Culture

An international team of astrophysicists from Southampton, Oxford and South Africa have detected a very hot, dense outflowing wind close to a black hole at least 25,000 light-years from Earth.

Lead researcher Professor Phil Charles from the University of Southampton explained that the gas (ionised helium and hydrogen) was emitted in bursts which repeated every 8 minutes, the first time this behaviour has been seen around a black hole. The findings have been published in the journal Monthly Notices of the Royal Astronomical Society.

The object Professor Charles' team studied was Swift J1357.2-0933 which was first discovered as an X-ray transient - a system that exhibits violent outbursts - in 2011. These transients all consist of a low-mass star, similar to our Sun and a compact object, which can be a white dwarf, neutron star or black hole. In this case, Swift J1357.2-0933 has a black hole compact object which is at least 6 times the mass of our Sun.

Material from the normal star is pulled by the compact object into a disc in between the two. Massive outbursts occur when the material in the disc becomes hot and unstable and it releases copious amounts of energy.

Professor Charles said: "What was particularly unusual about this system was that ground-based telescopes had revealed that its optical brightness displayed periodic dips in its output and that the period of these dips slowly changed from around 2 minutes to about 10 minutes as the outburst evolved. Such strange behaviour has never been seen in any other object.

"The cause of these remarkable, fast dips has been a hot topic of scientific debate ever since their discovery. So it was with great excitement that astronomers greeted the second outburst of this object in mid-2017, presenting an opportunity to study this strange behaviour in greater detail."

Professor Charles and his team recognised that key to getting the answer was to obtain optical spectra a number of times during each dip cycle, essentially studying how their colour changed with time. But with the object about 10,000 times fainter than the faintest star visible to the naked eye and the dip period of only around 8 minutes, a very big telescope had to be used.

So, they used SALT, the Southern African Large Telescope, the largest optical telescope in the southern hemisphere.

The University of Southampton is one of the founding UK partners in SALT, and together with their South African collaborators, are part of a multi-partner Large Science Programme to study transients of all types. Not only does SALT have the necessary huge collecting area (it has a 10m diameter mirror), but it is operated in a 100% queue-scheduled way by resident staff astronomers, meaning that it can readily respond to unpredictable transient events. This was perfect for Swift J1357.2-0933, and SALT obtained more than an hour of spectra, with one taken every 100 seconds.

"Our timely observations of this fascinating system demonstrates how the quick response of SALT, through its flexible queue-scheduled operation, makes it an ideal facility for follow-up studies of transient objects", said Dr David Buckley, the Principal Investigator of the SALT transient programme, based at the South African Astronomical Observatory, who also added, "With the instantaneous availability of a number of different instruments on SALT, we can also dynamically modify our observing plans to suit the science goals and react to results, almost in real-time"

Professor Charles added: "The results from these spectra were stunning. They showed ionised helium in absorption, which had never been seen in such systems before. This indicated that it must be both dense and hot - around 40,000 degrees. More remarkably, the spectral features were blue-shifted (due to the Doppler effect), indicating that they were blowing towards us at about 600km/s. But what really astonished us was the discovery that these spectral features were visible only during the optical dips in the light-curve. We have interpreted this quite unique property as due to a warp or ripple in the inner accretion disc that orbits the black hole on the dipping timescale. This warp is very close to the black hole at just 1/10 the radius of the disc."

What is driving this matter away from the black hole? It is almost certainly the radiation pressure of the intense X-rays generated close to the black hole. But it has to be much brighter than we see directly, suggesting that the material falling on to the black hole obscures it from direct view, like clouds obscuring the Sun. This occurs because we happen to be viewing the binary system from a vantage point where the disc appears edge-on, as depicted in the schematic illustration, and rotating blobs in this disc obscure our view of the central black hole.

Interestingly there are no eclipses by the companion star seen in either the optical or X-ray as might be expected. This is explained by it being very small, and constantly in the shadow of the disc. This inference comes from detailed theoretical modelling of winds being blown off accretion discs that was undertaken by one of the team, James Matthews at the University of Oxford, using supercomputer calculations.

