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.

Now physicists and biomedical researchers from Aalto University’s Department of Neuroscience and Biomedical Engineering and Department of Applied Physics have unearthed new characteristics of capillary waves, setting a record for their speed while doing so.

The paper was published today in Nature Communications.

By creating a synthetic surface inspired by lotus leaves, the interdisciplinary team, led by Assistant Professor Heikki Nieminen and Professor Robin Ras, brought new wave phenomena to light. Under water, an extremely water-repellent material known as a superhydrophobic surface, holds a plastron — a gas layer only micrometres thick — in place. The plastron in turn can protect the superhydrophobic surface against corrosion and contamination, or improve its hydrodynamics.

With the objective to deepen the understanding of superhydrophobicity, the team investigated the mechanical response of the plastron to highly focused ultrasound. In doing so, they generated ripples, which they dubbed ‘plastronic waves’.

‘Plastronic waves travelled along the water, the superhydrophobic surface and the gas layer 45 times faster than capillary waves normally do,’ Nieminen says.

Setting a wave speed record is only part of the result; using the same waves to monitor the plastron’s stability is another. Maintaining the delicate gas layer on top of the superhydrophobic surface is both highly important and very challenging.

‘Superhydrophobicity relies on the plastron’s stability to open new possibilities in submerged applications, for example, in improving equipment lifespan and operational efficiency in both industrial and biomedical environments. Our new technique is a tool for monitoring the gas layer’s stability better than previously,’ says the first author of the study, Postdoctoral Researcher Maxime Fauconnier, who also carried out the experiment.

In addition to furthering fundamental science, the discovery represents possible early stages for use in fields like biotechnology and materials science.

‘We showed that we could measure how the plastron changes and gradually dissolves into the water, by monitoring the variation of wave speed over time. This system could be used as a sensor in other applications. It could be useful in pharmacology and cell technology, for example,’ Fauconnier says.

The work was funded by the Research Council of Finland, the Finnish Cultural Foundation and the European Union’s HORIZON research and innovation programme.

The research adds to ongoing efforts by space agencies to protect astronauts against deconditioning/getting out of shape due to low gravity, a crucial aspect of their ability to perform spacewalks, handle equipment and repairs, and carry out other physically demanding tasks.

The study, which shows knee cartilage in mice grew healthier following jumping exercises, appears in the journal npj Microgravity.

“Since the next step in human exploration of space is going to Mars and spending long periods of time in permanent bases on the moon, cartilage damage is a really major issue that space agencies need to address despite how very poorly understood it is,” said study author Marco Chiaberge, an astrophysicist at Johns Hopkins University, the Space Telescope Science Institute, and the European Space Agency. “The positive effect we saw in these mice is huge, and the magnitude of it was unexpected. They can basically make their cartilage thicker if they jump. Maybe astronauts could use similar training before their flight as a preventive measure.”

Healthy cartilage is essential for pain-free movement, as it cushions joints and decreases bone friction. But cartilage heals slowly and does not regenerate as fast as other tissue. Prolonged periods of inactivity — whether from bed rest, injury, or space travel — can accelerate cartilage breakdown. Space radiation can also accelerate this effect, and European Space Agency experiments have shown evidence of cartilage degradation in astronauts who spend several months aboard the International Space Station.

“Think about sending somebody on a trip to Mars, they get there and they can’t walk because they developed osteoarthritis of the knees or the hips and their joints don’t function,” Chiaberge said. “Astronauts also perform spacewalks often. They serviced the Hubble Space Telescope five times, and in the future, they will need to spend more time in space and the Moon, where we will build larger telescopes to explore the universe and where they will need to stay as healthy as possible.”

Previous research has shown that treadmill running may help slow cartilage breakdown in rodents. The new Johns Hopkins study adds to the evidence by demonstrating that jump-based exercise may prevent articular cartilage loss in knees and could actually improve cartilage health.

The researchers found that mice in a nine-week program of reduced movement experienced cartilage thinning and cellular clustering, both early indicators of arthritis. But mice that performed jump training three times a week showed the opposite effect — thicker, healthier cartilage with normal cellular structure.

The study found the mice with reduced movement had a 14% reduction in cartilage thickness, while those in the jump-training group had a 26% increase compared to a control group. Additionally, the jumping mice had 110% thicker cartilage than the reduced activity group.

Jumping also enhanced bone strength. The team found shin bones in the jumping mice had 15% higher mineral density. Trabecular bone — spongy bone tissue that absorbs impact — was significantly thicker and more robust.

“Leg strength is particularly important and most highly impacted by microgravity, so any procedures that can address multiple aspects of muscle deconditioning, and maybe even reduce the two-hour daily exercise requirement in space, would be most welcome,” said author Mark Shelhamer, a professor of otolaryngology at the Johns Hopkins School of Medicine and former NASA Human Research Program Chief Scientist. “The same reasoning applies to bone integrity, including cartilage. There is increasing recognition of the importance of cartilage as a distinct component in bone integrity, and this study contributes to that understanding.”

While more research is needed to confirm whether humans would enjoy the same benefits, the findings offer promising information to protect cartilage and bone structure. Jumping exercises could be included in pre-flight routines to prepare joints for space travel, and specially designed exercise machines could help integrate similar workouts in space.

The study could help scientists explore how jump-based training might not only aid patients with arthritis but also boost cartilage health with generally applicable exercises, said author Chen-Ming Fan, a musculoskeletal biologist at Carnegie Science.

The researchers emphasized the need for further research to determine the ideal exercise volume and frequency for preserving and strengthening cartilage. Future work will also explore whether jump training could help reverse cartilage loss and whether the exercise could help astronauts restrengthen their cartilage and recover damage from space flight.

“Now that we got our first clue that one type of exercise can increase cartilage, which was completely unknown before, we could start looking into other types of cartilage. What about the meniscus? Could it also get thicker?” said Fan, who is also an adjunct professor at Johns Hopkins. “This research could help performance-enhancement studies, rather than just focusing on pathological conditions, and help athletes or virtually anyone interested in doing the right exercises to improve their performance.”

Other authors are Neelima Thottappillil, Anderson Furlanetto, Dylan Odell, Christine Wang, Stephen Hope, Stephen Smee, Joseph Rehfus, Colin Norman, and Aaron W. James of Johns Hopkins; Anna-Maria Liphardt of Universitätsklinikum Erlangen, Friedrich-Alexander-Universität; Anja Niehoff of German Sport University Cologne; and Marc J. Philippon and Johnny Huard of Steadman Philippon Research Institute.

This research was supported by a Space@Hopkins Seed Grant and by the Carnegie Science Endowment fund.