Baby star's fiery tantrum could create the building blocks of planets

Artist’s impression of a similar solar flare (a very large flare from EV Lac) available via the NASA website, use only with Image

A massive stellar flare on a baby star has been spotted by University of Warwick astronomers, shedding light on the origins of potentially habitable exoplanets.

One of the largest ever seen on a star of its type, the huge explosion of energy and plasma is around 10,000 times bigger than the largest solar flare ever recorded from our own Sun.

The discovery is detailed in a paper for the Monthly Notices of the Royal Astronomical Society and reveals how this huge 'tantrum' could even perturb the material orbiting a star which would create the building blocks for future planets.

The flare was seen on a young M-type star named NGTS J121939.5-355557, located 685 light years away. At around 2 million years old, it is what astronomers refer to as a pre-main sequence star which is yet to reach the size that it spends the majority of its lifecycle.

It was observed as part of a large flare survey of thousands of stars by University of Warwick PhD student James Jackman, as part of a project searching for explosive phenomena on stars outside our solar system. He used the Warwick-led Next-Generation Transit Survey (NGTS) telescope array in Chile which is designed to find exoplanets by collecting brightness measurements of hundreds of thousands of stars and is based at the European Southern Observatory's Paranal Observatory. His attention was drawn to NGTS J121939.5-355557 as it had one of the largest flares seen in these types of stars.

A stellar flare occurs when the magnetic field of a star rearranges itself, releasing huge amounts of energy in the process. This accelerates charged particles, or plasma, within the star which crash into its surface, heating it up to around 10,000 degrees. That energy produces optical and infra-red light, but also x-rays and gamma rays that can be picked up by telescopes on Earth and in orbit.

Magnetic fields on M stars are a lot stronger than those on our own sun and the astronomers calculated that this size of flare is a rare event, occurring anywhere from every three years to twice a decade.

James, who is studying in the University of Warwick's Department of Physics, said: "This is normally a star that shows little activity and stays a constant brightness. Then, on this one particular night, we saw it suddenly grow seven times brighter than normal for a few hours, which is pretty extreme. And then after that it goes back to normal.

"We see these types of flares on the Sun, but no-where near as big as this. On our Sun, you can do incredibly detailed studies on this kind of activity. It's difficult to extend that understanding to other stars because the data we need hasn't been available until now.

"This is an incredibly young star, only about 2 million years old. You'd call it a baby -- it's going to live for ten of billions of years, so it's in the first one percent of its lifetime. Even though it's much cooler than our Sun by about 2000 degrees it is roughly the same size, but pretty large for an M star. This is because it's still being formed from gas in the disc and contracting and cooling until it reaches the main sequence, staying at a certain radius and luminosity for billions of years.

"Finding out these kinds of details has only been possible thanks to the Gaia mission that began earlier this year."

The X-rays from these large flare events are thought to affect the formation of 'chondrules', flash-melted calcium-aluminium-rich grains in the star's protoplanetary disc. These gather together into asteroids that eventually coalesce into orbiting planets. The study adds to our understanding of how flares 'perturb' the protoplanetary disc, moving around the material that impacts on planet formation and affecting the eventual structure of a planetary system.

Professor Peter Wheatley, James's PhD supervisor, said: "A massive flare like this could be advantageous for planet formation, or it could be disruptive. This particular star won't have formed its planets yet so this type of flare activity is something that astronomers will need to take into account when considering planet formation.

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3D-printed robot hand plays the piano

Robot hand playing the piano.

Scientists have developed a 3D-printed robotic hand which can play simple musical phrases on the piano by just moving its wrist. And while the robot is no virtuoso, it demonstrates just how challenging it is to replicate all the abilities of a human hand, and how much complex movement can still be achieved through design.

The robot hand, developed by researchers at the University of Cambridge, was made by 3D-printing soft and rigid materials together to replicate of all the bones and ligaments -- but not the muscles or tendons -- in a human hand. Even though this limited the robot hand's range of motion compared to a human hand, the researchers found that a surprisingly wide range of movement was still possible by relying on the hand's mechanical design.

