Webb telescope unearths an ancient galaxy that shouldn't exist

Astronomers’ understanding of how galaxies form and the nature of dark matter could be completely upended, following new observations of a stellar population bigger than the Milky Way from more than 11 billion years ago.

The formation of galaxies is a fundamental paradigm underpinning modern astrophysics and predicts a strong decline in the number of massive galaxies in early cosmic times. Extremely massive quiescent galaxies (no longer forming stars) have recently been observed as early as one to two billion years after the Big Bang, which challenges previous theoretical models.

Indeed, new data from the James Webb Space Telescope (JWST) finds that a massive galaxy in the early universe — observed 11.5 billion years ago — has an extremely old population of stars formed much earlier — 1.5 billion years earlier in time. The observation upends current modelling, as not enough dark matter could have built up in sufficient concentrations to seed their formation.

Swinburne University of Technology’s Distinguished Professor Karl Glazebrook led the international team who used the JWST for spectroscopic observations of this massive quiescent galaxy. Their results were published in the journal Scientific Reports.

“We’ve been chasing this particular galaxy for seven years and spent hours observing it with the two largest telescopes on Earth to figure out how old it was — but it was too red and too faint, and we couldn’t measure it,” Glazebrook said. “In the end, we had to go off Earth and use the JWST to confirm its nature.”

Spectral analysis of the JWST data was led by Dr Themiya Nanayakkara, also from Swinburne, who said, “We are now going beyond what was possible to confirm the oldest massive quiescent monsters that exist deep in the universe.”

“This pushes the boundaries of our current understanding of how galaxies form and evolve,” Nanayakkara said. “The key question now is how they form so fast very early in the universe and what mysterious mechanisms lead to stopping them forming stars abruptly when the rest of the universe is doing so.”

Associate Professor Claudia Lagos, from the University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR), was crucial in developing the theoretical modelling of the evolution of dark matter concentrations for the study.

“Galaxy formation is in large part dictated by how dark matter concentrates,” she said. “Having these extremely massive galaxies so early in the universe is posing significant challenges to our standard model of cosmology. This is because we don’t think such massive dark matter structures as to host these massive galaxies have had time yet to form. More observations are needed to understand how common these galaxies may be and to help us understand how truly massive these galaxies are.”

Glazebrook hopes this could be a new opening for our understanding of the physics of dark matter.

“JWST has been finding increasing evidence for massive galaxies forming early in time — this result sets a new record for this phenomenon,” he said. “Although it is very striking, it is only one object. But we hope to find more — and if we do, this will really upset our ideas of galaxy formation.”

Pictured: This JWST Near Infrared Camera (NIRCam) image shows a red disk galaxy, but with images alone it is hard to distinguish from other objects. Spectral analysis of its light revealed its anomalous nature — it formed around 13 billion years ago, even though it contains ~4x more mass in stars than our Milky Way does today.