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Reçu aujourd’hui — 26 novembre 2025 6.5 📰 Sciences English

Diverging priorities shape opening day of ESA Ministerial 2025

26 novembre 2025 à 18:01

BREMEN, Germany –  As the 23 member states of the European Space Agency meet this week to decide its budget for the next three years, its three major contributors – Germany, France and Italy – are signaling they will heavily support the agency. Yet even as ESA leaders push for unity, officials from those countries […]

The post Diverging priorities shape opening day of ESA Ministerial 2025 appeared first on SpaceNews.

Did cannibal stars and boson stars populate the early universe?

26 novembre 2025 à 14:52

In the early universe, moments after the Big Bang and cosmic inflation, clusters of exotic, massive particles could have collapsed to form bizarre objects called cannibal stars and boson stars. In turn, these could have then collapsed to form primordial black holes – all before the first elements were able to form.

This curious chain of events is predicted by a new model proposed by a trio of scientists at SISSA, the International School for Advanced Studies in Trieste, Italy.

Their proposal involves a hypothetical moment in the early universe called the early matter-dominated (EMD) epoch. This would have lasted only a few seconds after the Big Bang, but could have been dominated by exotic particles, such as the massive, supersymmetric particles predicted by string theory.

“There are no observations that hint at the existence of an EMD epoch – yet!” says SISSA’s Pranjal Ralegankar. “But many cosmologists are hoping that an EMD phase occurred because it is quite natural in many models.”

Some models of the early universe predict the formation of primordial black holes from quantum fluctuations in the inflationary field. Now, Ralegankar and his colleagues, Daniele Perri and Takeshi Kobayashi propose a new and more natural pathway for forming primordial holes via an EMD epoch.

They postulate that in the first second of existence when the universe was small and incredibly hot, exotic massive particles emerged and clustered in dense haloes. The SISSA physicists propose that the haloes then collapsed into hypothetical objects called cannibal stars and boson stars.

Cannibal stars are powered by particles annihilating each other, which would have allowed the objects to resist further gravitational collapse for a few seconds. However, they would not have produced light like normal stars.

“The particles in a cannibal star can only talk to each other, which is why they are forced to annihilate each other to counter the immense pressure from gravity,” Ralegankar tells Physics World. “They are immensely hot, simply because the particles that we consider are so massive. The temperature of our cannibal stars can range from a few GeV to on the order of 1010 GeV. For comparison, the Sun is on the order of keV.”

Boson stars, meanwhile, would be made from pure a Bose–Einstein condensate, which is a state of matter whereby the individual particles quantum mechanically act as one.

Both the cannibal stars and boson stars would exist within larger haloes that would quickly collapse to form primordial black holes with masses about the same as asteroids (about 1014–1019 kg). All of this could have taken place just 10 s after the Big Bang.

Dark matter possibility

Ralegankar, Perri and Kobayashi point out that the total mass of primordial black holes that their model produces matches the amount of dark matter in the universe.

“Current observations rule out black holes to be dark matter, except in the asteroid-mass range,” says Ralegankar. “We showed that our models can produce black holes in that mass range.”

Richard Massey, who is a dark-matter researcher at Durham University in the UK, agrees that microlensing observations by projects such as the Optical Gravitational Lensing Experiment (OGLE) have ruled out a population of black holes with planetary masses, but not asteroid masses. However, Massey is doubtful that these black holes could make up dark matter.

“It would be pretty contrived for them to make up a large fraction of what we call dark matter,” he says. “It’s possible that dark matter could be these primordial black holes, but they’d need to have been created with the same mass no matter where they were and whatever environment they were in, and that mass would have to be tuned to evade current experimental evidence.”

In the coming years, upgrades to OGLE and the launch of NASA’s Roman Space Telescope should finally provide sensitivity to microlensing events produced by objects in the asteroid mass range, allowing researchers to settle the matter.

It is also possible that cannibal and boson stars exist today, produced by collapsing haloes of dark matter. But unlike those proposed for the early universe, modern cannibal and boson stars would be stable and long-lasting.

“Much work has already been done for boson stars from dark matter, and we are simply suggesting that future studies should also think about the possibility of cannibal stars from dark matter,” explains Ralegankar. “Gravitational lensing would be one way to search for them, and depending on models, maybe also gamma rays from dark-matter annihilation.”

