Heavens

Active galactic nuclei (AGNs) play a major role in galaxy evolution. Astronomers from the University of Groningen and Netherlands Institute for Space Research have now used a record-sized sample of galaxies to confirm that galaxy mergers have a positive effect on igniting AGNs. They were able to compile about ten times more images of merging galaxies than previous studies by using a machine-learning algorithm. The results were published on 27 May in the journal Astronomy & Astrophysics.

One of the bigger questions in astronomy is how galaxies evolve from clouds of gas and dust to the beautiful spiral structures we see in our Galactic neighbourhood. So-called active galactic nuclei (AGNs) form interesting research objects to answer part of this question, because there appears to be co-evolution between AGNs and galaxies. AGNs harbour supermassive black holes that emit huge amounts of energy after accreting gas from their surroundings. Some have large enough magnetic or gravitational fields to spit out jets from their poles, stretching thousands of lightyears.

Seeds for stars

Co-evolution is a two-way street. On the one hand, the evolution stage of a galaxy affects AGN activity. AGNs seem to thrive at a certain stage in a galaxy's evolution, because we see AGN activity peaking in galaxies at a particular distance, and therefore at a particular time in the past. On the other hand, AGN activity affects a galaxy's star formation. This could go either way. An AGN's jet pushes gas away as it propagates through the galaxy, forcing the gas to collide with other gas and thus creating clumps--seeds for new stars. But AGNs also emit energy, heating up the gas and thus preventing it to cool down and condense into clumps.

Astronomers from the University of Groningen and SRON Netherlands Institute for Space Research have now compiled a sample with a record-number of galaxies to study one of the factors that allegedly has a positive effect on igniting AGNs: mergers between galaxies. And they found a correlation, counting both ways. There are about 1.4 times more AGNs in mergers than in non-mergers. And the other way around, the researchers find about 1.3 times more mergers in samples of galaxies with an AGN compared to samples of galaxies without an AGN.

Large sample

The research team used a machine-learning algorithm to identify mergers. It gave them a sample that is about one order of magnitude larger than those in previous studies, making the correlation much more reliable. 'We have built a network to train the system to recognize mergers in a lot of pictures,' says first author Fangyou Gao. 'This enables us to use a large sample of two telescope surveys with tens of thousands of galaxies. AGNs are relatively easy to recognize, based on their spectrum. But mergers must be classified from images, which is typically a human's job. With machine learning, we can now have computers do this for us.'

Researchers at MIT and elsewhere have combined the power of a super collider with techniques of laser spectroscopy to precisely measure a short-lived radioactive molecule, radium monofluoride, for the first time.

Precision studies of radioactive molecules open up possibilities for scientists to search for new physics beyond the Standard Model, such as phenomena that violate certain fundamental symmetries in nature, and to look for signs of dark matter. The team's experimental technique could also be used to perform laboratory studies of radioactive molecules produced in astrophysical processes.

"Our results pave the way to high-precision studies of short-lived radioactive molecules, which could offer a new and unique laboratory for research in fundamental physics and other fields," says the study's lead author, Ronald Fernando Garcia Ruiz, assistant professor of physics at MIT.

Garcia Ruiz' colleagues include Alex Brinson, an MIT graduate student, along with an international team of researchers working at CERN, the European Organization for Nuclear Research, in Geneva. The results are published today in the journal Nature.

Reversing time

The simplest molecule is made from two atoms, each with a nucleus comprising a certain number of protons and neutrons that make one atom heavier than the other. Each nucleus is surrounded by a cloud of electrons. In the presence of an electric field, these electrons can be redistributed to create an extremely large electric field within the molecule.

Physicists have used molecules and their electric fields as miniature laboratories to study the fundamental properties of electrons and other subatomic particles. For instance, when a bound electron interacts with the molecule's electric field, its energy can change as a result, which scientists can measure to infer the electron's properties, such as its electrostatic dipole moment, which provides a measurement of its deviation from a spherical shape.

According to the Standard Model of particle physics, elementary particles should be roughly spherical, or have a negligible electrostatic dipole moment. If, however, a permanent electric dipole moment of a particle or a system exists , this would imply that certain processes in nature are not as symmetrical as physicists had assumed.

For instance, physicists believe that most fundamental laws of physics should remain unchanged with the direction of time -- a principle known as time reversal symmetry. That is, regardless of whether time runs forward or backward, gravity, for example, should cause a ball to fall off a cliff, or roll back up, along the same path in velocity and space. If, however, an electron is not perfectly spherical, this would indicate that time reversal symmetry is violate. This violation would provide a much-needed condition for explaining why there is more matter than antimatter in our universe.

By studying an electron's interactions with very strong electric fields, scientists might have a chance of precisely measuring their electric dipole moments. In certain molecules, the heavier their atoms, the stronger their internal electric field. Radioactive molecules -- those containing at least one unstable nuclei -- can be tailored to maximize their internal electric fields. Moreover, heavy radioactive nuclei can have pear-like shapes, which can amplify their symmetry-violating properties.

Because of their high electric fields and unique nuclear shapes, radioactive molecules would make natural laboratories in which to probe not only the electron's structure, but also symmetry-violating nuclear properties. But these molecules are short-lived, and scientists have been unable to pin them down .

"These radioactive molecules are very rare in nature and some of them cannot be found in our planet, but can be abundant in astrophysical processes such as stellar explosions, or neutron star mergers," Garcia Ruiz says. "So we have to make them artificially, and the main challenges have been that they can only be produced in small quantities at high temperatures, and can be very short-lived."

A needle in the dark

The team looked for a way to make radium monoflouride, or RaF -- a radioactive molecule that contains a very heavy, unstable radium atom, and a fluoride atom. This molecule is of particular interest because certain isotopes of the radium nucleus are themselves asymmetrical, resembling a pear, with more mass on one end of the nucleus than the other.

What's more, theorists had predicted that the energy structure of radium monofluoride would make the molecule amenable to laser cooling, a technique that uses lasers to bring down the temperature of molecules, and slow them down enough to perform precision studies. While most molecules have many energy states they can occupy, with large numbers of vibrational and rotational states, it turns out that radium monofluoride favors electronic transitions between a few main energy levels -- an unusually simple molecule to control, using laser cooling.

The team was able to measure molecules of RaF by first making small quantities of the molecule using CERN's Isotope mass Separator On-Line, or ISOLDE facility at CERN, which they then manipulated and studied with lasers using the Collinear Resonance Ionization Spectroscopy (CRIS) experiment.

In their experiment, the researchers utilized CERN's Proton Synchrotron Booster, a series of rings that receives protons from a particle accelerator and accelerates the protons. The team fired these protons at a target made of uranium carbide, at such high energies that the onslaught destroyed uranium, producing a shower of protons and neutrons that mixed to form a mix of radioactive nuclei, including radium.

