Category: English

Source: The Conversation – UK – By Adriana Alcaraz-Sanchez, Postdoctoral Fellow in Philosophy of Mind and Cognitive Science, University of Edinburgh

For some people, sleep brings a peculiar kind of wakefulness. Not a dream, but a quiet awareness with no content. This lesser-known state of consciousness may hold clues to one of science’s biggest mysteries: what it means to be conscious.

The state of conscious sleep has been widely described for centuries by different Eastern contemplative traditions. For instance, the Indian philosophical school of the Advaita Vedanta, grounded in the interpretation of the Vedas – one of the oldest texts in Hinduism – understands deep sleep or “sushupti” as a state of “just awareness” in which we merely remain conscious.

Similar interpretations of deep sleep are made by the Dzogchen lineage in Indo-Tibetan Buddhism. According to their teachings, different meditative practices can be followed during wakefulness and sleep to acknowledge the “essence” of consciousness. One of those meditative practices is that of dream yoga or luminosity yoga, which enables the practitioner to recognise the states of dream and sleep. This aims to bring them to a state of “pure awareness”, a state of being awake inside sleep without thoughts, images or even a sense of self.

For western science, this state poses a conundrum. How can you be aware without being aware of something? If these reports are accurate, they challenge mainstream theories that treat consciousness as always about an object. For example, my awareness of the laptop in front of me, or the blue sky rising above my window, or my own breathing. The existence of this state pushes us to reconsider what consciousness is.

Objectless sleep experiences

My colleagues and I set out to explore what a content-free state during sleep feels like in a series of studies. We first surveyed 573 people online about unusual forms of sleep experiences, including forms of sleep consciousness that might be simpler or more minimal. For example, an awareness following the dissolution of a dream, or a bare awareness of the fact that you are sound asleep.

We then conducted in-depth interviews with 18 participants, who reported they had experienced some form of objectless sleep experiences, using a protocol inspired by the micro-phenomenological interview. This is a research tool designed to help people recall and describe subtle aspects of their experience in fine detail.

In those studies, we found a spectrum of experiences we called “objectless sleep experiences” – conscious states that appear to lack an object of awareness. In all cases, participants who alluded to an objectless sleep experience reported having had an episode during sleep that lacked sensory content and that merely involved a feeling of knowing that they were aware.

Some of our participants’ experiences matched descriptions of conscious sleep as described in Eastern philosophical traditions; objectless and selfless, with no sense of “I” remaining. Participants reported that their selves seemed to have vanished or dissolved, a state reminiscent to that of “drug-induced ego-dissolution”, reported after the ingestion of psychedelic drug DMT, and in deep-meditative states.

Other reports from the participants in our study included a faint feeling of being “there” in an undefined state, or an awareness of “nothingness” or a “void”. A few people’s experiences involved traces of rudimentary forms of dreaming, the experience of being in a world, even if such a world appeared to be missing.

Although objectless sleep experiences like conscious sleep have mainly been linked to contemplative practices, such as dream yoga, our results indicate that people without knowledge of those practices also experienced this phenomenon. In fact, the results of our online survey did not indicate an association between engagement in meditative practices and objectless sleep experiences.

However the survey results did find that experience of lucid dreaming – which is when you realise you are dreaming but stay asleep – seemed to be correlated with objectless sleep experiences. It should be noted, though, that many participants who could lucid dream did not report objectless sleep experiences.

Read more:
I’m a lucid dream researcher – here’s how to train your brain to do it

Training for lucid sleep

The rarity of objectless sleep experiences make them difficult to study. We need training methods to induce these experiences so we can better understand them.

In our recent study, my colleagues and I tested a new induction protocol that combined meditation, visualisation and lucid dreaming techniques. Four participants learned to stay aware as they drifted into sleep and to signal that they were lucid with a pre-agreed eye movement. Portable EEG recordings, which measure the brain’s electrical activity, confirmed that some objectless states occurred during non-REM (slow-wave) sleep. Researchers believe non-REM sleep lacks the sort of complex conscious states we have while dreaming, although some other forms of sleep experiences, including simpler forms of dreaming, might occur.