This object has remarkable properties amongst an already interesting group of objects that have much to teach us about the end-points of stellar evolution and the formation of compact objects. We already know of a couple of dozen black hole binary systems in our Galaxy, which all have masses in the 5-15 solar mass range, and the single black hole at our Galactic Centre is around 4 million solar masses. They all grow by the accretion of matter that we have witnessed so spectacularly in this object. We also know that a substantial fraction of the accreting material is being blown away. When that happens from the supermassive black holes at the centres of galaxies, those powerful winds and jets can have a huge impact on the rest of the galaxy.

Professor Charles concluded "These short-period binary versions are a perfect way to study this physics in action."

Coral reefs are a hotspot of biodiversity, hosting numerous species of animals and fish that help one another maintain a harmonious environment. One of these species is the giant clam. They are the biggest shellfish in the world, with 13 species found so far. One of the most famous species, Tridacna gigas, can live more than 100 years and grow to more than a meter wide. Their size and beautiful shells have led to their popularity as ornaments and as a delicacy, but this has resulted in their endangerment.

Impressive size and beauty and are not the only notable facts about giant clams, they also play host to symbiotic algae: Zooxanthellae. These algae have a very important role in the maintenance of the coral reef, they provide food for the coral and clam through products of photosynthesis. About 80% of coral reef nutrition and 65-70% of giant clam nutrition comes from the symbiotic relationship with zooxanthellae. However, these algae are not able to survive without a host and don't appear to be present in large amounts in the water or sediment surrounding the coral reef.

"In the coral reef the water is very clear, this means there is no food floating around. The zooxanthellae feed the coral reefs." explains Professor Kazuhiko Koike, Graduate School of Integrated Sciences for Life at Hiroshima University and leader of this study.

Although these algae are vital to the coral reef, they must be obtained through the environment somehow because most of corals and giant clams do not obtain zooxanthellae from their parents.

"The only big mystery of coral reefs is where do the zooxanthellae come from?" says Koike.

To try and solve this mystery researchers from Hiroshima University, in a collaboration with The Fisheries Research and Education Agency Okinawa, Okinawa Prefectural Fisheries Research and Extension Center, and the National University of Singapore tried to find the mode of transmission of algae from clam to clam.

"One of my former students, Shota Ikeda, found that if a coral reef is very healthy the giant clams are always there." describes Koike. "There are many scientists with big research budgets already looking at coral. So, we changed our [research] model to the giant clam."

While researching the giant clams, a member of the research team (Shinya Morishima) noticed that the fecal pellets were full of zooxanthellae. When the algae were studied under a fluorescent microscope, the scientists observed that they were alive and active, with intact chloroplasts (parts of the cell that perform photosynthesis). The team then grew juvenile clams in the laboratory and fed them fecal pellets from adult giant clams originally harvested in Okinawa. 34% of the larvae took up the zooxanthellae from the fecal pellets and 5% of larvae established symbiosis with feces-borne zooxanthellae reached, a rate higher than current experimental methods.

The types of zooxanthellae contained in the larvae were similar to those in the fecal pellets and were photosynthetically active.

Although this is a preliminary study, Koike believes that this could help solve a big mystery to coral reef maintenance.

"This is the first step to expand our research to coral reefs." hopes Koike.

Under elevating temperature, due to global warming, more heat-resistant zooxanthella grow in the clams and so more are expelled in their fecal pellets. In the future Koike thinks that giant clams could provide these heat-resistant zooxanthellae to coral reefs to mitigate against coral bleaching caused by climate change.

Nanosecond pulsed electric fields (nsPEFs) produce strong electrical effects by focusing a high powered electrical pulse over a very short period of time. They are attracting attention as a method of physically stimulating matter in various fields, particularly in the life sciences. Recently, researchers from Kumamoto University in Japan found that stimulating immune cells with nsPEFs can cause them to respond as if they were being stimulated by bacteria.

Researchers from the Institute of Pulsed Power Science (IPPS) selected a human leukemia cell line that is frequently used to study blood cell differentiation, the HL-60 cell line, to test the effects of nsPEFs on immune cells. First, they differentiated the cells into neutrophils, the most abundant type of white blood cell. Neutrophils play an important role in the immune system because they use phagocytosis, secretions of antimicrobial proteins, and neutrophil extracellular traps (NETs) to kill bacteria infecting the body. NETs are created from neutrophil DNA that is released from their nucleus. This then forms an extracellular fibrous network that entraps bacteria and increases the local concentration of antimicrobials.

