ST/ Researchers demystify the unusual origin of the Geminids meteor shower

Paradigm

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Paradigm

34 min readJun 23, 2023

Space biweekly vol.79, 9th June — 23rd June

TL;DR

Princeton researchers used observations from NASA’s Parker Solar Probe mission to deduce that it was likely a violent, catastrophic event — such as a high-speed collision with another body or a gaseous explosion — that created the Geminids meteoroid stream. Mysteries surrounding the origin of the Geminids have long fascinated scientists because, while most meteor showers are created when a comet emits a tail of ice and dust, the Geminids stem from an asteroid — a chunk of rock that normally does not produce a tail. Until now, this unusual meteoroid stream had only been studied from Earth.
Extreme space weather threatens vital satellites orbiting the Earth, including the Global Navigation Satellite Systems (GNSS) which pass through the heart of the outer radiation belt. New research has now determined a series of benchmarks for the likely severity of extreme space weather events in GPS orbit.
Scientists have managed to weigh — more precisely than any other technique — a galaxy hosting a quasar, thanks to the fact that it acts as a gravitational lens. Detection of strong gravitational lensing quasars is expected to multiply with the launch of Euclid this summer.
Europa may have a metamorphic origin for the ocean. While some scientists speculated this, a research team shows that if Europa indeed formed from hydrated rocks (i.e., rocks have hydrogen and oxygen), then enough of Europa’s interior should get hot enough to release water directly from the hydrated rocks to form the ocean and ice shell.
The discovery of a rare type of white dwarf star system provides new understanding into stellar evolution.
A study looking at how the human brain reacts to traveling outside Earth’s gravity suggests frequent flyers should wait three years after longer missions to allow the physiological changes in their brains to reset.
Researchers reveal a theoretical breakthrough that may explain both the nature of invisible dark matter and the large-scale structure of the universe known as the cosmic web. The result establishes a new link between these two longstanding problems in astronomy, opening new possibilities for understanding the cosmos. The research suggests that the ‘clumpiness problem,’ which centres on the unexpectedly even distribution of matter on large scales throughout the cosmos, may be a sign that dark matter is composed of hypothetical, ultra-light particles called axions. The implications of proving the existence of hard-to-detect axions extend beyond understanding dark matter and could address fundamental questions about the nature of the universe itself.
Through the Gemini-North Telescope in Hawai’i, the chemical composition of WASP-76 b is revealed in unprecedented detail, giving new insights also into the composition of giant planets.
Astronomers have found that supermassive black holes obscured by dust are more likely to grow and release tremendous amounts of energy when they are inside galaxies that are expected to collide with a neighbouring galaxy.
Astronomers have created a vast infrared atlas of five nearby stellar nurseries by piecing together more than one million images. These large mosaics reveal young stars in the making, embedded in thick clouds of dust.
And more!

Space industry in numbers

The global smart space market size is projected to grow from USD 9.4 billion in 2020 to USD 15.3 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 10.2% during the forecast period. The increasing venture capital funding and growing investments in smart space technology to drive market growth.

Analysts at Morgan Stanley and Goldman Sachs have predicted that economic activity in space will become a multi-trillion-dollar market in the coming decades. Morgan Stanley’s Space Team estimates that the roughly USD 350 billion global space industry could surge to over USD 1 trillion by 2040.

Source: Satellite Industry Association, Morgan Stanley Research, Thomson Reuters. *2040 estimates

Space industry news

Latest research

Formation, Structure, and Detectability of the Geminids Meteoroid Stream

by W. Z. Cukier, J. R. Szalay in The Planetary Science Journal

The Geminids meteoroids light up the sky as they race past Earth each winter, producing one of the most intense meteor showers in our night sky.

Mysteries surrounding the origin of this meteoroid stream have long fascinated scientists because, while most meteor showers are created when a comet emits a tail of ice and dust, the Geminids stem from an asteroid — a chunk of rock that normally does not produce a tail. Until recently, the Geminids had only been studied from Earth. Now, Princeton researchers used observations from NASA’s Parker Solar Probe mission to deduce that it was likely a violent, catastrophic event — such as a high-speed collision with another body or a gaseous explosion — that created the Geminids. The findings narrow down hypotheses about this asteroid’s composition and history that would explain its unconventional behavior.

“Asteroids are like little time capsules for the formation of our solar system,” said Jamey Szalay, research scholar at the Princeton University space physics laboratory and co-author on the paper. “They were formed when our solar system was formed, and understanding their composition gives us another piece of the story.”

Number column density of the Geminids stream in the x–y (top) and y–z (bottom) planes as described by the Basic Model (left), Violent Creation Model (middle), and Cometary Creation Model (right) during the last two years of simulation. Densities are normalized to 1 in each panel independently.

Unlike most known meteor showers that come from comets, which are made of ice and dust, the Geminids stream seems to originate from an asteroid — a chunk of rock and metal — called 3200 Phaethon.

“Most meteoroid streams are formed via a cometary mechanism, it’s unusual that this one seems to be from an asteroid,” said Wolf Cukier, undergraduate class of 2024 at Princeton and lead author on the paper.

