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Category: physics – Page 59

Cosmological model proposes dark matter production during pre-Big Bang inflation

As physicists continue their struggle to find and explain the origin of dark matter, the approximately 80% of the matter in the universe that we can’t see and so far haven’t been able to detect, researchers have now proposed a model where it is produced before the Big Bang.

Their idea is that dark matter would be produced during a infinitesimally short inflationary phase when the size of the universe quickly expanded exponentially. The new model was published in Physical Review Letters by three scientists from Texas in the US.

An intriguing idea among cosmologists is that dark matter was produced through its interaction with a thermal bath of some species, and its abundance is created by “freeze-out” or “freeze-in.” In the freeze-out scenario, dark matter is in chemical equilibrium with the bath at the earliest times—the concentration of each does not change with time.

Delayed Big Bang for dark matter could be detected in gravitational waves

Was dark matter created some time after the Big Bang? Gravitational wave detectors could soon find the answer.

For now, the duo’s results suggest that the Dark Big Bang is far less constrained by past observations than Freese and Winkler originally anticipated. As Ilie explains, their constraints could soon be put to the test.

“We examined two Dark Big Bang scenarios in this newly found parameter space that produce gravitational wave signals in the sensitivity ranges of existing and upcoming surveys,” he says. “In combination with those considered in Freese and Winkler’s paper, these cases could form a benchmark for gravitational wave researchers as they search for evidence of a Dark Big Bang in the early universe.”

Is the Universe Infinite or Finite?

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Is the universe really infinite? Or could it close back on itself like a sphere? If it’s infinite, how can it expand? And is it true that there might be copies of you in it? Today I want to explain how much we know about those questions and what the expansion of space has to do with Hilbert’s Hotel.

This video comes with a quiz which you can take here: https://quizwithit.com/start_thequiz/.…

The Kurzgesagt video is here: • The Paradox of an Infinite Universe.

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Physicists Just Found a Quirk in Einstein’s Predictions of Space-Time

The fabric of space and time is not exempt from the effects of gravity. Plop in a mass and space-time curves around it, not dissimilar to what happens when you put a bowling ball on a trampoline.

This dimple in space-time is the result of what we call a gravity well, and it was first described over 100 years ago by Albert Einstein’s field equations in his theory of general relativity. To this day, those equations have held up. We’d love to know what Einstein was putting in his soup. Whatever it was, general relativity has remained pretty solid.

One of the ways we know this is because when light travels along that curved space-time, it curves along with it. This results in light that reaches us all warped and stretched and replicated and magnified, a phenomenon known as gravitational lensing. This quirk of space-time is not only observable and measurable, it’s an excellent tool for understanding the Universe.

Why Have 700 Stars Mysteriously Disappeared?

Why have 700 stars vanished how is it possible?

Of all the objects in the universe, stars are amongst the most fascinating. From the birth of newborn protostars to the dramatic final stages of their lives, the life cycle of stars has captivated the human imagination for centuries. Yet one of the greatest stellar mysteries is that of vanishing stars — stars that were once visible but have suddenly disappeared. While the mysteries behind them haven’t been completely unraveled, recent advances in telescope and monitoring technology have unveiled shocking truths about this extremely rare occurrence. Join us as we explore the concept of vanishing stars and unravel the mystery behind the disappearance of 700 known stars.
When we look up at the night sky, the stars appear eternal. In a sense, that’s true, as stars can live for millions or even billions of years, which is just mind-boggling compared to our own lifespans. However, like all living things, stars are born, they live, and they eventually die. Astrophysicists have made significant progress in understanding the life cycles of stars. However, when a star suddenly disappears, it raises more questions than answers. What could have caused it to vanish? Was it a natural event or something more unusual? The discovery that as many as a hundred stars may have disappeared from our observations in recent decades is a sobering reminder that our understanding of the universe is still incomplete. The vanishing stars challenge our assumptions and force us to confront the limitations of our knowledge. Keep watching as we explore some of the most groundbreaking discoveries in our understanding of vanishing stars and provide possible explanations to the stars that has vanished from our solar system and beyond in the last few decades.
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How Pulsar Signal Distortions Are Challenging What We Know About Space

Distortions in pulsar signals reveal flaws in galactic models, pointing to new opportunities for understanding the universe and studying cosmic waves.

By analyzing patterns in pulsar signals, researchers discovered discrepancies in existing models of how the galaxy impacts pulsar signals, suggesting that these models need updates. The findings not only deepen our understanding of the universe but also improve our ability to study phenomena like gravitational waves.

Dr. Sofia Sheikh from the SETI Institute led a groundbreaking study that explores how pulsar signals—emissions from the spinning remnants of massive stars—become distorted as they travel through space. Published on November 26 in The Astrophysical Journal, this research was conducted by a group of undergraduate students from the Penn State branch of the Pulsar Search Collaboratory, a student club dedicated to pulsar science.

Integrated multi-modal sensing and learning system could give robots new capabilities

Trying to understand the makeup and evolution of the solar system’s Kuiper belt has kept researchers busy since it was hypothesized soon after the discovery of Pluto in 1930. In particular, binary pairs of objects there are useful as indicators since their existence today paints a picture of how energetic or violent the evolution of the solar system was in its early days four billion years ago.

Looking closely at the evolution of an ultrawide (in separation) binary object, researchers included more physics that reveals much about their architecture and unfolding. They found that these ultrawide binaries may not have been formed in the primordial solar system as has been thought. Their work has been published in Nature Astronomy.

“In the outer reaches of the solar system, there exists a population of binary systems so widely separated that it seemed worth looking into whether or not they could even survive 4 billion years without being [completely] separated somehow,” said Hunter M. Campbell of the University of Oklahoma in the US.

Thermal photonics advances enable efficient subambient daytime radiative cooling for vertical surfaces

Radiative heat transfer is one of the most critical energy transfer mechanisms in nature. However, traditional blackbody radiation, due to its inherent characteristics, such as its non-directional, incoherent, broad-spectrum, and unpolarized nature, results in energy exchange between the radiating body and all surrounding objects, significantly limiting heat transfer efficiency and thermal flow control. These limitations hinder its practical application.

A recent study published in Science utilized thermal photonics to achieve cross-band synergistic control of thermal radiation in both angle and spectrum. The researchers then designed a directional emitter with cross-scale symmetry-breaking, angularly asymmetric and spectrally selective thermal emission, achieving daytime subambient radiative cooling on vertical surfaces.

The research team was led by Prof. Wei Li from the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences, in collaboration with Prof. Shanhui Fan’s team from Stanford University and Prof. Andrea Alu’s team from the City University of New York.

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