Dreamless sleep and consciousness research

Currently, there is a lack of agreement among scientists about what the basis of consciousness is. Some popular views assert that consciousness arises when information is broadcast in the brain. Yet, there are still debates about which sort of information the brain needs for cognitive processing.

Objectless sleep experiences expand our picture of what it is like to be conscious during sleep. Sleep consciousness has traditionally been widely studied in relation to dreams and dream-like experiences, but recently there has been a shift in this trend.

Minimal forms of consciousness, like that displayed by objectless sleep experiences, can pave the way to refine our theories of consciousness. Their existence hints at a form of awareness stripped of content altogether. Moreover, studying these sort of experiences can help us understand altered conscious states, including deep meditation, sensory deprivation, or even mind blanking – episodes in which our mind seems to go blank or go “nowhere”.

The fact people can be aware of “nothing” while asleep might tell us more about the mind than any dream ever could.

Adriana Alcaraz-Sanchez has received research funding from the following organisations: Scottish Graduate School of Arts and Humanities (SGSAH), European Research Council (ERC), International Association for the Study of Dreams (IASD), Graduate School of the University of Glasgow, and the Institute for the Advanced Studies in Humanities (IASH) at the University of Edinburgh

– ref. Can you be aware of nothing? The rare sleep experience scientists are trying to understand – https://theconversation.com/can-you-be-aware-of-nothing-the-rare-sleep-experience-scientists-are-trying-to-understand-263142

Source: The Conversation – UK – By Ming Gao, Research Fellow of East Asia Studies, Lund University

In the 2025 global gender gap index (GGGI), Japan ranks 118th out of 148 countries – still the lowest among the G7 nations and among the poorest performers globally. This is largely because of limited political participation by women. The current cabinet of prime minister Ishiba Shigeru says it all. In October 2024, Japan’s new prime minister appointed only two women to a 20-member cabinet – down from five in the previous lineup.

The decision was widely criticised as a setback for advancing female political representation and a clear sign that gender-equality policies were not a priority.

But the country has continued to take backward steps on gender. In January, Japan announced it would halt funding for the UN’s Committee on the Elimination of Discrimination against Women (Cedaw). The decision followed Cedaw’s recommendation that Japan revise its male-only imperial succession law to ensure gender equality in the line to the throne.

The funding halt sparked a strong backlash from rights advocates, who viewed it as further evidence of Japan’s resistance to addressing structural discrimination against women.

The debate over Japan’s imperial succession has surfaced periodically for decades. Since 1947, the Imperial Household Law has stipulated that only men from the patrilineal line can ascend what is known as the Chrysanthemum throne. This rule has led to concerns over the future of the imperial family, given the shrinking number of male heirs.

Japan’s Emperor Naruhito turned 65 on February 23 and has only three male heirs. These are his uncle Prince Hitachi (aged 89), his younger brother Crown Prince Fumihito (59), and his nephew Prince Hisahito, who is 18.

A poll of around 2,000 people taken in April 2024 by Kyodo News found 90% of respondents support allowing female emperors. Yet successive governments have remained steadfast in resisting change, with some citing the so-called unbroken imperial lineage (bansei ikkei).

Ishiba is known to favour allowing a female succession. But his administration’s financial retaliation against Cedaw signals otherwise. The decision is not merely a reaction to a non-binding recommendation – it reflects deeper discomfort with external scrutiny over Japan’s gender policies, which the current government has deprioritised.

Cedaw’s recommendation to Japan that it might reconsider its imperial succession system was not an isolated critique. The UN committee has regularly called on Japan to improve gender equality in multiple areas. These include workplace discrimination, representation in politics and legal protections against gender-based violence.

Cedaw’s recommendation on inclusive succession is neither legally binding nor “within the purview of the Committee’s competence”, as the committee itself acknowledges. As a result the government’s response – cutting funding – is more than just a reaction to Cedaw’s recommendation. It raises concerns about Japan’s commitment to gender equality full stop.

