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Ingredient missing from current dark matter theories

Observations by the NASA/ESA Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope (VLT) in Chile have found that something may be missing from the theories of how dark matter behaves. This missing ingredient may explain why researchers have uncovered an unexpected discrepancy between observations of the dark matter concentrations in a sample of massive galaxy clusters and theoretical computer simulations of how dark matter should be distributed in clusters. The new findings indicate that some small-scale concentrations of dark matter produce lensing effects that are 10 times stronger than expected.

Dark matter is the invisible glue that keeps stars, dust, and gas together in a galaxy. This mysterious substance makes up the bulk of a galaxy’s mass and forms the foundation of our Universe’s large-scale structure. Because dark matter does not emit, absorb, or reflect light, its presence is only known through its gravitational pull on visible matter in space. Astronomers and physicists are still trying to pin down what it is.

Galaxy clusters, the most massive and recently assembled structures in the Universe, are also the largest repositories of dark matter. Clusters are composed of individual member galaxies that are held together largely by the gravity of dark matter.

“Galaxy clusters are ideal laboratories in which to study whether the numerical simulations of the Universe that are currently available reproduce well what we can infer from gravitational lensing,” said Massimo Meneghetti of the INAF-Observatory of Astrophysics and Space Science of Bologna in Italy, the study’s lead author.

“We have done a lot of testing of the data in this study, and we are sure that this mismatch indicates that some physical ingredient is missing either from the simulations or from our understanding of the nature of dark matter,” added Meneghetti.

“There’s a feature of the real Universe that we are simply not capturing in our current theoretical models,” added Priyamvada Natarajan of Yale University in Connecticut, USA, one of the senior theorists on the team. “This could signal a gap in our current understanding of the nature of dark matter and its properties, as these exquisite data have permitted us to probe the detailed distribution of dark matter on the smallest scales.”

The distribution of dark matter in clusters is mapped by measuring the bending of light — the gravitational lensing effect — that they produce. The gravity of dark matter concentrated in clusters magnifies and warps light from distant background objects. This effect produces distortions in the shapes of background galaxies which appear in images of the clusters. Gravitational lensing can often also produce multiple images of the same distant galaxy.

The higher the concentration of dark matter in a cluster, the more dramatic its light-bending effect. The presence of smaller-scale clumps of dark matter associated with individual cluster galaxies enhances the level of distortions. In some sense, the galaxy cluster acts as a large-scale lens that has many smaller lenses embedded within it.

Hubble’s crisp images were taken by the telescope’s Wide Field Camera 3 and Advanced Camera for Surveys. Coupled with spectra from the European Southern Observatory’s Very Large Telescope (VLT), the team produced an accurate, high-fidelity, dark-matter map. By measuring the lensing distortions astronomers could trace out the amount and distribution of dark matter. The three key galaxy clusters, MACS J1206.2-0847, MACS J0416.1-2403, and Abell S1063, were part of two Hubble surveys: The Frontier Fields and the Cluster Lensing And Supernova survey with Hubble (CLASH) programs.

To the team’s surprise, in addition to the dramatic arcs and elongated features of distant galaxies produced by each cluster’s gravitational lensing, the Hubble images also revealed an unexpected number of smaller-scale arcs and distorted images nested near each cluster’s core, where the most massive galaxies reside. The researchers believe the nested lenses are produced by the gravity of dense concentrations of matter inside the individual cluster galaxies. Follow-up spectroscopic observations measured the velocity of the stars orbiting inside several of the cluster galaxies to therby pin down their masses.

“The data from Hubble and the VLT provided excellent synergy,” shared team member Piero Rosati of the Università degli Studi di Ferrara in Italy, who led the spectroscopic campaign. “We were able to associate the galaxies with each cluster and estimate their distances.”

“The speed of the stars gave us an estimate of each individual galaxy’s mass, including the amount of dark matter,” added team member Pietro Bergamini of the INAF-Observatory of Astrophysics and Space Science in Bologna, Italy.

By combining Hubble imaging and VLT spectroscopy, the astronomers were able to identify dozens of multiply imaged, lensed, background galaxies. This allowed them to assemble a well-calibrated, high-resolution map of the mass distribution of dark matter in each cluster.

The team compared the dark-matter maps with samples of simulated galaxy clusters with similar masses, located at roughly the same distances. The clusters in the computer model did not show any of the same level of dark-matter concentration on the smallest scales — the scales associated with individual cluster galaxies.

“The results of these analyses further demonstrate how observations and numerical simulations go hand in hand,” said team member Elena Rasia of the INAF-Astronomical Observatory of Trieste, Italy.

“With high-resolution simulations, we can match the quality of observations analysed in our paper, permitting detailed comparisons like never before,” added Stefano Borgani of the Università degli Studi di Trieste, Italy.

Astronomers, including those of this team, look forward to continuing to probe dark matter and its mysteries in order to finally pin down its nature.

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Can sunlight convert emissions into useful materials?

