For a few microseconds after the Big Bang, the universe was filled with an unusual state of matter. At temperatures reaching trillions of degrees, quarks and gluons moved freely in a dense, hot fluid known as quark-gluon plasma. As the universe expanded and cooled, these particles began combining to form protons and neutrons, the building blocks of ordinary matter.

Physicists can recreate this extreme environment today by colliding heavy atomic nuclei at nearly the speed of light inside particle accelerators. The collisions produce tiny droplets of quark-gluon plasma, each lasting only an extraordinarily brief period before breaking apart. Studying what happens inside these droplets is difficult. They are too small and short-lived for scientists to examine directly. Instead, researchers look at how other particles behave as they pass through the plasma. Their movements can reveal details about the fluid’s internal properties.

A study by physicists at the Massachusetts Institute of Technology (MIT) and the University of California, Santa Barbara (UCSB), has developed a new theoretical approach to this problem. Published in Physical Review Letters, the research examines how heavy subatomic particles respond to the forces exerted by a fluid when travelling at speeds close to that of light. The work extends a principle that physicists have relied on for more than a century: Albert Einstein’s explanation of Brownian motion.

The Problem with Einstein’s Explanation

In 1827, botanist Robert Brown noticed that pollen grains suspended in water moved continuously, even when the water appeared undisturbed. The movement was random, with the particles changing direction as though they were being pushed by invisible forces. Einstein explained this phenomenon in a 1905 paper. He showed that the apparently random movement resulted from collisions with the atoms and molecules in the surrounding fluid. These microscopic particles constantly strike a larger suspended particle, producing small, unpredictable changes in its motion.

Two effects determine how the particle moves. The fluid exerts drag, slowing it down, while microscopic collisions keep pushing it in different directions. The relationship between these forces can reveal information about the fluid’s temperature and microscopic composition. Scientists later applied this framework to a range of fluids, including quark-gluon plasma. However, the original theory was developed for particles moving at relatively low speeds. Heavy quarks travelling through an extremely hot plasma can move close to the speed of light, where the familiar relationship between drag and random fluctuations becomes inadequate.

Physicists have been aware of this limitation for about 20 years. MIT graduate researcher Jean Du Plessis and Bruno Scheihing-Hitschfeld of UCSB have now worked out a framework that accounts for the unusual behaviour of particles under these conditions.

When a Particle Receives an Unusually Large Kick

The researchers calculated the forces a heavy quark would experience while travelling through a fluid at relativistic speeds. They began with a simplified model in which the particle moved through a gas of weakly interacting quarks and gluons. This made it possible to calculate how the strong nuclear force would affect its momentum.

The team then examined the probability of different changes in the quark’s momentum. In the conventional Brownian motion model, small changes are common, while extremely large ones are rare. The resulting probability distribution takes the shape of a bell curve, with the most extreme movements appearing at its two ends. The calculations for relativistic heavy quarks produced a different pattern.

For smaller changes in momentum, the distribution still resembled a bell curve. At the outer ends, however, it became uneven. Large changes occurred more frequently than the conventional model would predict. A particularly interesting finding was that a large kick slowing the quark down was more likely than an equally large kick pushing it in the opposite direction.

This imbalance is important because it suggests that the movement of heavy quarks carries information that conventional Brownian motion models miss. “How often those large changes occur depends on the microscopic nature of the plasma,” Du Plessis said. Such events could therefore offer researchers another way to investigate what happens inside quark-gluon plasma. The researchers repeated their calculations for plasmas made up of different particles. They found that the same tilted probability distribution appeared across these different conditions. They also identified the mathematical pattern in an earlier calculation involving a strongly interacting plasma, despite the differences in the underlying microscopic physics. The finding points to a potentially universal feature of how relativistic particles interact with fluids.

Reading the Properties of the Early Universe

Quark-gluon plasma is known to behave more like a liquid than an ordinary gas. Experiments have shown that it flows with remarkably little internal resistance, suggesting that its constituent quarks and gluons interact strongly.

The new framework could help physicists investigate these interactions by examining how heavy quarks lose momentum as they travel through the plasma. Researchers can compare the theoretical predictions with measurements from particle accelerator experiments and use the differences to refine their understanding of the fluid. Du Plessis believes the primordial quark-gluon plasma was more strongly interacting than a simple Brownian motion model might suggest. Its behaviour, he says, was closer to that of a liquid than a gas.

