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Here Is Life Inside Black Holes? (Cosmology)

By considering test planet and photon orbits of the third kind inside a black hole, Dokuchaev for the first time suggested that the interiors of supermassive black holes may be inhabited by advanced civilizations living on planets with the third-kind orbits.

Till date, we know that rotating black hole has two photon orbits. As a black hole rotates, it drags space with it. The photon orbit that is closer to the black hole is moving in the same direction as the rotation, whereas the photon orbit further away is moving against it.

Now, in the recent paper, Dokuchaev for the first time considered the photon orbits of third kind, which are stable, periodic and neither come out of the black hole nor terminate at the singularity.

They suggested that the interiors of supermassive black holes may be inhabited by advanced civilizations living on planets with the third-kind orbits.

In principle, one can get information from the interiors of black holes by observing their white hole counterparts.

Reference: V. I. Dokuchaev, “Life inside black holes”, Arxiv, 2022.

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How An Advanced Civilizations Are Using Black Holes To Contact Us? (Astronomy)

In the recent paper, Jackson and Benford considered a possibility that advanced civilizations might build a complex energetic instrumentality called radiator, that they are using to send gravitational waves by using small black holes.

Several studies suggested that the intelligences elsewhere now command a complex energetic instrumentality and can send possible messages to civilizations such as ours, perhaps they want to speak to those who have mastered the far more difficult task of sensing gravitational waves compared to the vastly simpler detection of electromagnetic signals in a myriad of possible wavelengths. Which we now have.

Now, Jackson and Benford considered how an advanced civilization might build a radiator to send gravitational waves signals by using small black holes.

According to authors, micro black holes on the scale of centimeters but with masses of asteroids to planets are manipulated with a super advanced instrumentality, possibly with very large electromagnetic fields. The machine envisioned emits gravitational waves in the GHz frequency range.

If the source to receiver distance is a characteristic length in the galaxy, up to 10000 light years, the masses involved are at least planetary in magnitude.

“To provide the energy for this system we posit a very advanced civilization that has a Kerr black hole at its disposal and can extract energy by way of super-radiance.”

— wrote authors of the study

Finally, they concluded that these gravitational waves can be measured at interstellar distance using a LIGO like detector.

Featured image is a schematic representation of total ‘gravitational wave machine’ system. Note the ‘Superradiance machine’ is inward of the gravitational wave machines; the Home Star is located somewhere in this system.

Reference: A. A. Jackson, Gregory Benford, “A Gravitational Wave Transmitter”, Arxiv, 2022.

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Is there Singularity in Black Hole Mass? (Quantum / Cosmology)

It was recently pointed out by Barrau, Martineau and Renevey that the Planck scale black hole encounters with huge, Planck-scale temperatures. At such temperatures a Planck-size black hole mass increases infinitely large in a Planck time. Thus, any singularity in a theory of physics signals its breakdown. So, is there any way to get around of this problem? Yes, but the treatment is mostly classical.

Now, Jarmo Makela attempted a quantum-mechanical approach.

“In this paper we used the simplest possible model, where the black horizon area spectrum was evenly spaced. The use of such a model enabled us to carry out the calculations explicitly.”

— Jarmo Makela, Vaasa University of Applied Sciences.

Using model, he have shown that this singularity problem in the mass of black hole immersed in a heat bath may be avoided by means of an assumption that the stretched horizon of the black hole which, for all practical purposes, may be identified with the event horizon of the hole, consists of a fixed, finite number of discrete constituents.

His model implies that the black hole has a certain minimum temperature which, by means of an appropriate choice of the parameter of the model, agrees with the Hawking temperature of the hole.

However, if the temperature of the heat bath exceeds the Hawking temperature of the hole, the hole begins to absorb heat, and the constituents jump to higher excited states.

As a consequence, the Schwarzschild mass of the hole increases and, at the same time, the black hole heats up. When the time passes, the hole tends to a thermal equilibrium with the heat bath.

During this process the Schwarzschild mass of the black hole tends towards a certain maximum value, which is finite, and depends both on the temperature of the heat bath, and on the number of the constituents of the horizon. So, there is no singularity in the black hole mass.

“The results of our model provide support to the idea of a fundamentally discrete structure of space.”

— He concluded.

References: (1) Jarmo Malela, “Black Hole in a Heat Bath”, Arxiv, 2022. (2) Aurelien Barrau, Killian Martineau, Cyril Renevey, “The catastrophic fate of Schwarzschild black holes in a thermal bath”, Arxiv, 2022.

