Stars are born when a large cloud of gas and dust collapses in on itself. The leftover material that doesn’t make it into the star ends up circling around it, not unlike how water swirls around the drain before falling in. This swirling mass of gas and dust is called a protoplanetary disc, and it’s where planets like the Earth are born.

Protoplanetary discs are often thought to be shaped like dinner plates — thin, round and flat. However, recent telescope images from the Atacama Large Millimeter/Submillimeter Array (ALMA) show that this is not always the case. Some of the discs seen by ALMA have shadows on them, where the part of the disc closest to the star blocks some of the stellar light and casts a shadow onto the outer part of the disc. From this shadow pattern, it can be inferred that the inner part of the disc is oriented completely differently to the outer part, in what is called a broken disc.

In this research, the team used high performance computers to run three-dimensional simulations of a broken disc. The team then produced a mock observation, modelling what such a disc would look like if it were to be observed through a telescope, and how it would change over time.

As the inner disc moved through the gravitational pull of the central star, the shadow it cast moved across the outer disc. But instead of the shadow pattern moving around the disc like a clock-hand as expected, it rocked back and forth with a see-saw-like motion. So although the inside disc kept turning in the same direction, its shadow looked like it was rocking forwards and backwards. The team suggest this is caused by a geometric projection effect, which is likely to occur in all broken discs.

Our research is important because it bridges the gap between theory and observations. In the light of new observations from telescopes like JWST, our cutting-edge numerical techniques mean we have a variety of tools to interpret these data and to learn more about how planets are born.

Rebecca says: “JWST promises to give us a look at embryonic planetary systems in unprecedented detail, and with our new models we’ll be able to find out a lot more about the birth of planets.”

Video: https://youtu.be/jGYLuEx-I78

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Based on new data from an interactive tool that exploits data from the European Space Agency’s Gaia mission and other space science data sets, astronomers have created an animation to model dust in the Milky Way. The work was presented this week at the National Astronomy Meeting (NAM 2022) at the University of Warwick.

The animation shows the cumulative build-up of dust looking from Earth’s local neighbourhood to ~13000 lightyears towards the galactic centre — around 10% of the overall distance across the Milky Way. Close by, dust swirls all around but, further out, the concentration of dust along the galactic plane becomes clear. Two ‘windows’, one above and one below the galactic plane, are also revealed.

“Dust clouds are related to the formation and death of stars, so their distribution tells a story of how structures formed in the galaxy and how the galaxy evolves,” said Nick Cox, coordinator of the EXPLORE project which is developing the tools. “The maps are also important for cosmologists in revealing regions where there is no dust and we can have a clear, unobstructed view out of the Milky Way to study the Universe beyond, such as to make Deep Field observations with Hubble or the new James Webb Space Telescope.”

The tools used to create the animation combine data from the Gaia mission and the 2MASS All Sky Survey. The tools are part of a suite of applications designed to support studies of stars and galaxies, as well as lunar exploration, and have been developed through funding from the European Union’s Horizon 2020 Programme.

“State-of-the-art machine learning and visual analytics have the power to greatly enhance scientific return and discovery for space science missions, but their use is still relatively novel in the field of astronomy,” said Albert Zijlstra, of the University of Manchester and the EXPLORE project. “With a constant stream of new data, such as the recent third release of Gaia data in June 2022, we have an increasing wealth of information to mine — beyond the scope of what humans could process in a lifetime. We need tools like the ones we are developing for EXPLORE to support scientific discovery, such as by helping us to characterise properties within the data, or to pick out the most interesting or unusual features and structures.”

Video: https://youtu.be/K2hwjD5D7L0

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Shortly after sunset, pockets of super-heated gas called ‘plasma bubbles’ form in the upper atmosphere and stretch into space (up to 900km above the Earth’s surface). These bubbles start small and grow rapidly — from the size of a football pitch to that of a small country in just a couple of hours. As the bubbles grow bigger, they can prevent satellites from communicating with the Earth by blocking and warping their radio signals.

