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Category: cosmology – Page 277

A star in a distant galaxy blew up in a powerful explosion, solving an astronomical mystery.

Dr. Iair Arcavi, a Tel Aviv University researcher at the Raymond and Beverly Sackler Faculty of Exact Sciences, participated in a study that discovered a new type of stellar explosion — an electron-capture supernova. While they have been theorized for 40 years, real-world examples have been elusive. Such supernovas arise from the explosions of stars 8–9 times the mass of the sun. The discovery also sheds new light on the thousand-year mystery of the supernova from A.D. 1054 that was seen by ancient astronomers, before eventually becoming the Crab Nebula, that we know today.

A supernova is the explosion of a star following a sudden imbalance between two opposing forces that shaped the star throughout its life. Gravity tries to contract every star. Our sun, for example, counter balances this force through nuclear fusion in its core, which produces pressure that opposes the gravitational pull. As long as there is enough nuclear fusion, gravity will not be able to collapse the star. However, eventually, nuclear fusion will stop, just like gas runs out in a car, and the star will collapse. For stars like the sun, the collapsed core is called a white dwarf. This material in white dwarfs is so dense that quantum forces between electrons prevent further collapse.

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A new set of equations can precisely describe the reflections of the Universe that appear in the warped light around a black hole.

The proximity of each reflection is dependent on the angle of observation with respect to the black hole, and the rate of the black hole’s spin, according to a mathematical solution worked out by physics student Albert Sneppen of the Niels Bohr Institute in Denmark.

This is really cool, absolutely, but it’s not just really cool. It also potentially gives us a new tool for probing the gravitational environment around these extreme objects.

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Circa 2020

What are the fundamental laws that govern our universe? How did the matter in the universe today get there? What exactly is dark matter?

The questions may be eternal, but no human scientist has an eternity to answer them.

Now, thanks to NVIDIA technology and cutting-edge AI, the more than 1000 collaborators from 26 countries working on the Belle II particle physics experiment are able to learn more about these big questions, faster.

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A tachyon field might be responsible for cosmological inflation at an early time and contribute to cosmological dark matter at a later time. We investigate tachyonic inflation by analyzing a tachyon field with different potentials in the framework of loop quantum cosmology. No matter which tachyon field energy dominates at the bounce, the evolution of the background can be divided into three phases: super-inflation, damping, and slow-roll inflation. The duration of each phase depends on the initial condition. During the slow-roll inflation, when the initial condition is $$V(T_\mathrm{B})/\rho _\mathrm{c}\ge 10^{-6}$$ V(TB)/ρc≥10–6, the number of e-folds is very high ($$N\gg 60$$ N≫60) for $$V\propto T^{-n}$$ V∝T-n with $$n=1$$ n=1 and 1 / 2. For an exponential potential, to get enough e-folds, $$V(T_\mathrm{B})/\rho _\mathrm{c}$$ V(TB)/ρc should be greater than $$7.802\times 10^{-4}$$7.

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When we think about singularities, we tend to think of massive black holes in faraway galaxies or a distant future with runaway AI, but singularities are all around us. Singularities are simply a place where certain parameters are undefined. The North and South Pole, for example, are what’s known as coordinate singularities because they don’t have a defined longitude.

Optical singularities typically occur when the phase of with a specific wavelength, or color, is undefined. These regions appear completely dark. Today, some optical singularities, including optical vortices, are being explored for use in optical communications and particle manipulation but scientists are just beginning to understand the potential of these systems. The question remains—can we harness darkness like we harnessed light to build powerful, new technologies?

Now, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a new way to control and optical singularities. The technique can be used to engineer singularities of many shapes, far beyond simple curved or straight lines. To demonstrate their technique, the researchers created a singularity sheet in the shape of a heart.

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“You can also engineer dead zones in radio waves or silent zones in acoustic waves,” said Lim. “This research points to the possibility of designing complex topologies in wave physics beyond optics, from electron beams to acoustics.”

When we think about singularities, we tend to think of massive black holes in faraway galaxies or a distant future with runaway AI, but singularities are all around us. Singularities are simply a place where certain parameters are undefined. The North and South Pole, for example, are what’s known as coordinate singularities because they don’t have a defined longitude.

Optical singularities typically occur when the phase of light with a specific wavelength, or color, is undefined. These regions appear completely dark. Today, some optical singularities, including optical vortices, are being explored for use in optical communications and particle manipulation but scientists are just beginning to understand the potential of these systems. The question remains — can we harness darkness like we harnessed light to build powerful, new technologies?

Now, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a new way to control and shape optical singularities. The technique can be used to engineer singularities of many shapes, far beyond simple curved or straight lines. To demonstrate their technique, the researchers created a singularity sheet in the shape of a heart.

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A stunning new image from the South African MeerKAT telescope captures powerful radio emissions woven through space.

The radio emissions emanate from an enormous rotating black hole that lies at the center of an elliptical galaxy known as IC 4296. Energy released by matter falling into the black hole generates two radio jets of high energy gas on opposite sides of the galaxy — creating what is also known as a double-lobed radio galaxy.

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The size of a tennis ball. The mass of the Earth.

But that could change soon.

Current gravitational wave observatories are sensitive to the mergers of stellar-mass black holes. We’ve observed a few mergers involving neutron stars, but most have been between black holes on the order of tens of solar masses.

We can’t yet observe the gravitational waves of supermassive black holes in other galaxies, nor can we observe those of planet-sized worlds. Proposed detectors such as eLISA will allow us to observe the former, but it will take a novel new idea to detect the latter.

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Math about black holes:

If you’ve been following the arXiv, or keeping abreast of developments in high-energy theory more broadly, you may have noticed that the longstanding black hole information paradox seems to have entered a new phase, instigated by a pair of papers [1, 2] that appeared simultaneously in the summer of 2019. Over 200 subsequent papers have since appeared on the subject of “islands”—subleading saddles in the gravitational path integral that enable one to compute the Page curve, the signature of unitary black hole evaporation. Due to my skepticism towards certain aspects of these constructions (which I’ll come to below), my brain has largely rebelled against boarding this particular hype train. However, I was recently asked to explain them at the HET group seminar here at Nordita, which provided the opportunity (read: forced me) to prepare a general overview of what it’s all about. Given the wide interest and positive response to the talk, I’ve converted it into the present post to make it publicly available.

Well, most of it: during the talk I spent some time introducing black hole thermodynamics and the information paradox. Since I’ve written about these topics at length already, I’ll simply refer you to those posts for more background information. If you’re not already familiar with firewalls, I suggest reading them first before continuing. It’s ok, I’ll wait.

Done? Great; let me summarize the pre-island state of affairs with the following two images, which I took from the post-island review [3] (also worth a read):

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