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Category: cosmology – Page 134

Colorful Primordial Black Holes

Primordial black holes (PBHs)—hypothetical objects formed by the gravitational collapse of dense regions in the early Universe—have been invoked as dark-matter candidates. But for PBHs to constitute all dark matter, they’d have to be extremely light, possibly weighing less than small asteroids. Now Elba Alonso-Monsalve and David Kaiser of the Massachusetts Institute of Technology show that these diminutive PBHs could possess an exotic property—a net color charge (such a charge characterizes quarks and gluons in quantum chromodynamics theory) [1]. Such color-charged PBHs might have left potentially observable signatures, says Kaiser.

Observations rule out that stellar-mass PBHs could fully explain dark matter, but PBHs weighing between 1017 and 1022 g remain viable candidates. Since a PBH’s mass should relate to its age, this mass range corresponds to PBH formation immediately after the big bang, when the Universe was still a hot plasma of unconfined quarks and gluons. Most PBHs would have formed by engulfing large numbers of quarks and gluons having a distribution of color charges. These PBHs would be color-charge neutral and sufficiently massive to live until today. However, the duo’s calculations show that a few PBHs could have formed from regions so tiny that the charges of the absorbed gluons would be correlated, giving these PBHs a net charge.

Color-charged black holes have long been considered to be mathematically possible, but the new study is the first to propose a realistic formation mechanism, says Kaiser. The small sizes imply that they would have since evaporated. Yet their presence in the early Universe might have disrupted the distribution of protons and neutrons when the big bang created the first nuclear isotopes, leaving subtle traces in the cosmic abundance of the elements.

First Detection of Magnetism in Massive Stars Beyond Our Galaxy

New findings reveal magnetic fields in three massive stars in the Magellanic Clouds, shedding light on the influence of magnetism on stellar evolution and the formation of neutron stars and black holes. The use of advanced spectropolarimetry techniques was crucial to overcome past observational challenges.

Magnetic fields have been discovered in three massive, hot stars within our neighboring galaxies, the Large and Small Magellanic Clouds, for the first time. Although magnetic fields in massive stars are not new to our own galaxy, their detection in the Magellanic Clouds is particularly significant due to the abundance of young, massive stars in these galaxies. This discovery offers a rare chance to investigate actively forming stars and explore the maximum mass a star can achieve while maintaining stability.

Impact of magnetism on star evolution.

Researcher suggests that gravity can exist without mass, mitigating the need for hypothetical dark matter

Researchers for the first time showed, how gravity can exist without mass, providing an alternative theory that could potentially mitigate the need for dark matter…

Dark matter is a hypothetical form of matter that is implied by gravitational effects that can’t be explained by general relativity unless more matter is present in the universe than can be seen. It remains virtually as mysterious as it was nearly a century ago when first suggested by Dutch astronomer Jan Oort in 1932 to explain the so-called “missing mass” necessary for things like galaxies to clump together.

Now Dr. Richard Lieu at The University of Alabama in Huntsville (UAH) has published a paper in the Monthly Notices of the Royal Astronomical Society that shows, for the first time, how gravity can exist without mass, providing an alternative theory that could potentially mitigate the need for dark matter.

“My own inspiration came from my pursuit for another solution to the gravitational field equations of general relativity—the simplified version of which, applicable to the conditions of galaxies and clusters of galaxies, is known as the Poisson equation—which gives a finite gravitation force in the absence of any detectable mass,” says Lieu, a distinguished professor of physics and astronomy at UAH, a part of the University of Alabama System.

Brian Greene — What Was There Before The Big Bang?

The American theoretical physicist, Brian Greene explains various hypotheses about the causation of the big bang. Brian Greene is an excellent science communicator and he makes complex cosmological concepts more easy to understand.

The Big Bang explains the evolution of the universe from a starting density and temperature that is currently well beyond humanity’s capability to replicate. Thus the most extreme conditions and earliest times of the universe are speculative and any explanation for what caused the big bang should be taken with a grain of salt. Nevertheless that shouldn’t stop us to ask questions like what was there before the big bang.