The researchers then injected a gas of carbon tetrafluoride, which reacted with radium to make charged, or ionic molecules of radium monofluoride, which they separated from the rest of uranium's byproducts through a system of mass-separating magnets. They then pinned down the molecules in an ion trap and surrounded them with helium gas, which cooled the molecules down enough for the researchers to measure them.

Next, the team measured the molecules by reaccelerating and passing them through the CRIS setup, where the ionic molecules interacted with sodium atoms that gave an electron to each molecule to neutralize the beam of molecules in flight. The neutral molecules then continued through an interaction region, where the researchers also shone two laser beams -- one red, the other blue.

The team tuned the red laser's frequency up and down, and found that at certain wavelengths the laser resonated with the molecules, exciting an electron in the molecule to another energy level, such that the blue laser then had enough energy to remove the electron from the molecule. The resonantly excited molecules, made ionic again, were deflected and collected onto a particle detector, allowing the researchers to measure, for the first time, their energy levels, and the associated molecular properties which demonstrate that the structure of these molecules is indeed favorable for laser cooling.

"Previous to our measurements, all the energy levels of these molecules were unknown," Garcia Ruiz says. "This has been like trying to find a needle in a dark room, many hundreds of meters wide. Now that we've found the needle, we can measure the properties of that needle and start playing with it."

A 425-million-year-old millipede fossil from the Scottish island of Kerrera is the world's oldest "bug" -- older than any known fossil of an insect, arachnid or other related creepy-crawly, according to researchers at The University of Texas at Austin.

The findings offer new evidence about the origin and evolution of bugs and plants, suggesting that they evolved much more rapidly than some scientists believe, going from lake-hugging communities to complex forest ecosystems in just 40 million years.

"It's a big jump from these tiny guys to very complex forest communities, and in the scheme of things, it didn't take that long," said Michael Brookfield, a research associate at UT Austin's Jackson School of Geosciences and adjunct professor at the University of Massachusetts Boston. "It seems to be a rapid radiation of evolution from these mountain valleys, down to the lowlands, and then worldwide after that."

The research was recently published in the journal Historical Biology. Brookfield led the study with co-authors including Elizabeth Catlos, an associate professor in the Jackson School's Department of Geological Sciences, and Stephanie Suarez, a doctoral student at the University of Houston who made improvements to the fossil dating technique used in the study when she was an undergraduate at the Jackson School.

The team found that the ancient millipede fossil is 425 million years old, or about 75 million years younger than the age other scientists have estimated the oldest millipede to be using a technique known as molecular clock dating, which is based on DNA's mutation rate. Other research using fossil dating found that the oldest fossil of a land-dwelling, stemmed plant (also from Scotland) is 425 million years old and 75 million years younger than molecular clock estimates.

Although it's certainly possible there are older fossils of both bugs and plants, Brookfield said that the fact they haven't been found -- even in deposits known for preserving delicate fossils from this era -- could indicate that the ancient millipede and plant fossils that have already been discovered are the oldest specimens.

If that's the case, it also means both bugs and plants evolved much more rapidly than the timeline indicated by the molecular clock. Bountiful bug deposits have been dated to just 20 million years later than the fossils. And by 40 million years later, there's evidence of thriving forest communities filled with spiders, insects and tall trees.

"Who is right, us or them?" Catlos said. "We're setting up testable hypotheses - and this is where we are at in the research right now."

Given their potential evolutionary significance, Brookfield said that he was surprised that this study was the first to address the age of the ancient millipedes.

Suarez said a reason could be the difficulty of extracting zircons -- a microscopic mineral needed to precisely date the fossils -- from the ashy rock sediment in which the fossil was preserved. As an undergraduate researcher at the Jackson School, Suarez developed a technique for separating the zircon grain from this type of sediment. It's a process that takes practice to master. The zircons are easily flushed away when trying to loosen their grip on the sediment. And once they are successfully released from the surrounding rock, retrieving the zircons involves an eagle-eyed hunt with a pin glued to the tip of a pencil.

"That kind of work trained me for the work that I do here in Houston," Suarez said. "It's delicate work."

As an undergraduate, Suarez used the technique to find that a different millipede specimen, thought to be the oldest bug specimen at the time, was about 14 million years younger than estimated -- a discovery that stripped it of the title of oldest bug. Using the same technique, this study passes the distinction along to a new specimen.

EVANSTON, Ill. -- Move aside, AT2018COW. There is a new astronomical transient in the universe, and it is faster, heavier and brighter at radio wavelengths than its mysterious predecessors.

After astronomers visually spotted a bright burst in a tiny galaxy 500 million lightyears away from Earth in 2016, a Northwestern University-led team has determined that the anomaly is the third fast blue optical transient (FBOT) ever captured in radio- and X-ray wavelengths.

A highly luminous family of cosmic explosions, FBOTs have a track record for surprising astronomers with their fast, energetic, powerful bursts of energy. As their name implies, transients fade almost as quickly as they appear. Perhaps the most famous FBOT is AT2018COW ("The Cow") -- a rare event that appeared to be the birth of a black hole or a neutron star. But the newly identified FBOT, called CRTS-CSS161010 J045834-081803 or CSS161010 for short, has vastly overshadowed the Cow with the sheer speeds and heaviness of its material outflows.

CSS161010, in fact, has produced some of the fastest outflows in nature, launching gas and particles at more than 55% the speed of light. Its mind-boggling fast outflows also are the heaviest documented for its class.

"This was unexpected," said Northwestern's Deanne Coppejans, who is first author of the study. "We know of energetic explosions that can eject material at almost the speed of light, specifically gamma ray bursts, but they only launch a small amount of mass -- about 1 millionth the mass of the sun. CSS161010 launched 1 to 10 percent the mass of the sun at more than half the speed of light -- evidence that this is a new class of transient."

"We thought we knew what produced the fastest outflows in nature," said Northwestern's Raffaella Margutti, a senior author of the study. "We thought there were only two ways to produce them -- by collapsing a massive star with a gamma ray burst or two neutron stars merging. We thought that was it. With this study, we are introducing a third way to launch these outflows. There is a new beast out there, and it's able to produce the same energetic phenomenon."

The research will be published in the May 26 issue of the Astrophysical Journal.

Margutti is an assistant professor of physics and astronomy in Northwestern's Weinberg College of Arts and Sciences and a member of CIERA (Center for Interdisciplinary Exploration and Research in Astrophysics). Coppejans is a postdoctoral associate in CIERA and part of Margutti's transients research group.

What's an FBOT?