Using this 'passive' movement -- in which the fingers cannot move independently -- the robot was able to mimic different styles of piano playing without changing the material or mechanical properties of the hand. The results, reported in the journal Science Robotics, could help inform the design of robots that are capable of more natural movement with minimal energy use.

Complex movement in animals and machines results from the interplay between the brain (or controller), the environment and the mechanical body. The mechanical properties and design of systems are important for intelligent functioning, and help both animals and machines to move in complex ways without expending unnecessary amounts of energy.

"We can use passivity to achieve a wide range of movement in robots: walking, swimming or flying, for example," said Josie Hughes from Cambridge's Department of Engineering, the paper's first author. "Smart mechanical design enables us to achieve the maximum range of movement with minimal control costs: we wanted to see just how much movement we could get with mechanics alone."

Over the past several years, soft components have begun to be integrated into robotics design thanks to advances in 3D printing techniques, which has allowed researchers to add complexity to these passive systems.

The human hand is incredibly complex, and recreating all of its dexterity and adaptability in a robot is a massive research challenge. Most of today's advanced robots are not capable of manipulation tasks which small children can perform with ease.

"The basic motivation of this project is to understand embodied intelligence, that is, the intelligence in our mechanical body," said Dr Fumiya Iida, who led the research. "Our bodies consist of smart mechanical designs such as bones, ligaments, and skins that help us behave intelligently even without active brain-led control. By using the state-of-the-art 3D printing technology to print human-like soft hands, we are now able to explore the importance of physical designs, in isolation from active control, which is impossible to do with human piano players as the brain cannot be 'switched off' like our robot."

"Piano playing is an ideal test for these passive systems, as it's a complex and nuanced challenge requiring a significant range of behaviours in order to achieve different playing styles," said Hughes.

The robot was 'taught' to play by considering how the mechanics, material properties, environment and wrist actuation all affect the dynamic model of the hand. By actuating the wrist, it is possible to choose how the hand interacts with the piano, allowing the embodied intelligence of the hand to determine how it interacts with the environment.

The researchers programmed the robot to play a number of short musical phrases with clipped (staccato) or smooth (legato) notes, achieved through the movement of the wrist. "It's just the basics at this point, but even with this single movement, we can still get quite complex and nuanced behaviour," said Hughes.

Despite the limitations of the robot hand, the researchers say their approach will drive further research into the underlying principles of skeletal dynamics to achieve complex movement tasks, as well as learning where the limitations for passive movement systems lie.

"This approach to mechanical design can change how we build robotics," said Iida. "The fabrication approach allows us to design mechanically intelligent structures in a way that is highly scalable."

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More young and other traits help mammals adapt to urban environments

Species of mammals that live in urban environments produce more young compared to other mammals. But next to this common 'winning trait', mammals deal with different strategies to successfully inhabit cities. This is what Radboud University ecologist Luca Santini and colleagues found in a study that they will publish in Ecology Letters on 21 December. "This is the first step of many to understand why certain mammals manage to live in cities and why other species don't."

Mammals living in urban environments tend to be more of a nuisance to human inhabitants than birds, because they are often regarded as pests -- for example rats and bats -- and damage structures or goods -- as wild boars do. "It's important to gain more insight into how mammals live in urban environments, so we can eventually achieve a more peaceful coexistence," Santini says.

Traits that benefit urban mammals

Santini and colleagues collected studies from all over the world that recorded the number of mammal species in cities. "The large number of studies that have already been conducted show that birds in cities, for example crows, tend to be cleverer, meaning that they are better able to adapt to unexpected situations. However, mammals in cities are far less investigated, and only studies on a single mammal species, such as bats, have been carried out.

Mammals have way more diverse traits than birds, such as a higher diversity in body structure, size, life-history and ecology. Therefore, we were curious to know whether there are particular traits that are positively affecting the ability of mammal species to flourish in new ecosystems, such as urban environments."