The calculations do not directly tell scientists what the universe’s first fluid looked like. They offer a more precise way to interpret the behaviour of particles produced in laboratory collisions, bringing researchers closer to understanding the properties of matter during the universe’s earliest moments. The research received support from the US Department of Energy’s Office of Nuclear Physics, the US National Science Foundation and the Simons Foundation.

An international team of researchers from India and Belgium has developed portable particle detectors that could help scientists examine the interiors of mountains, tunnels and historical monuments without damaging them. The technology uses naturally occurring cosmic-ray particles to map variations in the density of objects, offering a potential approach to non-invasive imaging of large structures.

The detectors, developed using glass-based Resistive Plate Chambers (RPCs), achieved a particle-detection efficiency exceeding 95% during testing, according to a report published by Research Matters on October 24, 2026. The findings demonstrate the potential of compact detector systems to investigate dense materials and support future applications in geology, archaeology and infrastructure assessment.

The collaboration includes researchers from India’s National Institute of Science Education and Research (NISER), Bhubaneswar, and the Homi Bhabha National Institute (HBNI), alongside researchers from Belgian institutions, including Université catholique de Louvain and the Inter-University Institute for High Energies.

How cosmic rays reveal hidden structures

The technology uses muons, high-energy particles produced when cosmic rays interact with Earth’s atmosphere. These particles continuously reach the Earth’s surface and can penetrate substantial thicknesses of rock, concrete and other materials.

As muons travel through an object, some are absorbed or deflected depending on its density and thickness. By measuring the number and trajectories of particles passing through a structure, researchers can identify variations in internal density and reconstruct images of otherwise inaccessible areas.

The technique, known as muography, is comparable in principle to X-ray imaging, but uses naturally occurring particles instead of an artificial radiation source. It has previously been used to investigate geological formations, including volcanoes, and to explore archaeological structures.

However, conventional muon detectors can be bulky, difficult to transport and challenging to operate in remote locations. The new glass-based detectors aim to address some of these limitations through a compact design and sealed operation, reducing dependence on continuous gas supplies.

Testing the detector system

The researchers developed three glass RPC prototypes using thin glass electrodes separated by gas-filled gaps. When a muon passes through a chamber, it ionises the gas, generating an electrical signal that can be recorded to determine the particle’s position.

Electronic readout systems capture these signals and help reconstruct the trajectories of incoming particles. During testing, the detectors achieved an efficiency exceeding 95%, with a timing resolution of approximately 1.8 nanoseconds, according to the research report.

To examine the system’s ability to detect dense materials, the team conducted an absorption experiment using one prototype. During an open-sky measurement, researchers recorded nearly 55,000 muon tracks. After placing a lead block in the experimental setup, the recorded count fell to 30,894, demonstrating how dense material reduced the number of particles reaching the detector.

Representational image.Image credit:Pexels

The experiment provided proof of principle that the system could measure muon attenuation and support radiographic imaging. However, imaging complex structures such as mountains or monuments requires measurements from multiple directions and further computational reconstruction.

Applications and challenges ahead

Portable muon detectors could eventually help researchers investigate hidden cavities, examine geological formations, inspect tunnels and study the internal structures of historical monuments. Engineers could also explore their application in assessing infrastructure such as dams and bridges, although these uses would require additional testing and validation.

For cultural heritage conservation, muography could offer a valuable alternative where drilling or other invasive investigations risk damaging fragile structures. A 2025 review published in iScience highlighted the technique’s potential as a complementary, non-destructive method for studying cultural heritage objects, while noting that the relatively low flux of naturally occurring muons can require lengthy data-collection periods.

The technology is not yet a universal replacement for existing inspection methods. Its practical application will depend on factors such as spatial resolution, detector size, measurement duration and the complexity of the structure being examined.

The researchers have proposed further improvements, including lighter structural materials, larger detector areas and enhanced readout systems. These developments could make the detectors easier to deploy and improve the quality of reconstructed images.

When a massive star dies, its core can collapse into an extremely dense object called a neutron star. Despite being only about the size of a city, it can have a mass comparable to that of the Sun. Its powerful gravity can pull matter away from a nearby companion star, releasing energy in the form of X-rays as the material falls towards it.