The researchers then analyzed neutrophil and undifferentiated HL-60 cell responses to nsPEF exposure where they observed chromosomal DNA being released from neutrophils, and a special modification reaction called citrullination occurring in histones. Since these reactions only occurred in the neutrophils, the researchers considered these cellular responses to be equivalent to the formation of NETs that form when neutrophils are stimulated by bacteria. In other words, they seem to have found a way to stimulate neutrophils using nsPEFs to cause an immune cell response to bacteria without actually using bacteria.

"Many studies have shown that nsPEFs are promising for cancer treatment applications," said study leader, Professor Ken-ichi Yano from Kumamoto University's IPPS. "Our research has shown that nsPEFs can also be used to stimulate cells to determine their function. We believe this has a wide range of potential biomedical applications."

Astronomers have identified a rare moment in the life of some of the universe's most energetic objects.

Quasars were first observed 60 years ago, but their origins still remain a mystery.

Now researchers at Durham University, UK, have spotted what they suggest is a "brief transition phase" in the development of these galactic giants that could shed light on how quasars and their host galaxies evolve.

The research is published in Monthly Notices of the Royal Astronomical Society.

Quasars are powered by the energy from supermassive black holes at their centres as they feed on surrounding gases.

They are thousands of times brighter than galaxies like our Milky Way and the majority are blue in colour.

However, a significant number are red as they are viewed through huge clouds of dust and gas that obscure them from view.

The conventional view of red quasars is that they are actually blue quasars that are angled away from our line-of-sight.

Instead, the Durham team has ruled this model out and have shown that red quasars are like-ly to be the result of a brief, but violent, phase in the evolution of galaxies when the black hole ejects a large amount of energy into the surrounding clouds of dust and gas.

This injection of energy blows away the dust and gas to reveal a blue quasar.

Observations using radio telescopes support this theory by showing that black holes at the centre of red quasars produce a greater amount of radio emission than those at the centre of blue quasars.

Lead author Lizelke Klindt, a PhD researcher in Durham University's Centre for Extragalactic Astronomy, said: "How quasars develop has been the cause of significant uncertainty.

"What our results suggest is that quasars undergo a brief transition phase, changing colour from red to blue, when they emerge from the deep shroud of dust and gas surrounding them.

"What we believe we are seeing is a rare but important step in the life of these galactic beasts during galaxy evolution when their black holes are starting to shape their environments."

The researchers studied 10,000 red and blue quasars as they would have been seen seven to 11 billion years ago when the universe was relatively young using archival data from the Sloan Digital Sky Survey and the Very Large Array radio astronomy observatory.

They say their research could also tell us more about galaxy evolution.

Co-author Professor David Alexander, Head of Astronomy, at Durham University, said: "We expect that during this transition phase the energy from the supermassive black hole will burn off the gas needed to form stars.

"Without the gas the galaxy cannot continue to grow, so what we are possibly seeing is the start of a quasar effectively ending the life of the galaxy by destroying the very thing it needs to survive."

The researchers say the next step in their research is to use more in-depth data to understand the finer details of this transition phase.

In a new Ethology study, researchers examined information on two adjacent giraffe populations in Kenya to determine whether human activities and high predation affect their social networks.

One study site was a premier tourist destination with a high volume of human activity in the form of tourist traffic and lodges, alongside a high density of lions that preferentially prey on giraffe calves. The other was a private wildlife conservancy with minimal human activity and no lion population.

Giraffes at both sites showed preferences to associate with and avoid specific individuals, but the social bonds between individuals were stronger and more exclusive in the population exposed to high levels of human activity and lions. It was also more fragmented than the group with low disturbance.

"Wildlife populations are increasingly becoming restricted to enclosed conservation areas, and economic activities supporting conservation--or tourism--are increasing exponentially, yet there has been little consideration for how such an increase in human-related activity might affect the populations of animals they are working to protect," said lead author Zoe Muller, of the University of Bristol, in the UK. "If disturbance by humans affects the ability of animals to survive and reproduce, then this potentially puts the future survival of species at risk."

A new Economic Inquiry study finds that marijuana access leads to reductions in opioid-related deaths.

The study examined how the changing legal status of marijuana has impacted mortality in the United States over the past two decades. Investigators found that legalization and access to recreational marijuana reduced annual opioid mortality in the range of 20% to 35%, with particularly pronounced effects for synthetic opioids.