Larger litters, brains and bodies

The finding that stands out most is that all groups of urban mammals seem to produce more young. Santini explains: "In general, animals that produce larger litters do so to compensate for a high mortality rate amongst their young. This suggests that a high mortality rate due to, for example, road traffic accidents, persecution by humans, and predation by domestic cats and dogs could be a major selective pressure for mammals in urban environments."

Differences in other traits were less explicit. "For example a larger brain mass appears to be mostly associated with carnivores and primates who only occasionally visit urban environments, such as jackals, wolves, bears and baboons, rather than with mammals who permanently live in cities, such as genet cats and mongooses among carnivores, or hedgehogs and shrews among insectivores. We also found that carnivores and primates that sporadically visit cities tend to be larger than average. This may be because they need to cover large distances in short times."

Different strategies for different species

Overall, the results indicate that different groups of mammals use different strategies to deal with the urban environment. "However, because the number of mammal species in an urban environments compared to the total number of mammal species is quite small -- 190 out of approximately 6,000 species -- this makes the statistics quite challenging, which makes it hard to make definite statements about specific groups of mammals and traits."

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Beyond the black hole singularity

Our first glimpses into the physics that exist near the center of a black hole are being made possible using "loop quantum gravity" -- a theory that uses quantum mechanics to extend gravitational physics beyond Einstein's theory of general relativity. Loop quantum gravity, originated at Penn State and subsequently developed by a large number of scientists worldwide, is opening up a new paradigm in modern physics. The theory has emerged as a leading candidate to analyze extreme cosmological and astrophysical phenomena in parts of the universe, like black holes, where the equations of general relativity cease to be useful.

Previous work in loop quantum gravity that was highly influential in the field analyzed the quantum nature of the Big Bang, and now two new papers by Abhay Ashtekar and Javier Olmedo at Penn State and Parampreet Singh at Louisiana State University extend those results to black hole interiors. The papers appear as "Editors' suggestions" in the journals Physical Review Letters and Physical Review on December 10, 2018 and were also highlighted in a Viewpoint article in the journal Physics.

"The best theory of gravity that we have today is general relativity, but it has limitations," said Ashtekar, Evan Pugh Professor of Physics, holder of the Eberly Family Chair in Physics, and director of the Penn State Institute for Gravitation and the Cosmos. "For example, general relativity predicts that there are places in the universe where gravity becomes infinite and space-time simply ends. We refer to these places as 'singularities.' But even Einstein agreed that this limitation of general relativity results from the fact that it ignores quantum mechanics."

At the center of a black hole the gravity is so strong that, according to general relativity, space-time becomes so extremely curved that ultimately the curvature becomes infinite. This results in space-time having a jagged edge, beyond which physics no longer exists -- the singularity. Another example of a singularity is the Big Bang. Asking what happened before the Big Bang is a meaningless question in general relativity, because space-time ends, and there is no before. But modifications to Einstein's equations that incorporated quantum mechanics through loop quantum gravity allowed researchers to extend physics beyond the Big Bang and make new predictions. The two recent papers have accomplished the same thing for the black hole singularity.

"The basis of loop quantum gravity is Einstein's discovery that the geometry of space-time is not just a stage on which cosmological events are acted out, but it is itself a physical entity that can be bent," said Ashtekar. "As a physical entity the geometry of space-time is made up of some fundamental units, just as matter is made up of atoms. These units of geometry -- called 'quantum excitations' -- are orders of magnitude smaller than we can detect with today's technology, but we have precise quantum equations that predict their behavior, and one of the best places to look for their effects is at the center of a black hole." According to general relativity, at the center of a black hole gravity becomes infinite so everything that goes in, including the information needed for physical calculations, is lost. This leads to the celebrated 'information paradox' that theoretical physicists have been grappling with for over 40 years. However, the quantum corrections of loop quantum gravity allow for a repulsive force that can overwhelm even the strongest pull of classical gravity and therefore physics can continue to exist. This opens an avenue to show in detail that there is no loss of information at the center of a blackhole, which the researchers are now pursuing.

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Newly discovered adolescent star seen undergoing 'growth spurt'

3-panel layout, showing the outbursting star.

Astronomers have discovered a young star undergoing a rare growth spurt -- giving a fascinating glimpse into the development of these distant stellar objects.

