ST/ Largest, most detailed model of the early universe developed

Paradigm

Follow

Published in

Paradigm

35 min readMar 29, 2022

--

Space biweekly vol.48, 16th March — 29th March

TL;DR

Named after a goddess of the dawn, Thesan is a new universe simulation that models the first billion years of the universe with the highest resolution, over the largest volume, to date. The simulation helps explain how radiation shaped the early universe.
The further we move away from a heat source, the cooler the air gets. Bizarrely, the same can’t be said for the surface of the Sun, but scientists may have just explained a key part of why.
White dwarfs were once normal stars similar to the Sun but then collapsed after exhausting all their fuel. These interstellar remnants have historically been difficult to study. However, a recent study reveals new information about the movement patterns of these puzzling stars.
Astronomy’s newest mystery objects, odd radio circles or ORCs, have been pulled into sharp focus by an international team of astronomers using the world’s most capable radio telescopes.
Scientists studying V Hydrae (V Hya) have witnessed the star’s mysterious death throes in unprecedented detail. The team discovered six slowly-expanding rings and two hourglass-shaped structures caused by the high-speed ejection of matter out into space.
Astronomers identified a nearby star whose sunspot cycles appear to have stopped. Studying this star might help explain the unusual period from the mid 1600s to the early 1700s when our Sun paused its sunspot cycles.
Researchers have built the world’s first physics-based computer simulation of oxygen transport on Europa, finding that it’s possible for oxygen to drain through the moon’s icy shell and into its ocean of liquid water by hitching a ride on salt water under the moon’s ‘chaos terrains.’ The results show that not only is the transport possible, but that the amount of oxygen brought into Europa’s ocean could be on a par with the quantity of oxygen in Earth’s oceans today.
The Hayabusa2 mission has recently uncovered information on the physical characteristics of the asteroid ‘Ryugu,’ which, according to the conventional theory, forms from a collision between larger asteroids. Now, a study by scientists from Japan suggests that Ryugu is, in fact, an extinct comet. With a simple physical model that fits currently available observations, the study provides a better understanding of comets, asteroids, and the evolution of our solar system.
Researchers propose using the variations in distance between the Earth and the Moon, which can be measured with a precision of less than a centimeter, as a new gravitational wave detector within a frequency range that current devices cannot detect. The research could pave the way for the detection of signals from the early universe.
Nearly 15 years after the discovery of fast radio bursts (FRBs), the origin of the millisecond-long, deep-space cosmic explosions remains a mystery. That may soon change, thanks to the work of an international team of scientists which tracked hundreds of the bursts from five different sources and found clues in FRB polarization patterns that may reveal their origin.
Upcoming industry events. 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

The thesan project: Lyman-α emission and transmission during the Epoch of Reionization

by A Smith, R Kannan, E Garaldi, M Vogelsberger, R Pakmor, V Springel, L Hernquist in Monthly Notices of the Royal Astronomical Society

It all started around 13.8 billion years ago with a big, cosmological “bang” that brought the universe suddenly and spectacularly into existence. Shortly after, the infant universe cooled dramatically and went completely dark.

Then, within a couple hundred million years after the Big Bang, the universe woke up, as gravity gathered matter into the first stars and galaxies. Light from these first stars turned the surrounding gas into a hot, ionized plasma — a crucial transformation known as cosmic reionization that propelled the universe into the complex structure that we see today.

Now, scientists can get a detailed view of how the universe may have unfolded during this pivotal period with a new simulation, known as Thesan, developed by scientists at MIT, Harvard University, and the Max Planck Institute for Astrophysics.

Evolution of simulated properties in the main Thesan run. Time progresses from left to right. The dark matter (top panel) collapse in the cosmic web structure, composed of clumps (haloes) connected by filaments, and the gas (second panel from the top) follows, collapsing to create galaxies. These produce ionising photons that drive cosmic reionization (third panel from the top), heating up the gas in the process (bottom panel).

Named after the Etruscan goddess of the dawn, Thesan is designed to simulate the “cosmic dawn,” and specifically cosmic reionization, a period which has been challenging to reconstruct, as it involves immensely complicated, chaotic interactions, including those between gravity, gas, and radiation. The Thesan simulation resolves these interactions with the highest detail and over the largest volume of any previous simulation. It does so by combining a realistic model of galaxy formation with a new algorithm that tracks how light interacts with gas, along with a model for cosmic dust.

Upper left: Intrinsic Ly𝛼 surface brightness for a galaxy of mass 𝑀halo 1011 M at 𝑧 = 6. Upper right: False colour rendering of the escaped Ly𝛼 emission based on synthetic integral field unit (IFU) data generated with the colt Monte Carlo radiative transfer code. The spectroscopic information is blended from blue–green to yellow–red with the image opacity encoding the surface brightness. The rest-frame is defined by the frequency centroid of the intrinsic line profile shown in the left panel, while the emergent spectra in the remaining panels serve as velocity offset colour maps. Lower left: An alternative emission model that artificially reddens the initial frequency of unresolved Hii regions to explore the impact of local feedback-induced outflows on ISM scales. Lower right: An alternative transport model that incorporates wind particles to explore the role of galactic winds in shaping line profiles on CGM scales.

With Thesan, the researchers can simulate a cubic volume of the universe spanning 300 million light years across. They run the simulation forward in time to track the first appearance and evolution of hundreds of thousands of galaxies within this space, beginning around 400,000 years after the Big Bang, and through the first billion years.