FBOTs (pronounced F-bot) are a type of cosmic explosion initially detected in the optical wavelength. So hot that they glow blue, FBOTs reach peak brightness within a matter of days and then quickly fade -- much faster than standard supernovae rise and decay. Although astronomers recognized FBOTs as their own class in 2014, they assume these curious anomalies have been dotting our nightsky for much longer.

"These have probably been inside our archives for a long time, but we didn't recognize them as anything different," Margutti said. "We saw glitches in other galaxies that we couldn't explain. But we couldn't get information outside the optical wavelength, so we couldn't examine them further. We would just call them 'weird supernovae.'"

Margutti's team combines multiple observatories to gather more insight into these mysterious explosions. In 2016, researchers at the Catalina Real-time Transient Survey and the All Sky Automated Supernova Survey (ASAS-SN) independently spotted CSS161010 with optical wavelengths. An ASAS-SN team then approached Margutti and Coppejans to take a closer look using their expertise in X-ray and radio waves.

Because Northwestern has remote access to the Keck Observatory, which has the largest optical and infrared telescopes in the U.S., they were able to observe the phenomenon directly. (Northwestern is one of only four institutions in the U.S. to have such access.)

"The optical wavelengths can tell us about the particles moving slowly in an explosion. But 'moving slowly' is still 10,000 kilometers per second," Margutti said. "If you want to see the faster particles, then you have to use X-rays and radio waves. Then you can put them all together to see a more complete picture."

Although the astrophysicists concluded that CSS161010 is definitely an FBOT, they may never know its true, underlying nature. It simply flared up and then faded too quickly. Still, they have a guess.

"We think it's a very rare type of stellar explosion," Coppejans said. "Although it is less likely, CSS161010 could instead be a star being eaten by a medium-sized black hole."

"The Cow and CSS161010 were very different in how fast they were able to speed up these outflows," Margutti said. "But they do share one thing -- this presence of a black hole or neutron star inside. That's the key ingredient."

CSS161010's strange home

Before astronomers spotted CSS161010, they had not noticed the tiny galaxy in which it resided. The amazingly bright FBOT drew attention to a dwarf galaxy near the constellation Eridanus, which is shaped like a river in the southern celestial hemisphere. The host galaxy contains about 10 million stars, whereas the Milky Way comprises billions. With remote access to the Keck telescopes in Hawaii, the Northwestern researchers were able to glimpse the tiny galaxy, which looked like nothing more than a small smudge.

So far, astronomers have only found bright FBOTs like CSS161010 and the Cow in these tiny galaxies, which gives a clue into their nature. Although Margutti and Coppejans have not yet fully explored these clues, they speculate that tiny galaxies might be more likely to harbor transients because these galaxies contain such low levels of metals. (Astronomers use the word "metals" to include all materials except hydrogen and helium.)

The amount of metals affects how much mass stars lose throughout their lifetimes in the form of stellar wind. A star without metals can potentially retain more of its mass, producing a bigger explosion at the end of its life.

Giacomo Terreran, a postdoctoral associate at CIERA, took the Keck observations to investigate the galaxy and help understand the FBOT within it.

"Every time a star dies or neutron stars merge, they give metals back to the environment," Terreran said. "Tiny galaxies have a tiny amount of metals because not many stars have died there. This has an impact on how other stars live their lives. We believe that it's not by chance that we only find these very rare transients in these tiny galaxies."

For this work, an international team of astrophysicists used Keck Observatory's Low-Resolution Imaging Spectrometer and Deep Imaging and Multi-Object Spectrograph, the Multiple Mirror Telescope, the Chandra X-ray Observatory, the Karl J. Jansky Very Large Array and the Giant Metrewave Radio Telescope.

UNIVERSITY PARK, Pa. -- Adding an array of spices to your meal is a surefire way to make it more tasty, but new Penn State research suggests it may increase its health benefits, as well.

In a randomized, controlled feeding study, the researchers found that when participants ate a meal high in fat and carbohydrates with six grams of a spice blend added, the participants had lower inflammation markers compared to when they ate a meal with less or no spices.

"If spices are palatable to you, they might be a way to make a high-fat or high-carb meal more healthful," said Connie Rogers, associate professor of nutritional sciences. "We can't say from this study if it was one spice in particular, but this specific blend seemed to be beneficial."

The researchers used a blend of basil, bay leaf, black pepper, cinnamon, coriander, cumin, ginger, oregano, parsley, red pepper, rosemary, thyme and turmeric for the study, which was recently published in the Journal of Nutrition.

According to Rogers, previous research has linked a variety of different spices, like ginger and tumeric, with anti-inflammatory properties. Additionally, chronic inflammation has previously been associated with poor health outcomes like cancer, cardiovascular disease, and overweight and obesity, which affects approximately 72 percent of the U.S. population.

In more recent years, researchers have found that inflammation can spike after a person eats a meal high in fat or sugar. While it is not clear whether these short bursts -- called acute inflammation -- can cause chronic inflammation, Rogers said it's suspected they play a factor, especially in people with overweight or obesity.

"Ultimately the gold standard would be to get people eating more healthfully and to lose weight and exercise, but those behavioral changes are difficult and take time," Rogers said. "So in the interim, we wanted to explore whether a combination of spices that people are already familiar with and could fit in a single meal could have a positive effect."

For the study, the researchers recruited 12 men between the ages of 40 and 65, with overweight or obesity, and at least one risk factor for cardiovascular disease. Rogers said the sample was chosen because people in these demographics tend to be at a higher risk for developing poorer health outcomes.

In random order, each participant ate three versions of a meal high in saturated fat and carbohydrates on three separate days: one with no spices, one with two grams of the spice blend, and one with six grams of the spice blend. The researchers drew blood samples before and then after each meal hourly for four hours to measure inflammatory markers.

"Additionally, we cultured the white blood cells and stimulated them to get the cells to respond to an inflammatory stimulus, similar to what would happen while your body is fighting an infection," Rogers said. "We think that's important because it's representative of what would happen in the body. Cells would encounter a pathogen and produce inflammatory cytokines."

After analyzing the data, the researchers found that inflammatory cytokines were reduced following the meal containing six grams of spices compared to the meal containing two grams of spices or no spices. Rogers said six grams roughly translates to between one teaspoon to one tablespoon, depending on how the spices are dehydrated.

While the researchers can't be sure which spice or spices are contributing to the effect, or the precise mechanism in which the effect is created, Rogers said the results suggest that the spices have anti-inflammatory properties that help offset inflammation caused by the high-carb and high-fat meal.

Additionally, Rogers said that a second study using the same subjects, conducted by Penn State researchers Penny Kris-Etherton and Kristina Petersen, found that six grams of spices resulted in a smaller post-meal reduction of "flow mediated dilation" in the blood vessels -- a measure of blood vessel flexibility and marker of blood vessel health.