“Additionally, the stream is orbiting slightly outside of its parent body when it’s closest to the sun, which isn’t obvious to explain just by looking at it,” he added, referring to a recent study with Parker Solar Probe images of the Geminids led by Karl Battams of the Naval Research Laboratory.

When a comet travels close to the Sun it gets hotter, causing the ice on the surface to release a tail of gas, which in turn drags with it little pieces of ice and dust. This material continues to trail behind the comet as it stays within the Sun’s gravitational pull. Over time, this repeated process fills the orbit of the parent body with material to form a meteoroid stream. But because asteroids like 3200 Phaethon are made of rock and metal, they are not typically affected by the Sun’s heat the way comets are, leaving scientists to wonder what causes the formation of 3200 Phaethon’s stream across the night sky.

“What’s really weird is that we know that 3200 Phaethon is an asteroid, but as it flies by the Sun, it seems to have some kind of temperature-driven activity,” Szalay said. “Most asteroids don’t do that.”

Some researchers have suggested that 3200 Phaethon may actually be a comet that lost all of its snow, leaving only a rocky core resembling an asteroid. But the new Parker Solar Probe data show that although some of 3200 Phaethon’s activity is related to temperature, the creation of the Geminids stream was likely not caused by a cometary mechanism, but by something much more catastrophic.

Time evolution of the orbital elements of the average particle in the primary stream (m > 10−8 g) from the model variants and for (3200) Phaethon.

To learn about the origin of the Geminids stream, Cukier and Szalay used the new Parker Solar Probe data to model three possible formation scenarios, then compared these models to existing models created from Earth-based observations.

“There are what’s called the ‘basic’ model of formation of a meteoroid stream, and the ‘violent’ creation model,” Cukier said. “It’s called ‘basic’ because it’s the most straight-forward thing to model, but really these processes are both violent, just different degrees of violence.”

These different models reflect the chain of events that would transpire according to the laws of physics based on different scenarios. For example, Cukier used the basic model to simulate all of the chunks of material releasing from the asteroid with zero relative velocity — or with no speed or direction relative to 3200 Phaethon — to see what the resulting orbit would look like and compare it to the orbit shown by the Parker Solar Probe probe data.

He then used the violent creation model to simulate the material releasing from the asteroid with a relative velocity of up to one kilometer per hour, as if the pieces were knocked loose by a sudden, violent event. He also simulated the cometary model — the mechanism behind the formation of most meteoroid streams. The resulting simulated orbit matched the least with the way the Geminids orbit actually appears according to the Parker Solar Probe data, so they ruled out this scenario.

In comparing the simulated orbits from each of the models, the team found that the violent models were most consistent with the Parker Solar Probe data, meaning it’s likely that a sudden, violent event — such as a high-speed collision with another body or a gaseous explosion, among other possibilities — created the Geminids stream.

The research builds on the work of Szalay and several colleagues of the Parker Solar Probe mission, built and assembled at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, to assemble a picture of the structure and behavior of the large cloud of dust that swirls through the innermost solar system. They took advantage of Parker’s flight path — an orbit that swings it just millions of miles from the Sun, closer than any spacecraft in history — to get the best direct look at the dusty cloud of grains shed from passing comets and asteroids.

Although the probe doesn’t measure dust particles directly, it can track dust grains in a clever way: as dust grains pelt the spacecraft along its path, the high-velocity impacts create plasma clouds. These impact clouds produce unique signals in electric potential that are picked up by several sensors on the probe’s FIELDS instrument, which is designed to measure the electric and magnetic fields near the Sun.

“The first-of-its-kind data our spacecraft is gathering now will be analyzed for decades to come,” said Nour Raouafi, Parker Solar Probe project scientist at APL. “And it’s exciting to see scientists of all levels and skills digging into it to shed light on the Sun, the solar system and the universe beyond.”

Cukier said his passion for learning about outer space combined with departmental support are what motivated him to pursue this project. After taking a hands-on lab class offered by the Princeton space physics laboratory — where he gained practical experience building space instruments, like those currently sampling the Sun’s environment aboard Parker Solar Probe — and serving as treasurer for the undergraduate astronomy club, he decided he wanted to pursue extracurricular research. He was met with enthusiasm when he reached out to scientists in the Princeton Space Physics group. “Everyone is very supportive of undergraduate research, especially in astrophysics, because it’s really part of the departmental culture,” he said.

“It’s always wonderful when our students like Wolf can contribute so strongly to this sort of space research,” said David McComas, head of the Space Physics group and vice president for the Princeton Plasma Physics Laboratory (PPPL). “Many of us have been in awe of the Geminids meteor displays for years and it is awesome to finally have the data and research to show how they likely formed.”
Cukier said that he’s been drawn to watching the sky since he was a kid. “Planetary science is surprisingly accessible,” he said. “For the Geminids, for instance, anyone can go outside on December 14 this year at night and look up. It’s visible from Princeton, and some of the meteors are really bright. I’d highly recommend seeing it.”

Extreme Relativistic Electron Fluxes in GPS Orbit: Analysis of NS41 BDD‐IIR Data

by Nigel P. Meredith, Thomas E. Cayton, Michael D. Cayton, Richard B. Horne in Space Weather

High-energy ‘relativistic’ electrons — so-called “killer” electrons — are a major source of radiation damage to satellites and so understanding their patterns of activity is crucial. Bursts of charged particles and magnetic fields from the Sun can tear open the Earth’s magnetic field, giving rise to geomagnetic storms. During these events the number of killer electrons in the outer radiation belt can increase by orders of magnitude and become a significant space weather hazard.