Shaama Sharada calls carbon dioxide — the worst offender of global warming — a very stable, “very happy molecule.”

She aims to change that.

Recently published in the Journal of Physical Chemistry A, Sharada and a team of researchers at the USC Viterbi School of Engineering seek to break CO2 apart and convert the greenhouse gas into useful materials like fuels or consumer products ranging from pharmaceuticals to polymers.

Typically, this process requires a tremendous amount of energy. However, in the first computational study of its kind, Sharada and her team enlisted a more sustainable ally: the sun.

Specifically, they demonstrated that ultraviolet (UV) light could be very effective in exciting an organic molecule, oligophenylene. Upon exposure to UV, oligophenylene becomes a negatively charged “anion,” readily transferring electrons to the nearest molecule, such as CO2 — thereby making the CO2 reactive and able to be reduced and converted into things like plastics, drugs or even furniture.

“CO2 is notoriously hard to reduce, which is why it lives for decades in the atmosphere,” Sharada said. “But this negatively charged anion is capable of reducing even something as stable as CO2, which is why it’s promising and why we are studying it.”

The rapidly growing concentration of carbon dioxide in the earth’s atmosphere is one of the most urgent issues humanity must address to avoid a climate catastrophe.

Since the start of the industrial age, humans have increased atmospheric CO2 by 45%, through the burning of fossil fuels and other emissions. As a result, average global temperatures are now two degrees Celsius warmer than the pre-industrial era. Thanks to greenhouse gases like CO2, the heat from the sun is remaining trapped in our atmosphere, warming our planet.

The research team from the Mork Family Department of Chemical Engineering and Materials Science was led by third year Ph.D. student Kareesa Kron, supervised by Sharada, a WISE Gabilan Assistant Professor. The work was co-authored by Samantha J. Gomez from Francisco Bravo Medical Magnet High School, who has been part of the USC Young Researchers Program, allowing high school students from underrepresented areas to take part in STEM research.

Many research teams are looking at methods to convert CO2 that has been captured from emissions into fuels or carbon-based feedstocks for consumer products ranging from pharmaceuticals to polymers.

The process traditionally uses either heat or electricity along with a catalyst to speed up CO2 conversion into products. However, many of these methods are often energy intensive, which is not ideal for a process aiming to reduce environmental impacts. Using sunlight instead to excite the catalyst molecule is attractive because it is energy efficient and sustainable.

“Most other ways to do this involve using metal-based chemicals, and those metals are rare earth metals,” said Sharada. “They can be expensive, they are hard to find and they can potentially be toxic.”

Sharada said the alternative is to use carbon-based organic catalysts for carrying out this light-assisted conversion. However, this method presents challenges of its own, which the research team aims to address. The team uses quantum chemistry simulations to understand how electrons move between the catalyst and CO2 to identify the most viable catalysts for this reaction.

Sharada said the work was the first computational study of its kind, in that researchers had not previously examined the underlying mechanism of moving an electron from an organic molecule like oligophenylene to CO2. The team found that they can carry out systematic modifications to the oligophenylene catalyst, by adding groups of atoms that impart specific properties when bonded to molecules, that tend to push electrons towards the center of the catalyst, to speed up the reaction.

Despite the challenges, Sharada is excited about the opportunities for her team.

“One of those challenges is that, yes, they can harness radiation, but very little of it is in the visible region, where you can shine light on it in order for the reaction to occur,” said Sharada. “Typically, you need a UV lamp to make it happen.”

Sharada said that the team is now exploring catalyst design strategies that not only lead to high reaction rates but also allow for the molecule to be excited by visible light, using both quantum chemistry and genetic algorithms.

Gomez was a senior at the Bravo Medical Magnet school at the time she took part in the USC Young Researchers Program over the summer, working in Sharada’s lab. She was directly mentored and trained in theory and simulations by Kron. Sharada said Gomez’s contributions were so impressive that the team agreed she deserved an authorship on the paper.

Gomez said that she enjoyed the opportunity to work on important research contributing to environmental sustainability. She said her role involved conducting computational research, calculating which structures were able to significantly reduce CO2.

“Traditionally we are shown that research comes from labs where you have to wear lab coats and work with hazardous chemicals,” Gomez said. “I enjoyed that every day I was always learning new things about research that I didn’t know could be done simply through computer programs.”

“The first-hand experience that I gained was simply the best that I could’ve asked for, since it allowed me to explore my interest in the chemical engineering field and see how there are many ways that life-saving research can be achieved,” Gomez said.

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‘Black dwarf supernova’: Physicist calculates when the last supernova ever will happen

The end of the universe as we know it will not come with a bang. Most stars will very, very slowly fizzle as their temperatures fade to zero.

“It will be a bit of a sad, lonely, cold place,” said theoretical physicist Matt Caplan, who added no one will be around to witness this long farewell happening in the far far future. Most believe all will be dark as the universe comes to an end. “It’s known as ‘heat death,’ where the universe will be mostly black holes and burned-out stars,” said Caplan, who imagined a slightly different picture when he calculated how some of these dead stars might change over the eons.