The research is described in Physical Review D.

The post Did cannibal stars and boson stars populate the early universe? appeared first on Physics World.

Academic assassinations are a threat to global science

26 novembre 2025 à 12:00

The deliberate targeting of scientists in recent years has become one of the most disturbing, and overlooked, developments in modern conflict. In particular, Iranian physicists and engineers have been singled out for almost two decades, with sometimes fatal consequences. In 2007 Ardeshir Hosseinpour, a nuclear physicist at Shiraz University, died in mysterious circumstances that were widely attributed to poisoning or radioactive exposure.

Over the following years, at least five more Iranian researchers have been killed. They include particle physicist Masoud Ali-Mohammadi, who was Iran’s representative at the Synchrotron-light for Experimental Science and Applications in the Middle East project. Known as SESAME, it is the only scientific project in the Middle East where Iran and Israel collaborate.

Others to have died include nuclear engineer Majid Shahriari, another Iranian representative at SESAME, and nuclear physicist Mohsen Fakhrizadeh, who were both killed by bombing or gunfire in Tehran. These attacks were never formally acknowledged, nor were they condemned by international scientific institutions. The message, however, was implicit: scientists in politically sensitive fields could be treated as strategic targets, even far from battlefields.

What began as covert killings of individual researchers has now escalated, dangerously, into open military strikes on academic communities. Israeli airstrikes on residential areas in Tehran and Isfahan during the 12-day conflict between the two countries in June led to at least 14 Iranian scientists and engineers and members of their family being killed. The scientists worked in areas such as materials science, aerospace engineering and laser physics. I believe this shift, from covert assassinations to mass casualties, crossed a line. It treats scientists as enemy combatants simply because of their expertise.

The assassinations of scientists are not just isolated tragedies; they are a direct assault on the global commons of knowledge, corroding both international law and international science. Unless the world responds, I believe the precedent being set will endanger scientists everywhere and undermine the principle that knowledge belongs to humanity, not the battlefield.

Drawing a red line

International humanitarian law is clear: civilians, including academics, must be protected. Targeting scientists based solely on their professional expertise undermines the Geneva Convention and erodes the civilian–military distinction at the heart of international law.

Iran, whatever its politics, remains a member of the Nuclear Non-Proliferation Treaty and the International Atomic Energy Agency. Its scientists are entitled under international law to conduct peaceful research in medicine, energy and industry. Their work is no more inherently criminal than research that other countries carry out in artificial intelligence (AI), quantum technology or genetics.

If we normalize the preemptive assassination of scientists, what stops global rivals from targeting, say, AI researchers in Silicon Valley, quantum physicists in Beijing or geneticists in Berlin? Once knowledge itself becomes a liability, no researcher is safe. Equally troubling is the silence of the international scientific community with organizations such as the UN, UNESCO and the European Research Council as well as leading national academies having not condemned these killings, past or present.

Silence is not neutral. It legitimizes the treatment of scientists as military assets. It discourages international collaboration in sensitive but essential research and it creates fear among younger researchers, who may abandon high-impact fields to avoid risk. Science is built on openness and exchange, and when researchers are murdered for their expertise, the very idea of science as a shared human enterprise is undermined.

The assassinations are not solely Iran’s loss. The scientists killed were part of a global community; collaborators and colleagues in the pursuit of knowledge. Their deaths should alarm every nation and every institution that depends on research to confront global challenges, from climate change to pandemics.

I believe that international scientific organizations should act. At a minimum, they should publicly condemn the assassination of scientists and their families; support independent investigations under international law; as well as advocate for explicit protections for scientists and academic facilities in conflict zones.

Importantly, voices within Israel’s own scientific community can play a critical role too. Israeli academics, deeply committed to collaboration and academic freedom, understand the costs of blurring the boundary between science and war. Solidarity cannot be selective.

Recent events are a test case for the future of global science. If the international community tolerates the targeting of scientists, it sets a dangerous precedent that others will follow. What appears today as a regional assault on scientists from the Global South could tomorrow endanger researchers in China, Europe, Russia or the US.