A team of international researchers, including experts from the University of Exeter's Physics and Astronomy department, have observed a rare stellar outburst on a newfound star, called Gaia 17bpi.

Gaia 17bpi belongs to a group of stars known as FU Ori's, named after the original member of the group, FU Orionis found in the Orion constellation.

Typically these FU Ori stars, which are less than a few million years old, are hidden behind thick clouds of dust and are therefore hard to observe.

However, the research team spotted the star undertaking a dramatic phase of evolution, whereby matter swirling around falls onto the star, and so bulking up its mass. The team was able to see this stellar outburst through both infrared and visible light.

Gaia 17bpi is only the 25th member of the FU Ori class found to date, and one of only about a dozen caught in the act of an outburst.

The research is published in The Astrophysical Journal.

Professor Tim Naylor, from Exeter's Astrophysics group and co-author of the study said: "It's taken a lot of patient waiting and careful sifting of data to uncover this star, but once we realised what was going it has exceeded expectations.

"It also gives us insight into events which may have happened as the planets in our own Solar System were beginning to form from a disc of material around the sun."

Gaia 17bpi was first spotted by the European Space Agency's Gaia satellite, which scans the sky continuously and makes precise measurements of stars in visible light. When Gaia spots a change in a star's brightness, an alert goes out to the astronomy community.

Exeter graduate student , and co-author of the study Sam Morrell was the first to notice that the star had brightened. Fellow members of the research team took the discovery forward, and discovered that the star's brightening had been independently captured in infrared light by NASA's asteroid-hunting NEOWISE satellite at the same time that Gaia saw it, as well as one-and-a-half-years earlier.

NASA's infrared-sensing Spitzer Space Telescope also happened to have witnessed the beginning of the star's brightening phase twice back in 2014, giving the researchers a bonanza of infrared data.

"These FU Ori events are extremely important in our current understanding of the process of star formation but have remained almost mythical because they have been so difficult to observe," says Lynne Hillenbrand, professor of astronomy at Caltech and lead author of a new report. "This is actually the first time we've ever seen one of these events as it happens in both optical and infrared light, and these data have let us map the movement of material through the disk and onto the star."

The new findings shine light on some of the longstanding mysteries surrounding the evolution of young stars, including how a star acquires all of its mass. Theorists believe that FU Ori events -- in which mass is dumped from the disk onto the star over a total period of about 100 years -- may help solve the riddle.

The new study shows, with the most detail yet, how material moves from the midrange of a disk, in a region located around one astronomical unit -- the distance between the Earth and the sun -- from the star, to the star itself.

NEOWISE and Spitzer were the first to pick up signs of the buildup of material in the middle of the disk. As the material started to accumulate in the disk, it warmed up, giving off infrared light. Then, as this material fell onto the star, it heated up even more, giving off visible light, which is what Gaia detected.

"While NEOWISE's primary mission is detecting nearby solar system objects, it also images all of the background stars and galaxies as it sweeps around the sky every six months," says co-author Roc Cutri, lead scientist for the NEOWISE Data Center at IPAC, an astronomy and data center at Caltech. "NEOWISE has been surveying in this way for five years now, so it is very effective for detecting changes in the brightness of objects."

Carlos Contreras, a Postdoctoral Research Fellow from the University of Exeter and co-author of the study added: "The FU Ori-type outbursts could also have an impact on the early formation and evolution of the planets that form in the discs around young stars.

The discovery of Gaia 17bpi was the by-product of an Exeter programme that has been monitoring a large sample of young stars using the data from the Gaia satellite, to measure the frequency of the FU Ori events during the planet forming stage."

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A mountain of evidence on air pollution's harms to children

A new study led by researchers at the Columbia Center for Children's Environmental Health (CCCEH) organizes the available scientific evidence on the effects of air pollution on children's health. The paper in the journal Environmental Research is the first comprehensive review of the associations between various fossil fuel combustion pollutants and multiple health effects in children in the context of assessing the benefits of air pollution and climate change policies.

