SPACE/COSMOS
Study reveals the Phoenix galaxy cluster in the act of extreme cooling
Observations from NASA’s James Webb Space Telescope help to explain the cluster’s mysterious starburst, usually only seen in younger galaxies.
image:
The core of the Phoenix cluster is shown across the whole electromagnetic spectrum. The bright purples represent X-rays produced by the hot gas, and the dashed purple outlines show regions where this hot gas has been pushed away by the radio jets from the supermassive black hole. The radio jets themselves are shown in red colors. The blues and yellows represent visible light emitted by cool gas and stars. The green contours show the “warm” gas that is in the process of cooling, newly measured in the MIT study with JWST.
view moreCredit: NASA
The core of a massive cluster of galaxies appears to be pumping out far more stars than it should. Now researchers at MIT and elsewhere have discovered a key ingredient within the cluster that explains the core’s prolific starburst.
In a new study published in Nature, the scientists report using NASA’s James Webb Space Telescope (JWST) to observe the Phoenix cluster — a sprawling collection of gravitationally bound galaxies that circle a central massive galaxy some 5.8 billion light years from Earth. The cluster is the largest of its kind that scientists have so far observed. For its size and estimated age, the Phoenix should be what astronomers call “red and dead” — long done with any star formation that is characteristic of younger galaxies.
But astronomers previously discovered that the core of the Phoenix cluster appeared surprisingly bright, and the central galaxy seemed to be churning out stars at an extremely vigorous rate. The observations raised a mystery: How was the Phoenix fueling such rapid star formation?
In younger galaxies, the “fuel” for forging stars is in the form of extremely cold and dense clouds of interstellar gas. For the much older Phoenix cluster, it was unclear whether the central galaxy could undergo the extreme cooling of gas that would be required to explain its stellar production, or whether cold gas migrated in from other, younger galaxies.
Now, the MIT team has gained a much clearer view of the cluster’s core, using JWST’s far-reaching, infrared-measuring capabilities. For the first time, they have been able to map regions within the core where there are pockets of “warm” gas. Astronomers have previously seen hints of both very hot gas, and very cold gas, but nothing in between.
The detection of warm gas confirms that the Phoenix cluster is actively cooling and able to generate a huge amount of stellar fuel on its own.
“For the first time we have a complete picture of the hot-to-warm-to-cold phase in star formation, which has really never been observed in any galaxy,” says study lead author Michael Reefe, a physics graduate student in MIT’s Kavli Institute for Astrophysics and Space Research. “There is a halo of this intermediate gas everywhere that we can see.”
“The question now is, why this system?” adds co-author Michael McDonald, associate professor of physics at MIT. “This huge starburst could be something every cluster goes through at some point, but we’re only seeing it happen currently in one cluster. The other possibility is that there’s something divergent about this system, and the Phoenix went down a path that other systems don’t go. That would be interesting to explore.”
Hot and cold
The Phoenix cluster was first spotted in 2010 by astronomers using the South Pole Telescope in Antarctica. The cluster comprises about 1,000 galaxies and lies in the constellation Phoenix, after which it is named. Two years later, McDonald led an effort to focus in on Phoenix using multiple telescopes, and discovered that the cluster’s central galaxy was extremely bright. The unexpected luminosity was due to a firehose of star formation. He and his colleagues estimated that this central galaxy was turning out stars at a staggering rate of about 1,000 per year.
“Previous to the Phoenix, the most star-forming galaxy cluster in the universe had about 100 stars per year, and even that was an outlier. The typical number is one-ish,” McDonald says. “The Phoenix is really offset from the rest of the population.”
Since that discovery, scientists have checked in on the cluster from time to time for clues to explain the abnormally high stellar production. They have observed pockets of both ultrahot gas, of about 1 million degrees Fahrenheit, and regions of extremely cold gas, of 10 kelvins, or 10 degrees above absolute zero.