In the future, Rogers said she, Kris-Etherton and Petersen will be working on further studies to determine the affects of spices in the diet across longer periods of time and within a more diverse population.

A major roadblock to producing safe, clean and abundant fusion energy on Earth is the lack of detailed understanding of how the hot, charged plasma gas that fuels fusion reactions behaves at the edge of fusion facilities called "tokamaks." Recent breakthroughs by researchers at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) have advanced understanding of the behavior of the highly complex plasma edge in doughnut-shaped tokamaks on the road to capturing the fusion energy that powers the sun and stars. Understanding this edge region will be particularly important for operating ITER, the international fusion experiment under construction in France to demonstrate the practicality of fusion energy.

First-of-a-kind finding

Among the first-of-a-kind findings has been the discovery that accounting for the turbulent fluctuations in the magnetic fields that confine the plasma that fuels fusion reactions can significantly reduce the turbulent particle flux near the plasma edge. Computer simulations show that the net particle flux can go down by as much as 30 percent, despite the fact that the average magnitude of turbulent particle density fluctuation goes up by 60 percent -- indicating that even though the turbulent density fluctuations are more virulent, they are moving particles out of the device less effectively.

Researchers have developed a specialized code called "Gkeyll" -- pronounced just like "Jekyll" in Robert Louis Stevenson's "The Strange Case of Dr. Jekyll and Mr. Hyde" -- that makes these simulations feasible. The mathematical code, a form of modeling called "gyrokinetics," simulates the orbiting of plasma particles around the magnetic field lines at the edge of a fusion plasma.

"Our recent paper summarizes the Gkeyll group's efforts in the area of gyrokinetic simulation," said PPPL physicist Ammar Hakim, lead author of a Physics of Plasmas paper (link is external) that provides an overview of the group's achievements, based on an invited talk he gave at the American Physical Society's Division of Plasma Physics (APS-DPP) conference last Fall. The research, coauthored by scientists from six institutions, adapts a state-of-the-art algorithm to the gyrokinetic system to develop the "key numerical breakthroughs needed to provide accurate simulations," Hakim said.

Worldwide effort

Such breakthroughs are part of the worldwide effort to grasp the science behind the production of fusion reactions on Earth. Fusion reactions combine light elements in the form of plasma -- the hot, charged state of matter composed of free electrons and atomic nuclei that makes up 99 percent of the visible universe -- to generate massive amounts of energy that could provide a virtually inexhaustible supply of power to generate electricity for humanity.

Noah Mandell, a graduate student in the Princeton University Program in Plasma Physics, built on the team's work to develop the first gyrokinetic code able to handle magnetic fluctuations in what is called the plasma scrape-off layer (SOL) at the edge of tokamak plasmas. The British Journal of Plasma Physics has published andhighlighted his report as a featured article (link is external).

Mandell explores how blob-like plasma turbulence bends magnetic field lines, leading to the dynamics of "dancing field lines." He finds that field lines usually move smoothly but when dancing can abruptly reconfigure into reconnection events that cause them to converge and violently snap apart.

For a video of first computer simulations of kinetic plasma turbulence near the edge of fusion devices click here (link is external).

Mandell's findings are best described as "proof-of-concept" with regard to the magnetic fluctuations, he said. "We know there are more physical effects that need to be added to the code for detailed comparisons with experiments, but already the simulations are showing interesting properties near the plasma edge," he said. "The ability to handle bending of the magnetic field lines will also be essential for future simulations of edge localized modes (ELMs), which we would like to do better to understand the bursts of heat they cause that must be controlled to prevent tokamak damage."

Very challenging

What makes this finding unique is that previous gyrokinetic codes have simulated SOL blobs but assumed that the field lines were rigid, Mandell noted. Extending a gyrokinetic code to calculate the movement of magnetic fields lines is computationally very challenging, requiring special algorithms to ensure that two large terms balance each other to an accuracy of better than 1 part in a million.

Moreover, while codes that model turbulence in the core of the tokamak can include magnetic fluctuations, such codes cannot simulate the SOL region. "The SOL requires specialized codes like Gkeyll that can handle much larger plasma fluctuations and interactions with the walls of the reactor," Mandell said.

Future steps for the Gkeyll group will include investigating the precise physical mechanism that affects the dynamics of the plasma edge, an effect likely connected to the bending field lines. "This work provides stepping stones that I think are very important," Hakim said. "Without the algorithms that we made, these findings would be very difficult to apply to ITER and other machines."

In our 13.8 billion-year-old universe, most galaxies like our Milky Way form gradually, reaching their large mass relatively late. But a new discovery made with the Atacama Large Millimeter/submillimeter Array (ALMA) of a massive rotating disk galaxy, seen when the universe was only ten percent of its current age, challenges the traditional models of galaxy formation. This research appears on 20 May 2020 in the journal Nature.

Galaxy DLA0817g, nicknamed the Wolfe Disk after the late astronomer Arthur M. Wolfe, is the most distant rotating disk galaxy ever observed. The unparalleled power of ALMA made it possible to see this galaxy spinning at 170 miles (272 kilometers) per second, similar to our Milky Way.

"While previous studies hinted at the existence of these early rotating gas-rich disk galaxies, thanks to ALMA we now have unambiguous evidence that they occur as early as 1.5 billion years after the Big Bang," said lead author Marcel Neeleman of the Max Planck Institute for Astronomy in Heidelberg, Germany.

How did the Wolfe Disk form?

The discovery of the Wolfe Disk provides a challenge for many galaxy formation simulations, which predict that massive galaxies at this point in the evolution of the cosmos grew through many mergers of smaller galaxies and hot clumps of gas.

"Most galaxies that we find early in the universe look like train wrecks because they underwent consistent and often 'violent' merging," explained Neeleman. "These hot mergers make it difficult to form well-ordered, cold rotating disks like we observe in our present universe."

In most galaxy formation scenarios, galaxies only start to show a well-formed disk around 6 billion years after the Big Bang. The fact that the astronomers found such a disk galaxy when the universe was only ten percent of its current age, indicates that other growth processes must have dominated.

"We think the Wolfe Disk has grown primarily through the steady accretion of cold gas," said J. Xavier Prochaska, of the University of California, Santa Cruz and coauthor of the paper. "Still, one of the questions that remains is how to assemble such a large gas mass while maintaining a relatively stable, rotating disk."

