nature.