The research extends prior findings that medical marijuana laws reduce opioid mortality rates. The findings are timely given the scale of the opioid epidemic in the United States and growing calls for marijuana legalization throughout North America.

"Recreational marijuana laws affect a much larger population than medical marijuana laws, yet we know relatively little about their effects." said co-author Nathan W. Chan, PhD, of University of Massachusetts Amherst. "Focusing on the recent wave of recreational marijuana laws in the U.S., we find that opioid mortality rates drop when recreational marijuana becomes widely available via dispensaries."

In a Plants, People, Planet study, researchers investigated the evolution of the two most prevalent orchid viruses using information representing their global distribution. The study revealed that considerable international trade of cultivated orchids has effectively "homogenised" the genetic diversity of the viruses. In other words, the two viruses have displayed few genetic differences since their first emergence, across countries and host plants.

The findings are concerning because these patterns are suggestive of rapid and regular international movement of orchids and their related pathogens.

The rapid global dispersal of viruses not only has the potential to impact the lucrative orchid horticultural industry, it also threatens orchid species in the wild.

"Global trade has opened the doors to regular and rapid movements of both plants and their pathogens. Orchids are a highly threatened family and without better disease screening practice and phytosanitary regulation we may be placing wild populations at risk for unintentional spillover," said lead author Deborah J. Fogell, of the University of Kent, in the UK.

Soil organic matter has long been known to benefit farmers. The carbon in this organic matter acts as a food source for soil microbes, which then provide other nutrients to the crops grown. Microbes, insects and small soil critters produce materials that can improve soil structure and water retention. It's a healthy ecosystem every farmer wants to encourage.

Measuring changes in soil organic matter can be a challenge in intensively tilled soil that is used for vegetable production. Even in production systems with less soil disturbance, soil organic matter changes slowly. But, Eric Brennan and Veronica Acosta-Martinez are testing for soil enzymes as early indicators of improvements in soil health in a long-term systems study.

Brennan manages the study in an area of California known as the "Salad Bowl of the World." The Salinas Valley has high-input, organic vegetable production systems. "Farms in Salinas usually need to produce two or more vegetable crops per field annually to be profitable," says Brennan. "This production intensity complicates the adoption of winter cover cropping. This is why many farmers in this region prefer to use compost to add large amounts of organic matter to the soil."

Specifically, the team compared farming systems that received different amounts and types of organic matter. The sources were from compost and cover crops. They recently published their results in the Soil Science Society of America Journal.

"Our results on soil enzyme activity illustrate the importance of frequent cover-cropping in tillage-intensive, organic vegetable production," says Brennan. "This raises questions about the sustainability of organic and conventional vegetable systems if cover crops are seldom used. We need to find innovative strategies to help farmers increase cover cropping. The practice is shown to improve soil health. It also provides other benefits like reducing nitrogen leaching into ground water."

It's not that organic or conventional farmers in this region are against cover cropping. It's that their use can complicate many aspects of vegetable production.

Brennan's study showed that cover cropping annually - no matter the type of plant grown - greatly benefits the soil. The study found that annual inputs of compost have relatively small benefits. There was an increase in microbial activity with compost, but not as much as with annual cover crops.

There are some caveats in the study. This research was conducted in a loamy sand soil in Salinas Valley. Organic farmers in different regions may have different results. Using different types of fertilizers could impact results, as well.

"The growing body of information from this long-term trial challenges the overly-simplistic notion that certified organic management improves soil health or quality," says Brennan. He adds that the USDA organic standards require that certified farms show that their tillage and cultivation practices maintain or improve soil conditions. This refers to physical, chemical and biological factors. It also refers to minimizing soil erosion, which can worsen with intensive tilling.

The team hopes that future research will focus on different soil types, such a clay or loam soil. Evaluating changes over shorter increments would provide useful data, too. The soil enzyme data tells one part of the interesting story of this relatively long-term experiment.

A new Addiction Biology study provides the first evidence of a blunted response to stress-induced dopamine signaling in the brain's prefrontal cortex in individuals at high risk for psychosis who regularly used cannabis.

Little is known about the effects of cannabis on brain neurochemistry, and specifically about its impact on dopamine signaling. Of note, a recent analysis found a dose-response relationship between higher cannabis use and increased risk for schizophrenia, a condition associated with abnormal dopamine synthesis and release in the brain.