Science without borders can only exist if scientists are recognized and protected as civilians without borders. That principle is now under direct threat and the world must draw a red line – killing scientists for their expertise is unacceptable. To ignore these attacks is to invite a future in which knowledge itself becomes a weapon, and the people who create it expendable. That is a world no-one should accept.

The post Academic assassinations are a threat to global science appeared first on Physics World.

DNA as a molecular architect

26 novembre 2025 à 09:39

DNA is a fascinating macromolecule that guides protein production and enables cell replication. It has also found applications in nanoscience and materials design.

Colloidal crystals are ordered structures made from tiny particles suspended in fluid that can bond to other particles and add functionalisation to materials. By controlling colloidal particles, we can build advanced nanomaterials using a bottom-up approach. There are several ways to control colloidal particle design, ranging from experimental conditions such as pH and temperature to external controls like light and magnetic fields.

An exciting approach is to use DNA-mediated processes. DNA binds to colloidal surfaces and regulates how the colloids organize, providing molecular-level control. These connections are reversible and can be broken using standard experimental conditions (e.g., temperature), allowing for dynamic and adaptable systems. One important motivation is their good biocompatibility, which has enabled applications in biomedicine such as drug delivery, biosensing, and immunotherapy.

Programmable Atom Equivalents (PAEs) are large colloidal particles whose surfaces are functionalized with single-stranded DNA, while separate, much smaller DNA-coated linkers, called Electron Equivalents (EEs), roam in solution and mediate bonds between PAEs. In typical PAE-EE systems, the EEs carry multiple identical DNA ends that can all bind the same type of PAE, which limits the complexity of the assemblies and makes it harder to program highly specific connections between different PAE types.

In this study, the researchers investigate how EEs with arbitrary valency, carrying many DNA arms, regulate interactions in a binary mixture of two types of PAEs. Each EE has multiple single-stranded DNA ends of two different types, each complementary to the DNA on one of the PAE species. The team develops a statistical mechanical model to predict how EEs distribute between the PAEs and to calculate the effective interaction, a measure of how strongly the PAEs attract each other, which in turn controls the structures that can form.

Using this model, they inform Monte Carlo simulations to predict system behaviour under different conditions. The model shows quantitative agreement with simulation results and reveals an anomalous dependence of PAE-PAE interactions on EE valency, with interactions converging at high valency. Importantly, the researchers identify an optimal valency that maximizes selectivity between targeted and non-targeted binding pairs. This groundbreaking research provides design principles for programmable self-assembly and offers a framework that can be integrated into DNA nanoscience.

Read the full article

Designed self-assembly of programmable colloidal atom-electron equivalents

Xiuyang Xia et al 2025 Rep. Prog. Phys. 88 078101

Do you want to learn more about this topic?

Assembly of colloidal particles in solution by Kun Zhao and Thomas G Mason (2018)

The post DNA as a molecular architect appeared first on Physics World.

The link between protein evolution and statistical physics

26 novembre 2025 à 09:37

Proteins are made up of a sequence of building blocks called amino acids. Understanding these sequences is crucial for studying how proteins work, how they interact with other molecules, and how changes (mutations) can lead to diseases.

These mutations happen over vastly different time periods and are not completely random but strongly correlated, both in space (distinct sites along the sequences) and in time (subsequent mutations of the same site).

It turns out that these correlations are very reminiscent of disordered physical systems, notably glasses, emulsions, and foams.

A team of researchers from Italy and France have now used this similarity to build a new statistical model to simulate protein evolution.  They went on to study the role of different factors causing these mutations.

They found that the initial (ancestral) protein sequence has a significant influence on the evolution process, especially in the short term. This means that information from the ancestral sequence can be traced back over a certain period and is not completely lost.

The strength of interactions between different amino acids within the protein affects how long this information persists.

Although ultimately the team did find differences between the evolution of physical systems and that of protein sequences, this kind of insight would not have been possible without using the language of statistical physics, i.e. space-time correlations.

The researchers expect that their results will soon be tested in the lab thanks to upcoming advances in experimental techniques.

Read the full article

Fluctuations and the limit of predictability in protein evolution – IOPscience

S. Rossi et al, 2025 Rep. Prog. Phys. 88 078102

The post The link between protein evolution and statistical physics appeared first on Physics World.

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