Dr Nigel Meredith of BAS led an international team who analysed 20 years of data from a US GPS satellite to determine the 1 in 10, 1 in 50, and 1 in 100-year event levels. A 1 in 100-year event is an event of a size that will be equalled or exceeded on average once every 100 years.

Satellite operators, manufacturers, insurers, and governments need to prepare and mitigate against the risks posed by these electrons. Society is increasingly reliant on satellites for a variety of applications including communication, navigation, Earth observation and defence. As of April 2022, there were 5,465 operational satellites in Earth orbit, and most are exposed to energetic electrons for at least some of their orbit. In 2021, the overall global space economy generated revenues of $386 billion, an increase of four percent compared to the previous year.

Dr Nigel Meredith, space weather scientist and lead author of the study says: “The 1 in 100 year event levels reported in this study are important for industry and government. They serve as benchmarks against which to compare other extreme space weather events and to assess the potential impact of an extreme event.”

Summary plot of the NS41 Burst Detector Dosimeter IIR electron flux at L = 4.5 for April 2010.

These findings are vitally important to the satellite industry as engineers and operators require realistic estimates of the largest electron fluxes encountered in GPS orbit to prepare for the impacts of these extreme events and to improve the resilience of future satellites. The findings are essential for satellite insurers to help them ensure satellite operators are doing all they can to reduce risk and to evaluate realistic disaster scenarios

The difference between the 1 in 10 year and 1 in 100-year event varies depending on the energy of the electrons and the distance from Earth. These differences are largest at the highest energies furthest from the planet, varying between a factor of 3 and 10 for some of the highest electron energies over 35,000 km from the Earth’s surface. Such substantial increases could pose a significant additional risk to satellites operating in this region.

Like weather on our planet, space weather can vary greatly over minutes, days, seasons and the 11-year solar cycle. The researchers found that the majority of these killer electron events occurred during the solar cycle’s declining phases — seen twice during the 20-year period they studied — but the largest event was elsewhere, showing that extreme events can happen at any time.

Strong gravitational lensing by AGNs as a probe of the quasar–host relations in the distant Universe

by Martin Millon, Frédéric Courbin, Aymeric Galan, Dominique Sluse, Xuheng Ding, Malte Tewes, S. G. Djorgovski in Nature Astronomy

A team of researchers from EPFL have found a way to use the phenomenon of strong gravitational lensing to determine with precision — about 3 times more precise than any other technique — the mass of a galaxy containing a quasar, as well as their evolution in cosmic time. Knowing the mass of quasar host galaxies provides insight into the evolution of galaxies in the early universe, for building scenarios of galaxy formation and black hole development.

“The unprecedented precision and accuracy achieved with gravitational lensing provide a new avenue for obtaining robust mass estimates in the distant Universe, where conventional techniques lack precision and are susceptible to biases,” says EPFL astrophysicist Frédéric Courbin, senior author of the study.

“The masses of host galaxies have been measured in the past, but thanks to gravitational lensing, this is the first time that the measurement is so precise in the distant Universe,” explains Martin Millon, lead author of the study and currently at Stanford University on an SNF grant.

A quasar is a luminous manifestation of a supermassive black hole that accretes surrounding matter, sitting at the center of a host galaxy. It is generally difficult to measure how heavy a quasar’s host galaxy is because quasars are very distant objects, and also because they are so bright that they overshine anything within its vicinity. Gravitational lensing allows us to compute the mass of the lensing object. Thanks to Einstein’s theory of gravitation, we know how massive objects in the foreground of the night sky — the gravitational lens — can bend light coming from background objects. Resulting are strange rings of light, that are actually distortions of the background object’s light by the gravitational lens.

Courbin was cycling to the Sauverny Observatory, over a decade ago, when he realized that he could combine the two — quasars and gravitational lensing — to measure the mass of a quasar’s host galaxy. For this, he had to find a quasar in a galaxy that also acts as a gravitational lens.

The Sloan Digital Sky Survey (SDSS) database was a great place to search for gravitational lensing quasars candidates, but to be sure, Courbin had to see the lensing rings. In 2010, he and colleagues commissioned time on the Hubble Space Telescope to observe 4 candidates of which 3 showed lensing. Of the three, one stood out due to its characteristic gravitational lensing rings: SDSS J0919+2720. The HST image of SDSS J0919+2720 shows two bright objects in the foreground that each act as a gravitational lens, “probably two galaxies in the process of merging,” explains Courbin. The one on the left is a bright quasar, within a host galaxy too dim to be observed. The bright object on the right is another galaxy, the main gravitational lens. A faint object on the far left is a companion galaxy. The characteristic rings are deformed light coming from a background galaxy.

By carefully analyzing the gravitationally lensed rings in SDSS J0919+2720, it is possible to determine the mass of the two bright objects… in principle. Disentangling the masses of the various objects would have been impossible without the recent development of a wavelet-based lens modeling technique by co-author Aymeric Galan, currently at the Technical University of Münich (TUM), also on an SNF grant.