The United Nations has clashed with successive Japanese governments over a range of gender-related issues. These have included the refusal of Japan to allow brides to retain their maiden names. Cedaw has recommended that Japan amend the Civil Code over the surname requirement in 2003, 2009 and 2016. The most recent occasion is marked the recommendation as having high importance.

But the most important issue is over Japan’s treatment of what it called “comfort women” – the system of military sexual slavery before and during the second world war. Cedaw and other UN bodies have repeatedly urged Japan to resolve the issue by firstly recognising the gravity of the crimes involved and dealing with reparations for survivors and strengthen education on the issue.

Japan has frequently been accused of downplaying this issue. While official apologies have been made, they have frequently been coupled with denials or diplomatic efforts to dilute past statements. In its last report in 2016, Cedaw called on Japan to ensure its leaders and public officials “desist from making disparaging statements regarding responsibility, which have the effect of retraumatising victims”.

Poor track record

Japan’s relationship with international organisations addressing gender issues has long been uneasy and its domestic policies frequently lag behind international expectations. Reports from the committee have criticised Japan’s inadequate legal definitions of discrimination against women, limited access to justice for women, and the persistence of deep-seated gender stereotypes and patriarchal attitudes.

This year holds special significance for the UN, marking two major anniversaries. It’s the 30th anniversary of the United Nations fourth world conference on women. This produced the Beijing declaration and platform for action – the most widely endorsed global agenda for women’s rights. And it’s the 25th anniversary of the UN’s adoption of Resolution 1325. This established the Women, Peace and Security (WPS) agenda. WPS is now recognised as a key pillar of international peace and security, regarded by the European Parliament’s committee on women’s rights and gender equality as “central to contemporary global peace and security challenges”.

Amid increasing global support for women-led initiatives, Japan’s decision to halt funding for Cedaw in 2025 risks damaging its status as a responsible and respected nation on the world stage. It also risks alienating allies that prioritise gender equality in diplomacy.

In distancing itself from global norms, Japan risks not just falling behind, but falling out of step with most of its G7 peers.

Ming Gao receives funding from the Swedish Research Council. This research was produced with support from the Swedish Research Council grant “Moved Apart” (nr. 2022-01864). Ming Gao is a member of Lund University Profile Area: Human Rights.

– ref. Japan’s problem with women’s equality is getting worse, not better – https://theconversation.com/japans-problem-with-womens-equality-is-getting-worse-not-better-249762

Source: The Conversation – UK – By Alex Chepstow-Lusty, Research Associate, Geography, University of Sussex

Many tropical glaciers in the Andes are expected to disappear in the next few decades. Their meltwater sustains millions of people, feeding crops in the dry season, supplying Peru’s capital Lima and other big cities, and even boosting the Amazon river. As glaciers vanish, floods and droughts are becoming more extreme.

But my new research with colleagues suggests solutions may lie in environmental knowledge that the Incas and their predecessors developed centuries ago.

In January 2010, record rainfall caused massive flooding in the Cusco region of Peru. Bridges were washed away, 25,000 people were left homeless and 80% of harvests were destroyed. The railway to Machu Picchu was cut off. Losses were estimated at US$230 million (£170m).

This disaster took place in the heart of what was the Inca Empire, which once spanned an area from what is today near the Colombian border down to central Chile. The Incas’ efficient storage systems, sophisticated road network and ecological management supported up to 14 million people before European conquest and colonisation.

So could some of this modern-day catastrophe have been avoided if the landscape still retained its natural tree cover – forests and high-altitude vegetation that slow water and reduce erosion?

A new paper in the journal Ambio offers a long-term perspective. I was part of a team of researchers from the University of Sussex, the International Potato Center in Lima and Cusco-based NGO Ecoan, who examined microfossils such as pollen in sediment cores from Lake Marcacocha, near Cusco. These act as an environmental archive, recording shifts in vegetation, farming and climate over centuries.

The evidence shows that from around the year 1100, during a period of global warming known as the Medieval Climatic Anomaly, Andean communities moved higher up into the mountains. They built terraces, irrigated slopes, and planted trees such as alder to make the soil more fertile and provide wood.

