The James Webb Space Telescope (JWST) discovered what could be the earliest star clusters in the universe.
JWST spotted the five protoglobular clusters—swarms of millions of stars bound together by gravity—in the arc of the Cosmic Gems, a galaxy that formed just 460 million years after Big bang.
The Cosmic Gems rainbow gets its name from its appearance: when viewed from our solar system, the star-studded galaxy appears as a hair-thin crescent due to the powerful gravitational influence of a foreground galaxy, which magnifies and distorts the appearance of the distant galaxy.
The galaxy is the most highly accreted region observed in the first 500 million years of our universe, giving astronomers an unprecedented window into how the perturbations of the first stars sculpted galaxies during the cosmic dawn.
The cosmic dawn is the time spanning the first billion years of the universe. Approximately 400 million years after the Big Bang, the age of reionization began, in which light from nascent stars stripped hydrogen of its electrons, leading to fundamental reshaping of galaxy structures.
“The early universe is not what we expected,” a study by the first author Angela Adamo, an astronomer at Stockholm University, told Live Science. “Galaxies are brighter, they form stars at breakneck speed, and they do so in massive and dense star clusters. We are building a new understanding of how early galaxies formed.”
The researchers published their findings June 24 in the journal Nature.
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As stars form, they throw out material in the form of winds and jets of ionized plasma – a process known as stellar feedback.
“To form these 5 star clusters, this small galaxy had to do so with very high efficiency,” Adamo said. “The stellar feedback from the stars in the star clusters must have been enormous.”
Scientists discovered the Cosmic Gems rainbow in 2018 using the Hubble Space Telescope. Normally, galaxies from such an early time emit light that is too faint to be detected by telescopes. But a phenomenon called gravitational lensing can help astronomers see them.
As Einstein outlined in his theory of general relativity, gravity is the distortion and warping of space-time in the presence of matter and energy. This curved space in turn sets the rules for how energy and matter move.
This means that even though light travels in a straight line, it can be bent and magnified by the presence of gravity. In this case, the galaxy SPT-CL J0615-5746 lies between the Cosmic Gem arc and our solar system, bending and magnifying the early galaxy’s light so that it can be observed by telescopes.
By pointing JWST at this region of curved space, astronomers observed the arc of cosmic gems in unprecedented detail, discerning the five globular clusters nestled within. They found that the clusters are incredibly dense, being roughly three orders of magnitude denser than star-forming regions observed closer to Earth.
The clusters are among the first ever observed. But it’s not yet clear if they’re the first to exist, Adamo said.
“In general, I would expect star formation to occur in clusters even in very primordial galaxies,” she added. “But to form [massive] proto globular clusters, the host galaxy must be able to create and retain sufficient mass in gas. So it all depends on how fast the primordial galaxies can grow.”
To learn more about the region’s first cosmic carbons, the researchers will continue with spectroscopic analysis using JWST. This will allow astronomers to reconstruct the physical properties of the clusters, further constrain their ages, and trace the influence the cluster stars have had on their wider galaxy.