Punctuating the darkness could be silent fireworks — explosions of the remnants of stars that were never supposed to explode. New theoretical work by Caplan, an assistant professor of physics at Illinois State University, finds that many white dwarfs may explode in supernova in the distant far future, long after everything else in the universe has died and gone quiet.

In the universe now, the dramatic death of massive stars in supernova explosions comes when internal nuclear reactions produce iron in the core. Iron cannot be burnt by stars — it accumulates like a poison, triggering the star’s collapse creating a supernova. But smaller stars tend to die with a bit more dignity, shrinking and becoming white dwarfs at the end of their lives.

“Stars less than about 10 times the mass of the sun do not have the gravity or density to produce iron in their cores the way massive stars do, so they can’t explode in a supernova right now,” said Caplan. “As white dwarfs cool down over the next few trillion years, they’ll grow dimmer, eventually freeze solid, and become ‘black dwarf’ stars that no longer shine.” Like white dwarfs today, they’ll be made mostly of light elements like carbon and oxygen and will be the size of the Earth but contain about as much mass as the sun, their insides squeezed to densities millions of times greater than anything on Earth.

But just because they’re cold doesn’t mean nuclear reactions stop. “Stars shine because of thermonuclear fusion — they’re hot enough to smash small nuclei together to make larger nuclei, which releases energy. White dwarfs are ash, they’re burnt out, but fusion reactions can still happen because of quantum tunneling, only much slower, Caplan said. “Fusion happens, even at zero temperature, it just takes a really long time.” He noted this is the key for turning black dwarfs into iron and triggering a supernova.

Caplan’s new work, accepted for publication by Monthly Notices of the Royal Astronomical Society, calculates how long these nuclear reactions take to produce iron, and how much iron black dwarfs of different sizes need to explode. He calls his theoretical explosions “black dwarf supernova” and calculates that the first one will occur in about 10 to the 1100th years. “In years, it’s like saying the word ‘trillion’ almost a hundred times. If you wrote it out, it would take up most of a page. It’s mindbogglingly far in the future.”

Of course, not all black dwarfs will explode. “Only the most massive black dwarfs, about 1.2 to 1.4 times the mass of the sun, will blow.” Still, that means as many as 1 percent of all stars that exist today, about a billion trillion stars, can expect to die this way. As for the rest, they’ll remain black dwarfs. “Even with very slow nuclear reactions, our sun still doesn’t have enough mass to ever explode in a supernova, even in the far far future. You could turn the whole sun to iron and it still wouldn’t pop.”

Caplan calculates that the most massive black dwarfs will explode first, followed by progressively less massive stars, until there are no more left to go off after about 1032000 years. At that point, the universe may truly be dead and silent. “It’s hard to imagine anything coming after that, black dwarf supernova might be the last interesting thing to happen in the universe. They may be the last supernova ever.” By the time the first black dwarfs explode, the universe will already be unrecognizable. “Galaxies will have dispersed, black holes will have evaporated, and the expansion of the universe will have pulled all remaining objects so far apart that none will ever see any of the others explode.It won’t even be physically possible for light to travel that far.”

Even though he’ll never see one, Caplan remains unbothered. “I became a physicist for one reason. I wanted to think about the big questions- why is the universe here, and how will it end?” When asked what big question comes next, Caplan says, “Maybe we’ll try simulating some black dwarf supernova. If we can’t see them in the sky then at least we can see them on a computer.”

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Planet found orbiting small, cool star

Using the supersharp radio “vision” of the National Science Foundation’s continent-wide Very Long Baseline Array (VLBA), astronomers have discovered a Saturn-sized planet closely orbiting a small, cool star 35 light-years from Earth. This is the first discovery of an extrasolar planet with a radio telescope using a technique that requires extremely precise measurements of a star’s position in the sky, and only the second planet discovery for that technique and for radio telescopes.

The technique has long been known, but has proven difficult to use. It involves tracking the star’s actual motion in space, then detecting a minuscule “wobble” in that motion caused by the gravitational effect of the planet. The star and the planet orbit a location that represents the center of mass for both combined. The planet is revealed indirectly if that location, called the barycenter, is far enough from the star’s center to cause a wobble detectable by a telescope.

This technique, called the astrometric technique, is expected to be particularly good for detecting Jupiter-like planets in orbits distant from the star. This is because when a massive planet orbits a star, the wobble produced in the star increases with a larger separation between the planet and the star, and at a given distance from the star, the more massive the planet, the larger the wobble produced.

Starting in June of 2018 and continuing for a year and a half, the astronomers tracked a star called TVLM 513-46546, a cool dwarf with less than a tenth the mass of our Sun. In addition, they used data from nine previous VLBA observations of the star between March 2010 and August 2011.

Extensive analysis of the data from those time periods revealed a telltale wobble in the star’s motion indicating the presence of a planet comparable in mass to Saturn, orbiting the star once every 221 days. This planet is closer to the star than Mercury is to the Sun.