The presence of very hot gas is no surprise: Most massive galaxies, young and old, host black holes at their cores that emit jets of extremely energetic particles that can continually heat up the galaxy’s gas and dust throughout a galaxy’s lifetime. Only in a galaxy’s early stages does some of this million-degree gas cool dramatically to ultracold temperatures that can then form stars. For the Phoenix cluster’s central galaxy, which should be well past the stage of extreme cooling, the presence of ultracold gas presented a puzzle.
“The question has been: Where did this cold gas come from?” McDonald says. “It’s not a given that hot gas will ever cool, because there could be black hole or supernova feedback. So, there are a few viable options, the simplest being that this cold gas was flung into the center from other nearby galaxies. The other is that this gas somehow is directly cooling from the hot gas in the core.”
Neon signs
For their new study, the researchers worked under a key assumption: If the Phoenix cluster’s cold, star-forming gas is coming from within the central galaxy, rather than from the surrounding galaxies, the central galaxy should have not only pockets of hot and cold gas, but also gas that’s in a “warm” in-between phase. Detecting such intermediate gas would be like catching the gas in the midst of extreme cooling, serving as proof that the core of the cluster was indeed the source of the cold stellar fuel.
Following this reasoning, the team sought to detect any warm gas within the Phoenix core. They looked for gas that was somewhere between 10 kelvins and 1 million kelvins. To search for this Goldilocks gas in a system that is 5.8 billion light years away, the researchers looked to JWST, which is capable of observing farther and more clearly than any observatory to date.
The team used the Medium-Resolution Spectrometer on JWST’s Mid-Infrared Instrument (MIRI), which enables scientists to map light in the infrared spectrum. In July of 2023, the team focused the instrument on the Phoenix core and collected 12 hours’ worth of infrared images. They looked for a specific wavelength that is emitted when gas — specifically neon gas — undergoes a certain loss of ions. This transition occurs at around 300,000 kelvins, or 540,000 degrees Fahrenheit — a temperature that happens to be within the “warm” range that the researchers looked to detect and map. The team analyzed the images and mapped the locations where warm gas was observed within the central galaxy.
“This 300,000-degree gas is like a neon sign that’s glowing in a specific wavelength of light, and we could see clumps and filaments of it throughout our entire field of view,” Reefe says. “You could see it everywhere.”
Based on the extent of warm gas in the core, the team estimates that the central galaxy is undergoing a huge degree of extreme cooling and is generating an amount of ultracold gas each year that is equal to the mass of about 20,000 suns. With that kind of stellar fuel supply, the team says it’s very likely that the central galaxy is indeed generating its own starburst, rather than using fuel from surrounding galaxies.
“I think we understand pretty completely what is going on, in terms of what is generating all these stars,” McDonald says. “We don’t understand why. But this new work has opened a new way to observe these systems and understand them better.”
This work was funded, in part, by NASA.
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Written by Jennifer Chu, MIT News
Paper: “Directly Imaging the Cooling Flow in the Phoenix Cluster”
https://www.nature.com/articles/s41586-024-08369-x
Journal
Nature
Article Title
“Directly Imaging the Cooling Flow in the Phoenix Cluster”
Tidal energy measurements help SwRI scientists understand Titan’s composition, orbital history
Saturn moon is slowly recovering from a relatively recent event that affected its orbit
image:
SwRI scientists have determined that at the rate Titan’s orbit is changing, it should have acquired a circular orbit within about 350 million years. The fact that Titan currently has a noncircular or eccentric orbit implies that something occurred within the past 350 million years that perturbed its orbit.
view moreCredit: NASA/JPL/University of Arizona/University of Idaho
SAN ANTONIO — February 12, 2025 —Southwest Research Institute (SwRI) scientists are studying Saturn’s moon Titan to assess its tidal dissipation rate, the energy lost as it orbits the ringed planet with its massive gravitational force. Understanding tidal dissipation helps scientists infer many other things about Titan, such as the makeup of its inner core and its orbital history.