This latest study's results are important given the global trend to legalize cannabis and the growing evidence of the increased risks for psychosis in vulnerable youth.

"Regular cannabis use has a profound effect on cortical dopamine function, in particular in relation to the stress response, which is critical for young adults at risk for psychosis," said senior author Romina Mizrahi, MD, PhD, of the Centre for Addiction and Mental Health, in Toronto. "These results highlight the need for further research on the impact of cannabis on brain neurochemistry, especially in populations at risk for psychosis."

Erectile dysfunction (ED) was linked with loss of work productivity and with lower health-related quality of life in an International Journal of Clinical Practice study of more than 52,000 men from eight countries.

In the study of men aged 40 to 70 years in Brazil, China, France, Germany, Italy, Spain, the United Kingdom, and the United States, the overall ED prevalence was 49.7%, with Italy reporting the highest rate (54.7%). Men with ED reported significantly higher rates of staying home from work (7.1% versus 3.2%), working while sick (22.5% versus 10.1%), work productivity impairment (24.8% versus 11.2%), and activity impairment (28.6% versus 14.5%) than men without ED. They also had lower measures of health-related quality of life.

"This study shows that ED remains a prevalent concern, one that impacts work productivity and absenteeism," said co-author Wing Yu Tang, of Pfizer Inc. "Stemming from eight countries, the global coverage of the data also suggests that this issue is pervasive across geographies," added senior author Tarek Hassan, also of Pfizer Inc.

In an Acta Neurologica Scandinavia study of 182 patients with Parkinson's disease and 185 healthy controls, patients with Parkinson's disease had significantly lower levels of vitamin D in their blood. Also, patients with lower vitamin D levels were more likely to fall, and to experience sleep problems, depression, and anxiety.

The findings suggest that vitamin D supplementation may help to treat non-motor symptoms associated with Parkinson's disease.

"As various non-motor symptoms place a burden on individuals with Parkinson's disease and their caregivers, vitamin D might be a potential add-on therapy for improving these neglected symptoms," said senior author Chun Feng Liu, MD, PhD, of the Second Affiliated Hospital of Soochow University, in China.

Because smokers are less likely to develop ulcerative colitis (UC), a type of inflammatory bowel disease, patients with UC may be tempted to start smoking to lessen their symptoms. Researchers found no beneficial effects of smoking, however, in a nationwide study that included 6,754 patients with UC.

In the Alimentary Pharmacology & Therapeutics study, smokers and never-smokers with UC had similar outcomes with respect to flares, medication use, hospitalisations, and colon surgery. Also, smoking cessation did not worsen the course of disease in patients.

"We did not find any benefits of smoking in ulcerative colitis. We hope our study will give people with ulcerative colitis the confidence to avoid smoking and thereby improve their health in general," said lead author Jonathan Blackwell, BMBS, of St. George's Healthcare NHS Trust and St. George's University, in London.

"Extensive gender discrimination in healthcare access" for women in India, suggests study

Younger and older women and those living furthest away from major hospital most likely to miss out on healthcare

Women in India face "extensive gender discrimination" in access to healthcare, suggests a study of outpatient appointments at one major tertiary care hospital in Delhi, and published in the online journal BMJ Open.

Younger (30 and below) and older (60 and above) women and those living furthest away from the hospital were most likely to miss out.

The findings prompt the researchers to call for "systemic societal and governmental action to correct this gender discrimination."

Previous research on gender discrimination in developing countries has largely focused on the higher death rates among women compared to men. And unreliable data have primarily hindered systematic study of gender discrimination.

In a bid to rectify this, the researchers drew on 2,377,028 outpatient clinic appointments for all departments except obstetrics and gynaecology at a large public tertiary care hospital in Delhi in 2016.

They wanted to see if there were any gender differences in access and whether a patient's age and distance from the hospital might have any bearing on this.

Outpatients were split into five age groups: 0-16 years; 19-30; 31-44; 45-59; and 60 and above. More than 90% of them travelled from Delhi and three adjoining states: Haryana; Uttar Pradesh; and Bihar.

A total of 882,324 people visited the outpatient departments of the hospital an average of 2.69 times in 2016, adding up to a total of 2,377,028 visits.

