Webb Reveals Early-Universe Prequel to Huge Galaxy Cluster

Galaxy Protocluster (NIRCam Image)
Credits: Image: NASA, ESA, CSA, Takahiro Morishita (IPAC)
Image Processing: Alyssa Pagan (STScI)

Release Images

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Every giant was once a baby, though you may never have seen them at that stage of their development. NASA’s James Webb Space Telescope has begun to shed light on formative years in the history of the universe that have thus far been beyond reach: the formation and assembly of galaxies. For the first time, a protocluster of seven galaxies has been confirmed at a distance that astronomers refer to as redshift 7.9, or a mere 650 million years after the big bang. Based on the data collected, astronomers calculated the nascent cluster’s future development, finding that it will likely grow in size and mass to resemble the Coma Cluster, a monster of the modern universe.

“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, the lead author of the study published in the Astrophysical Journal Letters.

The precise measurements captured by Webb’s Near-Infrared Spectrograph (NIRSpec) were key to confirming the galaxies’ collective distance and the high velocities at which they are moving within a halo of dark matter – more than two million miles per hour (about one thousand kilometers per second).

The spectral data allowed astronomers to model and map the future development of the gathering group, all the way to our time in the modern universe. The prediction that the protocluster will eventually resemble the Coma Cluster means that it could eventually be among the densest known galaxy collections, with thousands of members.

“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 Benedetta Vulcani of the National Institute of Astrophysics in Italy, another member of the research team.

Galaxy clusters are the greatest concentrations of mass in the known universe, which can dramatically warp the fabric of spacetime itself. This warping, called gravitational lensing, can have a magnifying effect for objects beyond the cluster, allowing astronomers to look through the cluster like a giant magnifying glass. The research team was able to utilize this effect, looking through Pandora’s Cluster to view the protocluster; even Webb’s powerful instruments need an assist from nature to see so far.

Exploring how large clusters like Pandora and Coma first came together has been difficult, due to the expansion of the universe stretching light beyond visible wavelengths into the infrared, where astronomers lacked high-resolution data before Webb. Webb’s infrared instruments were developed specifically to fill in these gaps at the beginning of the universe’s story.

The seven galaxies confirmed by Webb were first established as candidates for observation using data from the Hubble Space Telescope’s Frontier Fields program. The program dedicated Hubble time to observations using gravitational lensing, to observe very distant galaxies in detail. However, because Hubble cannot detect light beyond near-infrared, there is only so much detail it can see. Webb picked up the investigation, focusing on the galaxies scouted by Hubble and gathering detailed spectroscopic data in addition to imagery.

The research team anticipates that future collaboration between Webb and NASA’s Nancy Grace Roman Space Telescope, a high-resolution, wide-field survey mission, will yield even more results on early galaxy clusters. With 200 times Hubble's infrared field of view in a single shot, Roman will be able to identify more protocluster galaxy candidates, which Webb can follow up to confirm with its spectroscopic instruments. The Roman mission is currently targeted for launch by May 2027.

“It is amazing the science we can now dream of doing, now that we have Webb,” said Tommaso Treu of the University of California, Los Angeles, a member of the protocluster research team. “With this small protocluster of seven galaxies, at this great distance, we had a one hundred percent spectroscopic confirmation rate, demonstrating the future potential for mapping dark matter and filling in the timeline of the universe’s early development.”

The James Webb Space Telescope is the world's premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

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About This Release:

Credits:

Media Contact:

Leah Ramsay
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science: Takahiro Morishita (IPAC)

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Contact Us: Direct inquiries to the News Team.

Related Links and Documents

• Science paper by T. Morishita, et al.

Source: NASA's James Webb Space Telescope/News

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The First Bubble in the Intergalactic Stew

A supercomputer simulation of a galaxy protocluster similar to costco-i that is surrounded by hot gas (yellow) boiling amid an intergalactic medium filled with much cooler gas (blue). Credit: The Three Hundred Collaboration

Maunakea, Hawaiʻi – Astrophysicists using W. M. Keck Observatory on Maunakea in Hawaiʻi have discovered a galaxy protocluster in the early universe surrounded by gas that is surprisingly hot.

This scorching gas hugs a region that consists of a giant collection of galaxies called COSTCO-I. Observed when the universe was 11 billion years younger, COSTCO-I dates back to a time when the gas that filled most of the space outside of visible galaxies, called the intergalactic medium, was significantly cooler. During this era, known as ‘Cosmic Noon,’ galaxies in the universe were at the peak of forming stars; their stable environment was full of the cold gas they needed to form and grow, with temperatures measuring around 10,000 degrees Celsius.

In contrast, the cauldron of gas associated with COSTCO-I seems ahead of its time, roasting in a hot, complex state; its temperatures resemble the present-day intergalactic medium, which sear from 100,000 to over 10 million degrees Celsius, often called the ‘Warm-Hot Intergalactic Medium’ (WHIM).

