These Are The Most Distant Star Clusters Ever Seen, And We Nearly Missed Them


    The Sparkler galaxy in Webb's First Deep Field. (NASA, ESA, CSA, STScI)

The very first deep field picture from the James Webb Space Telescope (JWST) has just delivered a new treasure from the early Universe. 

In a splash of light that has traveled for 9 billion years to reach us, astronomers have observed clusters of stars sparkling around a distant galaxy they have named the Sparkler. 

These clusters, whatever their nature, are very interesting indeed: could they be younger clumps, shattering with more latest star formation, or older globular clusters that could consist of an evasive population of stars, those that were the first to seams in the nascent Universe? 

A team of researchers has just determined that at least some of the clusters twinkling around the galaxy are of the latter kind – making them the most distant globular clusters we've discovered yet. 

"Glancing at the latest images from JWST and discovering old globular clusters around faraway galaxies was an unbelievable moment, one that wasn't possible with Hubble Space Telescope imaging," says astrophysict Kartheik Iyer of the University of Toronto in Canada, who co-led the research. 

Globular clusters are pretty usual in local space. We know of about 150 or so in the Milky Way, and they're mystifying. They are very dense, spherical clusters of around 100,000 to 1 million stars that are all the exactly same age and often much old – some of them almost as old as the Universe. 

They are idea of as 'fossils' that can tell us about the state of the Universe at the time the stars formed. 

Discovering them in the early Universe, with enough information to determine their nature, isn't easy either. Across such long distances, small, dim objects become much difficult to resolve. 

     An infographic showing where the Sparkler Galaxy lies, and how much sharper the JWST image is. (Canadian Space Agency with images from NASA, ESA, CSA, STScI; Mowla, Iyer et al. 2022)

One of the latest images it released, titled Webb's First Deep Field, contains a total 12.5 hours' exposure time, is extreme highest resolution image of the early Universe ever obtained. 

The team made a thorough research of the light emitted by the 12 clusters they identified, and for five of them, made no spotting of the oxygen expected for a cluster that is actively creating stars. This is what led them to the end that the objects are globular clusters that are no longer forming new stars, a state referred to as quiescence. 


The age of the clusters suggests that they were formed around the time the Universe, previously dark and nontransparent, became transparent, allowing light to stream freely. This means that their creation could be linked to the earliest stages of galaxy formation. 

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

The ghostly clusters moving around our own Milky Way may have just become even more exciting. 

The team's research paper has been published in The Astrophysical Journal Letters. 

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