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How Did Our Universe Ends Up Inside a Black Hole? (Cosmology)

In the recent paper, Enrique Gaztanaga conjecture a new start for our Universe that could explain both the Big Bang expansion and why we are inside a BH, without the need to restore to a Quantum Gravity singularity. His study recently appeared in the Journal Universe.

The standard model of cosmology assumes that our Universe began 14 billion years ago from a singular Big Bang creation. This can explain a vast range of different astrophysical data from a handful of free cosmological parameters. However, we have no direct evidence or fundamental understanding of some key assumptions: Inflation, Dark Matter and Dark Energy. Now, Enrique Gaztanaga reviewed the idea that cosmic expansion originates instead from gravitational collapse and bounce.

“I presented a brief review that summarizes several recent studies, suggesting a simpler explanation: the Black Hole Universe (BHU). The speciality of this study is, some previous studies misinterpreted super horizon scales as scales that were outside the BHU. This is clarified here together with some new details regarding the Big Bounce and the observational interpretation of super horizon perturbations.”

— Enrique Gaztanaga, Professor CSIC & author of the study.

© Enrique Gaztanaga

According to author, the collapse generates a Black Hole (BH) of mass M ≃ 5 × 1022 M that formed 25 billion years ago. As there is no pressure support, the cold collapse can continue inside in free fall until it reaches atomic nuclear saturation (GeV), when is halted by Quantum Mechanics, as two particles cannot occupy the same quantum state. The collapse then bounces like a core-collapse supernovae, producing the Big Bang expansion.

He also suggested that, cosmic acceleration results from the BH event horizon. During collapse, perturbations exit the horizon to re-enter during expansion, giving rise to the observed universe without the need for Inflation or Dark Energy.

“Using Ockham’s razor, this makes the BH Universe (BHU) model more compelling than the standard singular Big Bang creation.”

— He concluded.

Reference: Gaztanaga, E. How the Big Bang Ends Up Inside a Black Hole. Universe 2022, 8, 257.

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Do Stars That Host Massive Planets Rotate Slower Than Those Without Planets? (Planetary Science)

Robert Feldmann and colleagues have studied whether the presence of a detected planet is correlated with the rotation period of the host star. They found that, stars with detected transiting planets rotate on average 1.63 days slower than those without. Their study recently appeared in Arxiv.

Understanding the distribution of angular momentum during the formation of planetary systems is a key topic in astrophysics. Data from the Kepler and Gaia missions allow to investigate whether the angular momentum of stars is correlated with the occurrence of (massive) planets, i.e., do stars that host (massive) planets rotate slower than those without planets?

Now, Robert Feldmann and colleagues have performed a statistical analysis of the rotation period of 493 planet-hosting stars. These are matched to a control sample, without detected planets, with similar effective temperatures, masses, radii, metallicities, and ages.

They found that planet-hosting stars rotate on average 1.63 days slower.

They have also confirmed that stars hosting large planets have on average higher metallicities than stars hosting small planets.

Finally, they found that, sun-like stars showed a significant difference in stellar rotation periods depending on the existence of a planet: Δ𝑃rot = −2.53 days for Sun-like masses (Δ𝑃rot = −2.32 ± 0.50 days for Sun-like effective temperatures).

“Our study more generally demonstrates the importance of investigating the relation between stellar properties and the existence of planets. Further research and more data are clearly desirable. In particular, it would be interesting to investigate whether other surveys using different detection methods (e.g., radial velocity) confirms the inferred trend. By having access to larger samples thanks to upcoming data, future studies will be able to better characterise the rotational and stellar properties of planet-hosting stars.”

— they concluded.

Reference: Yves Sibony, Ravit Helled, Robert Feldmann, “The rotation of planet-hosting stars”, Arxiv, pp. 1-10, 2022. arXiv:2204.01421

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Why We Can Not Able To Observe Echoes From Wormholes Mimicking Black Holes? (Cosmology)

In the recent paper, Roman A. Konoplya and Alexander Zhidenko proposed a simple explanation why echoes from wormholes mimicking black holes may be so small that they cannot be observed. They showed that the essence of the effect is in the redistribution of the initial energy of gravitational wave among multiple universes, connected by a wormhole. Their study recently appeared in Arxiv.