“When most people think of tides they think of the movement of the oceans, in and out, with the passage of the Moon overhead, said Dr. Brynna Downey. “But that is just because water moves more freely than anything else. When the Moon passes overhead, the rock is also responding, just less perceptively. But that little bit of gravity that the Moon is imposing is what we call tidal dissipation.” Downey is a postdoctoral researcher at SwRI’s Solar System Science and Exploration Division in Boulder, Colorado and is lead author of a paper on this topic published in the journal Science Advances.
To measure tidal dissipation on the Moon, scientists shoot lasers from Earth at mirrors placed across its surface. This allows them to accurately measure the slightest movement. As this cannot be done on Titan, scientists have instead developed a way to infer dissipation rates based on the difference in Titan’s spin axis rotation from what would be expected absent any such force.
“Tidal dissipation in satellites affects their orbital and rotational evolution and their ability to maintain subsurface oceans,” Downey says. “Now that we have an estimate for the strength of tides on Titan, what does it tell us about how quickly the orbit is changing? What we discovered is that it’s changing very quickly on a geologic timescale.”
Downey and her co-author, Dr. Francis Nimmo of the University of California Santa Cruz, considered that the angle of Titan's spin pole orientation can only be due to friction and deduced a way to relate this angle to a tidal friction parameter. In this way, they were able to deduce some of the history of Titan from its current spin state. With future space missions planned to various moons such as Europa and Ganymede, two moons of Jupiter, Downey hopes that this method can be applied to other moons as well.
Friction in a satellite’s interior causes it to slowly progress toward a circular orbit. At the rate its orbit is changing, Titan should have acquired a circular orbit within about 350 million years. The fact that Titan currently has a noncircular or eccentric orbit implies that something occurred within the past 350 million years that perturbed its orbit.
“Any number of things, such as an impact or loss of an ancient satellite, could have affected the orbit and made it eccentric; our findings are agnostic as to the nature of the event, and others have proposed several options,” Downey said. “The bottom line is that we think something has disturbed Titan's orbit within the last 350 million years, which is relatively recent in solar system history. We are looking at a snapshot in time between that event and the point when it reaches a circular orbit again.”
To access the Science Advances paper “Titan’s spin state as a constraint on tidal dissipation” see https://www.science.org/doi/10.1126/sciadv.adl4741. For more information, visit https://www.swri.org/markets/earth-space/space-research-technology/space-science/planetary-science.
Titan
SwRI studied Saturn’s moon Titan to assess its tidal dissipation rate, the energy lost as it orbits the ringed planet with its massive gravitational force. Understanding tidal dissipation helps scientists infer many other things about Titan, such as the makeup of its inner core and its orbital history.
Credit
NASA/JPL-Caltech/Space Science Institute
Journal
Science Advances
Method of Research
Data/statistical analysis
Subject of Research
Not applicable
Article Title
Titan’s spin state as a constraint on tidal dissipation
Article Publication Date
5-Feb-2025
NASA successfully joins sunshade to Roman Observatory’s ‘exoskeleton’
image:
Technicians at NASA’s Goddard Space Flight Center in Greenbelt, Md., recently integrated the deployable aperture cover to the outer barrel assembly for the agency’s Nancy Grace Roman Space Telescope.
view moreCredit: NASA/Chris Gunn
NASA’s Nancy Grace Roman Space Telescope team has successfully integrated the mission’s deployable aperture cover — a visor-like sunshade that will help prevent unwanted light from entering the telescope — to the outer barrel assembly, another structure designed to shield the telescope from stray light in addition to keeping it at a stable temperature.
“It’s been incredible to see these major components go from computer models to building and now integrating them,” said Sheri Thorn, an aerospace engineer working on Roman’s sunshade at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Since it’s all coming together at Goddard, we get a front row seat to the process. We’ve seen it mature, kind of like watching a child grow up, and it’s a really gratifying experience.”