Star formation

The team also used the National Science Foundation's Karl G. Jansky Very Large Array (VLA) and the NASA/ESA Hubble Space Telescope to learn more about star formation in the Wolfe Disk. In radio wavelengths, ALMA looked at the galaxy's movements and mass of atomic gas and dust while the VLA measured the amount of molecular mass - the fuel for star formation. In UV-light, Hubble observed massive stars. "The star formation rate in the Wolfe Disk is at least ten times higher than in our own galaxy," explained Prochaska. "It must be one of the most productive disk galaxies in the early universe."

A 'normal' galaxy

The Wolfe Disk was first discovered by ALMA in 2017. Neeleman and his team found the galaxy when they examined the light from a more distant quasar. The light from the quasar was absorbed as it passed through a massive reservoir of hydrogen gas surrounding the galaxy - which is how it revealed itself. Rather than looking for direct light from extremely bright, but more rare galaxies, astronomers used this 'absorption' method to find fainter, and more 'normal' galaxies in the early universe.

"The fact that we found the Wolfe Disk using this method, tells us that it belongs to the normal population of galaxies present at early times," said Neeleman. "When our newest observations with ALMA surprisingly showed that it is rotating, we realized that early rotating disk galaxies are not as rare as we thought and that there should be a lot more of them out there."

"This observation epitomizes how our understanding of the universe is enhanced with the advanced sensitivity that ALMA brings to radio astronomy," said Joe Pesce, astronomy program director at the National Science Foundation, which funds the telescope. "ALMA allows us to make new, unexpected findings with almost every observation."

Retina is the only part of the central nervous system (CNS) that can be visualized noninvasively with optical imaging approaches. Direct retinal imaging plays an important role not only in understanding diseased eye and ocular therapeutic discovery, but also study of a variety of well-defined CNS disorders. Accumulated evidences have shown that certain neurodegenerative diseases that affect the brain and spinal cord also have manifestations in the retina, and ocular symptoms always precede traditional diagnosis of such diseases, such as Alzheimer's disease, Parkinson's disease and multiple sclerosis.

But as prevalent retinal imaging tools provide limited resolution, photos taken previously are often inadequate to resolve the subcellular structures and dynamics of retinal neurons, mainly attributed to the large optical aberrations of the living eye.

In a recent breakthrough, a team of scientists at the Hong Kong University of Science and Technology developed an adaptive optics two-photon excitation fluorescence microscopy (AO-TPEFM) using direct wavefront sensing for high-resolution in vivo fluorescence imaging of mouse retina, which allow in vivo fundus imaging at an unprecedented resolution after full AO correction. The advance will provide a much-needed tool to study biological processes in retina, and would also shed new light on the neurodegenerative diseases in the central nervous system (CNS).

Their work was published in the journal Light: Science & Applications on May 6, 2020.

"In this work, we advance two-photon microscopy for near-diffraction-limited and functional retinal imaging in living mice," said Prof. Jianan QU, lead researcher and Professor at the Department of Electronic and Computer Engineering, HKUST. "The localized two-photon fluorescence signals were used as nonlinear guide stars to achieve accurate measurement of ocular aberrations at the imaging location. We demonstrate that depth-resolved structures in different retinal layers can be resolved allowing for a wide range of studies which are infeasible otherwise."

AO is a technology used to improve the performance of an optical system by deforming a mirror in order to correct for the distortion(s). AO was first invented to remove the effects of atmospheric distortion in astronomical telescopes and laser communication systems.

In addition to enabling simultaneously functional calcium imaging of somas and dendrites of RGCs, AO-TPEFM also achieves precise axotomy and time-lapse imaging of axonal degeneration with femtosecond laser induced microsurgery.

"Direct wavefront sensing based on nonlinear fluorescent guide stars would be advantageous for accurate measurement of ocular aberrations at the exact imaging location, and thus permits highly efficient AO correction." said Prof. Qu. "As the technology is more widely deployed, AO-TPEFM could help investigate the development of neurodegenerative diseases, since the eye offers a window into nerves of the central nervous system that link the eye with the brain."

ITHACA, N.Y. - After examining a dozen types of suns and a roster of planet surfaces, Cornell University astronomers have developed a practical model - an environmental color "decoder" - to tease out climate clues for potentially habitable exoplanets in galaxies far away.

"We looked at how different planetary surfaces in the habitable zones of distant solar systems could affect the climate on exoplanets," said Jack Madden, who works in the lab of Lisa Kaltenegger, associate professor of astronomy and director of Cornell's Carl Sagan Institute.

"Reflected light on the surface of planets plays a significant role not only on the overall climate," Madden said, "but also on the detectable spectra of Earth-like planets."

Madden and Kaltenegger are co-authors of "How Surfaces Shape the Climate of Habitable Exoplanets," released May 18 in the Monthly Notices of the Royal Astronomical Society.

In their research, they combine details of a planet's surface color and the light from its host star to calculate a climate. For instance, a rocky, black basalt planet absorbs light well and would be very hot, but add sand or clouds and the planet cools; and a planet with vegetation and circling a reddish K-star will likely have cool temperatures because of how those surfaces reflect their suns' light.

"Think about wearing a dark shirt on a hot summer day. You're going to heat up more, because the dark shirt is not reflecting light. It has a low albedo (it absorbs light) and it retains heat," Madden said. "If you wear a light color, such as white, its high albedo reflects the light - and your shirt keeps you cool.

It's the same with stars and planets, Kaltenegger said.

"Depending on the kind of star and the exoplanet's primary color - or the reflecting albedo - the planet's color can mitigate some of the energy given off by the star," Kaltenegger said. "What makes up the surface of an exoplanet, how many clouds surround the planet, and the color of the sun can change an exoplanet's climate significantly."

Madden said forthcoming instruments like the Earth-bound Extremely Large Telescope will allow scientists to gather data in order to test a catalog of climate predictions.

"There's an important interaction between the color of a surface and the light hitting it," he said. "The effects we found based on a planet's surface properties can help in the search for life."

The surface of the planet Mars bears probable traces of 'sedimentary volcanism', a geological phenomenon that leads to the eruption of mud from underground. But how does a mixture of sediment and water behave in the open air on the Red Planet? Conditions there are extremely different from those on Earth - atmospheric pressure is 150 times lower and temperatures are generally negative. An international research team including Susan Conway, a CNRS researcher at the Laboratory of Planetology and Geodynamics (CNRS/Université de Nantes/Université Angers) recreated martian conditions in a low-pressure chamber to observe the flow of mud. These experiments showed that the mud can behave in the same way as certain lava flows on Earth that are called pahoehoe and are characterised by numerous lobes. On Mars, the outer surface of the mud would freeze on contact with the air, while the inner core remains liquid. This liquid can break the frozen crust to form a new flow lobe that refreezes (see video: https://youtu.be/HMr0nXmtI3w). These results, published in Nature Geoscience (May 18, 2020), confirm that sedimentary volcanism is indeed possible on Mars, and invites the scientific community to review Martian geological structures previously interpreted to be caused by lava.