“One of the biggest challenges in astrophysics is to understand how a supermassive black hole forms,” explains Galan. “Knowing its mass, how it compares to its host galaxy and how it evolves through cosmic times, are what allows us to discard or validate certain formation theories.”
“In the local Universe, we observe that the most massive galaxies also host the most massive black holes at their center. This could suggest that the growth of galaxies is regulated by the amount of energy radiated by their central black hole and injected into the galaxy. However, to test this theory, we still need to study these interactions not only locally but also in the distant Universe,” explains Millon.

Gravitational lensing events are very rare, with one galaxy in a thousand unveiling the phenomenon. Since quasars are seen in about one every thousand galaxies a quasar acting as a lens is one in a million. The scientists expect to detect hundreds of these lensing quasars with the ESA-NASA mission Euclid, to be launched this summer with a Falcon-9 SpaceX rocket.

Slow evolution of Europa’s interior: metamorphic ocean origin, delayed metallic core formation, and limited seafloor volcanism

by Kevin T. Trinh, Carver J. Bierson, Joseph G. O’Rourke in Science Advances

Jupiter’s moon, Europa, is slightly smaller than Earth’s Moon and is one of the most promising places to search for alien life.

Amid the Jovian system, Europa is of particular interest to scientists because of the strong evidence for nutrients, water and energy to potentially provide a habitable environment for some form of life beyond Earth. In addition, Europa is believed to be made up into four layers (from surface to center): an ice shell, salt water ocean, rocky mantle, and metallic core.

Like Earth, Europa’s ocean touches the rocky seafloor, which may allow for rock-water chemistry favorable for life. Some scientists also believe that the seafloor may host volcanoes, which can provide more energy and nutrients for a potential biosphere. ASU scientists Kevin Trinh, Carver Bierson and Joe O’Rourke of the School of Earth and Space Exploration investigated the consequences of Europa forming with low initial temperatures, using computer code that Trinh wrote.

Europa may have a metamorphic origin for the ocean. While some scientists speculated this, Trinh and his team show that if Europa indeed formed from hydrated rocks (i.e., rocks have hydrogen and oxygen), then enough of Europa’s interior should get hot enough to release water directly from the hydrated rocks to form the ocean and ice shell.

“The origin of Europa’s ocean is important because the moon’s potential to support life ultimately depends on the chemical ingredients and physical conditions during the ocean formation process,” said Kevin Trinh, graduate associate at ASU’s School Of Earth and Space Exploration.

Unlike large rocky planets, Europa’s accretional temperatures were probably too low for metallic core formation.

Many scientists studying this icy moon assumed that Europa formed with a metallic core during or shortly after accretion. This ASU study contradicts that prediction, instead arguing that Europa may not have started forming its metallic core until billions of years after accretion (if it happened at all).

“For most worlds in the solar system we tend to think of their internal structure as being set shortly after they finish forming. This work is very exciting because it reframes Europa as a world whose interior has been slowly evolving over its whole lifetime. This opens doors for future research to understand how these changes might be observed in the Europa we see today,” said Carver Bierson, postdoctoral research scholar at ASU’s School Of Earth and Space Exploration.

The existence of a metallic core is deeply tied to Europa’s internal heat, which may also be used to drive seafloor volcanism and contribute to a habitable seafloor environment. However, it is unclear whether Europa generated enough heat to form such a core. Trinh’s code calculates how heat is generated and distributed throughout a moon, which uses the same governing equations that many geodynamicists used for decades. The team’s novel result, however, comes from challenging the assumptions common to Europa modeling: A small moon like Europa could form as a cold mixture of ice, rock, and metal.

However, all of these processes require a hot interior. A small moon like Europa (~1% of Earth’s mass) may not have enough energy to trigger or sustain Earth-like processes — metallic core formation, seafloor volcanism, and ongoing rock-water geochemistry — which implies that Europa’s habitable potential is uncertain. The exact time at which Europa formed determines how much heat is available from the radioactive decay of a short-lived isotope of aluminum. Tidal heating (from gravitational interactions with Jupiter and other moons) also governs how quickly Europa’s interior separates into distinct layers.

This study implies that there may be limited hydrothermal activity and seafloor volcanism at Europa, which may hinder habitability. However, confident predictions require more data.

A 5.3-min-period pulsing white dwarf in a binary detected from radio to X-rays

by Ingrid Pelisoli, T. R. Marsh, David A. H. Buckley,et al in Nature Astronomy

The discovery of a rare type of white dwarf star system provides new understanding into stellar evolution.

White dwarfs are small, dense stars typically the size of a planet. They are formed when a star of low mass has burnt all its fuel, losing its outer layers. Sometimes referred to as “stellar fossils,” they offer insight into different aspects of star formation and evolution.

A rare type of white dwarf pulsar has been discovered for the second time only, in research led by the University of Warwick. White dwarf pulsars include a rapidly spinning, burnt-out stellar remnant called a white dwarf, which lashes its neighbour — a red dwarf — with powerful beams of electrical particles and radiation, causing the entire system to brighten and fade dramatically over regular intervals. This is owing to strong magnetic fields, but scientists are unsure what causes them.