So far, the simulations align with what few observations astronomers have of the early universe. As more observations are made of this period, for instance with the newly launched James Webb Space Telescope, Thesan may help to place such observations in cosmic context. For now, the simulations are starting to shed light on certain processes, such as how far light can travel in the early universe, and which galaxies were responsible for reionization.

“Thesan acts as a bridge to the early universe,” says Aaron Smith, a NASA Einstein Fellow in MIT’s Kavli Institute for Astrophysics and Space Research. “It is intended to serve as an ideal simulation counterpart for upcoming observational facilities, which are poised to fundamentally alter our understanding of the cosmos.”

Smith and Mark Vogelsberger, associate professor of physics at MIT, Rahul Kannan of the Harvard-Smithsonian Center for Astrophysics, and Enrico Garaldi at Max Planck have introduced the Thesan simulation through three papers.

Left: Position and velocity offsets between the Ly𝛼 luminosity and mass centroids for each halo at 𝑧 = 6. Galaxies with higher SFRs (denoted by colour) can differ by up to 10 kpc and 100 km s􀀀1, affecting the systemic position 𝒓 𝛼 and velocity 𝒗𝛼 for IGM transmission. Right: One-dimensional velocity dispersions with Ly𝛼 luminosity (𝜎𝛼) and mass (𝜎halo) weights for each halo. For reference, we include a line of equality, median halo counts, and bin-averaged colours showing the maximum of the rotation curve 𝑉max. The intrinsic Ly𝛼 line widths before resonant scattering are up to 2 times narrower than would be inferred by 𝜎halo or 𝑉max.

In the earliest stages of cosmic reionization, the universe was a dark and homogenous space. For physicists, the cosmic evolution during these early “dark ages” is relatively simple to calculate.

“In principle you could work this out with pen and paper,” Smith says. “But at some point gravity starts to pull and collapse matter together, at first slowly, but then so quickly that calculations become too complicated, and we have to do a full simulation.”

To fully simulate cosmic reionization, the team sought to include as many major ingredients of the early universe as possible. They started off with a successful model of galaxy formation that their groups previously developed, called Illustris-TNG, which has been shown to accurately simulate the properties and populations of evolving galaxies. They then developed a new code to incorporate how the light from galaxies and stars interact with and reionize the surrounding gas — an extremely complex process that other simulations have not been able to accurately reproduce at large scale.

“Thesan follows how the light from these first galaxies interacts with the gas over the first billion years and transforms the universe from neutral to ionized,” Kannan says. “This way, we automatically follow the reionization process as it unfolds.”

Finally, the team included a preliminary model of cosmic dust — another feature that is unique to such simulations of the early universe. This early model aims to describe how tiny grains of material influence the formation of galaxies in the early, sparse universe.

Relative probability distributions for a given integrated (T int IGM, bottom panels) and maximum (T max IGM , top panels) band transmission at each redshift (different colour curves) considering all haloes.

With the simulation’s ingredients in place, the team set its initial conditions for around 400,000 years after the Big Bang, based on precision measurements of relic light from the Big Bang. They then evolved these conditions forward in time to simulate a patch of the universe, using the SuperMUC-NG machine — one of the largest supercomputers in the world — which simultaneously harnessed 60,000 computing cores to carry out Thesan’s calculations over an equivalent of 30 million CPU hours (an effort that would have taken 3,500 years to run on a single desktop). The simulations have produced the most detailed view of cosmic reionization, across the largest volume of space, of any existing simulation. While some simulations model across large distances, they do so at relatively low resolution, while other, more detailed simulations do not span large volumes.

“We are bridging these two approaches: We have both large volume and high resolution,” Vogelsberger emphasizes.

Early analyses of the simulations suggest that towards the end of cosmic reionization, the distance light was able to travel increased more dramatically than scientists had previously assumed.

“Thesan found that light doesn’t travel large distances early in the universe,” Kannan says. “In fact, this distance is very small, and only becomes large at the very end of reionization, increasing by a factor of 10 over just a few hundred million years.”

Example angular distributions of the IGM transmission at a velocity offset of 200 km s1, T 200 IGM .

The researchers also see hints of the type of galaxies responsible for driving reionization. A galaxy’s mass appears to influence reionization, though the team says more observations, taken by James Webb and other observatories, will help to pin down these predominant galaxies.

“There are a lot of moving parts in [modeling cosmic reionization],” Vogelsberger concludes. “When we can put this all together in some kind of machinery and start running it and it produces a dynamic universe, that’s for all of us a pretty rewarding moment.”

High-frequency heating of the solar wind triggered by low-frequency turbulence

by Squire, J., Meyrand, R., Kunz, M.W. et al. in Nature Astronomy

The further we move away from a heat source, the cooler the air gets. Bizarrely, the same can’t be said for the Sun, but University of Otago scientists may have just explained a key part of why.

Study lead Dr Jonathan Squire, of the Department of Physics, says the surface of the Sun starts at 6000 degree C, but over a short distance of only a few hundred kilometers, it suddenly heats up to more than a million degrees, becoming its atmosphere, or corona.

Electric field noise and numerical cooling.

“This is so hot that the gas escapes the Sun’s gravity as ‘solar wind’, and flies into space, smashing into Earth and other planets. “We know from measurements and theory that the sudden temperature jump is related to magnetic fields which thread out of the Sun’s surface. But, exactly how these work to heat the gas is not well understood — this is known as the Coronal Heating Problem.
“Astrophysicists have several different ideas about how the magnetic-field energy could be converted into heat to explain the heating, but most have difficulty explaining some aspect of observations,” he says.

Dr Squire and co-author Dr Romain Meyrand have been working with scientists at Princeton University and the University of Oxford and found two previous theories can be merged into one to solve a key piece of the ‘problem’.