The researchers calculated the number of 'missing' patients by looking at the difference between the actual number of women who visited the hospital and those that should have come, had men and women visited in the same proportions as the sex ratio of the overall population would suggest, based on the 2011 census.

Almost two thirds (63%) of these visits were made by male patients, with a total of 1,494,444 visits compared to 882,584 (37%) visits by female patients, equivalent to a sex ratio of 1.69.

This is significantly greater than the overall sex ratio of the population of 1.09, say the researchers.

After adjusting for different hospital departments, they estimated that nearly twice as many hospital visits were made by men and boys as were made by women and girls in the younger age groups, with sex ratios of 1.93 and 2.01 for 0-18 year olds and 19-30 year olds, respectively.

The ratio fell to 1.43 and 1.4 for those aged 31-44 and 45-59, respectively, but rose again to 1.75 for those aged 60 and above.

This U-shaped curve was the same for patients from all four locations.

After taking account of age and hospital department, the overall sex ratio increased with distance from the hospital: 1.41 for Delhi; 1.70 for Haryana, the neighbouring state, 1.98 for Uttar Pradesh, a state further away; and 2.37 for Bihar, the state furthest away from Delhi.

Comparing the total number of actual visits to those that should have taken place based on the population sex ratio, 402,722 female outpatient visits were 'missing' from these four locations--nearly half (49%) the actual number, calculate the researchers.

This is an observational study, and as such, can't establish cause. The study also relied on data from one hospital and so may not have covered all referrals from each state, including women from more distant states who might have preferred to use healthcare facilities closer to home.

Nevertheless, the findings suggest "extensive" discrimination in access to healthcare, with younger and older women and those living further away from the hospital, especially likely to miss out.

"This calls for systematic societal and governmental action," say the researchers, who go on to say that their study "has important implications for gender-related health policy which has so far focused on maternal health."

They conclude: "The findings suggest local healthcare infrastructure should be strengthened, with the biggest beneficiaries being younger and older women who are most neglected and discriminated against."

Barcelona, 8 August, 2019-. Up to 11% of new childhood asthma cases could be prevented each year if European countries complied with the WHO PM2.5 air quality guidelines. Moreover, 33% of new annual cases could be prevented in European countries if they were able to reduce air pollution levels to lowest levels recorded in the literature. Those are the conclusions of a study led by the Barcelona Institute for Global Health (ISGlobal), an institution supported by "la Caixa", and published in the European Respiratory Journal.

Asthma is the most common chronic disease in children. Emerging evidence suggests that exposure to air pollution may increase the risk of developing this respiratory disease during childhood. The new study has estimated the burden of childhood asthma in 18 European countries and more than 63.4 million children and has concluded that a large number of cases may be attributable to air pollution exposure. The attributable percentage of new annual cases varies according to each of the three pollutants studied: 33% for PM2.5, 23% for NO2 and 15% for black carbon (BC).

The study used census population data from 18 European countries and obtained incidence rates of asthma in children from the Global Burden of Disease (GBD) study database. Exposure to the different pollutants was calculated using a harmonized European statistical model (land use regression) based on multiple measurements in Europe. To estimate the burden of childhood asthma, researchers posed two different scenarios: the first one was based on the maximum air pollution levels recommended by the World Health Organisation (WHO) air quality guidelines. The second scenario took as a reference the lowest air pollution levels recorded among 41 previous studies.

The analysis for the first scenario revealed that 66,600 childhood asthma cases (11% of the total incident cases) could be prevented per year if the 18 countries under study complied with the WHO air quality guideline for PM2.5. Compliance with the NO2 guideline was estimated to prevent 2,400 childhood asthma cases per year (0.4% of the total incident cases).

"The analysis showed that, while meeting the WHO recommendations for PM2.5 would imply a significant reduction in the percentage of annual childhood asthma cases, that is not the case with NO2, where 0.4% of the cases would be prevented. Therefore, our estimations show that the current NO2 WHO air quality guideline value seems to provide much less protection than the PM2.5 guideline. We suggest that these values require update and lowering to be better suited in protecting children's health", says David Rojas-Rueda, one of the scientists who led this study at the Barcelona Institute for Global Health.