A key theory which explains the strong magnetic fields is the “dynamo model” — that white dwarfs have dynamos (electrical generators) in their core, as does the Earth, but much more powerful. But for this theory to be tested, scientists needed to search for other white dwarf pulsars to see if their predictions held true.

773 light years away from Earth and spinning 300 times faster than our planet, the white dwarf pulsar has a size similar to the Earth, but a mass at least as large as the Sun. This means that a teaspoon of white dwarf material would weigh around 15 tons. White dwarfs begin their lives at extremely hot temperatures before cooling down over billions of years, and the low temperature of J1912−4410 points to an advanced age.

Constraints from the binary mass function.

Dr Ingrid Pelisoli, University of Warwick’s Department of Physics, said: “The origin of magnetic fields is a big open question in many fields of astronomy, and this is particularly true for white dwarf stars. The magnetic fields in white dwarfs can be more than a million times stronger than the magnetic field of the Sun, and the dynamo model helps to explain why. The discovery of J1912−4410 provided a critical step forward in this field.
“We used data from a few different surveys to find candidates, focusing on systems that had similar characteristics to AR Sco. We followed up any candidates with ULTRACAM, which detects the very fast light variations expected of white dwarf pulsars. After observing a couple dozen candidates, we found one that showed very similar light variations to AR Sco. Our follow-up campaign with other telescopes revealed that every five minutes or so, this system sent a radio and X-ray signal in our direction.

This confirmed that there are more white dwarf pulsars out there, as predicted by previous models. There were other predictions made by the dynamo model, which were confirmed by the discovery of J1912−4410. Due to their old age, the white dwarfs in the pulsar system should be cool. Their companions should be close enough that the gravitational pull of the white dwarf was in the past strong enough to capture mass from the companion, and this causes them to be fast spinning. All of those predictions hold for the new pulsar found: the white dwarf is cooler than 13,000K, spins on its axis once every five minutes, and the gravitational pull of the white dwarf has a strong effect in the companion.

“This research is an excellent demonstration that science works — we can make predictions and put them to test, and that is how any science progresses.”

Impacts of spaceflight experience on human brain structure

by Heather R. McGregor, Kathleen E. Hupfeld, et al in Scientific Reports

As we enter a new era in space travel, a study looking at how the human brain reacts to traveling outside Earth’s gravity suggests frequent flyers should wait three years after longer missions to allow the physiological changes in their brains to reset.

Researchers studied brain scans of 30 astronauts from before and after space travel. Their findings reveal that the brain’s ventricles expand significantly in those who completed longer missions of at least six months, and that less than three years may not provide enough time for the ventricles to fully recover. Ventricles are cavities in the brain filled with cerebrospinal fluid, which provides protection, nourishment and waste removal to the brain. Mechanisms in the human body effectively distribute fluids throughout the body, but in the absence of gravity, the fluid shifts upward, pushing the brain higher within the skull and causing the ventricles to expand.

“We found that the more time people spent in space, the larger their ventricles became,” said Rachael Seidler, a professor of applied physiology and kinesiology at the University of Florida and an author of the study. “Many astronauts travel to space more than one time, and our study shows it takes about three years between flights for the ventricles to fully recover.”

Pre- to post-flight FW volume changes associated with previous number of missions.

Seidler, a member of the Norman Fixel Institute for Neurological Diseases at UF Health, said based on studies so far, ventricular expansion is the most enduring change seen in the brain resulting from spaceflight.

“We don’t yet know for sure what the long-term consequences of this is on the health and behavioral health of space travelers,” she said, “so allowing the brain time to recover seems like a good idea.”

Of the 30 astronauts studied, eight traveled on two-week missions, 18 were on six-month missions, and four were in space for approximately one year. The ventricular enlargement tapered off after six months, the study’s authors reported.

“The biggest jump comes when you go from two weeks to six months in space,” Seidler said. “There is no measurable change in the ventricles’ volume after only two weeks.”

With increased interest in space tourism in recent years, this is good news, as shorter space junkets appear to cause little physiological changes to the brain, she said. While researchers cannot yet study astronauts who have been in space much longer than a year, Seidler said it’s also good news that the expansion of the brain’s ventricles levels off after about six months.

“We were happy to see that the changes don’t increase exponentially, considering we will eventually have people in space for longer periods,” she said.

Ultra-light axions and the S 8 tension: joint constraints from the cosmic microwave background and galaxy clustering

by Keir K. Rogers, Renée Hložek, Alex Laguë, Mikhail M. Ivanov, Oliver H.E. Philcox, Giovanni Cabass, Kazuyuki Akitsu, David J.E. Marsh in Journal of Cosmology and Astroparticle Physics

In a study, researchers at the University of Toronto reveal a theoretical breakthrough that may explain both the nature of invisible dark matter and the large-scale structure of the universe known as the cosmic web. The result establishes a new link between these two longstanding problems in astronomy, opening new possibilities for understanding the cosmos.

The research suggests that the “clumpiness problem,” which centres on the unexpectedly even distribution of matter on large scales throughout the cosmos, may be a sign that dark matter is composed of hypothetical, ultra-light particles called axions. The implications of proving the existence of hard-to-detect axions extend beyond understanding dark matter and could address fundamental questions about the nature of the universe itself.