The popular theories are based on heating caused by turbulence, and heating caused by a type of magnetic wave called ion cyclotron waves.

“Both, however, have some problem — turbulence struggles to explain why Hydrogen, Helium and Oxygen in the gas become as hot as they do, while electrons remain surprisingly cold; while the magnetic waves theory could explain this feature, there doesn’t seem to be enough of the waves coming off the Sun’s surface to heat up the gas,” Dr Meyrand says.

The group used six-dimensional supercomputer simulations of the coronal gas to show how these two theories are actually part of the same process, linked together by a bizarre effect called the ‘helicity barrier’. This intriguing occurrence was discovered in an earlier Otago study, led by Dr Meyrand.

“If we imagine plasma heating as occurring a bit like water flowing down a hill, with electrons heated right at the bottom, then the helicity barrier acts like a dam, stopping the flow and diverting its energy into ion cyclotron waves. In this way, the helicity barrier links the two theories and resolves each of their individual problems,” he explains.

For this latest study, the group stirred the magnetic field lines in simulations and found the turbulence created the waves, which then caused the heating.

“As this happens, the structures and eddies that form end up looking extremely similar to cutting-edge measurements from NASA’s Parker Solar Probe spacecraft, which has recently become the first human-made object to actually fly into the corona.
“This gives us confidence that we are accurately capturing key physics in the corona, which — coupled with the theoretical findings about the heating mechanisms — is a promising path to understanding the coronal heating problem,” Dr Meyrand says.

Understanding more about the Sun’s atmosphere and the subsequent solar wind is important because of the profound impacts they have on Earth, Dr Squire explains. Effects which result from solar wind’s interaction with the Earth’s magnetic field is called ‘space weather’, which causes everything from Aurora to satellite-destroying radiation and geomagnetic currents which damage the power grid.

“All of this is sourced, fundamentally, by the corona and its heating by magnetic fields, so as well as being interesting for our general understanding of the solar system, the solar-corona’s dynamics can have profound impacts on Earth.
“Perhaps, with a better understanding of its basic physics, we will be able to build better models to predict space weather in the future, thus allowing the implementation of protection strategies that could head off — literally — billions of dollars of damage.”

The velocity distribution of white dwarfs in Gaia EDR3

by Daniel Mikkola, Paul J. McMillan, David Hobbs, John Wimarsson in Monthly Notices of the Royal Astronomical Society

White dwarfs were once normal stars similar to the Sun but then collapsed after exhausting all their fuel. These interstellar remnants have historically been difficult to study. However, a recent study from Lund University in Sweden reveals new information about the movement patterns of these puzzling stars.

White dwarfs have a radius of about 1 percent of the Sun’s. They have about the same mass, which means they have an astonishing density of about 1 tonne per cubic centimeter. After billions of years, white dwarfs will cool down to a point where they stop emitting visible light, and turn into so-called black dwarfs.

The first white dwarf that was discovered was 40 Eridani A. It is a bright celestial body 16.2 light-years from Earth, surrounded by a binary system consisting of the white dwarf 40 Eridani B and the red dwarf 40 Eridani C. Ever since it was discovered in 1783, astronomers have tried to learn more about white dwarfs in order to gain a deeper understanding of the evolutionary history of our home galaxy.

Panel a. Dispersions in𝑈, 𝑉 , and𝑊 calculated for samples all_100, red_100, and blue_100 using a moving window in absolute magnitude and shown with black, red, and blue colours respectively. The shaded region shows the 1𝜎 uncertainty. The red and blue lines appear to be separate for brighter white dwarfs in all three directions but become mixed towards the fainter end of the sequence. Panel b. Same as a. but for samples all_200, red_200, and blue_200. For these WDs the split between the red and the blue sequences is much more pronounced and now clearly so at all absolute magnitudes. The red sequence appears to have a larger velocity dispersion in all directions and at almost all absolute magnitudes.

“Thanks to observations from the Gaia space telescope, we have for the first time managed to reveal the three-dimensional velocity distribution for the largest catalogue of white dwarfs to date. This gives us a detailedpicture of their velocity structurewith unparalleled detail,” says Daniel Mikkola, doctoral student in astronomy at Lund University.

Thanks to Gaia, researchers have measured positions and velocities for about 1.5 billion stars. But only recently have they been able to completely focus on the white dwarfs in the Solar neighbourhood.

“We have managed to map the white dwarfs’ velocities and movement patterns. Gaia revealed that there are two parallel sequences of white dwarfs when looking at their temperature and brightness. If we study these separately, we can see that they move in different ways, probably as a consequence of them having different masses and lifetimes,” says Daniel Mikkola.

The velocity distribution of WDs in 𝑈 and 𝑉 .

The results can be used to develop new simulations and models to continue to map the history and development of the Milky Way. Through an increased knowledge of the white dwarfs, the researchers hope to be able to straighten out a number of question marks surrounding the birth of the Milky Way.

“This study is important because we learned more about the closest regions in our galaxy. The results are also interesting because our own star, the Sun, will one day turn into a white dwarf just like 97 percent of all stars in the Milky Way,” concludes Daniel Mikkola.

MeerKAT uncovers the physics of an Odd Radio Circle

by Ray P Norris, J D Collier, Roland M Crocker et al in Monthly Notices of the Royal Astronomical Society

Astronomy’s newest mystery objects, odd radio circles or ORCs, have been pulled into sharp focus by an international team of astronomers using the world’s most capable radio telescopes.