Llamas and their cousins alpacas were vital as they were hardy, light-footed, and supplied wool, fuel and fertiliser. Their communal dung heaps even show up in the lake sediments, revealed by spikes in fossils of certain dung-eating mites that thrived when llama caravans were pastured nearby.

Together, these practices stabilised soils, reduced erosion, and allowed large populations to thrive in the Andes.

An ecological and social transformation

When the Spanish arrived in the 1530s, this balance was upended. New livestock – cattle, sheep and goats – trampled vegetation and eroded soils. Their free-ranging herds left waste across the landscape, unlike llamas and their easily-collectible dung.

At the same time, the Spaniards cut down forests for timber and charcoal, in contrast to the Inca who had imposed harsh penalties to protect their woodland resources. The 17th century Spanish pastor and chronicler, Bernabé Cobo, remarked that a Spanish household used as much fuel in one day as a native household would in an entire month.

The lake sediments record the ecological damage of the era: excess nutrients from dung, more erosion, and a collapse of the Inca’s sustainable land management.

This isn’t a simple story in which the Inca were perfect for the environment and the Spaniards entirely negative, but there are clear lessons to be learned. The indigenous people, normally pushed to poorer lands at high altitude, adapted to what pragmatically works.

In the Andes, many highland communities still support each other through deep-rooted traditions, involving collaboration and reciprocity. Some of the most promising climate solutions today build on this heritage.

Communities restoring Andean vegetation

One co-author of the paper, Cusco biologist Tino Aucca Chutas, founded the NGO Ecoan in 2000, to protect rare high-altitude Polylepis cloud forests. These gnarled, moss-covered trees capture water from clouds and release it slowly, making them vital for downstream water supply. Only small fragments of the original forests remain.

Through the regional movement Accion Andina, founded by Ecoan and non-profit organisation Global Forest Generation, 12 million Polylepis trees have been planted across the Andes. In 2023, Accion Andina was awarded the prestigious global Earthshot Prize. The ultimate goal is to fully restore the forests over the next century.

Another co-author, Graham Thiele of the International Potato Center in Lima, argues that native agroforestry – combining traditional crops, trees and llamas – should be part of a “second climate-smart agricultural revolution” in the Andes.

The Andes are at the sharp end of climate change. The glaciers are retreating, rainfall is becoming more erratic, and disasters like the Cusco floods will happen more often. But history shows societies have adapted before.

Inca-style terraces, cloud forests and llamas aren’t relics of the past – they are the tools required now, particularly vital with the glaciers soon gone. As South America faces a looming water crisis, the clock is ticking, and the lessons of the Inca may be more urgent than ever.

Alex Chepstow-Lusty has received funding from NERC, CNRS and the French Institute of Andean Studies.

– ref. Lessons from the Incas: how llamas, terraces and trees could help the Andes survive climate change – https://theconversation.com/lessons-from-the-incas-how-llamas-terraces-and-trees-could-help-the-andes-survive-climate-change-258148

Source: The Conversation – UK – By Stephanie Brown, Lecturer in Criminology, University of Hull

A recent YouGov poll found that the word that Americans most associate with the middle ages is “violent”. Medieval towns may appear to be full of random violence, every alleyway a potential crime scene, every tavern brawl ending in bloodshed. But our recent research reveals a more complex, and in some ways familiar, reality.

In 14th-century London, York and Oxford, lethal violence clustered in a small number of hotspots, often no more than 200 or 300 metres long. Just as in modern cities, crime was not evenly spread but concentrated in certain streets and intersections where people, goods and status converged. The surprising difference is that in the middle ages, the busiest and wealthiest areas were often the most dangerous.

Our Medieval Murder Map project uses coroners’ inquests (jury investigations into suspicious deaths) to pinpoint the locations of 355 homicides between 1296 and 1398. These records detail where the body was found, when the attack happened, the weapon used, and sometimes the quarrels, rivalries or insults that triggered it.