GAINESVILLE, Fla. --- Catnip is most famous for its ability to launch felines into a euphoric frenzy, but the origin of its cat-attracting chemical is a remarkable example of evolutionary innovation.

While the compound nepetalactone drives two-thirds of cats batty, likely by mimicking sex pheromones, its real purpose is protecting catnip from pests. Nepetalactone belongs to a class of chemicals called iridoids, which can repel insects as effectively as DEET.

Many of catnip's relatives in the mint family use iridoids as chemical armor. But an international team of researchers found the ancient ancestor of catnip lost a key iridoid-making gene. Descendants in this lineage - herbs such as basil, oregano, rosemary, lemon balm and mint - had to lean on other defenses, with one notable exception: catnip, which revived the family tradition by evolving a new iridoid production line from scratch.

The findings, including the first detailed look at catnip's nepetalactone recipe, were published today in Science Advances. They provide crucial insights into how plants lose and regain defensive compounds, said study co-author Pamela Soltis, Florida Museum of Natural History curator and University of Florida distinguished professor.

"If we know how evolutionarily flexible a trait is, we can hypothesize about how easy or difficult it might be to modify the trait in another species through plant breeding, genetic engineering or gene editing," she said. "It might be possible to make a crop more resistant to pests if we know that a close relative re-evolved a compound that had previously been lost."

Many plants in the mint family also have medicinally important compounds, said study co-author Douglas Soltis, Florida Museum curator and UF distinguished professor, pointing to iridoid-derived cancer treatments as an example.

"Understanding these plants' underlying biochemical pathways is key to using them for human health," he said.

Researchers sequenced the genomes of two species of catnip and hyssop, a close relative that does not produce iridoids. By comparing the genomes, analyzing the mint family tree and studying ancestral genes and enzymes, they were able to trace the sequence of events that led to the loss of iridoid production in catnip's ancestor between 55-65 million years ago and its re-emergence tens of millions of years later.

The deletion of a gene erased the ability of plants in the subfamily Nepetoideae to make iridoids. Whether the gene deletion was the result of a sudden mutation or a gradual "phasing out" of iridoid production as these plants switched to other chemical defenses remains unclear, Pamela Soltis said.

Without this gene, catnip had to co-opt a related gene to build a new biochemical pathway for making iridoids, beginning about 20 million years ago, Douglas Soltis said.

"It's sort of like, 'I lost my screwdriver, and this one isn't quite the same, but it will work,'" he said, quoting "Jurassic Park" character Ian Malcolm: "'Life, uh, finds a way.'"

The new pathway resulted in nepetalactone, which maintains some hallmark iridoid features, but has a unique chemical structure and properties, the researchers said. The enzymes involved in its production are not found in any related plant species.

"There is a lot of evolutionary back-and-forth in all sorts of characteristics in plants - such as the origin of succulence in cacti, jade plants and aloe, or multiple derivations of red or purple pigments in distantly related species," Pamela Soltis said. "But whenever the 'same' thing re-evolves, it always turns out that it has done so slightly differently - always with a 'twist.'"

Why catnip re-evolved the ability to produce iridoids is "the next big question," Douglas Soltis said.

"As the mint family migrated across Eurasia, semi-arid habitats could have imposed new selective pressures," he said. "Maybe iridoids are more effective as defense compounds in those environments. That can't explain the origin of the new pathway, but it can explain the selection for it once it originates."

Three earthquakes in the Monterey Bay Area, occurring in 1838, 1890 and 1906, happened without a doubt on the San Andreas Fault, according to a new paper by a Portland State University researcher.

The paper, "New Insights into Paleoseismic Age Models on the Northern San Andreas Fault: Charcoal In-built ages and Updated Earthquake Correlations," was recently published in the Bulletin of the Seismological Society of America.

Assistant Professor of Geology at PSU Ashley Streig said the new research confirms what her team first discovered in 2014: three earthquakes occurred within a 68-year period in the Bay Area on the San Andreas Fault.

"This is the first time there's been geologic evidence of a surface rupture from the historic 1838 and 1890 earthquakes that we knew about from newspapers and other historical documents," Streig said. "It basically meant that the 1800s were a century of doom."

Building on the 2014 study, Streig said they were able to excavate a redwood slab from a tree felled by early Europeans, from one meter below the surface in the Bay Area. The tree was toppled before the three earthquakes in question occurred. That slab was used to determine the precise date logging first occurred in the area, and pinpointed the historic dates of the earthquakes. Further, they were able use the slab to develop a new model for determining recurrence intervals and more exact dating.

Streig used the dating technique wiggle matching for several measured carbon 14 samples from the tree slab and compared them with fluctuations in atmospheric carbon 14 concentrations over time to fingerprint the exact death of the tree and confirm the timing of the earthquakes. Because the researchers had an exact age from the slab, they were able to test how well the most commonly used material, charcoal, works in earthquake age models.

Charcoal is commonly used for dating and to constrain the ages of prehistoric earthquakes and develop an earthquake recurrence interval, but Streig said the charcoal can be hundreds of years older than the stratigraphic layer containing it, yielding an offset between what has been dated and the actual age of the earthquake. The new technique accounts for inbuilt charcoal ages -- which account for the difference in time between the wood's formation and the fire that generated said charcoal -- and can better estimate the age of the event being studied.

"We were able to evaluate the inbuilt age of the charcoal incorporated in the deposits and find that charcoal ages are approximately 322 years older than the actual age of the deposit -- so previous earthquake age models in this area using detrital charcoal would be offset roughly by this amount," she said.

New earthquake age modeling using a method to correct for this charcoal inbuilt age, and age results from the tree stump are what give Streig absolute certainly that the 1838 and 1890 earthquakes in question occurred on the San Andreas Fault and during those years.

"We put the nail in the coffin," she added.

DURHAM, N.C. - Electrical engineers at Duke University have devised a low-cost method for passively locating sources of radio waves such as Wi-Fi and cellular communication signals.

Their technique could lead to inexpensive devices that can find radio wave devices like cellular phones or Wi-Fi emitters, or cameras that capture images using the radio waves already bouncing all around us.

The results appear online on May 12 in the journal Optica.

"In this paper we achieved spectral images of microwave noise sources themselves, which means we can locate radio and microwave sources, like antennas, while simultaneously characterizing what frequencies they are emitting over," said Aaron Diebold, an electrical and computer engineering research assistant at Duke, who led the research. "At optical frequencies, that would be like getting a color image of a hot object like a stove burner. While that is pretty simple optically, it takes different techniques in the radio and microwave regime."