When first revealed in 2020 by the ASKAP radio telescope, owned and operated by Australia’s national science agency CSIRO, odd radio circles quickly became objects of fascination. Theories on what causes them ranged from galactic shockwaves to the throats of wormholes.A new detailed image, captured by the South African Radio Astronomy Observatory’s MeerKAT radio telescope is providing researchers with more information to help narrow down those theories.

(Left) The original discovery of ORC1 in the Evolutionary Map of the Universe (EMU) science survey team’s ASKAP radio telescope data. (Right) The follow-up observation of ORC1 with the MeerKAT radio telescope.

There are now three leading theories to explain what causes ORCs: They could be the remnant of a huge explosion at the centre of their host galaxy, like the merger of two supermassive black holes; They could be powerful jets of energetic particles spewing out of the galaxy’s centre; or They might be the result of a starburst ‘termination shock’ from the production of stars in the galaxy. To date ORCs have only been detected using radio telescopes, with no signs of them when researchers have looked for them using optical, infrared, or X-ray telescopes. Dr Jordan Collier of the Inter-University Institute for Data Intensive Astronomy, who compiled the image from MeerKAT data said continuing to observe these odd radio circles will provide researchers with more clues.

“People often want to explain their observations and show that it aligns with our best knowledge. To me, it’s much more exciting to discover something new, that defies our current understanding,” Dr Collier said.

The rings are enormous — about a million light years across, which is 16 times bigger than our own galaxy. Despite this, odd radio circles are hard to see. Professor Ray Norris from Western Sydney University and CSIRO, one of the authors on the paper, said only five odd radio circles have ever been revealed in space.

“We know ORCs are rings of faint radio emissions surrounding a galaxy with a highly active black hole at its centre, but we don’t yet know what causes them, or why they are so rare,” Professor Norris said.

Data from SARAO’s MeerKAT radio telescope data (green) showing the odd radio circles, is overlaid on optical and near infra-red data from the Dark Energy Survey.

Professor Elaine Sadler, Chief Scientist of CSIRO’s Australia Telescope National Facility, which includes ASKAP, said for now, ASKAP and MeerKAT are working together to find and describe these objects quickly and efficiently.

“Nearly all astronomy projects are made better by international collaboration — both with the teams of people involved and the technology available,” Professor Sadler said.. “ASKAP and MeerKAT are both precursors to the international SKA project. Our developing understanding of odd radio circles is enabled by these complementary telescopes working together.”

To really understand odd radio circles scientists will need access to even more sensitive radio telescopes such as those of the SKA Observatory, which is supported by more than a dozen countries including the UK, Australia, South Africa, France, Canada, China and India.

“No doubt the SKA telescopes, once built, will find many more ORCs and be able to tell us more about the lifecycle of galaxies,” Professor Norris said. “Until the SKA becomes operational, ASKAP and MeerKAT are set to revolutionise our understanding of the Universe faster than ever before.”

Five Decades of Chromospheric Activity in 59 Sun-like Stars and New Maunder Minimum Candidate HD 166620

by Anna C. Baum, Jason T. Wright, Jacob K. Luhn, Howard Isaacson in The Astronomical Journal

The number of sunspots on our Sun typically ebbs and flows in a predictable 11-year cycle, but one unusual 70-year period when sunspots were incredibly rare has mystified scientists for three hundred years. Now a nearby Sun-like star seems to have paused its own cycles and entered a similar period of rare starspots, according to a team of researchers at Penn State. Continuing to observe this star could help explain what happened to our own Sun during this “Maunder Minimum” as well as lend insight into the Sun’s stellar magnetic activity, which can interfere with satellites and global communications and possibly even affect climate on Earth. The star — and a catalog of 5 decades of starspot activity of 58 other Sun-like stars — is described in a new paper.

Starspots appear as a dark spot on a star’s surface due to temporary lower temperatures in the area resulting from the star’s dynamo — the process that creates its magnetic field. Astronomers have been documenting changes in starspot frequency on our Sun since they were first observed by Galileo and other astronomers in the 1600s, so there is a good record of its 11-year cycle. The exception is the Maunder Minimum, which lasted from the mid 1600s to early 1700s and has perplexed astronomers ever since.

Activity vs. time in 59 Sun-like stars: the complete figure set (59 images) is available in the online journal.

“We don’t really know what caused the Maunder Minimum, and we have been looking to other Sun-like stars to see if they can offer some insight,” said Anna Baum, an undergraduate at Penn State at the time of the research and first author of the paper. “We have identified a star that we believe has entered a state similar to the Maunder Minimum. It will be really exciting to continue to observe this star during, and hopefully as it comes out of, this minimum, which could be extremely informative about the Sun’s activity three hundred years ago.”

The research team pulled data from multiple sources to stitch together 50 to 60 years of starspot data for 59 stars. This included data from the Mount Wilson Observatory HK Project — which was designed to study stellar surface activity and ran from 1966 to 1996 — and from planet searches at Keck Observatory which include this kind of data as part of their ongoing search for exoplanets from 1996 to 2020. The researchers compiled a database of stars that appeared in both sources and that had other readily available information that might help explain starspot activity. The team also made considerable efforts to standardize measurements from the different telescopes to be able to compare them directly and otherwise clean up the data.

The team identified or confirmed that 29 of these stars have starspot cycles by observing at least two full periods of cycles, which often last more than a decade. Some stars did not appear to have cycles at all, which could be because they are rotating too slowly to have a dynamo and are magnetically ‘dead’ or because they are near the end of their lives. Several of the stars require further study to confirm whether they have a cycle.