Small, cool stars like TVLM 513-46546 are the most numerous stellar type in our Milky Way Galaxy, and many of them have been found to have smaller planets, comparable to Earth and Mars.

“Giant planets, like Jupiter and Saturn, are expected to be rare around small stars like this one, and the astrometric technique is best at finding Jupiter-like planets in wide orbits, so we were surprised to find a lower mass, Saturn-like planet in a relatively compact orbit. We expected to find a more massive planet, similar to Jupiter, in a wider orbit,” said Salvador Curiel, of the National Autonomous University of Mexico. “Detecting the orbital motions of this sub-Jupiter mass planetary companion in such a compact orbit was a great challenge,” he added.

More than 4,200 planets have been discovered orbiting stars other than the Sun, but the planet around TVLM 513-46546 is only the second to be found using the astrometric technique. Another, very successful method, called the radial velocity technique, also relies on the gravitational effect of the planet upon the star. That technique detects the slight acceleration of the star, either toward or away from Earth, caused by the star’s motion around the barycenter.

“Our method complements the radial velocity method which is more sensitive to planets orbiting in close orbits, while ours is more sensitive to massive planets in orbits further away from the star,” said Gisela Ortiz-Leon of the Max Planck Institute for Radio Astronomy in Germany. “Indeed, these other techniques have found only a few planets with characteristics such as planet mass, orbital size, and host star mass, similar to the planet we found. We believe that the VLBA, and the astrometry technique in general, could reveal many more similar planets.”

A third technique, called the transit method, also very successful, detects the slight dimming of the star’s light when a planet passes in front of it, as seen from Earth.

The astrometric method has been successful for detecting nearby binary star systems, and was recognized as early as the 19th Century as a potential means of discovering extrasolar planets. Over the years, a number of such discoveries were announced, then failed to survive further scrutiny. The difficulty has been that the stellar wobble produced by a planet is so small when seen from Earth that it requires extraordinary precision in the positional measurements.

“The VLBA, with antennas separated by as much as 5,000 miles, provided us with the great resolving power and extremely high precision needed for this discovery,” said Amy Mioduszewski, of the National Radio Astronomy Observatory. “In addition, improvements that have been made to the VLBA’s sensitivity gave us the data quality that made it possible to do this work now,” she added.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

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The quiet Sun is much more active than we thought

Solar activity varies in 11-year cycles. As the activity cycle switches to a new one, the Sun is usually very calm for several years.

For a long time, researchers have believed that there is not much of interest going on in the Sun during the passive period, therefore not worth studying. Now this assumption is showed to be false by Juha Kallunki, Merja Tornikoski and Irene Björklund, researchers at Metsähovi Radio Observatory, in their peer-reviewed research article published in Solar Physics. This is the first time that astronomers are systematically studying the phenomena of the solar minimum.

Not all phenomena could be explained — yet

The researchers reached their conclusion by examining the solar radio maps detected by the Metsähovi Radio Observatory and comparing them with the data collected by a satellite observing the Sun in the ultraviolet range. The solar maps showed active areas, or radio brightenings, which can be observed on the maps as hotter areas than the rest of the solar surface. According to researchers, there are three explanations for radio brightenings.

First, some brightenings were observed in the polar areas on the solar maps that could be identified as coronal holes. Particle flows, or solar winds, ejected by coronal holes can cause auroras when they reach the Earth’s atmosphere. The corona is the outer atmosphere of the Sun.

Second, the researchers observed brightenings from which, based on other observations, ejections of hot material from the surface of the sun could be detected.

Third, radio brightenings were found in areas where, based on satellite observations, strong magnetic fields were detected.

Researchers also found radio brightenings in some areas where no explanatory factor was found on the basis of satellite observations.

‘The other sources used did not explain the cause of the brightening. We don’t know what causes those phenomena. We must continue our research’, Kallunki says.

Additional observations and research are also needed to predict whether the phenomena of the solar minimum indicate something about the next active period, about its onset and intensity, for example. Each one of the last four cycles has been weaker than the previous one. Researchers do not know why the activity curves do not rise as high as during the previous cycles.

‘Solar activity cycles do not always last exactly 11 years, either’, explains Docent Merja Tornikoski.

‘A new activity period will not be identified until it is already ongoing. In any case, these observations of the quiet phase we are now analysing are clearly during a period when activity is at its lowest. Now we are waiting for a new rise in activity.’

Solar storms can cause danger

On the Earth, solar activity can be seen as auroras, for example. Solar activity can even cause major damage, as solar storms caused by solar flares can damage satellites, electricity networks and radio frequency communications. Research helps to prepare for such damage.

‘In solar storms, it takes 2 to 3 days before the particles hit the Earth. They reach satellites higher up in orbit much faster, which would leave us even less time to prepare for damage’, Kallunki points out.