The researchers say their goal is to expand the kinds of health outcomes used in calculations of the health and economic benefits of implementing clean air and climate change policies which are largely limited to the effects of air pollution on premature deaths and other outcomes in adults. The new paper aggregates research on outcomes, including adverse birth outcomes, cognitive and behavioral problems, and asthma incidence.

"Policies to reduce fossil fuel emissions serve a dual purpose, both reducing air pollution and mitigating climate change, with sizable combined health and economic benefits," says first author Frederica Perera, PhD, director of CCCEH and professor of Environmental Health Sciences. "However, because only a few adverse outcomes in children have been considered, policymakers and the public have not yet seen the extent of the potential benefits of clean air and climate change policies, particularly for children."

The researchers reviewed 205 peer-reviewed studies published between January 1, 2000 and April 30, 2018 which provided information on the relationship between the concentration of exposures to air pollutants and health outcomes. The studies relate to fuel combustion by-products, including toxic air pollutants such as particulate matter (PM2.5), polycyclic aromatic hydrocarbons (PAH), and nitrogen dioxide (NO2). A table provides information on the risk of health outcomes for exposure by study, encompassing research on six continents.

"There is extensive evidence on the many harms of air pollution on children's health," says Perera. "Our paper presents these findings in a convenient fashion to support clean air and climate change policies that protect children's health."

The World Health Organization (WHO) has estimated that more than 40 percent of the burden of environmentally related disease and about 90 percent of the burden of climate change is borne by children under five, although that age group constitutes only 10 percent of the global population. The direct health impacts in children of air pollution from fossil fuel combustion include adverse birth outcomes, impairment of cognitive and behavioral development, respiratory illness, and potentially childhood cancer. As a major driver of climate change, combustion of fossil fuel is also directly and indirectly contributing to illness, injury, death, and impaired mental health in children through more frequent and severe heat events, coastal and inland flooding, drought, forest fires, intense storms, the spread of infectious disease vectors, increased food insecurity, and greater social and political instability. These impacts are expected to worsen in the future.

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Small changes in oxygen levels have big implications for ocean life

This is Lucicutia hulsemannae, a copepod that stays at the Lower Oxycline of the Oxygen Minimum Zone (OMZ). The organism is remarkably tolerant of extremely low oxygen levels, but very sensitive to small changes in those levels.

Oceanographers at the University of Rhode Island have found that even slight levels of ocean oxygen loss, or deoxygenation, have big consequences for tiny marine organisms called zooplankton.

Zooplankton are important components of the food web in the expanse of deep, open ocean called the midwater. Within this slice of ocean below the surface and above the seafloor are oxygen minimum zones (OMZs), large regions of very low oxygen. Unlike coastal "dead zones" where oxygen levels can suddenly plummet and kill marine life not acclimated to the conditions, zooplankton in OMZs are specially adapted to live where other organisms -- especially predators -- cannot. But OMZs are expanding due to climate change, and even slight changes to the low oxygen levels can push zooplankton beyond their extraordinary physiological limits.

"Although the animals in the ocean's oxygen minimum zone have adapted over millions of years to the very low oxygen of this extreme and widespread midwater habitat, they are living at the very limits of their physiological capability," said Karen Wishner, a professor of oceanography at URI's Graduate School of Oceanography and lead author of a new paper on deoxygenation and zooplankton in the Eastern Tropical North Pacific OMZ. "Our research shows that they are sensitive to very small changes in oxygen, and decrease in abundance when oxygen gets just a little bit lower."

The research team, which this week published their findings in Science Advances, found more natural variability in oxygen levels in the OMZ than previously known. This has a direct effect on the distribution of many types of zooplankton because, as the team discovered, the organisms respond to a less than 1 percent reduction in oxygen levels.

While zooplankton have had millions of years to adapt to conditions in the OMZ, these low oxygen zones may expand rapidly due to climate change, leading to major unanticipated changes to midwater ecosystems. For example, an expansion of the OMZ into shallower waters may make zooplankton more susceptible to predators like fish. If this leads to a zooplankton population crash, it will have impacts all the way up the food chain.

