A team of Canadian astronomers utilized the James Webb Telescope (JWST) to detect the most distant globular clusters yet identified – dense collections of millions of stars that could represent relics of the universe’s first and oldest stars.
The first look at Webb’s first Deep Field image showed some of the oldest galaxies in the universe.
Lamiya Mowla, a post-doctoral researcher at the Dunlap Institute for Astronomy & Astrophysics, says that JWST was made to find the first stars and galaxies and to help us figure out how complex things in the universe, like chemical elements and the building blocks of life, came to be. Mowla was a co-lead author on the study, which was done by the Canadian NIRISS Unbiased Cluster Survey (CANUCS) team.
The Sparkler Galaxy
The astronomers focused on “the Sparkler galaxy,” which is nine billion light years away, in the exquisitely detailed Webb’s First Deep Field photograph. The compact particles that appear as little yellow-red spots orbiting this galaxy were dubbed “sparkles.” by the researchers.
These sparkles could be either new clusters that are still making stars or old globular clusters. The new clusters were made three billion years after the Big Bang, when star formation was at its peak.
Globular clusters are ancient groups of stars from a galaxy’s infancy that offer information about the galaxy’s early stages of development and growth. Based on their preliminary examination of 12 of these small objects, the researchers discovered that five of them are not just globular clusters, but also among the oldest known.
“Looking at the first images from JWST and discovering old globular clusters around distant galaxies was an incredible moment — one that wasn’t possible with previous Hubble Space Telescope imaging,”
said Kartheik G. Iyer, the study’s co-lead author and post-doctoral researcher at the Dunlap Institute for Astronomy & Astrophysics.
Because they could see the sparkles at different wavelengths, the CANUCS team was able to model them and better grasp their physical attributes, such as how old they are and how many stars they contain. They hipe that the discovery that globular clusters may be detected from such wide distances with JWST will inspire additional research and searches for comparable objects.
The Milky Way galaxy is known to include approximately 150 globular clusters, but how and when these dense groupings of stars formed is unknown.
Astronomers know that globular clusters can be quite old, but measuring their ages is extremely difficult. It has never been done before, and it is only possible with the James Webb Space Telescope, to figure out how old the first stars in faraway galaxies are by looking at globular clusters that are very far away.
Clusters like these, which were just found in the Sparkler galaxy, were made soon after the first stars were made.
“Because the Sparkler galaxy is much farther away than our own Milky Way, it is easier to determine the ages of its globular clusters. We are observing the Sparkler as it was nine billion years ago, when the universe was only four-and-a-half billion years old, looking at something that happened a long time ago. Think of it as guessing a person’s age based on their appearance — it’s easy to tell the difference between a five and 10-year-old, but hard to tell the difference between a 50- and 55-year-old,”
SMACS 0723 Galaxy Cluster Distortion
Until now, astronomers could not observe the Sparkler galaxy’s surrounding compact objects using only the Hubble Space Telescope. With JWST’s better resolution and sensitivity, Webb’s First Deep Field image showed for the first time the small specks around the galaxy.
The Sparkler galaxy is unique in that it is enlarged by a factor of 100 due to a phenomenon known as gravitational lensing, in which the SMACS 0723 galaxy cluster in the foreground distorts what lies behind it, much like a big magnifying glass. Also, gravitational lensing makes three different views of the Sparkler galaxy, which helps scientists learn more about the galaxy.
This study of the Sparkler galaxy shows how powerful it can be to combine the special features of the JWST with the natural magnification of the gravitational lensing technique.
NIRCam Plus Hubble
The researchers integrated new data from the JWST’s Near-Infrared Camera (NIRCam) with archival data from the Hubble Space Telescope.
NIRCam detects dim objects by employing longer and redder wavelengths to view beyond what the human eye and even the Hubble Space Telescope can see. Both the lensing effect of the galaxy cluster and the high resolution of JWST made it possible to observe compact objects.
The Near-Infrared Imager and Slitless Spectrograph (NIRISS) instrument on the JWST provided independent confirmation that the objects are old globular clusters because the researchers did not observe oxygen emission lines — spectrally measurable emissions given off by young clusters that are actively forming stars. NIRISS also assisted in deciphering the geometry of the Sparkler’s triple-lensed images.
JWST’s made-in-Canada NIRISS equipment was crucial in helping the scientists establish the relationship between the three images of the Sparkler glalxy and its globular clusters.
“Seeing several of the Sparkler’s globular clusters imaged three times made it clear that they are orbiting around the Sparkler galaxy rather than being simply in front of it by chance,”
said co-author says Marcin Sawicki, professor at Saint. Mary’s University.
JWST observations of the CANUCS fields commenced this October. Using its data, it will examine five enormous clusters of galaxies, around which the researchers anticipate discovering additional such systems. In the future, scientists will create a model of the Sparkler galaxy cluster to figure out how the lensing effect works and do more in-depth analyses to figure out how the history of star formation happened.
Lamiya Mowla et al. The Sparkler: Evolved High-redshift Globular Cluster Candidates Captured by JWST. ApJL 2022 937 L35
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