The cases from the coroners’ records were geocoded (turning a description of a place, like an address, into a pair of numbers, latitude and longitude, to show its exact position) using thematic maps provided by the scientific team of the Historic Towns Trust. What emerges is a vivid street-level picture of urban violence seven centuries ago.

The patterns are striking. Homicides clustered in markets, major thoroughfares, waterfronts and ceremonial spaces. These were areas of intense activity, where economic and social life intersected and where conflicts could be played out before a public audience.

Sundays were particularly deadly. After a morning of churchgoing, the afternoon often brought drinking, games and arguments. Violence peaked around curfew in the early evening.

A tale of three cities

The three cities we looked at differed sharply in their overall levels of violence. Oxford’s homicide rate was three to four times higher than that of London or York.

This was not random. The medieval university attracted young men aged between 14 and 21, many living far from home, armed and steeped in a culture of honour and group loyalty. Students organised themselves into “nations” based on their regional origins and quarrels between northerners and southerners regularly erupted into street battles.

Legal privileges for clerics, which included students, meant that they were often immune from prosecution under common law, creating a climate in which serious violence could flourish with little fear of punishment.

Each city’s hot-spots had their own character. In London, Westcheap, the commercial and ceremonial heart of the city, saw murders linked to guild rivalries, professional feuds and public revenge attacks. The bustling Thames Street waterfront, by contrast, was home to sudden quarrels among sailors and merchants, sometimes escalating from petty disputes into fatal encounters.

In York, one of the most dangerous spots was the main southern approach through Micklegate to Ouse Bridge. This was more than just a gateway into the town – it was a commercial and civic hub, lined with shops and inns, and the site of processions and public gatherings. Such a space naturally drew travellers, traders, and townspeople into close contact and into conflict.

Another York hot-spot was Stonegate, a prestigious street that formed part of the ceremonial route to York Minster. These patterns reflect York’s particular blend of commerce, ceremony and civic life, where spaces of wealth and display doubled as stages for rivalry, revenge and the public assertion of honour.

In Oxford, the concentration of killings in and around the university quarter reflected the constant tensions between students and townspeople and the factionalism within the student body itself. Clashes were often fuelled by drink, insults and a readiness to defend group honour with swords or knives.

The geography of medieval violence was shaped by visibility as much as opportunity. Busy streets and central markets offered the greatest number of potential rivals and bystanders and so were ideal stages for settling disputes in ways that preserved or enhanced reputation. Public killings could send a powerful message, whether to a rival guild, a hostile faction or the wider community.

In this sense, the urban logic of violence in the middle ages echoes patterns found in modern cities, where certain micro-locations consistently generate higher crime rates. The difference is that in medieval England, poverty was not the main driver. Poorer, peripheral neighbourhoods saw fewer homicide inquests, while affluent and prestigious districts often drew the most danger.

The Medieval Murder Map offers a rare opportunity to see the medieval city as its inhabitants experienced it: a landscape where the streets themselves shaped the rhythms of danger, and where wealth, power and proximity could be as deadly as poverty and neglect. Far from being random, medieval violence followed rules – and those rules were written in the geography of the city.

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Stephanie Brown has received funding from the Economic and Social Research Council (ESRC).

Manuel Eisner does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

– ref. Our medieval murder maps reveal the surprising geography of violence in 14th-century English cities – https://theconversation.com/our-medieval-murder-maps-reveal-the-surprising-geography-of-violence-in-14th-century-english-cities-263380

Source: The Conversation – UK – By Rowland Atkinson, Professor and Research Chair in Inclusive Societies, University of Sheffield

News stories in recent months have claimed that more than 16,500 millionaires are expected to leave the UK in 2025 due to the country’s increasing tax burden. Notably, the abolition of “non-dom” tax rules has been touted as one of the reasons for this “millionaire flight”. It might seem that efforts to tax very wealthy residents is foolish – killing the goose that lays the golden egg.

It is hard to overstate how important the topic of taxation is. Most people’s daily lives are heavily underwritten by everything that income from taxes can buy – public services like healthcare and education, defence, roads and infrastructure, to name just a few.

