Revealed: The Oldest Star Clusters

Using the James Webb Telescope, astronomers have identified the oldest star clusters in the Universe.

Thousands of galaxies flood this near-infrared, high-resolution image of galaxy cluster SMACS 0723 Image credit NASA, ESA, CSA, STScI

Being able to view stars and and galaxies helps us to a deeper understanding of the formation and complexity of the Universe – and of Life itself.

The Canadian astronomers are from the Dunlap Institute for Astronomy & Astrophysics in the University of Toronto’s Faculty of Arts & Science.

From left: Kartheik Iyer, Vince Estrada-Carpenter, Guillaume Desperez, Lamiya Mowla, Marcin Sawicki, Victoria Strait, Gabe Brammer and Kate Gould (on laptop screen), Ghassan Sarrouh, Chris Willott, Bob Abraham, Gael Noirot, Yoshi Asada, Nick Martis Image credit: Lamiya Mowla and Kartheik Iyer

The observations concentrated on ‘the Sparkler galaxy’ – 9 billion light years away.

 Kartheik G. Iyer, a post-doctoral researcher at the Dunlap Institute for Astronomy & Astrophysics , explained:

“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.

“Since we could observe the sparkles across a range of wavelengths, we could model them and better understand their physical properties – like how old they are and how many stars they contain. We hope the knowledge that globular clusters can be observed at from such great distances with JWST will spur further science and searches for similar objects.”

The researchers studied the Sparkler galaxy located in Webb’s First Deep Field and used JWST to determine that five of the sparkling objects around it are globular clusters. Image credit: Canadian Space Agency with images from NASA, ESA, CSA, STScI; Mowla, Iyer et al. 2022.

Until now, astronomers could not see the surrounding compact objects of the Sparkler galaxy with the Hubble Space Telescope. This changed with JWST’s increased resolution and sensitivity, unveiling the tiny dots surrounding the galaxy for the first time in Webb’s First Deep Field image.

The Sparkler galaxy is special because it is magnified by a factor of 100 due to an effect called gravitational lensing – where the SMACS 0723 galaxy cluster in the foreground distorts what is behind it, much like a giant magnifying glass. Moreover, gravitational lensing produces three separate images of the Sparkler, allowing astronomers to study the galaxy in greater detail.

Gravitational lensing is used by astronomers to study very distant and very faint galaxies. Image credit: NASA, ESA & L. Calçada

The researchers combined new data from JWST’s Near-Infrared Camera (NIRCam) with Hubble Scape Telescope archival data. NIRCam detects faint objects using longer and redder wavelengths to observe past what is visible to the human eye and even the Hubble Space Telescope. Both magnifications due to the lensing by the galaxy cluster and the high resolution of JWST are what made observing compact objects possible.

The Canadian-made 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 – emissions with measurable spectra given off by young clusters that are actively forming stars. NIRISS also helped unravel the geometry of the triply lensed images of the Sparkler.

Marcin Sawicki, a professor at Saint. Mary’s University who is Canada Research Chair in Astronomy commneted:

“JWST’s made-in-Canada NIRISS instrument was vital in helping us understand how the three images of the Sparkler and its globular clusters are connected. 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.”

Link to the results of the study: The Sparkler: Evolved High-redshift Globular Cluster Candidates Captured by JWST, published in The Astrophysical Journal Letters.

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