The sunshade functions like a heavy-duty version of blackout curtains you might use to keep your room extra dark. It will make Roman more sensitive to faint light from across the universe, helping astronomers see dimmer and farther objects. Made of two layers of reinforced thermal blankets, the sunshade is designed to remain folded during launch and deploy after Roman is in space. Three booms will spring upward when triggered electronically, raising the sunshade like a page in a pop-up book.
The sunshade blanket has an inner and outer layer separated by about an inch, much like a double-paned window. “We’re prepared for micrometeoroid impacts that could occur in space, so the blanket is heavily fortified,” said Brian Simpson, Roman’s deployable aperture cover lead at NASA Goddard. “One layer is even reinforced with Kevlar, the same thing that lines bulletproof vests. By placing some space in between the layers we reduce the risk that light would leak in, because it’s unlikely that the light would pass through both layers at the exact same points where the holes were.”
Over the course of a few hours, technicians meticulously joined the sunshade to the outer barrel assembly — both Goddard-designed components — in the largest clean room at NASA Goddard. The outer barrel assembly will help keep the telescope at a stable temperature and, like the sunshade, help shield the telescope from stray light and micrometeoroid impacts. It’s fitted with heaters to help ensure the telescope’s mirrors won’t experience wide temperature swings, which make materials expand and contract.
“Roman is made up of a lot of separate components that come together after years of design and fabrication,” said Laurence Madison, a mechanical engineer at NASA Goddard. “The deployable aperture cover and outer barrel assembly were built at the same time, and up until the integration the two teams mainly used reference drawings to make sure everything would fit together as they should. So the successful integration was both a proud moment and a relief!”
Both the sunshade and outer barrel assembly have been extensively tested individually, but now that they’re connected engineers are assessing them again. Following the integration, the team tested the sunshade deployment.
“Since the sunshade was designed to deploy in space, the system isn’t actually strong enough to deploy itself in Earth’s gravity,” said Matthew Neuman, a mechanical engineer working on Roman’s sunshade at NASA Goddard. “So we used a gravity negation system to offset its weight and verified that everything works as expected.”
Next, the components will undergo thermal vacuum testing together to ensure they will function as planned in the temperature and pressure environment of space. Then they’ll move to a shake test to assess their performance during the extreme vibrations they’ll experience during launch.
Technicians will join Roman’s solar panels to the outer barrel assembly and sunshade this spring, and then integrate them with the rest of the observatory by the end of the year.
The mission has now passed a milestone called Key Decision Point-D, marking the official transition from the fabrication stage that culminated in the delivery of major components to the phase involving assembly, integration, testing, and launch. The Roman observatory remains on track for completion by fall 2026 and launch no later than May 2027.
To virtually tour an interactive version of the telescope, visit:
https://roman.gsfc.nasa.gov/interactive/
In this photo, technician Brenda Estavia is installing the innermost layer of the sunshade onto the deployable aperture cover structure of NASA’s Nancy Grace Roman Space Telescope.
Credit
NASA/Jolearra Tshiteya
This photo shows the deployable aperture cover for NASA's Nancy Grace Roman Space Telescope as seen through the outer barrel assembly. Both components will help shield the telescope from stray light, improving Roman’s sensitivity to faint light from across the universe.
Credit
NASA/Chris Gunn
Super-precise timing unlocked: satellites get a big boost
image:
The CSS-ground time synchronization system (Consists of two parts, space system and ground system).
view moreCredit: Satellite Navigation
A new carrier-phase-based method for satellite-ground time synchronization has ushered in a new era of precision, achieving picosecond-level accuracy that far surpasses traditional methods. This unprecedented advancement promises to revolutionize global navigation systems, deep space exploration, and fundamental physics research. By seamlessly integrating pseudocode and carrier phase observations, the new technique effectively addresses common errors such as motion delays, relativistic effects, and atmospheric disturbances, enabling a level of time synchronization stability and accuracy never before possible.