Claims of fleeing millionaires centre on the UK as a high-tax economy. The state chooses, so the thinking goes, to stifle talent or encourage it to move to lower-tax countries. But these observations don’t always stand up to scrutiny when we look more broadly at the statistics and get into the methods underpinning them.

The idea of a wealth exodus is a powerful metaphor – a kind of inverse of the suggestion that rich countries are deluged by migrants. After all, who wants to see any exodus from the UK – especially of the richest among us? But we also want those with the most to pay into a system to improve the fortunes of the people with the least.

So let’s turn back to the question of tax. Non-doms (rich long-term UK residents who claim to be “domiciled” elsewhere and who will in future have to pay tax on all income they earn, whether overseas or in the UK) and thousands of other people are apparently leaving for lower-tax regimes. But where have these claims come from?

Consultancy firm Henley & Partners, the company behind the projected 16,500 fleeing millionaires figure, says it advises people on obtaining citizenship through investment. The company has been tracking the locations of the rich using data from research firm New World Wealth and their findings have been used widely across the UK media.

But New World Wealth’s database tends to focus on entrepreneurs and company founders (around 50% of the 150,000 on its database). This group is often more mobile, with wealthier millionaires being more easily tracked than millionaires with fewer assets. Such figures do not include property millionaires.

Second, Henley & Partners says that migration figures are based, among several other measures, on evidence of whether the millionaires in the database spend more than six months in another country. This means that someone who, for example, lived overseas for seven months of the year but retained a UK passport, home and business could be counted as an out-migrant.

Another problem is that one way migration data is verified is by using sites like LinkedIn to notionally identify where millionaires are working. But this may not be where they actually live.

Henley & Partners says both it and New World Wealth have been tracking “millionaires on the move” for more than a decade. New World Wealth says it uses multiple sources to map millionaire migration, including data from investment migration schemes and enquiries about these schemes, property registers, company registers, data from high-end removal firms, as well as information about new family offices being set up. And Henley & Partners says it has never funded any lobby group or political party.

(Swiss bank UBS/Credit Suisse has also forecast a large number of millionaires leaving the UK – from 3.06 million “total millionaires” (someone who is a millionaire based on all their assets), it projects a fall to 2.54 million by 2028.)

More millionaires

But even working with these estimates (around 9,000 for 2024 and the 16,500 figure for 2025) gives a number of rich people leaving or expected to leave the UK that hovers between close to zero and 1% of the UK population of millionaires.

Bear in mind that the number of homes worth more than a million pounds in Britain is now around 702,000, and that the number of people with a million pounds or more in personal wealth is more than 3 million.

All of this suggests the estimates of out-migration constitute a tiny fraction of the UK’s millionaire population. These could be the UK’s wealthiest millionaires and biggest taxpayers – but without better data it’s impossible to say for certain.

There’s other evidence to challenge the idea that high taxes are pushing the UK’s wealthy population out. A survey by pressure group Patriotic Millionaires found that most people who are wealthy are concerned about the state of the UK and are willing to pay more. It is also important to note that wealth taxes are very popular among the general population.

In our work on London’s super-rich we saw that millionaires are attached to the city, seeing it as an unrivalled location globally. There is a lot of money around and a lot of property wealth – but also many who are willing to pay more in taxes.

But there are those who lobby to create a more advantageous tax environment for the wealthy. The income of these sectors is driven by high-value sales – whether of a business, shares and assets or luxury goods, for example.

Some newspapers, writers, influencers and those in the finance, luxury and property sectors may have good reason to perpetuate a sense of a wealth exodus. For them it may be a good story, but we feel it needs to be challenged.

Ongoing reports of wealth migration have had significant consequences. It has already been suggested that Chancellor Rachel Reeves is considering reversing the decision to abolish non-dom status, for example. This had been expected to bring to the exchequer of £12.7 billion over five years. But, so far, the non-dom exodus does not appear to be happening.

The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.