This discovery marks the first time astrophysicists have identified a patch of ancient gas showing characteristics of the modern-day intergalactic medium; it is by far the earliest known part of the universe that’s boiled up to temperatures of today’s WHIM.

The research, which is led by a team from the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, part of the University of Tokyo), is published in today’s issue of The Astrophysical Journal Letters.

A simulated visualization depicts the scenario of large-scale heating around a galaxy protocluster, using data from supercomputer simulations. This is believed to be a similar scenario to that observed in the COSTCO-I protocluster. The yellow area in the center of the picture represents a huge, hot gas blob spanning several million light years. The blue color indicates cooler gas located in the outer regions of the protocluster and the filaments connecting the hot gas with other structures. The white points embedded within the gas distribution is light emitted from stars. Simulation Credit: The THREE HUNDRED Collaboration

“If we think about the present-day intergalactic medium as a gigantic cosmic stew that is boiling and frothing, then COSTCO-I is probably the first bubble that astronomers have observed, during an era in the distant past when most of the pot was still cold,” said Khee-Gan Lee, an assistant professor at Kavli IPMU and co-author of the paper.

The team observed COSTCO-I when the universe was only a quarter of its present age. The galaxy protocluster has a total mass of over 400 trillion times the mass of our Sun and spans several million light years.

While astronomers are now regularly discovering such distant galaxy protoclusters, the team found something strange when they checked the ultraviolet spectra covering COSTCO-I’s region using Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS). Normally, the large mass and size of galaxy protoclusters would cast a shadow when viewed in the wavelengths specific to neutral hydrogen associated with the protocluster gas. 

No such absorption shadow was found at the location of COSTCO-I. 

“We were surprised because hydrogen absorption is one of the common ways to search for galaxy protoclusters, and other protoclusters near COSTCO-I do show this absorption signal,” said Chenze Dong, a Master’s degree student at the University of Tokyo and lead author of the study. “The sensitive ultraviolet capabilities of LRIS on the Keck I Telescope allowed us to make hydrogen gas maps with high confidence, and the signature of COSTCO-I simply wasn’t there.”

The absence of neutral hydrogen tracing the protocluster implies the gas in the protocluster must be heated to possibly million-degree temperatures, far above the cool state expected for the intergalactic medium at that distant epoch. 

This figure compares observed hydrogen absorption in vicinity of the COSTCO-I galaxy protocluster (top panel), compared with the expected absorption given the presence of the protocluster as computed from computer simulations. Strong hydrogen absorption is shown in red, lower while weak absorption is shown in blue, and intermediate absorption is denoted as green or yellow colors. The black dots in the figure show where astronomers have detected galaxies in that area. At the position of COSTCO-I (with its center marked as a star in both panels), astronomers found that the observed hydrogen absorption is not of much different from the mean value of the universe at that epoch. This is surprising because one would expect to find extended hydrogen absorption spanning millions of light years in that region corresponding to the high observed concentration of galaxies. This figure is adapted from the Dong et al. 2023 Astrophysical Journal Letters article. Credit: Dong et al.

“The properties and origin of the WHIM remains one of the biggest questions in astrophysics right now. To be able to glimpse at one of the early heating sites of the WHIM will help reveal the mechanisms that caused the intergalactic gas to boil up into the present-day froth,” said Lee. “There are a few possibilities for how this can happen, but it might be either from gas heating up as they collide with each other during gravitational collapse, or giant radio jets might be pumping energy from supermassive black holes within the protocluster.”

The intergalactic medium serves as the gas reservoir that feeds raw material into galaxies. Hot gas behaves differently from cold gas, which determines how easily they can stream into galaxies to form stars. As such, having the ability to directly study the growth of the WHIM in the early universe enables astronomers to build up a coherent picture of galaxy formation and the lifecycle of gas that fuels it.

Source: W. M. Keck Observatory

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About LRIS

The Low Resolution Imaging Spectrometer (LRIS) is a very versatile and ultra-sensitive visible-wavelength imager and spectrograph built at the California Institute of Technology by a team led by Prof. Bev Oke and Prof. Judy Cohen and commissioned in 1993. Since then it has seen two major upgrades to further enhance its capabilities: the addition of a second, blue arm optimized for shorter wavelengths of light and the installation of detectors that are much more sensitive at the longest (red) wavelengths. Each arm is optimized for the wavelengths it covers. This large range of wavelength coverage, combined with the instrument’s high sensitivity, allows the study of everything from comets (which have interesting features in the ultraviolet part of the spectrum), to the blue light from star formation, to the red light of very distant objects. LRIS also records the spectra of up to 50 objects simultaneously, especially useful for studies of clusters of galaxies in the most distant reaches, and earliest times, of the universe. LRIS was used in observing distant supernovae by astronomers who received the Nobel Prize in Physics in 2011 for research determining that the universe was speeding up in its expansion.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain..

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