Accurate time synchronization is the backbone of many critical technologies, from navigation and communication to cutting-edge research in physics. However, conventional methods like pseudocode-based synchronization, typically limited to sub-nanosecond accuracy, have long struggled with persistent challenges, including atmospheric interference, hardware noise, and the complexities of relativistic effects. These issues have hindered the precision and reliability of time synchronization in dynamic environments, particularly in satellite-to-ground communications. The need for more reliable and accurate methods has become increasingly urgent.
In a recent study (DOI: 10.1186/s43020-024-00155-4) published on January 20, 2025, in Satellite Navigation, researchers from the National Time Service Center of the Chinese Academy of Sciences unveiled a novel carrier-phase-based approach for satellite-ground time synchronization, demonstrated through the China Space Station (CSS)-ground system. This groundbreaking method achieves picosecond-level accuracy, marking a transformative leap in the field of satellite-ground time synchronization.
The innovative carrier-phase-based technique introduced in the study utilizes both pseudocode and carrier phase observations to achieve unmatched precision. Laboratory experiments confirmed the system's remarkable stability, with accuracy reaching picosecond levels. Further satellite-to-ground tests validated its effectiveness, demonstrating that this new method delivers time synchronization accuracy well beyond the capabilities of traditional methods. Allan Deviation analysis revealed a drastic improvement in stability, with results showing an enhancement by nearly an order of magnitude compared to existing pseudocode-based techniques.
What sets this method apart is its ability to correct for a wide range of errors. Motion delays, relativistic effects, and atmospheric disturbances are effectively compensated for, thanks to a triple-frequency mode designed to account for ionospheric and tropospheric delays. By integrating precise orbit determination and real-time atmospheric data, the researchers have enhanced the method's accuracy. Additionally, the approach minimizes hardware biases and short-term fluctuations, ensuring robust performance even in the most dynamic environments. This carrier-phase-based solution offers not only unprecedented precision but also exceptional stability, making it a transformative breakthrough for high-precision time synchronization.
Dr. Shuaihe Gao, the lead researcher of the project, emphasized, “Our carrier-phase-based method is a game-changer in satellite-ground time synchronization. Achieving picosecond-level accuracy sets a new benchmark for high-precision synchronization, which is essential for the future of space exploration and fundamental physics research.”
The implications of this breakthrough extend far beyond the laboratory. In global navigation satellite systems (GNSS), it promises to significantly enhance positioning accuracy, benefiting sectors like transportation and logistics. For deep space exploration, precise time synchronization is crucial for spacecraft navigation and communication. In the realm of fundamental physics, the technique supports experiments that demand ultra-high precision, such as tests of relativity and quantum mechanics. Moreover, the technology holds the potential to refine global clock networks, facilitating more accurate scientific measurements and the dissemination of precise time. This breakthrough is set to revolutionize time synchronization across a range of applications, propelling advances in both Earth science and space exploration.
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References
DOI
Original Source URL
https://doi.org/10.1186/s43020-024-00155-4
Funding information
This research was funded by National Key Research and Development Program (NO.2023YFB3906500), Space Application System of China Manned Space Program, and the National Nature Science Foundation of China (Grant NO.42030105 and NO.12273045).
About Satellite Navigation
Satellite Navigation (E-ISSN: 2662-1363; ISSN: 2662-9291) is the official journal of Aerospace Information Research Institute, Chinese Academy of Sciences. The journal aims to report innovative ideas, new results or progress on the theoretical techniques and applications of satellite navigation. The journal welcomes original articles, reviews and commentaries.
Journal
Satellite Navigation
Subject of Research
Not applicable
Article Title
An improved carrier-phase-based method for precise time synchronization using the observations from the China Space Station-ground synchronization system