“If confirmed with future telescope observations and lab experiments, finding axion dark matter would be one of the most significant discoveries of this century,” says lead author Keir Rogers, Dunlap Fellow at the Dunlap Institute for Astronomy & Astrophysics in the Faculty of Arts & Science at the University of Toronto. “At the same time, our results suggest an explanation for why the universe is less clumpy than we thought, an observation that has become increasingly clear over the last decade or so, and currently leaves our theory of the universe uncertain.”

Dark matter, comprising 85 percent of the universe’s mass, is invisible because it does not interact with light. Scientists study its gravitational effects on visible matter to understand how it is distributed in the universe. A leading theory proposes that dark matter is made of axions, described in quantum mechanics as “fuzzy” due to their wave-like behaviour. Unlike discrete point-like particles, axions can have wavelengths larger than entire galaxies. This fuzziness influences the formation and distribution of dark matter, potentially explaining why the universe is less clumpy than predicted in a universe without axions.

This lack of clumpiness has been observed in large galaxy surveys, challenging the other prevailing theory that dark matter consists only of heavy, weakly interacting sub-atomic particles called WIMPs. Despite experiments like the Large Hadron Collider, no evidence supporting the existence of WIMPs has been found.

“In science, it’s when ideas break down that new discoveries are made and age-old problems are solved,” says Rogers.

For the study, the research team — led by Rogers and including members of associate professor Renée Hložek’s research group at the Dunlap Institute, as well as from the University of Pennsylvania, Institute for Advanced Study, Columbia University and King’s College London — analyzed observations of relic light from the Big Bang, known as the Cosmic Microwave Background (CMB), obtained from the Planck 2018, Atacama Cosmology Telescope and South Pole Telescope surveys. The researchers compared these CMB data with galaxy clustering data from the Baryon Oscillation Spectroscopic Survey (BOSS), which maps the positions of approximately a million galaxies in the nearby universe. By studying the distribution of galaxies, which mirrors the behavior of dark matter under gravitational forces, they measured fluctuations in the amount of matter throughout the universe and confirmed its reduced clumpiness compared to predictions.

The researchers then conducted computer simulations to predict the appearance of relic light and the distribution of galaxies in a universe with long dark matter waves. These calculations aligned with CMB data from the Big Bang and galaxy clustering data, supporting the notion that fuzzy axions could account for the clumpiness problem.

Future research will involve large-scale surveys to map millions of galaxies and provide precise measurements of clumpiness, including observations over the next decade with the Rubin Observatory. The researchers hope to compare their theory to direct observations of dark matter through gravitational lensing, an effect where dark matter clumpiness is measured by how much it bends the light from distant galaxies, akin to a giant magnifying glass. They also plan to investigate how galaxies expel gas into space and how this affects the dark matter distribution to further confirm their results.

Understanding the nature of dark matter is one of the most pressing fundamental questions and key to understanding the origin and future of the universe. Presently, scientists do not have a single theory that simultaneously explains gravity and quantum mechanics — a theory of everything. The most popular theory of everything over the last few decades is string theory, which posits another level below the quantum level, where everything is made of string-like excitations of energy. According to Rogers, detecting a fuzzy axion particle could be a hint that the string theory of everything is correct.

“We have the tools now that could enable us to finally understand something experimentally about the century-old mystery of dark matter, even in the next decade or so — and that could give us hints to answers about even bigger theoretical questions,” says Rogers. “The hope is that the puzzling elements of the universe are solvable.”

Vanadium oxide and a sharp onset of cold-trapping on a giant exoplanet

by Stefan Pelletier, Björn Benneke, Mohamad Ali-Dib, et al in Nature

An international team led by Stefan Pelletier, a Ph.D. student at Université de Montréal’s Trottier Institute for Research on Exoplanets announced today having made a detailed study of the extremely hot giant exoplanet WASP-76 b.

Using the MAROON-X instrument on the Gemini-North Telescope, the team was able to identify and measure the abundance of 11 chemical elements in the atmosphere of the planet. Those include rock-forming elements whose abundances are not even known for giant planets in the Solar System such as Jupiter or Saturn.

“Truly rare are the times when an exoplanet hundreds of light years away can teach us something that would otherwise likely be impossible to know about our own Solar System,” said Pelletier. “This is the case with this study.”

WASP-76 b is a strange world. It reaches extreme temperatures because it is very close to its parent star, a massive star 634 light-years away in the constellation of Pisces: approximately 12 times closer than Mercury is to the Sun. With a mass similar to that of Jupiter, but almost six times bigger by volume, it is quite “puffy.” Since its discovery by the Wide Angle Search for Planets (WASP) program in 2013, many teams have studied it and identified various elements in its atmosphere. Notably, in a study also published in 2020, a team found an iron signature and hypothesised that there could be iron rain on the planet. Aware of these studies, Pelletier became motivated to obtain new, independent observations of WASP-76 b using the MAROON-X high-resolution optical spectrograph on the Gemini-North 8-metre Telescope in Hawai’i, part of the International Gemini Observatory, operated by NSF’s NOIRLab.

“We recognized that the powerful new MAROON-X spectrograph would enable us to study the chemical composition of WASP-76 b with a level of detail unprecedented for any giant planet,” says UdeM astronomy professor Björn Benneke, co-author of the study and Stefan Pelletier’s PhD research supervisor.

