Has Webb spotted the first stars?

If you have never looked at the First Deep Field image captured by the James Webb Space Telescope, you need to.

James webb space telescope's first deep field
The Sparkler Galaxy within the JWST’s First Deep Field. Credit: Lamiya Mowla with images from NASA, ESA, CSA, STScI; Mowla, Iyer et al. 2022

Within the beautifully detailed image, you can see crowds of some of the universe’s earliest galaxies, sparkling like jewels through the vast expanse of space and time.

Looking deeper into the image, a Canadian research team has discovered the most distant globular clusters ever identified, which may contain the first and oldest stars in the universe. Finding these is a task for which Webb was specifically built.

“Webb was built to find the first stars and the first galaxies and to help us understand the origins of complexity in the universe, such as the chemical elements and the building blocks of life,” says Lamiya Mowla, Dunlap Fellow at the Dunlap Institute for Astronomy & Astrophysics at the University of Toronto and co-lead author of the study.

An image of a globular cluster
Globular clusters, like NGC 6441 one of the most massive and luminous globular clusters in the Milky Way, are compact and dense with stars. Credit: ESA/Hubble/NASA/G.Piotto

The researchers focussed on the Sparkler galaxy, known for the small yellow-red dot ‘sparkles’ of star clusters surrounding it. Five of the 12 ‘sparkles’ analysed turned out to be globular clusters, which are typically found in the bulge and the halo around galaxies and contain many old and red stars. Because they are so tightly-packed, these clusters are typically very stable and last for billions of years.

The find was made by the aptly named CANUCS: Canadian NIRISS Unbiased Cluster Survey.

The globular clusters were identified by the CANUCS team due to the lack of oxygen lines in the NIRISS (Near-Infrared Imager and Slitless Spectrograph) data.

The presence of oxygen is important. If detected, it would suggest the clusters were much younger and actively engaged in star formation.

Read more: A relic of the ancient universe

Diagram describing gravitational lensing
This illustration shows a phenomenon known as gravitational lensing, which is used by astronomers to study very distant and very faint galaxies. Credit: NASA/ESA/L.Calçada

JWST’s incredible resolution and sensitivity (and a fortunate natural magnification due to gravitational lensing by a foreground galaxy) allowed these ‘sparkles’ to be observed for the first time – something Hubble’s instruments (Webb’s predecessor) could never have been able to do. Using multiwavelength observations of the clusters, scientists can better model and understand their physical properties like age and the number of stars within it.

For globular clusters so distant and so old, this represents a chance to glimpse into the dressing room of the very early universe.

“These newly identified clusters were formed close to the first time it was even possible to form stars,” says Mowla. “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.”

As Webb peers deeper into space, we can all expect to understand more about the origins of our universe, and ultimately ourselves, too

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