Webb serves up baby pictures of galaxy cluster in infant cosmos

The galaxies highlighted in this James Webb Space Telescope image of the Pandora galaxy cluster have been spectroscopically confirmed at a redshift of 7.9, or 650 million years after the Big Bang. They are the earliest galaxies yet confirmed to be part of a developing cluster. Image: NASA, ESA, CSA, Takahiro Morishita (IPAC); image processing: Alyssa Pagan (STScI)

The hunt for the first stars and galaxies continues to push astronomers closer and closer to the Big Bang, raising more questions about how they formed so rapidly in the infant universe.

Researchers using the James Webb Space Telescope have now found a protocluster of seven galaxies that were shining just 650 million years after the birth of the cosmos, a grouping that may have since evolved into a monster rivalling the Coma Cluster hosting more than 1,000 galaxies and trillions of stars.

The seven galaxies in question were first observed by the Hubble Space Telescope as part of a study utilising gravitational lensing to observe extremely remote galaxies. Gravitational lensing refers to the way the collective gravity of an intervening massive object, in this case the Pandora galaxy cluster, can magnify the light from even more remote background objects that might otherwise be undetectable.

To find out how far away the galaxies might be and whether they are gravitationally bound, astronomers needed the infrared power of the James Webb Space Telescope. Webb’s Near-Infrared Spectrograph, of NIRSpec, showed all seven galaxies were moving at the same velocity at roughly the same collective distance.

“This is a very special, unique site of accelerated galaxy evolution, and Webb gave us the unprecedented ability to measure the velocities of these seven galaxies and confidently confirm that they are bound together in a protocluster,” said Takahiro Morishita of IPAC-California Institute of Technology, lead author of a study published in the Astrophysical Journal Letters.

The NIRSpec data showed the galaxies were moving in a halo of dark matter at more than 1,000 kilometres per second (2 million miles per hour). The data indicate the protocluster could eventually evolve into one of the densest collections of galaxies in the cosmos.

“We can see these distant galaxies like small drops of water in different rivers, and we can see that eventually they will all become part of one big, mighty river,” said team member Benedetta Vulcani of the National Institute of Astrophysics in Italy.