Located in Kirkkonummi, Aalto University Metsähovi is the only astronomical radio observatory and continuously operational astronomical observation station in Finland. Metsähovi is internationally known for its unique, continuous datasets, including a solar monitoring programme spanning over 40 years that has collected data from scientifically very interesting high radio frequencies. This is possible thanks to the exceptionally precise mirror surface of the Metsähovi radio telescope.

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Water molecules are gold for nanocatalysis

Nanocatalysts made of gold nanoparticles dispersed on metal oxides are very promising for the industrial, selective oxidation of compounds, including alcohols, into valuable chemicals. They show high catalytic activity, particularly in aqueous solution. A team of researchers from Ruhr-Universität Bochum (RUB) has been able to explain why: Water molecules play an active role in facilitating the oxygen dissociation needed for the oxidation reaction. The team of Professor Dominik Marx, Chair of Theoretical Chemistry, reports in the high-impact journal ACS Catalysis on 14 July 2020.

Rushing for gold

Most industrial oxidation processes involve the use of agents, such as chlorine or organic peroxides, that produce toxic or useless by-products. Instead, using molecular oxygen, O2, and splitting it to obtain the oxygen atoms needed to produce specific products would be a greener and more attractive solution. A promising medium for this approach is the gold/metal oxide (Au/TiO2) system, where the metal oxide titania (TiO2) supports nanoparticles of gold. These nanocatalysts can catalyse the selective oxidation of molecular hydrogen, carbon monoxide and especially alcohols, among others. A crucial step behind all reactions is the dissociation of O2, which comprises a usually high energy barrier. And a crucial unknown in the process is the role of water, since the reactions take place in aqueous solutions.

In a 2018 study, the RUB group of Dominik Marx, Chair of Theoretical Chemistry and Research Area coordinator in the Cluster of Excellence Ruhr Explores Solvation (Resolv), already hinted that water molecules actively participate in the oxidative reaction: They enable a stepwise charge-transfer process that leads to oxygen dissociation in the aqueous phase. Now, the same team reveals that solvation facilitates the activation of molecular oxygen (O2) at the gold/metal oxide (Au/TiO2) nanocatalyst: In fact, water molecules help to decrease the energy barrier for the O2 dissociation. The researchers quantified that the solvent curbs the energy costs by 25 per cent compared to the gas phase. “For the first time, it has been possible to gain insights into the quantitative impact of water on the critical O2 activation reaction for this nanocatalyst — and we also understood why,” says Dominik Marx.

Mind the water molecules

The RUB researchers applied computer simulations, the so-called ab initio molecular dynamics simulations, which explicitly included not only the catalyst but also as many as 80 surrounding water molecules. This was key to gain deep insights into the liquid-phase scenario, which contains water, in direct comparison to the gas phase conditions, where water is absent. “Previous computational work employed significant simplifications or approximations that didn’t account for the true complexity of such a difficult solvent, water,” adds Dr. Niklas Siemer who recently earned his PhD at RUB based on this research.

Scientists simulated the experimental conditions with high temperature and pressure to obtain the free energy profile of O2 in both liquid and gas phase. Finally, they could trace back the mechanistic reason for the solvation effect: Water molecules induce an increase of local electron charge towards oxygen that is anchored at the nanocatalyst perimeter; this in turn leads to the less energetic costs for the dissociation. In the end, say the researchers, it’s all about the unique properties of water: “We found that the polarizability of water and its ability to donate hydrogen bonds are behind oxygen activation,” says Dr. Munoz-Santiburcio. According to the authors, the new computational strategy will help to understand and improve direct oxidation catalysis in water and alcohols.

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An origin story for a family of oddball meteorites

Most meteorites that have landed on Earth are fragments of planetesimals, the very earliest protoplanetary bodies in the solar system. Scientists have thought that these primordial bodies either completely melted early in their history or remained as piles of unmelted rubble.

But a family of meteorites has befuddled researchers since its discovery in the 1960s. The diverse fragments, found all over the world, seem to have broken off from the same primordial body, and yet the makeup of these meteorites indicates that their parent must have been a puzzling chimera that was both melted and unmelted.

Now researchers at MIT and elsewhere have determined that the parent body of these rare meteorites was indeed a multilayered, differentiated object that likely had a liquid metallic core. This core was substantial enough to generate a magnetic field that may have been as strong as Earth’s magnetic field is today.

Their results, published in the journal Science Advances, suggest that the diversity of the earliest objects in the solar system may have been more complex than scientists had assumed.

“This is one example of a planetesimal that must have had melted and unmelted layers. It encourages searches for more evidence of composite planetary structures,” says lead author Clara Maurel, a graduate student in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS). “Understanding the full spectrum of structures, from nonmelted to fully melted, is key to deciphering how planetesimals formed in the early solar system.”

Maurel’s co-authors include EAPS professor Benjamin Weiss, along with collaborators at Oxford University, Cambridge University, the University of Chicago, Lawrence Berkeley National Laboratory, and the Southwest Research Institute.

