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 is the first discovery of star clusters in a newborn galaxy, as it was when the 13.8-billion-year-old universe was less than 500 million years old.
Originally discovered by the Hubble Space Telescope and officially designated as SPT0615-JD1, the Cosmic Gems Arc is a newborn gravitationally lensed 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 approximately 97% of the universe’s lifetime.
The international team of astronomers behind the discovery found five young massive star clusters in the Cosmic Gems arc. These clusters existed during a period when young galaxies were going through intense bursts of star formation and emitting huge 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 epoch.
Studying these five star clusters could teach astronomers a lot about this early period in the universe.
Related: The James Webb Space Telescope observes the never-before-seen behavior of stars in a distant nebula (video, photo)
“The surprise and amazement was incredible when we first opened the JWST images,” said team leader Angela Adamo of Stockholm University and the Oskar Klein Center in Sweden. “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 know we were looking at star clusters in such a young galaxy!”
The newly discovered star clusters in the Cosmic Gems arc are remarkable for their massive and dense nature. The density of the five star clusters is significantly greater than the density of nearby star clusters.
A helping hand from Einstein
The reionization epoch is so important because it was the phase in which the first light sources in the universe—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 found 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 could be the primary drivers of reionization.
By studying reionization, scientists can learn more about the processes that created large-scale structures in the universe. This may reveal how the remarkably smooth distribution of matter during the early cosmic times gave way to the highly structured universe of galaxies (and clusters of galaxies) that astronomers have seen in the later epochs of the universe.
More specifically, these five early star clusters can show where stars formed and how they were distributed during the early universe. This offers a unique opportunity to study star formation as well as the inner workings of small galaxies at an unprecedented distance, the study team says.
“JWST’s incredible sensitivity and angular resolution at near-infrared wavelengths, combined with the gravitational lensing provided by the massive foreground galaxy cluster, made this discovery possible,” said Larry Bradley, principal investigator of the observing program that captured the data. . “No other telescope could have made this discovery.”
To see objects as far away as 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 a distortion of the very fabric of space and time, unified as a four-dimensional entity called “space-time”. The more mass an object has, the more space-time distortion it causes.
When light from background sources passes through this distortion, its path curves. The closer the light passes to the deforming object, the more its path curves. As a result, light from a single object can arrive at an observer like JWST more than once and at different times.
This means that light sources can appear in multiple places in the same image, their positions can be moved to apparent positions or, most usefully, their light is amplified. The second phenomenon is called “gravitational lensing”, with the body between the distant background object and Earth being called the “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 galaxies.
“What’s special about the Cosmic Gems arc is that we can actually split the galaxy into parsecs with gravitational lensing!” said Adamo.
How do globular clusters merge?
One promising follow-up study coming from this JWST observation of early clusters concerns how arrangements of stars, called “globular clusters,” form. As seen in our own 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 the key may be that the massive and dense young star clusters in the Cosmic Gems arc could be the start of globular cluster formation. This means that they could provide an incredibly useful window into the early stages of the birth of a globular cluster.
These five star clusters could also help to understand other aspects of cosmic evolution.
“The high stellar densities found in clusters give us the first hint of the processes going on inside them and provide new insight into the possible formation of very massive stars and black hole seeds, both of which are important for the evolution of galaxies,” Adamo said.
The study of the Cosmic Gems arc will continue with the research team already planning to observe this early galaxy with JWST’s Near Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI) during Cycle 3 operations of the $10 billion space telescope. .
“The NIRSpec observations will allow us to confirm the redshift of the galaxy and study the ultraviolet radiation of star clusters, which will be used to study their physical properties in more detail,” Bradley said. “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 the study now intend to study other galaxies to look for star clusters similar to these five.
“I’m sure there are other similar systems in the early universe waiting to be discovered, which will allow us to better understand 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.