Recent years a hypothesis that a black hole might, in reality be, a wormhole constructed in such a special way, that it can mimic the black hole behavior, became extremely popular. Unless the motion of celestial bodies on the other side of the wormhole’s throat significantly affects the matter in our spacetime, the observable proper oscillation frequencies called quasinormal modes as well as shadow and other optical characteristics would be the same for the black hole and the wormhole which is the black-hole mimicker. The only difference would come as a small modification of the gravitational quasinormal ringing at very later times, called echoes. Therefore, the phenomenon of gravitational echoes attracted enormous attention of theoreticians & astrophysicists. At the same time, numerous attempts to observe echoes have not succeeded so far.

Now, by using a simple model, Roman A. Konoplya and Alexander Zhidenko suggested a simple explanation why we might not be able to observe gravitational echoes.

They suggested that, this is because of the two phenomena, the splitting of energy between universes and redistribution of energy among multiple universes, connected by a wormhole.

“And, if we consider a case of wormhole, which connects more than three universes, it is clear that the resulting echoes will be even much smaller compared to wormhole connecting two universes, because more of its energy dissipates to other universes.”

Thus, they concluded that echoes can be unobservable when the wormhole, which mimics a black hole, connects not two, but many universes.

Featured image: A wormhole connecting three universes © Roman A. Konoplya and Alexander Zhidenko

Reference: Roman A. Konoplya, Alexander Zhidenko, “Can the abyss swallow gravitational waves or why we do not observe echoes?”, Arxiv, 2022.

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This New Vector Dark Matter Can Be Produced In Weyl R² Inflation (Cosmology)

Working on a scaling invariant theory of gravity with a quadratic scalar curvature, namely the Weyl R² gravity, Yue-Liang Wu and colleagues ponder on a new kind of vector dark matter: Weyl gauge boson (WGB). They demonstrated three parameter ranges for viable dark matter production. Their study appeared in Arxiv.

Dark matter and inflation are two key elements to understand the origin of cosmic structures in modern cosmology, and yet their exact physical models remain largely uncertain. The Weyl scaling invariant theory of gravity may provide a feasible scheme to solve these two puzzles jointly, which contains a massive gauge boson playing the role of dark matter candidate, and allows the quadratic scalar curvature term, namely R², to realize a viable inflationary mechanism in agreement with current observations.

Now, Yue-Liang Wu and colleagues ponder on the production of dark matters in the Weyl R² model, including the contribution from the non-perturbative production due to the quantum fluctuations from inflationary vacuum and perturbative ones from scattering.

“In our previous study, we discussed Weyl R² inflation and briefly the production of dark matter. However, the intrinsic connection between the inflaton and WGB has not been fully explored. Now, in this study, we first use the latest cosmological observations to update the preferred parameter space for Weyl R² inflation. Second, we identify the viable dark matter mass range by considering all the production channels.”

They demonstrated that there are generally three parameter ranges for viable dark matter production: (1) If the reheating temperature is larger than 10⁴ GeV, the Weyl gauge boson as dark matter can be produced abundantly with mass larger than the inflation scale ∼1013 GeV. (2) Small mass region with 2×10¯11 GeV for a higher reheating temperature. (3) Annihilation channel becomes important in the case of higher reheating temperature, which enables the Weyl gauge boson with mass up to 4×1016 GeV to be produced through freeze-in.

Reference: Qing-Yang Wang, Yong Tang, Yue-Liang Wu, “Dark Matter Production in Weyl R² Inflation”, Arxiv, 2022.

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How Primordial Black Holes Forms In Our Universe? (Cosmology)

Eugene A. Lim and colleagues studied the formation of black holes from subhorizon and superhorizon perturbations in a matter dominated universe with 3+1D numerical relativity simulations. They demonstrated that superhorizon non-linear perturbations can collapse and form PBHs in a matter dominated universe, using full numerical relativity. They showed that, depending on the mass of the initial perturbation shell, this happens via either the direct collapse or the accretion collapse mechanisms. Their study appeared in the Journal of Cosmology and Astroparticle Physics.

Primordial black hole is a hypothetical type of black hole that formed soon after the Big Bang. Various primordial black hole formation mechanisms have been already discussed on our website. These mechanisms include the formation of PBHs during inflation, the collision of bubbles that result from first order phase transitions, the collapse of cosmic strings etc etc.

Now, Eugene A. Lim and colleagues studied the formation of black holes from subhorizon and superhorizon perturbations in a matter dominated universe with 3+1D numerical relativity simulations.