“This continuous, more than 50-year time series allows us to see things that we never would have noticed from the 10-year snapshots that we were doing before,” said Jason Wright, professor of astronomy and astrophysics at Penn State and an author of the paper. “Excitingly, Anna has found a promising star that was cycling for decades but appears to have stopped.”

According to the researchers, the star — called HD 166620 — was estimated to have a cycle of about 17 years but has now entered a period of low activity and has shown no signs of starspots since 2003.

“When we first saw this data, we thought it must have been a mistake, that we pulled together data from two different stars or there was a typo in the catalog or the star was misidentified,” said Jacob Luhn, a graduate student at Penn State when the project began who is now at the University of California, Irvine. “But we double and triple checked everything. The times of observation were consistent with the coordinates we expected the star to have. And there aren’t that many bright stars in the sky that Mount Wilson observed. No matter how many times we checked, we always come to the conclusion that this star has simply stopped cycling.”

HD 166620 appears to have entered a Maunder minimum between its final observations with HIRES-1 and first observations with HIRES-2. HD 101501 experienced 10 yr of lower activity, a much lower amplitude cycle than the rest of its cycle.

The researchers hope to continue studying this star throughout its minimum period and potentially as it comes out of its minimum and begins to cycle once again. This continued observation could provide important information about how the Sun and stars like it generate their magnetic dynamos.

“There’s a big debate about what the Maunder Minimum was,” said Baum, who is now a doctoral student at Lehigh University studying stellar astronomy and asteroseismology . “Did the Sun’s magnetic field basically turn off? Did it lose its dynamo? Or was it still cycling but at a very low level that didn’t produce many sunspots? We can’t go back in time to take measurements of what it was like, but if we can characterize the magnetic structure and magnetic field strength of this star, we might start to get some answers.”

A better understanding of the surface activity and magnetic field of the Sun could have several important implications. For example, strong stellar activity can disable satellites and global communications, and one particularly strong solar storm disabled a power grid in Quebec in 1989. It has also been suggested that sunspot cycles may have a connection to climate on Earth. Additionally, the researchers said that information from this star could impact our search for planets beyond our solar system.

“Starspots and other forms of surface magnetic activity of stars interfere with our ability to detect the planets around them,” said Howard Isaacson, a research scientist at the University of California, Berkeley, and an author of the paper. “Improving our understanding of a star’s magnetic activity might help us improve our detection efforts.”

The Asteroid 162173 Ryugu: a Cometary Origin

by Hitoshi Miura, Eizo Nakamura, Tak Kunihiro in The Astrophysical Journal Letters

Asteroids hold many clues about the formation and evolution of planets and their satellites. Understanding their history can, therefore, reveal much about our solar system. While observations made from a distance using electromagnetic waves and telescopes are useful, analyzing samples retrieved from asteroids can yield much more detail about their characteristics and how they may have formed. An endeavor in this direction was the Hayabusa mission, which, in 2010, returned to Earth after 7 years with samples from the asteroid Itokawa.

The successor to this mission, called Hayabusa2, was completed near the end of 2020, bringing back material from Asteroid 162173 “Ryugu,” along with a collection of images and data gathered remotely from close proximity. While the material samples are still being analyzed, the information obtained remotely has revealed three important features about Ryugu. Firstly, Ryugu is a rubble-pile asteroid composed of small pieces of rock and solid material clumped together by gravity rather than a single, monolithic boulder. Secondly, Ryugu is shaped like a spinning top, likely caused by deformation induced by quick rotation. Third, Ryugu has a remarkably high organic matter content.

Of these, the third feature raises a question regarding the origin of this asteroid. The current scientific consensus is that Ryugu originated from the debris left by the collision of two larger asteroids. However, this cannot be true if the asteroid is high in organic content (which will confirmed once the analyses of the returned samples are complete). What could, then, be the true origin of Ryugu?

A model of water ice sublimation from a porous cometary nucleus. (a) The cometary nucleus is initially assumed to consist mainly of water ice particles with a small amount of rocky debris uniformly contained within. (b) The water ice sublimates from the outer layer and the primitive region shrinks. © The remaining rocky debris accumulates on the surface to form a dust mantle. Since the dust mantle is highly porous and therefore permeable, the water vapor generated inside leaks out through the dust mantle. (d) Finally, the cometary nucleus transforms to a rocky asteroid after almost complete sublimation of water ice.

In a recent effort to answer this question, a research team led by Associate Professor Hitoshi Miura of Nagoya City University, Japan, proposed an alternative explanation backed up by a relatively simple physical model. As explained in their paper, the researchers suggest that Ryugu, as well as similar rubble-pile asteroids, could, in fact, be remnants of extinct comets. This study was carried out in collaboration with Professor Eizo Nakamura and Associate Professor Tak Kunihiro from Okayama University, Japan.

Comets are small bodies that form on the outer, colder regions of the solar system. They are mainly composed of water ice, with some rocky components (debris) mixed in. If a comet enters the inner solar system — the space delimited by the asteroid belt “before” Jupiter — heat from the solar radiation causes the ice to sublimate and escape, leaving behind rocky debris that compacts due to gravity and forms a rubble-pile asteroid.

This process fits all the observed features of Ryugu, as Dr. Miura explains, “Ice sublimation causes the nucleus of the comet to lose mass and shrink, which increases its speed of rotation. As a result of this spin-up, the cometary nucleus may acquire the rotational speed required for the formation of a spinning-top shape. Additionally, the icy components of comets are thought to contain organic matter generated in the interstellar medium. These organic materials would be deposited on the rocky debris left behind as the ice sublimates.”