"Further loss of oxygen in ocean waters is predicted in the future as a result of global warming, and these animals may be unable to adapt and persist," Wishner said. "They are important components of the food web of oceanic ecosystems, and their loss could potentially impact top predators, including whales and commercially important fisheries."

From Science Daily

Himalayan marmot genome offers clues to life at extremely high altitudes

This image shows a pair of Himalayan marmots.

Himalayan marmots can survive at altitudes up to 5,000 meters in the Himalayan regions of India, Nepal, and Pakistan and on the Qinghai-Tibetan Plateau of China, where many of them face extreme cold, little oxygen, and few other resources. Now, researchers have sequenced the first complete Himalayan marmot genome, which may help them to better explain how the marmots live in such extremes.

The findings, which appear December 20 in the journal iScience, hint at the genetic mechanisms underlying high-altitude adaptation and hibernation, the researchers say. They also serve as a valuable resource for researchers studying marmot evolution, highland disease, and cold adaptation.

"As one of the highest-altitude-dwelling mammals, the Himalayan marmot is chronically exposed to cold temperature, hypoxia, and intense UV radiation," said Enqi Liu of Xi'an Jiaotong University Health Science Center in China. "They also hibernate for more than six months during the wintertime."

Those striking biological features led Liu and his team, including first author Liang Bai, to consider the Himalayan marmot as an ideal animal model for studying the molecular mechanisms of adaptation to extreme environments. To begin, they sequenced and assembled a complete draft genome of a male Himalayan marmot. They also re-sequenced 20 other Himalayan marmots, including individuals living at high and low altitudes, and four other marmot species. Additionally, RNA sequencing was done to compare gene-expression differences between marmots in a state of torpor and awake marmots.

The DNA data show that the Himalayan marmot diverged from the Mongolian marmot about 2 million years ago. The researchers identified two genes, Slc25a14 and ?Aamp (a processed pseudogene), that have been selected in different directions in marmots living at low versus high altitudes, suggesting they are related to survival in high-altitude populations under conditions of extremely low oxygen.

They further suggest that Slc25a14 may have an important neuroprotective role. The shift in ?Aamp affects the stability of RNA encoding the gene Aamp, which may be a protective strategy to prevent the excess growth of new blood vessels under extremely low-oxygen conditions.

The RNA sequencing data show that gene-expression changes occur in the liver and brain during hibernation. These include genes in the fatty acid metabolism pathway as well as blood clotting and stem cell differentiation.

Interestingly, a previous study suggested that because the hibernator's brain is exposed to near-freezing temperatures and has decreased blood flow, there is an increased risk of blood clots, the researchers note. Their brain stem cells may also be better prepared to repair injuries as an adaptation needed to survive extreme environmental stresses.

The researchers say they plan to continue improving the quality of the Himalayan marmot's genome. They note that the Himalayan marmot is also known for being highly susceptible to woodchuck hepatitis virus and is a natural host and transmitter of the plague to humans.

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Mighty morphing materials take complex shapes

A face made of a unique polymer at Rice University takes shape when cooled and flattens when heated. The material may be useful in the creation of soft robots and for biomedical applications.

Rice University scientists have created a rubbery, shape-shifting material that morphs from one sophisticated form to another on demand.

The shapes programmed into a polymer by materials scientist Rafael Verduzco and graduate student Morgan Barnes appear in ambient conditions and melt away when heat is applied. The process also works in reverse.

The smooth operation belies a battle at the nanoscale, where liquid crystals and the elastomer in which they're embedded fight for control. When cool, the shape programmed into the liquid crystals dominates, but when heated, the crystals relax within the rubber band-like elastomer, like ice melting into water.

In most of the samples Barnes has made so far -- including a face, a Rice logo, a Lego block and a rose -- the material takes on its complex shape at room temperature, but when heated to a transition temperature of about 80 degrees Celsius (176 degrees Fahrenheit), it collapses into a flat sheet. When the heat is removed, the shapes pop back up within a couple of minutes.

As fanciful as this seems, the material shows promise for soft robots that mimic organisms and in biomedical applications that require materials that take pre-programmed shapes at body temperature.