Locating sources of these types of waves is already possible, but the techniques and equipment required are complex. Such devices traditionally use an array of many small, power-hungry antennae that cause these devices to become bulky and expensive. And because radio waves are so much larger than light waves, the methods used in optical frequencies are prohibitively complex and would result in extremely large detectors and other machinery.

In the new paper, the researchers turn to metamaterials instead. Metamaterials are synthetic materials composed of many individual engineered features, which together produce properties not found in nature through their structure rather than their chemistry. In this case, the metamaterial is a collection of squares containing inlaid wires in specific shapes that can be dynamically tuned to interact with radio waves passing through them.

By having some squares allow radio waves to pass through and others that block them, the researchers can create what is known as a coded aperture.

"We use the different patterns to encode data into a single measurement, which boosts the signal strength relative to what you would get with just a single, small antenna," said Mohammadreza Imani, a research scientist at Duke who will be joining Arizona State University as an assistant professor in electrical and computer engineering later this year. "We also use the metamaterials to 'stamp' the different frequencies of the data, which allows us to tease them apart."

To understand how a coded aperture boosts signal, consider the grade-school experiment of looking at a solar eclipse by using a hole punched in cardboard to create an image on the sidewalk. As anyone who has ever done this knows, the smaller the hole, the sharper the detail of the eclipse. But a smaller hole also makes it dimmer and harder to see.

The solution is to make many tiny pinholes to create an array of eclipses, and then to use a computer to reconstruct them into a single image. This way you get the sharpness of the tiny pinhole with the brightness of a large pinhole. The key is in knowing the pattern of the holes -- also known as the coded aperture -- which the researchers control with the metamaterials.

The metamaterials also modulate various frequencies differently as they pass through the coded aperture, which allows the researchers to deduce the frequencies of the waves being detected.

The researchers demonstrated the usefulness of this approach in the paper. They first showed that they can "see" and identify the shape of radio waves emitted by a smiley-face-shaped antenna. They then showed that their system can work in the real world by locating radio wave sources in three dimensions relative to one another.

The researchers plan to continue to refine their methods in the hope of eventually being able to take "pictures" of objects and scenes with nothing more than the radio waves bouncing off of them.

"Passive imaging occurs in situations where you don't control the source, like taking a photo using light from the sun or light bulbs," said David R. Smith, the James B. Duke Distinguished Professor of Electrical and Computer Engineering at Duke. "At microwave frequencies, there are lots of signals bouncing around constantly. These ambient RF waves could provide enough illumination for a metasurface imager to reconstruct images using the techniques described in this research."

TORONTO, May 11, 2020 -- The oldest molecular fluids in the solar system could have supported the rapid formation and evolution of the building blocks of life, new research in the journal Proceedings of the National Academy of Sciences reveals.

An international group of scientists, led by researchers from the Royal Ontario Museum (ROM) and co-authors from McMaster University and York University, used state-of-the-art techniques to map individual atoms in minerals formed in fluids on an asteroid over 4.5 billion years ago.

Studying the ROM's iconic Tagish Lake meteorite, scientists used atom-probe tomography, a technique capable of imaging atoms in 3D, to target molecules along boundaries and pores between magnetite grains that likely formed on the asteroid's crust. There, they discovered water precipitates left in the grain boundaries on which they conducted their ground-breaking research.

"We know water was abundant in the early solar system," explains lead author Dr. Lee White, Hatch postdoctoral fellow at the ROM, "but there is very little direct evidence of the chemistry or acidity of these liquids, even though they would have been critical to the early formation and evolution of amino acids and, eventually, microbial life."

This new atomic-scale research provides the first evidence of the sodium-rich (and alkaline) fluids in which the magnetite framboids formed. These fluid conditions are preferential for the synthesis of amino acids, opening the door for microbial life to form as early as 4.5 billion years ago.

"Amino acids are essential building blocks of life on Earth, yet we still have a lot to learn about how they first formed in our solar system," says Beth Lymer, a PhD student at York University and co-author of the study. "The more variables that we can constrain, such as temperature and pH, allows us to better understand the synthesis and evolution of these very important molecules into what we now know as biotic life on Earth."

The Tagish Lake carbonaceous chondrite was retrieved from an ice sheet in B.C.'s Tagish Lake in 2000, and later acquired by the ROM, where it is now considered to be one of the museums iconic objects. This history means that the sample used by the team has never been above room temperature or exposed to liquid water, allowing the scientists to confidently link the measured fluids to the parent asteroid.

By using new techniques, such as atom probe tomography, the scientists hope to develop analytical methods for planetary materials returned to Earth by space craft, such as by NASA's OSIRIS-REx mission or a planned sample-return mission to Mars in the near future.

"Atom probe tomography gives us an opportunity to make fantastic discoveries on bits of material a thousand times thinner than a human hair," says White. "Space missions are limited to bringing back tiny amounts of material, meaning these techniques will be critical to allowing us to understand more about the solar system while also preserving material for future generations."

At an idyllic island in the Mediterranean Sea, ocean covers up the site of a vast volcanic explosion from 3200 years ago. A few hundred kilometers north-west, three other islands still have their volcanic histories from a few million years ago mostly intact. No explosions there. So why the differences between the Santorini caldera and the Aegina, Methana and Poros lava domes? Researchers used volcanic "fingerprints' and plate tectonics research to find out why.

The end of a civilisation

A big volcano blew up about 3200 years ago, right next to where Santorini island is in Greece today. During that eruption, liquid molten rock under the ground (magma) built up immense pressure, and then erupted into a lava explosion. The impact was so intense that the volcano collapsed into a huge basin called a caldera.

What had been an island-volcano, was then overrun by ocean, an event considered partially responsible for the demise of the Minoan civilisation.

Santorini Island became a popular travel destination with big ocean-going ships sailing over the caldera. The village of Phira perches on the cliff-edge of the remains of the volcano.

As idyllic as it looks, the Santorini volcano underneath the ocean still constitutes the biggest volcanic hazard for Europe, together with the Vesuvius volcano in Italy.

Toothpaste rather than fireworks

A few hundred kilometers north-west of Santorini, in Greece's Saronic gulf much closer to Athens, a completely different kind of "volcano" looks much less dramatic.

The small islands of Aegina, Methana and Poros sport rounded hills with roads winding uphill in hairpin bends. These hills have volcanic ancestry too - but they are nothing like Santorini.

Here, liquid lava didn't explode in a big eruption.

"There is no evidence that that large dramatic events ever took place at these islands," says Prof Marlina A. Elburg, a Geology researcher at the University of Johannesburg.

