This “baby cluster” of galaxies from the early universe mystifies astronomers

A “baby cluster” of galaxies could challenge cosmic models

Dating just a billion years after the Big Bang, JADES-ID1 may be the oldest and most distant protocluster of galaxies astronomers have ever seen.

By Lee Billings edited by Clara Moskowitz

Astronomers have spotted a mysteriously mature “baby cluster” of galaxies in the early universe, just a billion years after the big bang. Although not a full-fledged galaxy cluster, the protocol is still larger and more advanced in development than most models can easily explain – and may also be the most distant ever observed. Unveiled using NASA’s Chandra X-ray Observatory and the James Webb Space Telescope (JWST), the protocluster’s strange stature was announced last week in a study published in Nature.

“Galaxy clusters are often considered to be at the crossroads between astrophysics and cosmology,” says Elena Rasia, an astrophysicist at the University of Michigan, who was not involved in the work. They are natural laboratories for studying how galaxies interact And how supermassive black holes develop. Tracking how clusters assemble over vast expanses of time and space also informs our knowledge of the cosmic web And cosmological parameters who shape it. According to Rasia, this so far unique protocol could be important from both points of view.

Called JADES-ID1 due to its location within the JWST Advanced Deep Extragalactic Survey (JADES), the protocol was first reported alongside approximately two dozen other candidate early universe objects in a separate study published last year. JWST data suggests that JADES-ID1 contains at least 66 young galaxies, and this latest study measures the protocluster to be about 20 trillion times more massive than our solar system. Most of this mass is in the form of invisible elements dark matterbut as Chandra revealed, the protocol is also embedded in a huge cloud of hot gas illuminated by X-rays.

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The Chandra data was crucial in confirming the authenticity of the protocol, says the study’s lead author, Ákos Bogdán, an astrophysicist at the Center for Astrophysics | Harvard and Smithsonian. Attracted by the immense gravitational field of a galaxy cluster, the incoming gas accumulates and generates shock waves, heating up to millions of degrees and creating the glow of X-rays; Astronomers call this diffuse intergalactic “atmosphere” the intracluster medium, and it is generally a sign of a mature, sedentary system. For JADES-ID1, however, it is more of a baby cluster that grew rapidly by engulfing the surrounding gas, about two billion years ago. the previous X-ray-Bright protocol holding a record burst onto the cosmic scene.

JADES-ID1 “is really the youngest cluster with an X-ray emitting atmosphere,” says Bogdán. “And this discovery greatly expands the boundaries of the X-ray protocol, a lot older times than the previous examples. Given the enormous inferred mass of JADES-ID1 and the very small number of sky astronomers surveyed to find this object, he adds, “we were either extremely lucky [to see it] or we are faced with a region of the universe that is growing unusually rapidly.

Standard models of cluster formation predict that something this large should not exist this early in the history of the universe. And, assuming it continues its prodigious growth further into more recent cosmic epochs, JADES-ID1 would eventually become an abnormally oversized galaxy cluster. But it remains to be seen whether the existence of this voluminous protocol really requires the rewriting of school textbooks.

“It is true that we do not really understand how such structures can form and appear so advanced so early,” says Klaus Dolag, a computational astrophysicist at the Ludwig Maximilian University of Munich, who was not involved in the JADES-ID1 studies. But, Dolag adds, “we may already have an idea of ​​what’s going on here.”

In a 2023 studyDolag and colleagues performed robust simulations of protocluster assembly only about half a billion years later than JADES-ID1, finding that many of these virtual objects then developed detectable X-ray atmospheres. But among the largest and earliest protoclusters in the 2023 study, none became supersized galaxy clusters as the simulation progressed into the modern universe. Instead, their growth slowed as they matured and depleted available reservoirs of surrounding gas. If the same behavior is true for JADES-ID1, Dolag says, its large and early observed size would be less mysterious.

Stefano Borgani, an astrophysicist at the University of Trieste in Italy who was not involved in any of these studies, notes that because the X-ray detection of JADES-ID1 and other early protoclusters pushes Chandra to its limits, it is difficult for researchers to assess how much they actually know about these extreme systems. “A clearer understanding of whether [JADES-ID1] Our current understanding of how cosmic structures form will have to wait for a next generation of X-ray telescopes” with Chandra’s sharp vision but greater sensitivity, he says.

Bogdán agrees that astronomers need to study additional protocols of the same type. “The next steps should be to find more systems like this and create larger samples of protoclusters in the early universe so that we are not dependent on a single object,” he says.

Solving the mystery of this group of mature babies will lead to important advances no matter what, Dolag says. “Either we learn something new about the complex interplay of various physical processes that shape galaxy formation, or we learn that there is indeed a flaw in our general model of cosmology that leads us to oversimplify.”