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Category: cosmology – Page 3

The Big Bang is often described as the explosive birth of the universe—a singular moment when space, time and matter sprang into existence. But what if this was not the beginning at all? What if our universe emerged from something else—something more familiar and radical at the same time?

In a new paper, published in Physical Review D, my colleagues and I propose a striking alternative. Our calculations suggest the Big Bang was not the start of everything, but rather the outcome of a gravitational crunch or collapse that formed a very massive black hole—followed by a bounce inside it.

This idea, which we call the black hole , offers a radically different view of cosmic origins, yet it is grounded entirely in known physics and observations.

Read more | >

The Big Bang is often described as the explosive birth of the universe – a singular moment when space, time and matter sprang into existence. But what if this was not the beginning at all? What if our universe emerged from something else – something more familiar and radical at the same time?

In a new paper, published in Physical Review D, my colleagues and I propose a striking alternative. Our calculations suggest the Big Bang was not the start of everything, but rather the outcome of a gravitational crunch or collapse that formed a very massive black hole – followed by a bounce inside it.

This idea, which we call the black hole universe, offers a radically different view of cosmic origins, yet it is grounded entirely in known physics and observations.

Read more | >

Across the cosmos, many stars can be found in pairs, gracefully circling one another. Yet one of the most dramatic pairings occurs between two orbiting black holes, formed after their massive progenitor stars exploded in supernova blasts. If these black holes lie close enough together, they will ultimately collide and form an even more massive black hole.

Sometimes a black hole is orbited by a neutron star—the dense corpse of a star also formed from a supernova explosion but which contains less mass than a black hole. When these two bodies finally merge, the black hole will typically swallow the neutron star whole.

To better understand the extreme physics underlying such a grisly demise, researchers at Caltech are using supercomputers to simulate black hole–neutron star collisions. In one study appearing in The Astrophysical Journal Letters, the team, led by Elias Most, a Caltech assistant professor of theoretical astrophysics, developed the most detailed simulation yet of the violent quakes that rupture a neutron star’s surface roughly a second before the black hole consumes it.

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A new study has revealed a novel effect caused by dark photons—hypothetical particles thought to make up a portion of the universe’s elusive dark matter. This discovery, made within the framework of Einstein–Cartan–Holst gravity, provides new insights into the fundamental interactions between matter and gravity.

The study was conducted by Prof. Gao Zhifu from the Xinjiang Astronomical Observatory of the Chinese Academy of Sciences, in collaboration with Dr. Luiz Carlos Garcia de Andrade from the State University of Rio de Janeiro, Brazil. Their findings, which include the first identification of a key physical quantity known as the Barbero–Immirzi (BI) parameter induced by dark photons, are published in The European Physical Journal C.

A large portion of the universe is filled with invisible matter known as , and the dark photon is one of its leading theoretical candidates. As a hypothetical particle beyond the Standard Model, the dark photon exhibits electromagnetic-like interactions through kinetic mixing with the ordinary photon. Unlike photons, however, dark photons possess mass and interact much more weakly with charged particles.

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Wormholes are a popular feature in science fiction, the means through which spacecraft can achieve faster-than-light (FTL) travel and instantaneously move from one point in spacetime to another. And while the General Theory of Relativity forbids the existence of “traversable wormholes,” recent research has shown that they are actually possible within the domain of quantum physics.

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As federal funding cuts impact decades of research, scientists could turn to black holes for cheaper, natural alternatives to expensive facilities searching for dark matter and similarly elusive particles that hold clues to the universe’s deepest secrets, a new Johns Hopkins study of supermassive black holes suggests.

The findings, which appear in Physical Review Letters, could help complement multi-billion-dollar expenses and decades of construction needed for research complexes like Europe’s Large Hadron Collider, the largest and highest-energy particle accelerator in the world.

“One of the great hopes for particle colliders like the Large Hadron Collider is that it will generate particles, but we haven’t seen any evidence yet,” said study co-author Joseph Silk, an astrophysics professor at Johns Hopkins University and the University of Oxford, UK.

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Merging neutron stars are excellent targets for multi-messenger astronomy. This modern and still very young method of astrophysics coordinates observations of the various signals from one and the same astrophysical source. When two neutron stars collide, they emit gravitational waves, neutrinos and radiation across the entire electromagnetic spectrum. To detect them, researchers need to add gravitational wave detectors and neutrino telescopes to ordinary telescopes that capture light.

Precise models and predictions of the expected signals are essential in order to coordinate these observatories, which are very different in nature.

“Predicting the multi-messenger signals from binary neutron star mergers from first principles is extremely difficult. We have now succeeded in doing just that,” says Kota Hayashi, a postdoctoral researcher in the Computational Relativistic Astrophysics department at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute) in the Potsdam Science Park. “Using the Fugaku supercomputer in Japan, we have performed the longest and most complex simulation of a binary neutron star to date.”

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