According to the results of the second scenario, if the 18 countries were able to meet the lowest levels of PM2.5 recorded by previous studies, more than 190,000 annual cases (or 33% of incident cases) could be prevented. The number of new cases that could be avoided per year if the lowest levels of NO2 and black carbon were achieved would be 135,000 (or 23%) and 89,000 (or 15% of all incident cases), respectively.

Overall, these estimates are in line with two previous studies conducted in the UK which found that the percentage of annual incident childhood asthma attributable to NO2 was 22%. Another study estimated that 4 million new paediatric asthma cases could be attributable to NO2 pollution annually, 64% of which occur in urban centres.

Haneen Khreis, lead author of the study and an associated researcher at the Center for Advancing Research in Transportation Emissions, Energy, and Health at the Texas A&M Transportation Institute, believes this new analysis is "a call for urgent action". "Only in the past two years, several analyses on air pollution and onset of childhood asthma have emerged, strengthening the case from different research teams that air pollution is contributing substantially to the burden of paediatric asthma", Khreis commented. "Largely, these impacts are preventable and there are numerous policy measures which can reduce the ambient levels of, and children's exposures to, outdoor air pollution. We can and should do something about it".

The 18 European countries covered in the study are Austria, Belgium, Denmark, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Lithuania, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom. Countries from Eastern Europe were not included due to the lack of air pollution exposure data in the region.

Gravitational wave researchers at the University of Birmingham have developed a new model that could help astronomers track down the origin of heavy black hole systems in the Universe.

Black holes are formed following the collapse of stars and possibly supernova explosions. These colossally dense objects are measured in terms of solar masses (M?) - the mass of our sun.

Typically, stars will only form black holes with masses of up to 45 M?. These systems then pair and merge together, producing gravitational waves that are observed by the LIGO and Virgo detectors.

Stellar collapse, however, causes instabilities that prevent the formation of heavier black holes - so a new model is needed to explain the existence of binary black hole systems with masses larger than about 50 M?.

These objects are thought to be formed from binary black holes which have then gone on to merge with other black holes. Scientists believe that these 'next generation' black holes --made up of the merger of their 'parents' -- might be the heavier black holes observable by LIGO and Virgo.

In a new study, published in Physical Review D Rapid Communications, researchers from the University of Birmingham's Institute for Gravitational Wave Astronomy, suggest that future detections of multiple generations of black-hole mergers would allow us to figure out their birthplace. They have produced new calculations that could help astronomers better understand these mergers - and where to find them.

"Star clusters - groups of stars that are bound together by gravity - might act like black-hole 'nurseries', providing an ideal environment to grow generations of black holes, " explains Dr Davide Gerosa, lead author of the paper. "But in order to know what type of star clusters are most likely to be capable of producing these, we first need to know something about the physical conditions that would be needed."

The team believes they have found part of the solution to this puzzle by calculating the likely 'escape speed' a cluster needs to have to be able to host a black hole with a mass above 50 M?. The escape speed is the velocity at which an object would need to be travelling to escape gravitational pull. For instance, a rocket leaving earth would need to be travelling at 11km/s (25,000 mph) to get into orbit.

When they merge, black holes receive recoils or kick. Much like a gun recoils as a bullet is shot, black holes recoil as gravitational waves are emitted. The next generation of black holes can form only if their parents have not been 'kicked out' of the cluster, i.e. only if the escape speed of the cluster is large enough.

The team calculated that observing black holes with mass above 50 M? would suggest that the cluster where they lived had an escape speed larger than about 50km/s.

Co-author Professor Emanuele Berti from Johns Hopkins University, explains: "Gravitational wave observations provide an unprecedented opportunity to understand the astrophysical settings where black holes form and evolve. A very massive event would point towards a dense environment with large escape speed".

Where might you find these types of dense clusters? Many predictions for LIGO and Virgo so far concentrated on 'globular clusters' - spherical collections of about a million stars tightly bound together in the outskirts of galaxies. Their escape speed, however, is too low. This new study finds globular clusters are unlikely to host multiple generations of black holes. Astronomers will need to look further afield: nuclear star clusters, found towards the centre of some galaxies are dense enough and might provide the type of environment needed to produce these objects.

"Gravitational-wave astronomy is revolutionizing our understanding of the Universe," says Dr Gerosa. "We are all waiting for upcoming results from LIGO and Virgo to put these and other astrophysical predictions to the test".