"Thick blocky lava oozed out of magma chambers under the ground at these islands between 5.3 to 2.6 million years ago, during the Pliocene. The lava was so thick, it was more like toothpaste or putty than liquid. It formed lava domes rather than lava volcanoes.

"After a few million years' worth of weathering, they're well camouflaged hills, but they are still considered volcanically active," she says.

How is it possible that volcanoes so close in geological time and space can behave to differently? The researchers used several techniques to find out.

Finding volcanic 'fingerprints'

Elburg and co-author Ingrid Smet, a PhD candidate at the time, analysed samples of the lavas in new whole rock analyses, in research published in Lithos.

The study followed on their previous research on the lavas at Methana, also published in Lithos.

They looked for the ratios of very specific elements in the samples, called isotope signatures. Isotope signatures work similar to 'fingerprints' for lavas - they help researchers figure out what the lavas were made of, where, and when they were formed.

"Mostly the isotope signatures matched what one would expect from where the islands are located in the Aegean volcanic arc," says Elburg.

But there were surprises too.

Subterranean recycling machine

Underneath all these volcanoes at Aegina, Methana, Poros and Santorini, something else is going on in deep inside the crust of planet Earth. Running roughly east to west underneath the Mediterranean Sea is the Aegean volcanic arc. This arc is where the African tectonic plate 'dives under' the Aegean microplate.

The 'diving under' process is called subduction by geologists. It means that one part of the cool outer crust of Earth starts moving underneath another part of the crust, getting 'recycled' inside the hot liquid rock of the Earth's mantle.

The islands of Aegina, Methana, Poros and Santorini are not just islands with volcanoes. All of them are an integral part of Earth's 'recycling machine' that keeps renewing the crust underneath the planet's oceans.

This raises the question: Why do these islands have such different 'lava histories', even though all of them are on the edge of the Aegean plate?

Some of the answers have to do with what goes into the lava "mixes" for the volcanoes.

Variable lava mix recipes

The African plate 'dives under' the Aegean plate in an oceanic trench in the Mediterranean Sea. This happens very slowly at a few centimeters per year. Which means the pristine cold basalt of the down-going African plate's crust has been soaking in ocean water for millions of years before it enters the much warmer magma underneath the over-riding Aegean plate.

"The crust of the down-going plate now consists of altered rocks, containing minerals with water in them. These minerals become unstable during subduction because of the increasing pressure and temperature, and release their water," says Elburg.

"This water lowers the melting point of the mantle, similar to what happens when adding salt to ice. That is why the mantle under the over-riding starts to melt. It is this molten material, or magma, that flows/oozes out of volcanoes/lava domes as lava."

Another possible ingredient of the differing lavas is sediments in the oceanic trench at the subduction zone. At the Aegean Arc the down-going plate is covered by a very thick pile of ocean sediments. Some of the sediment is former continental crust.

A lot of this sediment is 'scraped off' when the plate subducts and forms an accretionary (or build-up) wedge. However, some of it is also going down into the mantle and getting mixed with the melting mantle wedge, she says.

Same plate, different lavas

Since Aegina, Methana, Poros and Santorini volcanoes are all part of the same subduction zone, the different volcanic activity raises several big questions. One of these is:

Why the thick blocky lava at the western volcanic centres Aegina, Methana and Poros 2.5 to 2 million years ago, but liquid lava at Santorini 3200 years ago?

The answers to this creates other questions about the recycling behaviour of the planet we live on.

But subduction zones are tricky to study. It's not possible to go to one of those and come back with some sample materials. Scientists still need more understanding of what role the overriding plate plays; how much interaction there is between ascending magmas and the crust they ascend through; and whether subduction-related magmas obtain their geochemical signature from the sediment that is recycled back into the earth, says Elburg.

"The answers to these questions can help us understand to what extent the melting processes that started at more than 100 kilometers deep in the mantle, continue when the magma is closer to the surface of the earth," she says.

"This process of 'crustal contamination' is yet another 'Earth recycling machine', which may also influence the potential for ore deposits - like in the Andes, where major copper deposits are found, and where this 'intracrustal recycling' is thought to play an important role".

Deeper vs shallower

One way of studying lavas is to put thin slices (called thin sections) under a microscope and identify the minerals. Because minerals need different conditions to form, their presence can say a lot about where and how magmas were mixed.

In this study the minerals indicated that Santorini lavas were more liquid because they formed at inside shallower magma chambers, while the western volcanic centre lavas were thicker and more blocky because they formed in deeper magma chambers.

"The thin sections of the Santorini lavas display pyroxenes and significant plagioclase. This indicates that the magma from which the crystals formed was located at shallow depths in the earth," says Elburg.

And there is an invisible reason the magma was at shallower depths at Santorini.

"The tectonic plate above Santorini's magma chambers is being pulled apart. In geology terms, it is under localised extension. And because the plate is being stretched out and Santorini is in the middle of it, Santorini happens to be at the thinnest part of the plate.

"With a magma chamber at a shallower depth, the roof will cave in when the chamber starts emptying itself during an eruption. This makes the eruption even worse and creates a caldera, as at Santorini," she adds.

No explosions

In contrast, when they looked at the thin sections of the thick blocky lavas from Aegina and Methana, they found hornblende. The mineral was absent in the Santorini lavas.

Hornblende can only form if the magma is deep enough in the Earth. This indicates that the magma chambers on Aegina and Methana should be located deeper than on Santorini.

"With the magma chambers at greater depths for the western Aegina- Methana-Poros volcanoes, that makes for changes in the lava. There the magma chambers underneath the lava domes did not cave in. Additionally, the crystallization of the amphibole mineral group that includes hornblende, makes magma more viscous, or sticky. So it is more difficult for the magma to come to the surface in the first place.

Over-riding plate vs sediment

To figure out whether the over-riding plate or the ocean sediments were the bigger factor in creating thick blocky lavas, the researchers analysed specific 'lava fingerprints'. These radiogenic isotope ratios gave them the best indication on which materials were mixed into the underground magmas for those lavas.

"We compared Santorini with Aegina-Poros-Methana lavas in terms of their geochemistry on 87Sr/86Sr, 143Nd/144Nd and 208Pb/204Pb. They were distinctly different. Then by combining the radiogenic isotope signature of the lavas with trace element ratios, we managed to pinpoint the down-going sediment as the biggest influence creating thick blocky lavas, not the overriding plate.

No one lava size

"We found that Aegina and Methana-Poros have their own individual volcanic histories, even though they're part of the Aegean arc.

"This means that a simple one-size-fits-all explanation, based on crustal contamination history, for the difference in eruptive style compared to Santorini does not work.

"Modern subduction zones are not all alike. Even in one volcanic arc, more than one eruptive style points to differences in subduction processes," concludes Elburg.