Brian Greene mentions the possibility that time itself may have originated with the birth of the cosmos about 13.8 billion years ago.

To understand how the Universe came to be, scientists combine mathematical models with observations and develop workable theories which explain the evolution of the cosmos. The Big Bang theory, which is built upon the equations of classical general relativity, indicates a singularity at the origin of cosmic time.

However, the physical theories of general relativity and quantum mechanics as currently realized are not applicable before the Planck epoch, which is the earliest period of time in the history of the universe, and correcting this will require the development of a correct treatment of quantum gravity.

Certain quantum gravity treatments imply that time itself could be an emergent property. Which leads some physicists to conclude that time did not exist before the Big Bang. While others are open to the possibility of time preceding the big bang.

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New Theory Changes Everything: SIDM and Dark Matter Collision!

Discover the groundbreaking Self-Interacting Dark Matter (SIDM) theory that suggests dark matter particles might collide and interact with each other. Learn how recent studies on the El Gordo galaxy cluster support this revolutionary idea, potentially changing our understanding of the universe’s structure and evolution. Dive into the cosmic dance and stay updated with the latest space discoveries!

Chapters:
00:00 Introduction.
00:44 The Dance of Self-Interacting Dark Matter.
02:39 Unveiling the Strengths and Weaknesses of CDM and SIDM
05:14 Exploring Dark Matter: Methods and Future Prospects.
09:20 Outro.
09:37 Enjoy.

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Are white holes dawning at last?

As opposed to black holes, white holes are thought to eject matter and light while never absorbing any. Detecting these as yet hypothetical objects could not only provide evidence of quantum gravity but also explain the origin of dark matter.

No one today questions the existence of black holes, objects from which nothing, not even light, can escape. But after they were first predicted in 1915 by Einstein’s general theory of relativity, it took many decades and multiple observations to show that they actually existed. And when it comes to white holes, history may well repeat itself. Such objects, which are also predicted by general relativity, can only eject matter and light, and as such are the exact opposite of black holes, which can only absorb them. So, just as it is impossible to escape from a black hole, it is equally impossible to enter a white one, occasionally and perhaps more aptly dubbed a “white fountain”. For many, these exotic bodies are mere mathematical curiosities.

First DESI results shine a light on Hubble tension

The expansion of the universe has been a well-established fact of physics for almost a century. By the turn of the millennium the rate of this expansion, referred to as the Hubble constant (H 0), had converged to a value of around 70 km s –1 Mpc –1. However, more recent measurements have given rise to a tension: whereas those derived from the cosmic microwave background (CMB) cluster around a value of 67 km s –1 Mpc –1, direct measurements using a local distance-ladder (such as those based on Cepheids) mostly prefer larger values around 73 km s –1 Mpc –1. This disagreement between early-and late-universe measurements, respectively, stands at the 4–5 σ level, thereby calling for novel measurements.

One such source of new information are large galaxy surveys, such as the one currently being performed by the Dark Energy Spectroscopic Instrument (DESI). This Arizona-based instrument uses 5,000 individual robots that optimise the focal plane of the detector to allow it to measure 5,000 galaxies at the same time. The goal of the survey is to provide a detailed 3D map, which can be used to study the evolution of the universe by focussing on the distance between galaxies. During its first year of observation, the results of which have now been released, DESI has provided a catalogue of millions of objects.

Small fluctuations in the density of the early universe resulted not only in signatures in the CMB, as measured for example by the Planck probe, but also left imprints in the distribution of baryonic matter. Each over-dense region is thought to contain dark matter, baryonic matter and photons. The gravitational force from dark matter on the baryons is countered by radiation pressure from the photons. From the small over-densities, baryons are dragged along by photon pressure until these two types of particles decoupled during the recombination era. The original location of the over-density is surrounded by a sphere of baryonic matter, which typically is at a distance referred to as the sound horizon. The sound horizon at the moment of decoupling, denoted r d, leaves an imprint that has since evolved to produce the density fluctuations in the universe that seeded large-scale structures.

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