Oddball irons

The solar system formed around 4.5 billion years ago as a swirl of super-hot gas and dust. As this disk gradually cooled, bits of matter collided and merged to form progressively larger bodies, such as planetesimals.

The majority of meteorites that have fallen to Earth have compositions that suggest they came from such early planetesimals that were either of two types: melted, and unmelted. Both types of objects, scientists believe, would have formed relatively quickly, in less than a few million years, early in the solar system’s evolution.

If a planetesimal formed in the first 1.5 million years of the solar system, short-lived radiogenic elements could have melted the body entirely due to the heat released by their decay. Unmelted planetesimals could have formed later, when their material had lower quantities of radiogenic elements, insufficient for melting.

There has been little evidence in the meteorite record of intermediate objects with both melted and unmelted compositions, except for a rare family of meteorites called IIE irons.

“These IIE irons are oddball meteorites,” Weiss says. “They show both evidence of being from primordial objects that never melted, and also evidence for coming from a body that’s completely or at least substantially melted. We haven’t known where to put them, and that’s what made us zero in on them.”

Magnetic pockets

Scientists have previously found that both melted and unmelted IIE meteorites originated from the same ancient planetesimal, which likely had a solid crust overlying a liquid mantle, like Earth. Maurel and her colleagues wondered whether the planetesimal also may have harbored a metallic, melted core.

“Did this object melt enough that material sank to the center and formed a metallic core like that of the Earth?” Maurel says. “That was the missing piece to the story of these meteorites.”

The team reasoned that if the planetesimal did host a metallic core, it could very well have generated a magnetic field, similar to the way Earth’s churning liquid core produces a magnetic field. Such an ancient field could have caused minerals in the planetesimal to point in the direction of the field, like a needle in a compass. Certain minerals could have kept this alignment over billions of years.

Maurel and her colleagues wondered whether they might find such minerals in samples of IIE meteorites that had crashed to Earth. They obtained two meteorites, which they analyzed for a type of iron-nickel mineral known for its exceptional magnetism-recording properties.

The team analyzed the samples using the Lawrence Berkeley National Laboratory’s Advanced Light Source, which produces X-rays that interact with mineral grains at the nanometer scale, in a way that can reveal the minerals’ magnetic direction.

Sure enough, the electrons within a number of grains were aligned in a similar direction — evidence that the parent body generated a magnetic field, possibly up to several tens of microtesla, which is about the strength of Earth’s magnetic field. After ruling out less plausible sources, the team concluded that the magnetic field was most likely produced by a liquid metallic core. To generate such a field, they estimate the core must have been at least several tens of kilometers wide.

Such complex planetesimals with mixed composition (both melted, in the form of a liquid core and mantle, and unmelted in the form of a solid crust), Maurel says, would likely have taken over several million years to form — a formation period that is longer than what scientists had assumed until recently.

But where within the parent body did the meteorites come from? If the magnetic field was generated by the parent body’s core, this would mean that the fragments that ultimately fell to Earth could not have come from the core itself. That’s because a liquid core only generates a magnetic field while still churning and hot. Any minerals that would have recorded the ancient field must have done so outside the core, before the core itself completely cooled.

Working with collaborators at the University of Chicago, the team ran high-velocity simulations of various formation scenarios for these meteorites. They showed that it was possible for a body with a liquid core to collide with another object, and for that impact to dislodge material from the core. That material would then migrate to pockets close to the surface where the meteorites originated.

“As the body cools, the meteorites in these pockets will imprint this magnetic field in their minerals. At some point, the magnetic field will decay, but the imprint will remain,” Maurel says. “Later on, this body is going to undergo a lot of other collisions until the ultimate collisions that will place these meteorites on Earth’s trajectory.”

Was such a complex planetesimal an outlier in the early solar system, or one of many such differentiated objects? The answer, Weiss says, may lie in the asteroid belt, a region populated with primordial remnants.

“Most bodies in the asteroid belt appear unmelted on their surface,” Weiss says. “If we’re eventually able to see inside asteroids, we might test this idea. Maybe some asteroids are melted inside, and bodies like this planetesimal are actually common.”

This research was funded, in part, by NASA.

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First ever image of a multi-planet system around a sun-like star captured by ESO telescope

The European Southern Observatory’s Very Large Telescope (ESO’s VLT) has taken the first ever image of a young, Sun-like star accompanied by two giant exoplanets. Images of systems with multiple exoplanets are extremely rare, and — until now — astronomers had never directly observed more than one planet orbiting a star similar to the Sun. The observations can help astronomers understand how planets formed and evolved around our own Sun.

Just a few weeks ago, ESO revealed a planetary system being born in a new, stunning VLT image. Now, the same telescope, using the same instrument, has taken the first direct image of a planetary system around a star like our Sun, located about 300 light-years away and known as TYC 8998-760-1.

“This discovery is a snapshot of an environment that is very similar to our Solar System, but at a much earlier stage of its evolution,” says Alexander Bohn, a PhD student at Leiden University in the Netherlands, who led the new research published today in the Astrophysical Journal Letters.