Numerical results. (a) The shrinkage of the cometary nucleus due to water ice sublimation. The time variations of the radii of the primitive region and the dust mantle are shown by dashed and solid curves, respectively. (b) The change in angular velocity of the cometary nucleus associated with the shrinkage due to water ice sublimation. The spin-up rate in the vertical axis is the angular velocity when the radius of the primitive region contracts to the value given by the horizontal axis as the ratio with respect to the initial angular velocity.

To test their hypothesis, the research team conducted numerical simulations using a simple physical model to calculate the time it would take for the ice to sublimate and the increase in rotational speed of the resulting asteroid due to it. The results of their analysis suggested that Ryugu has likely spent a few tens of thousands of years as an active comet before moving into the inner asteroid belt, where the high temperatures vaporized its ice and turned it into a rubble-pile asteroid.

Overall, this study indicates that spinning top-shaped, rubble-pile objects with high organic content, such as Ryugu and Bennu (the target of the OSIRIS-Rex mission) are comet-asteroid transition objects (CATs). “CATs are small objects that were once active comets but have become extinct and apparently indistinguishable from asteroids,” explains Dr. Miura. “Due to their similarities with both comets and asteroids, CATs could provide new insights into our solar system.”

Downward Oxidant Transport Through Europa’s Ice Shell by Density-Driven Brine Percolation

by Marc A. Hesse, Jacob S. Jordan, Steven D. Vance, Apurva V. Oza in Geophysical Research Letters

Salt water within the icy shell of Jupiter’s moon Europa could be transporting oxygen into an ice-covered ocean of liquid water where it could potentially help sustain alien life, according to a team of researchers led by The University of Texas at Austin.

This theory has been proposed by others, but the researchers put it to the test by building the world’s first physics-based computer simulation of the process, with oxygen hitching a ride on salt water under the moon’s “chaos terrains,” landscapes made up of cracks, ridges and ice blocks that cover a quarter of the icy world. The results show that not only is the transport possible, but that the amount of oxygen brought into Europa’s ocean could be on a par with the quantity of oxygen in Earth’s oceans today.

An image of chaos terrain on the surface of Jupiter’s moon Europa. Credit: NASA/JPL-Caltech/SETI Institute.

“Our research puts this process into the realm of the possible,” said lead researcher Marc Hesse, a professor at the UT Jackson School of Geosciences Department of Geological Sciences. “It provides a solution to what is considered one of the outstanding problems of the habitability of the Europa subsurface ocean.”

Europa is a top spot to look for alien life because scientists have detected signs of oxygen and water, along with chemicals that could serve as nutrients. However, the moon’s ice shell — which is estimated to be about 15 miles thick — serves as a barrier between water and oxygen, which is generated by sunlight and charged particles from Jupiter striking the icy surface. If life as we know it exists in the ocean, there needs to be a way for oxygen to get to it. According to Hesse, the most plausible scenario based on the available evidence is for the oxygen to be carried by salt water, or brine.

Scientists think that chaos terrains form above regions where Europa’s ice shell partially melts to form brine, which can mix with oxygen from the surface. The computer model created by the researchers showed what happens to the brine after the formation of the chaos terrain.

The model showed the brine draining in a distinct manner, taking the form of a “porosity wave” that causes pores in the ice to momentarily widen — allowing the brine to pass through before sealing back up. Hesse compares the process to the classic cartoon gag of a bulge of water making its way down a garden hose. This mode of transport appears to be an effective way to bring oxygen through the ice, with 86% of the oxygen taken up at the surface riding the wave all the way to the ocean. But the available data allows for a wide range of oxygen levels delivered to Europa’s ocean over its history — with estimates ranging by a factor of 10,000.

The physics-based model built by the researchers shows brine and oxygen at Europa’s surface being carried by a “porosity wave” (spherical shape) through the moon’s ice shell to the liquid water ocean below. The chart shows time (in thousands of years) and ice shell depth (in kilometers). Red indicates higher levels of oxygen. Blue represents lower levels of oxygen.

According to co-author Steven Vance, a research scientist at NASA’s Jet Propulsion Laboratory (JPL) and the supervisor of its Planetary Interiors and Geophysics Group, the highest estimate would make the oxygen levels in Europa’s ocean similar to those in Earth’s oceans — which raises hope about the potential for that oxygen to support life in the hidden sea.

“It’s enticing to think of some kind of aerobic organisms living just under the ice,” he said.

Vance said that NASA’s upcoming 2024 Europa Clipper mission may help improve estimates for oxygen and other ingredients for life on the icy moon.

Kevin Hand, a scientist focused on Europa research at NASA JPL who was not part of the study, said that the study presents a compelling explanation for oxygen transport on Europa.

“We know that Europa has useful compounds like oxygen on its surface, but do those make it down into the ocean below, where life can use them?” he said. “In the work by Hesse and his collaborators, the answer seems to be yes.”

Frequency-dependent polarization of repeating fast radio bursts — implications for their origin

by Yi Feng, Di Li, Yuan-Pei Yang, Yongkun Zhang, Weiwei Zhu, in Science

Nearly 15 years after the discovery of fast radio bursts (FRBs), the origin of the millisecond-long, deep-space cosmic explosions remains a mystery.

That may soon change, thanks to the work of an international team of scientists — including UNLV astrophysicist Bing Zhang — which tracked hundreds of the bursts from five different sources and found clues in FRB polarization patterns that may reveal their origin.

The degree of linear polarization for FRB sources is consistent with RM scattering.