Independent confirmation of the VO detection on WASP-76b.

Within the Sun, the abundances of almost all elements in the periodic table are known with great accuracy. In the giant planets in our Solar System, however, that’s true for only a handful of elements, whose compositions remain poorly constrained. And this has hampered understanding of the mechanisms governing the formation of these planets.

As it is so close to its star, WASP-76 b has a temperature well above 2000°C. At these degrees, many elements that would normally form rocks here on Earth (like magnesium and iron) are vaporised and present in gaseous form in the upper atmosphere. Studying this peculiar planet enables unprecedented insight into the presence and abundance of rock-forming elements in giant planets, since in colder giant planets like Jupiter these elements are lower in the atmosphere and impossible to detect.

The abundance of many elements measured by Pelletier and his team in the exoplanet’s atmosphere — such as manganese, chromium, magnesium, vanadium, barium and calcium — matches those of its host star as well as of our own Sun very closely. These abundances are not random: they are the direct product of the Big Bang, followed by billions of years of stellar nucleosynthesis, so scientists measure roughly the same composition in all stars. It is, however, different from the composition of rocky planets like Earth, which are formed in a more complex manner. The results of this new study indicate that giant planets could maintain an overall composition that reflects that of the protoplanetary disc from which they formed. However, other elements were depleted in the planet compared to the star — a result Pelletier found particularly interesting.

“These elements that appear to be missing in WASP-76 b’s atmosphere are precisely those that require higher temperatures to vaporise, like titanium and aluminium, “ he said. “Meanwhile, the ones that matched our predictions, like manganese, vanadium, or calcium, all vaporise at slightly lower temperatures.”

The discovery team’s interpretation is that the observed composition of the upper atmospheres of giant planets can be extremely sensitive to temperature. Depending on an element’s temperature of condensation, it will be in gas form and present in the upper part of the atmosphere, or condense into liquid form where it will sink to deeper layers. When in gas form, it plays an important role in absorbing light and can be seen in astronomers’ observations. When condensed, it cannot be detected by astronomers and becomes completely absent from their observations.

“If confirmed, this finding would mean that two giant exoplanets that have slightly different temperatures from one another could have very different atmospheres, “ said Pelletier. “Kind of like two pots of water, one at -1°C that is frozen, and one that is at +1°C that is liquid. For example, calcium is observed on WASP-76 b, but it may not be on a slightly colder planet.”

Another interesting finding by Pelletier’s team is the detection of a molecule called vanadium oxide. This is the first time it has been unambiguously detected on an exoplanet, and is of great interest to astronomers because they know it can have a big impact on hot giant planets.

“This molecule plays a similar role to ozone in Earth’s atmosphere: it is extremely efficient at heating up the upper atmosphere,” explained Pelletier. “This causes the temperatures to increase as a function of altitude, instead of decreasing as is typically seen on colder planets.”

One element, nickel, is clearly more abundant in the exoplanet’s atmosphere than what the astronomers were expecting. Many hypotheses could explain that; one is that WASP-76 b could have accreted material from a planet similar to Mercury. In our Solar System, the small rocky planet is enriched with metals like nickel because of how it was formed.

Pelletier’s team also found that the asymmetry in iron absorption between the east and west hemispheres of WASP-76 b reported in previous studies is similarly present for many other elements. This means the underlying phenomenon causing this is thus probably a global process such as a difference in temperature or clouds being present on one side of the planet but not the other, rather than being the result of condensation into liquid form as was previously suggested.

Obscured AGN enhancement in galaxy pairs at cosmic noon: evidence from a probabilistic treatment of photometric redshifts

by Sean L Dougherty, C M Harrison, Dale D Kocevski, D J Rosario in Monthly Notices of the Royal Astronomical Society

Astronomers have found that supermassive black holes obscured by dust are more likely to grow and release tremendous amounts of energy when they are inside galaxies that are expected to collide with a neighbouring galaxy.

Galaxies, including our own Milky Way, contain supermassive black holes at their centres. They have masses equivalent to millions, or even billions, times that of our Sun. These black holes grow by ‘eating’ gas that falls on to them. However, what drives the gas close enough to the black holes for this to happen is an ongoing mystery. One possibility is that when galaxies are close enough together, they are likely to be gravitationally pulled towards each other and ‘merge’ into one larger galaxy.

In the final stages of its journey into a black hole, gas lights up and produces a huge amount of energy. This energy is typically detected using visible light or X-rays. However, the astronomers conducting this study were only able to detect the growing black holes using infrared light. The team made use of data from many different telescopes, including the Hubble Space Telescope and infrared Spitzer Space Telescope.

The researchers developed a new technique to determine how likely it is that two galaxies are very close together and are expected to collide in the future. They applied this new method to hundreds of thousands of galaxies in the distant universe (looking at galaxies formed 2 to 6 billion years after the Big Bang) in an attempt to better understand the so-called ‘cosmic noon’, a time when most of the Universe’s galaxy and black hole growth is expected to have taken place.