– ref. Millionaires may not be fleeing the UK in droves – but there are reasons these stories persist – https://theconversation.com/millionaires-may-not-be-fleeing-the-uk-in-droves-but-there-are-reasons-these-stories-persist-259591

Source: The Conversation – UK – By Cosimo Inserra, Reader in Astrophysics – Associate Dean of EDI, Cardiff University

Stars often end their lives with a dazzling explosion, creating and releasing material into the universe. This will then seed new life, leading to a cosmic cycle of birth, death and rebirth.

Astronomers around the world have been studying these explosions, called supernovae (derived from the Latin “an extremely bright new star”), and have discovered tens of different types.

In 2021, astronomers observed a bright supernova, dubbed SN2021yfj, two billion light years away. In a recent paper, published in Nature, astronomers observed it for more than a month and discovered that it exhibits the visible signatures of heavier elements – such as argon, silicon and sulphur – since the onset of the explosion. This was previously unobserved in any stellar explosion.

Supernovas violently eject stellar material into the cosmos, roughly keeping the same onion structure the star had before its death. This means that lighter materials – such as hydrogen and helium – will be in the outer layers and heavier ones – such as iron, silicon and sulphur – in the inner layers.

However, massive stars can lose part of their layers during their evolution via winds (like the Sun), great eruptions (like the star Eta Carinae), or a gravitational and energetic “tug of war” with a companion star in a binary system. When this happens, circumstellar material will form around the star and will eventually be hit by the ejected material in the explosion.

In a galaxy, there are an enormous number of stars. If you think that there are at least two trillion observed galaxies, you can picture what a vast playground of discoveries scientists play with every day. Although not all stars end with an explosion, the proportion is large enough to allow scientists to confirm and study their shell structure and chemical composition.

The luminosity (brightness) of the new discovery in terms of timeframe and behaviour was similar to other known and well-studied stellar explosions. The chemical signatures discovered in their electromagnetic spectra (colours) and their appearance over time pointed to a thick inner stellar layer expelled by the star.

This was then struck by material left in the star and expelled during the explosion. However, some traces of light elements were also present, in direct clash with the heavy elements as they should be found in stellar layers far apart from each other.

The astronomers measured the layer velocity to be around 1,000 km/s, consistent with that of massive stars called Wolf-Rayet, previously identified as progenitor stars of similar stellar explosions. They modelled both the luminosity behaviour and electromagnetic spectra composition and found the thick layer, rich in silicon and sulphur, to be more massive than that of our Sun but still less than the material ejected in the final explosion.

Heavy elements

The new discovery, the first of its kind, revealed the formation site of the heavy elements and confirmed with direct observations the complete sequence of concentric shells in massive stars. Some stars develop internal “onion-like” layers of heavier elements produced by nuclear fusion, which are called shells. The latest findings have left the astronomy community with new questions: what process can strip stars down to their inner shells? Why do we see lighter elements if the star has been stripped to the inner shells?

This new supernova type is clearly another curveball thrown by the Universe to the scientists. The energy and the layers composition cannot be explained with the current massive star evolution theory. In the framework of mass loss driven by wind (a continuous stream of particles from the star), a star stripped down to the region where heavy elements form is difficult to explain.

A possible explanation would require invoking an unusual scenario where SN2021yfi actually consists of two stars – a binary system. In this case, the stripping down of the principal star would be carried out by a strong stellar wind produced by the companion star.

An even more exotic explanation is that SN2021yfi is an extremely massive star, up to 140 times that our Sun. Instabilities in the star would release very massive shells at different stages of its evolution. These shells would eventually collide with each other while the star collapsed into a black hole, leading to no further material released into the cosmos during the explosion.

To improve our understanding of stellar evolution, we would need to observe more such objects. But our comprehension could be limited by their intrinsic rarity – because the possibility of finding another explosion like SN2021yfi is less than 0.00001%.

Cosimo Inserra receives funding from Foundation MERAC (Mobilising European Research in Astrophysics and Cosmology) and the Engineering and Physical Sciences Research Council (EPSRC).

– ref. Supernovae: a first-of-its-kind star explosion raises new questions about these momentous events – https://theconversation.com/supernovae-a-first-of-its-kind-star-explosion-raises-new-questions-about-these-momentous-events-263554