“Even though astronomers have indirectly detected thousands of planets in our galaxy, only a tiny fraction of these exoplanets have been directly imaged,” says co-author Matthew Kenworthy, Associate Professor at Leiden University, adding that “direct observations are important in the search for environments that can support life.” The direct imaging of two or more exoplanets around the same star is even more rare; only two such systems have been directly observed so far, both around stars markedly different from our Sun. The new ESO’s VLT image is the first direct image of more than one exoplanet around a Sun-like star. ESO’s VLT was also the first telescope to directly image an exoplanet, back in 2004, when it captured a speck of light around a brown dwarf, a type of ‘failed’ star.

“Our team has now been able to take the first image of two gas giant companions that are orbiting a young, solar analogue,” says Maddalena Reggiani, a postdoctoral researcher from KU Leuven, Belgium, who also participated in the study. The two planets can be seen in the new image as two bright points of light distant from their parent star, which is located in the upper left of the frame (click on the image to view the full frame). By taking different images at different times, the team were able to distinguish these planets from the background stars.

The two gas giants orbit their host star at distances of 160 and about 320 times the Earth-Sun distance. This places these planets much further away from their star than Jupiter or Saturn, also two gas giants, are from the Sun; they lie at only 5 and 10 times the Earth-Sun distance, respectively. The team also found the two exoplanets are much heavier than the ones in our Solar System, the inner planet having 14 times Jupiter’s mass and the outer one six times.

Bohn’s team imaged this system during their search for young, giant planets around stars like our Sun but far younger. The star TYC 8998-760-1 is just 17 million years old and located in the Southern constellation of Musca (The Fly). Bohn describes it as a “very young version of our own Sun.”

These images were possible thanks to the high performance of the SPHERE instrument on ESO’s VLT in the Chilean Atacama desert. SPHERE blocks the bright light from the star using a device called coronagraph, allowing the much fainter planets to be seen. While older planets, such as those in our Solar System, are too cool to be found with this technique, young planets are hotter, and so glow brighter in infrared light. By taking several images over the past year, as well as using older data going back to 2017, the research team have confirmed that the two planets are part of the star’s system.

Further observations of this system, including with the future ESO Extremely Large Telescope (ELT), will enable astronomers to test whether these planets formed at their current location distant from the star or migrated from elsewhere. ESO’s ELT will also help probe the interaction between two young planets in the same system. Bohn concludes: “The possibility that future instruments, such as those available on the ELT, will be able to detect even lower-mass planets around this star marks an important milestone in understanding multi-planet systems, with potential implications for the history of our own Solar System.”

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High-order synthetic dimensions in waveguide photonic lattices

In physics, a very intuitive way of describing the evolution of a system proceeds via the specification of functions of the spatiotemporal coordinates. Yet, there often exist other degrees of freedom in terms of which the physical entities pertaining to a variety of structures can be seen to evolve and that are not amenable to a description via spatial coordinates.

Yet, there often exist other degrees of freedom in terms of which the physical entities pertaining to a variety of structures can be seen to evolve and that are not amenable to a description via spatial coordinates.

This is precisely the idea of synthetic dimensions: coexisting frameworks in which a wavefunction, defined in specific degrees of freedom, takes another form that “lives” in a domain with much higher dimensions than what the structures’ (apparent) geometry would suggest. This approach is rather appealing as it can be used to access and probe dimensions beyond our 3-dimensional world, e.g. 5-dimensional or 8-dimensional, etc.

In our recent work we have shown that a multitude of high-dimensional synthetic lattices naturally emerge in (abstract) photon-number space when a multiport photonic lattice is excited by N indistinguishable photons. More precisely, the Fock-representation of N-photon states in systems composed of M evanescently coupled single-mode waveguides yields to a new layer of abstraction, where the associated states can be visualized as the energy levels of a synthetic atom. In full analogy with ordinary atoms, such synthetic atoms feature allowed and disallowed transitions between its energy levels.

These concepts have far-reaching implications as they open a route to the simultaneous realization of, in principle, an infinite number of lattices and graphs with different numbers of nodes and many dimensions. This possibility is rather appealing for realizing parallel quantum random walks where the corresponding walkers can perform different numbers of steps on different, planar and nonplanar, multidimensional graphs that depend on the number of photons involved in each process. These quantum walks can be implemented, for instance, by exciting a simple four-waveguide system with a standard quantum light source comprising infinite coherent superpositions of states, e.g. a coherent state . Similarly, the symmetric excitation of a two-waveguide system with identical photons, when properly viewed in abstract space, feature the phenomena of discrete diffraction and Bloch oscillations.

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A binary star as a cosmic particle accelerator

Scientists have identified the binary star Eta Carinae as a new kind of source for very high-energy (VHE) cosmic gamma-radiation. Eta Carinae is located 7500 lightyears away in the constellation Carina in the Southern Sky and, based on the data collected, emits gamma rays with energies up to 400 gigaelectronvolts (GeV), some 100 billion times more than the energy of visible light.

