The The James Webb Space Telescope (JWST) discovered what could be the oldest star clusters in the universe.
JWST spotted five protoglobular clusters—swarms of millions of stars bound together by gravity—inside the Cosmic Gems arc, a galaxy that formed just 460 million years after Big Bang.
The Cosmic Gems arc gets its name from its appearance: When viewed from our solar system, the star-studded galaxy looks like a hair-thin crescent, thanks to the strong gravitational pull of the foreground galaxy, which magnifies and distorts the appearance of the distant galaxy.
The galaxy is the most magnified region observed in the first 500 million years of our universe, giving astronomers an unprecedented window into how the motions of the first stars shaped galaxies during the cosmic dawn.
The Cosmic Dawn is the time spanning the first billion years of the universe. About 400 million years after the Big Bang, an epoch of reionization began, in which light from newborn stars stripped hydrogen of its electrons, leading to fundamental reshaping of galaxy structures.
“The early universe is not what we expected,” says the first author of the study Angela Adamo, an astronomer at Stockholm University, told Live Science. “Galaxies are more luminous, forming stars at breakneck speeds, and doing so in massive and dense clusters. We’re building a new understanding of how early galaxies formed.”
The researchers published their findings on June 24 in the journal Nature.
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Lights on at the space mine
How stars are formed they throw away the 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 it with very high efficiency,” Adamo said. “The stellar feedback from the stars in the clusters must have been tremendous.
Scientists discovered the Cosmic Gems arc in 2018 using the Hubble Space Telescope. Galaxies from this early age typically emit light that is too faint to be detected by telescopes. But a phenomenon called gravitational lensing can help astronomers view them.
As Einstein outlined in his theory of general relativity, gravity is the curvature and deformation of space-time in the presence of matter and energy. This curved space in turn determines the rules for the movement of energy and matter.
This means that even though light travels in a straight line, light 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 to be observed by telescopes.
By pointing JWST at this region of curved space, astronomers observed the arc of the Cosmic Gems in unprecedented detail and distinguished the five globular clusters embedded within it. They found that the star clusters were incredibly dense, roughly three orders of magnitude denser than the star-forming regions observed closer to Earth.
The clusters are some of the first ever observed. But it’s still unclear whether they’re the first to exist, Adamo said.
“In principle, I would expect star formation to occur in a clustered manner even in fairly primordial galaxies,” she added. “But to create [massive] protoglobular clusters, the host galaxy must be able to create and retain enough mass in the gas. So it all depends on how fast the primordial galaxies can grow.”
To learn more about the first glowing embers in space in this region, scientists will continue spectroscopic analysis with JWST. This will allow astronomers to reconstruct the physical properties of clusters, further constrain their ages, and trace the impact the cluster’s stars have had on their wider galaxy.