A novel experiment has revealed a phenomenon called the Bohr–Weisskopf effect in a pear-shaped nucleus in a molecule for the first time.
Category: physics – Page 9
Black hole mergers could give rise to observable gravitational-wave tails
Black holes, regions of spacetime in which gravity is so strong that nothing can escape, are intriguing and extensively studied cosmological phenomena. Einstein’s general theory of relativity predicts that when two black holes merge, they emit ripples in spacetime known as gravitational waves.
Once the gravitational waves originating from black hole mergers fade, subtle hints of these waves could remain, known as late-time gravitational-wave tails. While the existence of these tails has been widely theorized about in the past, it was not yet conclusively confirmed.
Researchers at Niels Bohr Institute, University of Lisbon and other institutes worldwide recently performed black hole merger simulations based on Einstein’s general relativity equations, to further probe the existence of late-time gravitational-wave tails. Their simulations, outlined in a paper in Physical Review Letters, suggest that these tails not only exist, but could also have a larger amplitude than originally predicted and could thus be observed in future experiments.
Ultrafast light-driven electron slide discovered
When an intense laser pulse hits a stationary electron, it performs a trembling motion at the frequency of the light field. However, this motion dies down after the pulse, and the electron comes to rest again at its original location. If, however, the light field changes its strength along the electron’s trajectory, the electron builds up an additional drift motion with each oscillation, which it retains even after the pulse. The spatial light intensity acts like a slope that the electron slides down.
This effect, known for decades, is called ponderomotive acceleration. However, due to the low spatial dependence of intensity even in focused light beams, this light-driven sliding effect can only be clearly observed for long-lasting laser pulses with many oscillations of the field.
In a recent study, researchers have demonstrated pronounced ponderomotive acceleration during just a single light oscillation. The crucial trick was the use of sharp metallic needle tips, which exhibit an extremely strong spatial variation in light intensity when illuminated with laser light. The work is published in the journal Nature Physics.
Astronomers discover new pulsating ultraluminous X-ray source
Using ESA’s XMM-Newton satellite, European astronomers have observed ultraluminous X-ray sources (ULXs) in the galaxy NGC 4631. As a result, they detected a new pulsating ULX, which received the designation X-8. The research is published November 6 on the arXiv preprint server.
ULXs are point sources in the sky that are so bright in X-rays that each emits more radiation than a million suns emit at all wavelengths. They are less luminous than active galactic nuclei, but more consistently luminous than any known stellar process. Although numerous studies of ULXs have been conducted, the basic nature of these sources still remains unknown.
Some persistent ULXs exhibit pulsations and therefore are categorized as ultraluminous X-ray pulsars (ULXPs). Discovering and studying objects of this type could be crucial for advancing our understanding of accretion physics—for instance, mechanisms that enable the sustained X-ray luminosities of ULXs which exceed the Eddington limit.
Statistical mechanics for networks of real neurons
Our ability to perceive, think, or act relies on coordinated activity in large networks of neurons in the brain. This review examines recent progress in connecting ideas from statistical physics, such as maximum entropy methods and the renormalization group, to quantitative experiments that record the electrical activity of thousands of neurons simultaneously. This quantitative bridge between the new data and statistical physics models uncovers new, quantitatively reproducible behaviors and makes clear that abstract theoretical principles in studies of the brain can have the level of predictive power that we expect in other areas of physics.
A Mathematician’s Model Brings Science Fiction’s Wormholes Closer to Reality
Could a tunnel through space and time—long a dream of science fiction—ever exist in theory? According to Arya Dutta, a Ph.D. student in Mathematics at the Katz School, the answer might be yes, at least on paper.
Accepted for publication in the International Journal of Geometric Methods in Modern Physics, Dutta’s study, “Thin-shell Wormhole with a Background Kalb–Ramond Field,” explored a mathematical model of a wormhole—a hypothetical shortcut through spacetime that could, in theory, connect two distant regions of the universe. “A wormhole allows faster-than-light travel or even time travel,” said Dutta. “It hasn’t been observed yet, but theoretical research has advanced a lot.”
‘Impossible’ merger of two massive black holes explained
In 2023, astronomers detected a huge collision. Two unprecedentedly massive black holes had crashed an estimated 7 billion light-years away. The enormous masses and extreme spins of the black holes puzzled astronomers. Black holes like these were not supposed to exist.
Now, astronomers with the Flatiron Institute’s Center for Computational Astrophysics (CCA) and their colleagues have figured out just how these black holes may have formed and collided. The astronomers’ comprehensive simulations—which follow the system from the lives of the parent stars through to their ultimate death—uncovered the missing piece that previous studies had overlooked: magnetic fields.
“No one has considered these systems the way we did; previously, astronomers just took a shortcut and neglected the magnetic fields,” says Ore Gottlieb, astrophysicist at the CCA and lead author of the new study on the work published in The Astrophysical Journal Letters. “But once you consider magnetic fields, you can actually explain the origins of this unique event.”
Harnessing intricate, self-organized plasma patterns to destroy PFAS
Increasing the surface area when plasma and water interact could help scale up a technology that destroys contaminants such as PFAS, detergents and microbial contaminants in drinking water, new research from the University of Michigan shows.
Under certain conditions, when plasma comes in contact with water, it can self-organize, forming intricate patterns resembling stars, wagon wheels or gears that expand the contact area. While the physics of plasma self organization remains elusive, a better understanding can help harness it for more efficient water decontamination.
The U-M research team captured the first images of the water surface below the self-organizing plasma, revealing that the plasma exerts an electrical force on the water that distorts the surface and also generates surface waves.