Scientists at Bengaluru’s Raman Research Institute (RRI) have studied these X-ray signals from Centaurus X-3, a star system about 24,000 light-years from Earth. By examining changes in the signals, the researchers identified a stream of matter flowing towards the neutron star and found evidence of a rotating disk of material around it. This is an unusual finding because such disks are not commonly expected in this type of star system. The discovery could help scientists better understand how matter moves around neutron stars and how these distant objects produce X-rays.

Star That Pulls in Matter

Centaurus X-3 is in the constellation Centaurus. It belongs to a class of systems known as high-mass X-ray binaries. These systems contain a neutron star and a massive companion star held together by gravity.

A neutron star forms when the core of a massive star collapses at the end of its life. It packs roughly the Sun’s mass into a sphere only about the size of a city. Its gravity is so strong that it can pull in material from a nearby companion star. As this material falls towards the neutron star, it releases enormous amounts of energy, including X-rays. Scientists study this radiation to understand how the material behaves and how the system works.

Centaurus X-3 is also a pulsar. Its neutron star rotates and sends out radiation from regions near its magnetic poles. As the star spins, these beams sweep across space. When a beam passes an observing satellite, the satellite detects a pulse of radiation, much as a lighthouse produces a repeating flash as it turns. These regular pulses provide scientists with a way to study the neutron star and its surroundings.

What the Changing Signals Revealed

The radiation from Centaurus X-3 does not come only from the neutron star itself. Some of it interacts with nearby material, including the surface of the companion star, gas flowing away from it and matter surrounding the neutron star. This material absorbs radiation and emits it again. Scientists call this secondary radiation.

Changes in this radiation can help researchers work out what is happening around the neutron star. However, Centaurus X-3 is so far away that telescopes cannot clearly distinguish its surrounding structures. It appears as a single point of light. Scientists must therefore piece together the system’s structure from the signals they receive.

Earlier observations had shown that the intensity of certain secondary X-ray emission lines changed as the neutron star rotated. An emission line is a feature in a spectrum that can reveal information about the material producing or interacting with the radiation. A research team led by Kinjal Roy of RRI examined four such emission lines in detail. The researchers found that the structure producing these changes must be rotating along with the neutron star.

The pattern helped them identify the likely source which is a stream of matter moving towards the neutron star.

Following the stream of matter

This stream is part of a process called accretion, in which a compact object draws in material from its surroundings. In Centaurus X-3, the stream carries matter from an accretion disk towards the neutron star. The disk is a rotating structure of gas and other material that moves around the star before being drawn inwards. The neutron star’s magnetic field then guides the incoming matter towards its magnetic poles.

The stream also changes what an observing satellite sees. As it moves around the neutron star, it can come between the satellite and the star, partially blocking the direct radiation. When this happens, the primary X-ray signal weakens. At the same time, radiation from the stream itself becomes stronger in the observed signal.

The researchers used these changing signals to connect the observed variations to the movement of matter around the neutron star. The evidence for an accretion stream also points to an accretion disk feeding it. This matters because scientists generally expect high-mass X-ray binaries to gather material in a different way.

Why an accretion disk matters

In many high-mass X-ray binaries, a neutron star captures gas directly from the stream of material blown away by its companion star. This is known as stellar-wind accretion. An accretion disk involves a different arrangement: material gathers into a rotating structure before flowing towards the neutron star. The findings from Centaurus X-3 indicate that this disk-based process is taking place in a system where it is not generally expected.

That difference matters when scientists calculate how the system produces and releases radiation. If their models leave out the disk, they may fail to account for some of the radiation coming from the surrounding material.

“Accretion disk is not expected to occur in [HMXBs] So, if an accretion disk is forming in this system, emission models have to be modified,” Roy said in the Department of Science and Technology’s announcement. He added that future models of Centaurus X-3 would need to account for radiation from the disk.

The research does not mean that scientists have directly photographed the disk. Instead, they have used the changing X-ray signals to infer the presence and behaviour of structures that remain too distant to resolve clearly. Published in The Astrophysical Journal, the study adds to the understanding of Centaurus X-3, one of the most widely studied binary pulsars. It also shows how small changes in radiation can reveal the movement of matter around objects that are otherwise beyond the reach of direct observation.

By identifying the flow responsible for the changing signals, the researchers have provided a more detailed picture of how this neutron star draws in material. That picture will help scientists refine their models of Centaurus X-3 and examine whether similar processes occur in other high-mass X-ray binaries.