To predict plasma bubbles, a team of researchers has collated 8 years of data from the SWARM satellite mission. The spacecraft has an automatic bubble detector on-board called the Ionospheric Bubble Index. This compares changes in the density of electrons and the magnetic field strength to check if bubbles are present: a strong correlation between the two indicates the presence of a plasma bubble.

The satellite flies at an altitude of 460km (about 30x higher than a commercial plane) through the middle of most plasma bubbles. The model combines the data collection from SWARM with a machine learning approach to make predictions on the likelihood of a plasma bubble event occurring at any time.

The results show that the number of plasma bubble events varies from season to season, just like the weather, and that the number of events increases with solar activity. Despite this, the model finds location to be a far more crucial element in predicting plasma bubbles than the time of year, with most events occurring over a region in the Atlantic called the South Atlantic Anomaly. The AI model predicts events with an accuracy of 91% across different tests.

Reddy says: “Just like the weather forecast on earth, we need to be able to forecast bubbles to prevent major disruptions to satellite services. Our aim is to be able to say something like: “At 8pm tomorrow there is a 30% chance of a bubble appearing over the Horn of Africa.” This kind of information is extremely useful for spacecraft operators and for people who depend on satellite data every day, just like you and me.”

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“The forests are not keeping up with these large fires,” said study co-author James Randerson, the Ralph J. and Carol M. Cicerone Professor of Earth system science at UCI. Across the entire state, tree cover area has declined 6.7 percent since 1985. “These are big changes in less than four decades,” he said.

It’s the first time that researchers have been able to measure tree population declines in California, and attribute the changes to such pressures as wildfires, drought stress and logging.

For the study, the UCI-led team used satellite data from the USGS and NASA’s Landsat mission to study vegetation changes between 1985 and 2021. They found that one of the starkest declines in tree cover was in Southern California, where 14 percent of the tree population in local mountain ranges vanished, potentially permanently.

“The ability of forests to recover from fire appears to be dwindling in the south,” said Jonathan Wang, a postdoctoral researcher in Randerson’s research group, who led the study published in AGU Advances. “At the same time, the state’s coverage of shrubs and grasses is rising, which could foreshadow more permanent ecosystem shifts.”

The rate and scale of decline varies across the state. Tree cover in the Sierra Nevada, for instance, stayed relatively stable until around 2010, then began dropping precipitously. The 8.8 percent die-off in the Sierra coincided with a severe drought from 2012 to 2015, followed by some of the worst wildfires in the state’s history, including the Creek Fire in 2020.

Fortunately “in the north, there’s plenty of recovery after fire,” said Wang, perhaps because of the region’s higher rainfall and cooler temperatures. But even there, high fire years in 2018, 2020 and 2021 have taken a visible toll.

The tree decline has also affected carbon storage abilities in the state, said Randerson, who added that the next step is to precisely quantify the impact on forests’ ability to absorb anthropogenic carbon dioxide. Co-author Michael Goulden, a UCI professor of Earth system science and director of the Center for Ecosystem Climate Solutions, is using the data to understand how changes in forest cover are affecting water resources, carbon storage and fire behavior across the state.

“This threat to California’s climate solutions isn’t going away anytime soon,” Wang said. “We might be entering a new age of intense fire and vulnerable forests.”

Collaborators include Clarke Knight and John Battles from UC Berkeley. The research was supported by California’s Strategic Growth Council and the UC National Laboratories grant program, along with long-term funding from NASA and the U.S. Department of Energy’s Office of Science.

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It was 2020, and the Philadelphia Orchestra, like so many cultural institutions, had suspended performances due to the COVID-19 pandemic. Through P.J. Brennan, chief medical officer of the University of Pennsylvania Health System, the Orchestra sought expertise to help understand whether its musicians could return to playing in a safe physical arrangement that would minimize the chances of exposing one another, or their audiences, to SARS-CoV-2.

“The Orchestra director didn’t want the musicians to be far apart; they needed to be close together to produce the best sound,” says Arratia, of the School of Engineering and Applied Science. “And yet, if they needed to be separated with plexiglass, that also posed a problem.” The musicians reported problems hearing one another and poor sightlines with plexiglass dividers. “The challenge was, how can we get away from this to the point where they can play unobstructed but still safely,” Arratia says.

