Using the James Webb Space Telescope (JWST), astronomers have discovered star clusters in the “Cosmic Gems” arc that existed only 460 million years after the Big Bang. This marks the first discovery of star clusters in a newborn galaxy, seen as it was when the 13.8 billion universe was less than 500 million years old.
The Cosmic Gems rainbow, originally discovered by the Hubble Space Telescope and officially designated SPT0615-JD1, is a young gravitationally lensed galaxy about 13.3 billion light-years from Earth. This means that the light from this galaxy observed by 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 arc of the Cosmic Gems. These clusters existed during a period when young galaxies were undergoing intense bursts of star formation and were emitting huge amounts of ultraviolet light. This radiation may be responsible for triggering one of the two major phases in the evolution of the universe: the cosmic reionization epoch.
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,” Angela Adamo of Stockholm University and the Oscar Klein Center in Sweden and team leader said in a statement. “We saw a small chain of bright points mirrored from one side to the other – these cosmic gems are star clusters! Without JWST, we wouldn’t have known we were looking at star clusters in such a young galaxy!”
The newly discovered star clusters in the Cosmic Gems 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 hand out from Einstein
The age of reionization is so important because it was the stage when the first light sources in the cosmos—early galaxies, stars, and supermassive quasars powered by black holes—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 this 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 could reveal how the remarkably smooth distribution of matter in 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.
Specifically, these five early star clusters can show where stars formed and how they were distributed during the early evolution of the cosmos. This offers a unique opportunity to study star formation as well as the inner workings of young galaxies at an unprecedented distance, the research team says.
“JWST’s incredible sensitivity and angular resolution at near-infrared wavelengths, combined with gravitational lensing provided by the massive foreground galaxy cluster, enabled this discovery,” Larry Bradley, the observing program’s principal investigator, said in the statement , which 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 to warp together as a four-dimensional entity called “space-time”. The more mass an object has, the more spacetime distortion it causes.
When light from background sources passes through this distortion, its path curves. The closer the light travels to the deforming object, the more its path is distorted. 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 shifted to visible positions, or, most 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 “lens”.
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.
“What’s special about the Cosmic Gems arc is that thanks to gravitational lensing, we can actually slice the galaxy down to the rocks of a parsec!” Adamo said.
How are globular clusters assembled?
A promising follow-up study that comes out of this JWST observation of early star clusters concerns how arrangements of stars called “globular clusters” form. As seen in our own galaxy, the Milky Way, globular clusters are ancient remnants of intense bursts of star formation in the early universe.
Scientists aren’t entirely sure how these spherical conglomerates of tightly packed, gravitationally bound stars come together, but it may be key that the massive and dense young star clusters in the Cosmic Gem arc may be the initial stages of globular cluster formation. This means they could provide an incredibly useful window into the early stages of the globular cluster’s birth.
These five star clusters could also help to understand 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 interiors, giving new insights into the possible formation of very massive stars and black hole seeds that are important for the evolution of galaxies,” Adamo said.
The Cosmic Gems arc survey will continue with the team behind this survey already planning to observe this early galaxy with JWST’s Near Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI) instruments during Cycle 3 of the space telescope’s operations on worth 10 billion dollars.
“The NIRSpec observations will allow us to confirm the redshift of the galaxy and probe the ultraviolet emission of the star clusters, which will be used to study their physical properties in more detail,” Bradley said. “MIRI observations will allow us to probe the properties of the ionized gas.”
These spectroscopic observations should reveal exactly how intense star formation was in the active sites of this young galaxy.
The astronomers behind this study now also intend to study other galaxies to look for star clusters similar to these five.
“I am confident that there are other systems like this waiting to be discovered in the early universe, allowing us to improve our understanding of early galaxies,” said team member Eros Vanzella of the National Institute of Astrophysics (INAF).
The team’s research was published Monday (June 24) in the journal Nature.