With a specialised telescope in Namibia a DESY-led team of researchers has proven a certain type of binary star as a new kind of source for very high-energy cosmic gamma-radiation. Eta Carinae is located 7500 lightyears away in the constellation Carina (the ship’s keel) in the Southern Sky and, based on the data collected, emits gamma rays with energies all the way up to 400 gigaelectronvolts (GeV), some 100 billion times more than the energy of visible light. The team headed by DESY’s Stefan Ohm, Eva Leser and Matthias Füßling is presenting its findings, made at the gamma-ray observatory High Energy Stereoscopic System (H.E.S.S.), in the journal Astronomy & Astrophysics. An accompanying multimedia animation explains the phenomenon. “With such visualisations we want to make the fascination of research tangible,” emphasises DESY’s Director of Astroparticle Physics, Christian Stegmann.

Eta Carinae is a binary system of superlatives, consisting of two blue giants, one about 100 times, the other about 30 times the mass of our sun. The two stars orbit each other every 5.5 years in very eccentric elliptical orbits, their separation varying approximately between the distance from our Sun to Mars and from the Sun to Uranus. Both these gigantic stars fling dense, supersonic stellar winds of charged particles out into space. In the process, the larger of the two loses a mass equivalent to our entire Sun in just 5000 years or so. The smaller one produces a fast stellar wind travelling at speeds around eleven million kilometres per hour (about one percent of the speed of light).

A huge shock front is formed in the region where these two stellar winds collide, heating up the material in the wind to extremely high temperatures. At around 50 million degrees Celsius, this matter radiates brightly in the X-ray range. The particles in the stellar wind are not hot enough to emit gamma radiation, though. “However, shock regions like this are typically sites where subatomic particles are accelerated by strong prevailing electromagnetic fields,” explains Ohm, who is the head of the H.E.S.S. group at DESY. When particles are accelerated this rapidly, they can also emit gamma radiation. In fact, the satellites “Fermi,” operated by the US space agency NASA, and AGILE, belonging to the Italian space agency ASI, already detected energetic gamma rays of up to about 10 GeV coming from Eta Carinae in 2009.

“Different models have been proposed to explain how this gamma radiation is produced,” Füßling reports. “It could be generated by accelerated electrons or by high-energy atomic nuclei.” Determining which of these two scenarios is correct is crucial: very energetic atomic nuclei account for the bulk of the so-called Cosmic Rays, a subatomic cosmic hailstorm striking Earth constantly from all directions. Despite intense research for more than 100 years, the sources of the Cosmic Rays are still not exhaustively known. Since the electrically charged atomic nuclei are deflected by cosmic magnetic fields as they travel through the universe, the direction from which they arrive at Earth no longer points back to their origin. Cosmic gamma rays, on the other hand, are not deflected. So, if the gamma rays emitted by a specific source can be shown to originate from high-energy atomic nuclei, one of the long-sought accelerators of cosmic particle radiation will have been identified.

“In the case of Eta Carinae, electrons have a particularly hard time getting accelerated to high energyies, because they are constantly being deflected by magnetic fields during their acceleration, which makes them lose energy again,” says Leser. “Very high-energy gamma radiation begins above the 100 GeV range, which is rather difficult to explain in Eta Carinae to stem from electron acceleration.” The satellite data already indicated that Eta Carinae also emits gamma radiation beyond 100 GeV, and H.E.S.S. has now succeeded in detecting such radiation up to energies of 400 GeV around the time of the close encounter of the two blue giants in 2014 and 2015. This makes the binary star the first known example of a source in which very high-energy gamma radiation is generated by colliding stellar winds.

“The analysis of the gamma radiation measurements taken by H.E.S.S. and the satellites shows that the radiation can best be interpreted as the product of rapidly accelerated atomic nuclei,” says DESY’s PhD student Ruslan Konno, who has published a companion study, together with scientists from the Max Planck Institute for Nuclear Physics in Heidelberg. “This would make the shock regions of colliding stellar winds a new type of natural particle accelerator for cosmic rays.” With H.E.S.S., which is named after the discoverer of Cosmic Rays, Victor Franz Hess, and the upcoming Cherenkov Telescope Array (CTA), the next-generation gamma-ray observatory currently being built in the Chilean highlands, the scientists hope to investigate this phenomenon in greater detail and discover more sources of this kind.

“I find science and scientific research extremely important,” says Nicolai, who sees close parallels in the creative work of artists and scientists. For him, the appeal of this work also lay in the artistic mediation of scientific research results: “particularly the fact that it is not a film soundtrack, but has a genuine reference to reality,” emphasizes the musician and artist. Together with the exclusively composed sound, this unique collaboration of scientists, animation artists and musician has resulted in a multimedia work that takes viewers on an extraordinary journey to a superlative double star some 7500 light years away.

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