The research is described in the Royal Society of Chemistry journal Soft Matter.

"These are made with two-step chemistry that has been done for a long time," said Verduzco, a professor of chemical and biomolecular engineering and of materials science and nanoengineering. "People have focused on patterning liquid crystals, but they hadn't thought about how these two networks interact with each other.

"We thought if we could optimize the balance between the networks -- make them not too stiff and not too soft -- we could get these sophisticated shape changes."

The liquid crystal state is easiest to program, he said. Once the material is given shape in a mold, five minutes of curing under ultraviolet light sets the crystalline order. Barnes also made samples that switch between two shapes.

"Instead of simple uniaxial shape changes, where you have something that lengthens and contracts, we're able to have something that goes from a 2D shape to a 3D shape, or from one 3D shape to another 3D shape," she said.

The lab's next target is to lower the transition temperature. "Activation at body temperature opens us up to a lot more applications," Barnes said. She said tactile smartphone buttons that appear when touched or reactive braille text for the visually impaired are within reach.

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Faint starlight in Hubble images reveals distribution of dark matter

Abell S1063, a galaxy cluster, was observed by the NASA/ESA Hubble Space Telescope as part of the Frontier Fields program. The huge mass of the cluster -- containing both baryonic matter and dark matter -- acts as cosmic magnification glass and deforms objects behind it. In the past astronomers used this gravitational lensing effect to calculate the distribution of dark matter in galaxy clusters.

Astronomers using data from the NASA/ESA Hubble Space Telescope have employed a revolutionary method to detect dark matter in galaxy clusters. The method allows astronomers to "see" the distribution of dark matter more accurately than any other method used to date and it could possibly be used to explore the ultimate nature of dark matter. The results were published in the journal Monthly Notices of the Royal Astronomical Society.

In recent decades astronomers have tried to understand the true nature of the mysterious substance that makes up most of the matter in the Universe -- dark matter -- and to map its distribution in the Universe. Now two astronomers from Australia and Spain have used data from the Frontier Fields programme of the NASA/ESA Hubble Space Telescope to accurately study the distribution of dark matter.

"We have found a way to 'see' dark matter," explains Mireia Montes (University of New South Wales, Australia), lead author of the study. "We have found that very faint light in galaxy clusters, the intracluster light, maps how dark matter is distributed."

Intracluster light is a byproduct of interactions between galaxies. In the course of these interactions, individual stars are stripped from their galaxies and float freely within the cluster. Once free from their galaxies, they end up where the majority of the mass of the cluster, mostly dark matter, resides.

"These stars have an identical distribution to the dark matter, as far as our current technology allows us to study," explained Montes. Both the dark matter and these isolated stars -- which form the intracluster light -- act as collisionless components. These follow the gravitational potential of the cluster itself. The study showed that the intracluster light is aligned with the dark matter, tracing its distribution more accurately than any other method relying on luminous tracers used so far.

This method is also more efficient than the more complex method of using gravitational lensing. While the latter requires both accurate lensing reconstruction and time-consuming spectroscopic campaigns, the method presented by Montes utilises only deep imaging. This means more clusters can be studied with the new method in the same amount of observation time.

The results of the study introduce the possibility of exploring the ultimate nature of dark matter. "If dark matter is self-interacting we could detect this as tiny departures in the dark matter distribution compared to this very faint stellar glow," highlights Ignacio Trujillo (Instituto de Astrofísica de Canarias, Spain), co-author of the study. Currently, all that is known about dark matter is that it appears to interact with regular matter gravitationally, but not in any other way. To find that it self-interacts would place significant constraints on its identity.

For now, Montes and Trujillo plan to survey more of the original six clusters to see if their method remains accurate. Another important test of their method will be the observation and analysis of additional galaxy clusters by other research teams, to add to the data set and confirm their findings.

The team can also look forward to the application of the same techniques using future space-based telescopes like the NASA/ESA/CSA James Webb Space Telescope, which will have even more sensitive instruments able to resolve faint intracluster light in the distant Universe.

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