FRBs produce electromagnetic radio waves, which are essentially oscillations of electric and magnetic fields in space and time. The direction of the oscillating electric field is described as the direction of polarization. By analyzing the frequency of polarization in FRBs observed from various sources, scientists revealed similarities in repeating FRBs that point to a complex environment near the source of the bursts.

“This is a major step towards understanding the physical origin of FRBs,” said Zhang, a UNLV distinguished professor of astrophysics who coauthored the paper and contributed to the theoretical interpretation of the phenomena.

To make the connection between the bursts, an international research team, led by Yi Feng and Di Li of the National Astronomical Observatories of the Chinese Academy of Sciences, analyzed the polarization properties of five repeating FRB sources using the massive Five-hundred-meter Aperture Spherical radio Telescope (FAST) and the Robert C. Byrd Green Bank Telescope (GBT). Since FRBs were first discovered in 2007, astronomers worldwide have turned to powerful radio telescopes like FAST and GBT to trace the bursts and to look for clues on where they come from and how they’re produced.

Though still considered mysterious, the source of most FRBs is widely believed to be magnetars, incredibly dense, city-sized neutron stars that possess the strongest magnetic fields in the universe. They typically have nearly 100% polarization. Conversely, in many astrophysical sources that involve hot randomized plasmas, such as the Sun and other stars, the observed emission is unpolarized because the oscillating electric fields have random orientations. That’s where the cosmic detective work kicks in.

FAST detected 1,652 pulses from the active repeater FRB 121102. Even though the bursts from the source were discovered to be highly polarized with other telescopes using higher frequencies — consistent with magnetars — none of the bursts detected with FAST in its frequency band were polarized, despite FAST being the largest single-dish radio telescope in the world.

“We were very puzzled by the lack of polarization,” said Feng, first author on the newly released paper. “Later, when we systematically looked into other repeating FRBs with other telescopes in different frequency bands — particularly those higher than that of FAST, a unified picture emerged.”

Correlations between RM, scattering time sca and rotation measure magnitude |RM| for repeating FRBs.

According to Zhang, the unified picture is that every repeating FRB source is surrounded by a highly magnetized dense plasma. This plasma produces different rotation of the polarization angle as a function of frequency, and the received radio waves come from multiple paths due to scattering of the waves by the plasma. When the team accounted for just a single adjustable parameter, Zhang says, the multiple observations revealed a systematic frequency evolution, namely depolarization toward lower frequencies.

“Such a simple explanation, with only one free parameter, could represent a major step toward a physical understanding of the origin of repeating FRBs,” he says.

Bridging the μHz Gap in the Gravitational-Wave Landscape with Binary Resonances

by Diego Blas, Alexander C. Jenkins in Physical Review Letters

Researchers from the UAB, IFAE and University College London propose using the variations in distance between the Earth and the Moon, which can be measured with a precision of less than a centimeter, as a new gravitational wave detector within a frequency range that current devices cannot detect.

Gravitational waves, predicted by Albert Einstein at the start of the 20th century and detected for the first time in 2015, are the new messengers of the most violent processes taking place in the universe. The gravitational wave detectors scan different frequency ranges, similar to moving a dial when tuning into a radio station. Nevertheless, there are frequencies that are impossible to cover with current devices and which may harbour signals that are fundamental to understanding the cosmos. One particular example can be seen in microhertz waves, which could have been produced at the dawn of our universe, and are practically invisible to even the most advanced technology available today.

SGWB sensitivity curves of current and future GW experiments, as well as our forecasts.

In an article, researchers Diego Blas from the Department of Physics at the Universitat Autònoma de Barcelona (UAB) and the Institut de Física d’Altes Energies (IFAE), and Alexander Jenkins from the University College London (UCL), point out that a natural gravitational wave detector exists in our immediate environment: the Earth-Moon System. The gravitational waves constantly hitting this system generate tiny deviations in the Moon’s orbit. Although these deviations are minute, Blas and Jenkins plan on taking advantage of the fact that the Moon’s exact position is known with an error of at most one centimeter, thanks to the use of lasers sent from different observatories which are continuously reflected upon mirrors left on the surface of the Moon by the Apollo space mission and others. This incredible precision, with an error of one billionth of a part at most, is what may allow a small disturbance caused by ancient gravitational waves to be detected. The Moon’s orbit lasts approximately 28 days, which translates into a particularly relevant sensitivity when it comes to microhertz, the frequency range researchers are interested in.

Similarly, they also propose using the information other binary systems in the universe may provide as gravitational wave detectors. This is the case of pulsar binary systems distributed throughout the galaxy, systems in which the pulsar’s radiation beam allows obtaining the orbit of these stars with incredible precision (with a precision of one millionth). Given that these orbits last approximately 20 days, the passing of gravitational waves in the microhertz frequency range affect them particularly. Blas and Jenkins concluded that these systems could also be potential detectors of these types of gravitational waves.

Forecast exclusion regions of the FOPT parameter space for various SGWB searches at 2038 sensitivity.

With these “natural detectors” in the microhertz frequency range, Blas and Jenkins were able to propose a new form of studying gravitational waves emitted by the distant universe. Specifically, those produced by the possible presence of transitions in highly energetic phases of the early universe, commonly seen in many models.

“What is most interesting perhaps is that this method complements future ESA/NASA missions, such as LISA, and observatories participating in the Square Kilometer Array (SKA) project, to reach an almost total coverage of the gravitational waves from the nanohertz (SKA) to the centihertz (LIGO/VIRGO) frequency ranges. This coverage is vital to obtaining a precise image of the evolution of the universe, as well as its composition,” Diego Blas explains. “Covering the microhertz frequency range is a challenge, which now may be feasible without the need of building new detectors, and only observing the orbits of systems we already know. This connection between fundamental aspects of the universe and more mundane objects is particularly fascinating and can eventually lead to the detection of the earliest signals we have ever seen, and thus change what we know about the cosmos,” he concludes.