Now, in a publication in Nature Communications, Arratia, Jerolmack, and colleagues report on their findings, which suggest the aerosols musicians produce dissipate within about six feet. The results not only informed the arrangement of the Philadelphia Orchestra as they resumed performances in the summer of 2020 but also laid the groundwork for how other musical groups might think about safely gathering and playing.

“Having experts like Paulo and Doug, who could measure particle size and trajectory and distance and velocity, were really valuable in making decisions for the orchestra,” says Brennan, who now serves on the Orchestra’s Board of Directors. “Those decisions included the spacing between players, the distancing between sections, who needed to mask. As they gathered this information, along with the testing and case tracking that Penn Medicine was doing, it helped us make decisions with confidence.”

Experimental approach

The research hinged on the questions of how many aerosol particles the musicians generated, how densely the particles were emitted from the instruments, and how fast they traveled through the air.

“You can have a big jet of air coming out, but if the aerosol concentration is very low it doesn’t much matter,” says Jerolmack, of the School of Arts & Sciences. “Or you can have a lot of aerosols that get concentrated in a narrow beam. Those things are important to understand.”

To gather data, the researchers invited Orchestra musicians to campus, bringing along their wind instruments, including flutes, tubas, clarinets, trumpets, oboes, and bassoons.

In order to visualize and track the aerosols flowing out of the instruments as the musicians played, the researchers operated a humidifier that emitted water vapor droplets at the bell end of the instruments. This arrangement was only shifted for the flute player, for whom the humidifier was placed near the musician’s mouth instead of the bell, since air travels over the mouthpiece while playing that instrument.

The researchers then shone a laser beam through the “fog” created by the humidifier, lighting up the aerosol particles and allowing them to be captured by a high-speed camera and particle counter.

“It’s just like on a rainy day; you will see the water drops if the sun shines through,” Arratia says.

The musicians played scales continuously for two minutes. It proved somewhat surprising to the researchers to find that the wind instrument musicians produced aerosols that were similar in concentration to those emitted during normal breathing and speaking, from about 0.3 to 1 micrometer in diameter.

Particles of this size, the researchers say, are small enough to travel far through the air, provided the air flow is strong enough to take them there. Thus, measuring their concentration and the flow became important to understand the potential risk of a musician potentially passing SARS-CoV-2 to another person.

Evaluating the velocity of the flow, the researchers measured speeds of roughly 0.1 meters per second, orders of magnitude slower than that of a cough of sneeze, which can travel 5 to 10 meters per second. The flute was an outlier but still only reached flow speeds of around 0.7 meters per second.

“When you observe the flow, you see these puffs and eddies, and we know that they spread, but we didn’t know if there was going to be anything general at all between these instruments,” says Jerolmack. “Here, we found that by measuring only flow and aerosol concentration and counts, we can make predictions about how far aerosols will travel.”

Music’s flow

Based on their observations, the aerosols produced by these “mini-concerts” dissipated, settling into the flow of the background air draft, within about 2 meters, or 6 feet — reassuringly similar, the researchers say, to what has been measured for ordinary speaking or breathing. Only flute and trombone-generated aerosols traveled beyond that distance, for the flute perhaps because the air travels over the instrument instead of the instrument acting like a mask to prevent the spread of aerosols.

Overall, woodwind instruments emitted slightly lower concentrations of aerosols than brass instruments, perhaps because the wooden elements of the instrument absorbed some of the humidity and the numerous holes along the instrument may reduce the flow of some of the aerosols, the researchers speculate.

Because the measurements the researchers made were not connected to any specific quality of SARS-CoV-2, they can be used to extrapolate how transmission of other respiratory pathogens could be affected by making music.

“Now you have something to work with for potential future concerns, maybe an outbreak of influenza or something like that,” says Arratia. “You can use our findings about flow, plug in your numbers about infectiousness and viral loads, and adapt it to understand risk.

“This was not exactly a problem that we work on routinely, but we felt compelled to take it on,” he says. “It was a lot of fun, and we were lucky to have a problem to work on that made a meaningful difference during the difficult times of the pandemic.”