An artist’s impression of a dusty region around a black hole. The most dust-enshrouded black holes can completely stop X-rays and visible light escaping, but the same dust can be heated by a growing black hole and will glow brightly at infrared wavelengths. Credit: ESA/NASA, the AVO project and Paolo Padovani

Understanding how black holes grew during this time is fundamental in modern day galactic research, especially as it may give us an insight into the supermassive black hole situated inside the Milky Way, and how our galaxy evolved over time. As they are so far away, only a small number of cosmic noon galaxies meet the required criteria to get precise measurements of their distances. This makes it very difficult to know with high precision if any two galaxies are very close to each other.

This study presents a new statistical method to overcome the previous limitations of measuring accurate distances of galaxies and supermassive black holes at cosmic noon. It applies a statistical approach to determine galaxy distances using images at different wavelengths and removes the need for spectroscopic distance measurements for individual galaxies. Data arriving from the James Webb Space Telescope over the coming years is expected to revolutionise studies in the infrared and reveal even more secrets about how these dusty black holes grow.

Sean Dougherty, postgraduate student at Newcastle University and lead author of the paper, says, “Our novel approach looks at hundreds of thousands of distant galaxies with a statistical approach and asks how likely any two galaxies are to be close together and so likely to be on a collision course.”

Dr Chris Harrison, co-author of the study, “These supermassive black holes are very challenging to find because the X-ray light, which astronomers have typically used to find these growing black holes, is blocked, and not detected by our telescopes. But these same black holes can be found using infrared light, which is produced by the hot dust surrounding them.”

He adds, “The difficulty in finding these black holes and in establishing precise distance measurements explains why this result has previously been challenging to pin down these distant ‘cosmic noon’ galaxies. With JWST we are expecting to find many more of these hidden growing black holes. JWST will be far better at finding them, therefore we will have many more to study, including ones that are the most difficult to find. From there, we can do more to understand the dust that surrounds them, and find out how many are hidden in distant galaxies.”

VISIONS: the VISTA Star Formation Atlas

by Stefan Meingast, João Alves, Hervé Bouy, et al in Astronomy & Astrophysics

Using ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA), astronomers have created a vast infrared atlas of five nearby stellar nurseries by piecing together more than one million images. These large mosaics reveal young stars in the making, embedded in thick clouds of dust. Thanks to these observations, astronomers have a unique tool with which to decipher the complex puzzle of stellar birth.

“In these images we can detect even the faintest sources of light, like stars far less massive than the Sun, revealing objects that no one has ever seen before,” says Stefan Meingast, an astronomer at the University of Vienna in Austria and lead author of the new study published today in Astronomy & Astrophysics. “This will allow us to understand the processes that transform gas and dust into stars.”

Stars form when clouds of gas and dust collapse under their own gravity, but the details of how this happens are not fully understood. How many stars are born out of a cloud? How massive are they? How many stars will also have planets?

To answer these questions, Meingast’s team surveyed five nearby star-forming regions with the VISTA telescope at ESO’s Paranal Observatory in Chile. Using VISTA’s infrared camera VIRCAM, the team captured light coming from deep inside the clouds of dust. “The dust obscures these young stars from our view, making them virtually invisible to our eyes. Only at infrared wavelengths can we look deep into these clouds, studying the stars in the making,” explains Alena Rottensteiner, a PhD student also at the University of Vienna and co-author of the study.

Ongoing star formation processes as observed by VIRCAM/VISTA in the VISIONS program, using color images assembled from the near-infrared passbands J, H, and KS. The top panel shows L1688 in the Ophiuchus star-forming complex, depicting several dozen prominent young stellar objects located within one of the closest embedded clusters to Earth.

The survey, called VISIONS, observed star-forming regions in the constellations of Orion, Ophiuchus, Chamaeleon, Corona Australis and Lupus. These regions are less than 1500 light-years away and so large that they span a huge area in the sky. The diameter of VIRCAM’s field of view is as wide as three full Moons, which makes it uniquely suited to map these immensely big regions.

The team obtained more than one million images over a period of five years. The individual images were then pieced together into the large mosaics released here, revealing vast cosmic landscapes. These detailed panoramas feature dark patches of dust, glowing clouds, newly-born stars and the distant background stars of the Milky Way.

Since the same areas were observed repeatedly, the VISIONS data will also allow astronomers to study how young stars move. “With VISIONS we monitor these baby stars over several years, allowing us to measure their motion and learn how they leave their parent clouds,” explains João Alves, an astronomer at the University of Vienna and Principal Investigator of VISIONS. This is not an easy feat, as the apparent shift of these stars as seen from Earth is as small as the width of a human hair seen from 10 kilometres away. These measurements of stellar motions complement those obtained by the European Space Agency’s Gaia mission at visible wavelengths, where young stars are hidden by thick veils of dust.

The VISIONS atlas will keep astronomers busy for years to come. “There is tremendous long-lasting value for the astronomical community here, which is why ESO steers Public Surveys like VISIONS,” says Monika Petr-Gotzens, an astronomer at ESO in Garching, Germany, and co-author of this study. Moreover, VISIONS will set the groundwork for future observations with other telescopes such as ESO’s Extremely Large Telescope (ELT), currently under construction in Chile and set to start operating later this decade. “The ELT will allow us to zoom into specific regions with unprecedented detail, giving us a never-seen-before close-up view of individual stars that are currently forming there,” concludes Meingast.