The rapidly evolving AGB star, V Hya: ALMA finds a multi-ring circus with high velocity outflow

by R. Sahai, P-S. Huang, S. Scibelli, M. R. Morris, K. Hinkle, C-F. Lee in The Astrophysical Journal

Scientists studying V Hydrae (V Hya) have witnessed the star’s mysterious death throes in unprecedented detail. Using the Atacama Large Millimeter/submillimeter Array (ALMA) and data from the Hubble Space Telescope (HST), the team discovered six slowly-expanding rings and two hourglass-shaped structures caused by the high-speed ejection of matter out into space.

V Hya is a carbon-rich asymptotic giant branch (AGB) star located approximately 1,300 light-years from Earth in the constellation Hydra. More than 90-percent of stars with a mass equal to or greater than the Sun evolve into AGB stars as the fuel required to power nuclear processes is stripped away. Among these millions of stars, V Hya has been of particular interest to scientists due to its so-far unique behaviors and features, including extreme-scale plasma eruptions that happen roughly every 8.5 years and the presence of a nearly invisible companion star that contributes to V Hya’s explosive behavior.

“Our study dramatically confirms that the traditional model of how AGB stars die — through the mass ejection of fuel via a slow, relatively steady, spherical wind over 100,000 years or more — is at best, incomplete, or at worst, incorrect,” said Raghvendra Sahai, an astronomer at NASA’s Jet Propulsion Laboratory, and the principal researcher on the study. “It is very likely that a close stellar or substellar companion plays a significant role in their deaths, and understanding the physics of binary interactions is both important across astrophysics and one of its greatest challenges. In the case of V Hya, the combination of a nearby and a hypothetical distant companion star is responsible, at least to some degree, for the presence of its six rings, and the high-speed outflows that are causing the star’s miraculous death.”

Mark Morris, an astronomer at UCLA and a co-author on the research added, “V Hydra has been caught in the process of shedding its atmosphere — ultimately most of its mass — which is something that most late-stage red giant stars do. Much to our surprise, we have found that the matter, in this case, is being expelled as a series of outflowing rings. This is the first and only time that anybody has seen that the gas being ejected from an AGB star can be flowing out in the form of a series of expanding ‘smoke rings.’”

The six rings have expanded outward from V Hya over the course of roughly 2,100 years, adding matter to and driving the growth of a high-density flared and warped disk-like structure around the star. The team has dubbed this structure the DUDE, or Disk Undergoing Dynamical Expansion.

“The end state of stellar evolution — when stars undergo the transition from being red giants to ending up as white dwarf stellar remnants — is a complex process that is not well understood,” said Morris. “The discovery that this process can involve the ejections of rings of gas, simultaneous with the production of high-speed, intermittent jets of material, brings a new and fascinating wrinkle to our exploration of how stars die.”
Sahai added, “V Hya is in the brief but critical transition phase that does not last very long, and it is difficult to find stars in this phase, or rather ‘catch them in the act. We got lucky and were able to image all of the different mass-loss phenomena in V Hya to better understand how dying stars lose mass at the end of their lives.”

In addition to a full set of expanding rings and a warped disk, V Hya’s final act features two hourglass-shaped structures — and an additional jet-like structure — that are expanding at high speeds of more than half a million miles per hour (240 km/s). Large hourglass structures have been observed previously in planetary nebulae, including MyCn 18 — also known as the Engraved Hourglass Nebula — a young emission nebula located roughly 8,000 light-years from Earth in the southern constellation of Musca, and the more well-known Southern Crab Nebula, an emission nebula located roughly 7,000 light-years from Earth in the southern constellation Centaurus.

Sahai said, “We first observed the presence of very fast outflows in 1981. Then, in 2022, we found a jet-like flow consisting of compact plasma blobs ejected at high speeds from V Hya. And now, our discovery of wide-angle outflows in V Hya connects the dots, revealing how all these structures can be created during the evolutionary phase that this extra-luminous red giant star is now in.”

Channel/velocity maps of the 13COJ=3{2 emission derived from our best-t spatio-kinematic model of the DUDE (orange contours) overlaid on the observed (colorscale) maps of 13COJ=3{2 from the DUDE in VHya.

Due to both the distance and the density of the dust surrounding the star, studying V Hya required a unique instrument with the power to clearly see matter that is both very far away and also difficult or impossible to detect with most optical telescopes. The team enlisted ALMA’s Band 6 (1.23mm) and Band 7 (.85mm) receivers, which revealed the star’s multiple rings and outflows in stark clarity.

“The processes taking place at the end stages of low mass stars, and during the AGB phase in particular, have long fascinated astronomers and have been challenging to understand,” said Joe Pesce, an astronomer and NSF program officer for NRAO/ALMA. “The capabilities and resolution of ALMA are finally allowing us to witness these events with the extraordinary detail necessary to provide some answers and enhance our understanding of an event that happens to most of the stars in the Universe.”

Sahai added that the incorporation of infrared, optical, and ultraviolet data into the study created a complete multi-wavelength picture of what might be one of the greatest shows in the Milky Way, at least for astronomers. “Each time we observe V Hya with new observational capabilities, it becomes more and more like a circus, characterized by an even bigger variety of impressive feats. V Hydrae has impressed us with its multiple rings and acts, and because our own Sun may one day experience a similar fate, it has us at rapt attention.”