FIG. 1. Direct collapse and accretion driven mechanisms © Eugene A. Lim

They found that there are two primary mechanisms of formation depending on the initial perturbation’s mass and geometry — via direct collapse of the initial overdensity and via post-collapse accretion of the ambient dark matter.

In particular, for the latter case, the initial perturbation does not have to satisfy the hoop conjecture for a black hole to form.

In both the direct collapse and accretion collapse formation cases, the duration of the formation the process is around a Hubble time, and the initial mass of the black hole is:

For post formation, they found that the PBH undergoes rapid mass growth beyond the self-similar limit MBH∝H¯1, at least initially.

“We argue that this implies that most of the final mass of the PBH is accreted from its ambient surroundings post formation.”, they concluded.

Reference: Eloy de Jong, Josu C. Aurrekoetxea and Eugene A. Lim, “Primordial black hole formation with full numerical relativity”, Journal of Cosmology and Astroparticle Physics, volume 2022(029). Link to paper

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Investigating how magnetic fields heat gases on the sun by studying turbulence and wave theory (Planetary Science)

The further we move away from a heat source, the cooler the air gets. Bizarrely, the same can’t be said for the sun, but University of Otago scientists may have just explained a key part of why.

Study lead Dr. Jonathan Squire, of the Department of Physics, says the surface of the sun starts at 6,000 C, but over a short distance of only a few hundred kilometers, it suddenly heats up to more than a million degrees, becoming its atmosphere, or corona.

“This is so hot that the gas escapes the sun’s gravity as ‘solar wind,’ and flies into space, smashing into Earth and other planets.

“We know from measurements and theory that the sudden temperature jump is related to magnetic fields which thread out of the sun’s surface. But, exactly how these work to heat the gas is not well understood—this is known as the Coronal Heating Problem.

“Astrophysicists have several different ideas about how the magnetic-field energy could be converted into heat to explain the heating, but most have difficulty explaining some aspect of observations,” he says.

Dr. Squire and co-author Dr. Romain Meyrand have been working with scientists at Princeton University and the University of Oxford and found two previous theories can be merged into one to solve a key piece of the “problem.” The group’s findings have just been published in Nature Astronomy.

The popular theories are based on heating caused by turbulence, and heating caused by a type of magnetic wave called ion cyclotron waves.

“Both, however, have some problem—turbulence struggles to explain why Hydrogen, Helium and Oxygen in the gas become as hot as they do, while electrons remain surprisingly cold; while the magnetic waves theory could explain this feature, there doesn’t seem to be enough of the waves coming off the sun’s surface to heat up the gas,” Dr. Meyrand says.

The group used six-dimensional supercomputer simulations of the coronal gas to show how these two theories are actually part of the same process, linked together by a bizarre effect called the “helicity barrier.”

This intriguing occurrence was discovered in an earlier Otago study, led by Dr. Meyrand.

“If we imagine plasma heating as occurring a bit like water flowing down a hill, with electrons heated right at the bottom, then the helicity barrier acts like a dam, stopping the flow and diverting its energy into ion cyclotron waves. In this way, the helicity barrier links the two theories and resolves each of their individual problems,” he explains.

For this latest study, the group stirred the magnetic field lines in simulations and found the turbulence created the waves, which then caused the heating.

“As this happens, the structures and eddies that form end up looking extremely similar to cutting-edge measurements from NASA’s Parker Solar Probe spacecraft, which has recently become the first man-made object to actually fly into the corona.

“This gives us confidence that we are accurately capturing key physics in the corona, which—coupled with the theoretical findings about the heating mechanisms—is a promising path to understanding the coronal heating problem,” Dr. Meyrand says.

“Understanding more about the sun’s atmosphere and the subsequent solar wind is important because of the profound impacts they have on Earth,” Dr. Squire explains.

“Effects which result from solar wind’s interaction with the Earth’s magnetic field is called ‘space weather,’ which causes everything from Aurora to satellite-destroying radiation and geomagnetic currents which damage the power grid.

“All of this is sourced, fundamentally, by the corona and its heating by magnetic fields, so as well as being interesting for our general understanding of the solar system, the solar-corona’s dynamics can have profound impacts on Earth.

“Perhaps, with a better understanding of its basic physics, we will be able to build better models to predict space weather in the future, thus allowing the implementation of protection strategies that could head off—literally—billions of dollars of damage.”

Reference: Jonathan Squire, High-frequency heating of the solar wind triggered by low-frequency turbulence, Nature Astronomy (2022). DOI: 10.1038/

Provided by University of Otago

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