Researcher shows that black holes do not exist

Researcher shows that black holes do not exist: She and Hawking both agree that as a star collapses under its own gravity, it produces Hawking radiation. However, in her new work, Mersini-Houghton shows that by giving off this radiation, the star also sheds mass. So much so that as it shrinks it no longer has the density to become a black hole.
Before a black hole can form, the dying star swells one last time and then explodes. A singularity never forms and neither does an event horizon.

Black Holes Aren’t Black After All, Say Theoretical Physicists — The Physics arXiv Blog — Medium

Black Holes Aren’t Black After All, Say Theoretical Physicists — The Physics arXiv Blog — Medium: Stephen Hawking proposed a potential solution earlier this year. His idea is that gravitational collapse can never continue beyond the so-called event horizon of a black hole beyond which information is lost. Gravitational collapse would approach the boundary but never go beyond it...

Turbulent black holes grow fractal skins as they feed - physics-math - 28 April 2014 - New Scientist

Turbulent black holes grow fractal skins as they feed - physics-math - 28 April 2014 - New Scientist: "We showed that when you throw stuff into a black hole, the surface of the black hole responds like a fluid – and in particular, it can become turbulent...  More precisely, the horizon itself becomes a fractal..."

To investigate what the horizon of a black hole looks like at mealtime, Adams took advantage of a mathematical duality between Einstein's equations of general relativity – which describe gravity near black holes – and fluid dynamics...

Led by Paul Chesler, who is a post-doc researcher at Harvard, the team first modelled a turbulent fluid system. They then translated it into the black hole regime and let it develop with time. When they looked again, the horizon of the black hole appeared to have developed an infinite surface area.

Stephen Hawking: 'There are no black holes' : Nature News & Comment

Stephen Hawking: 'There are no black holes' : Nature News & Comment: Now Hawking proposes a third, tantalizingly simple, option. Quantum mechanics and general relativity remain intact, but black holes simply do not have an event horizon to catch fire. The key to his claim is that quantum effects around the black hole cause space-time to fluctuate too wildly for a sharp boundary surface to exist.

In place of the event horizon, Hawking invokes an “apparent horizon”, a surface along which light rays attempting to rush away from the black hole’s core will be suspended. In general relativity, for an unchanging black hole, these two horizons are identical, because light trying to escape from inside a black hole can reach only as far as the event horizon and will be held there, as though stuck on a treadmill. However, the two horizons can, in principle, be distinguished. If more matter gets swallowed by the black hole, its event horizon will swell and grow larger than the apparent horizon.

Did a hyper-black hole spawn the Universe? : Nature News & Comment

Did a hyper-black hole spawn the Universe? : Nature News : ...in the bulk universe the event horizon of a 4D black hole would be a 3D object — a shape called a hypersphere. When Afshordi’s team modeled the death of a 4D star, they found that the ejected material would form a 3D brane surrounding that 3D event horizon, and slowly expand.


The authors postulate that the 3D Universe we live in might be just such a brane — and that we detect the brane’s growth as cosmic expansion. “Astronomers measured that expansion and extrapolated back that the Universe must have begun with a Big Bang — but that is just a mirage,” says Afshordi.

The model also naturally explains our Universe’s uniformity...

How to model a white hole in your kitchen sink

How to model a white hole in your kitchen sink: When a stream of tap water hits the flat surface of the sink, it spreads out into a thin disc bounded by a raised lip, called the hydraulic jump… More recently, physicists have suggested that, if the water waves inside the disc move faster than the waves outside, the jump could serve as an analogue event horizon. Water can approach the ring from outside, but it can't get in.

"The jump would therefore constitute a one-directional membrane or white hole," wrote physicist Gil Jannes and Germain Rousseaux of the University of Nice Sophia Antipolis in France and colleagues in a study on ArXiv Oct. 8. "Surface waves outside the jump cannot penetrate in the inner region; they are trapped outside in precisely the same sense as light is trapped inside a black hole."

‘Point of no return’ found | Harvard Gazette

‘Point of no return’ found | Harvard Gazette: According to Einstein’s theory of general relativity, a black hole’s mass and spin determine how close material can orbit before becoming unstable and falling in toward the event horizon. The team was able to measure this innermost stable orbit and found that it’s only 5.5 times the size of the black hole’s event horizon. This size suggests that the accretion disk is spinning in the same direction as the black hole.

How To Build A Black Hole Laser - Technology Review

How To Build A Black Hole Laser - Technology Review: Their idea is to create a black hole next to a white hole so that their event horizons are separated by just a few hundred micrometres and create a small cavity. Then they show that when light is fired into this cavity, it is reflected off the white hole horizon onto the black hole horizon, back to the white again and so on...
Their real triumph, however, is in showing how such a device could be made in the lab...
...a very intense beam can create a huge gradient in the refractive index. This gradient can be so steep that it behaves like an event horizon. In fact, a single pulse can create black hole horizon at its leading edge and a white hole horizon at its trailing edge.

What a trip through a wormhole would look like

What a trip through a wormhole would look like: As you emerge from the black hole, you enter a wormhole where the flow of space turns around and you start to accelerate back outward. The wormhole ends at the entrance to a white hole, which is a time-reversed version of a black hole.  Instead of falling inward, space falls outwards at a speed faster than light.  Soon you experience another flash of radiation, this time containing a picture of the entire future of the universe.

Naked black-hole hearts live in the fifth dimension

Naked black-hole hearts live in the fifth dimension: Lehner has now proposed another situation where naked singularities might exist: in the extra dimensions proposed by string theory. The rub is that this time, they aren't unusual.

To understand why, think of black holes as points in the four dimensions we experience - three of space and one of time. These become "black strings" when extended into a fifth dimension of space (see diagram).

Black strings are unstable and break up into smaller black holes like a stream of water splitting into droplets. Lehner showed that at the point where a smaller black hole pinches off from the stream, the black hole's radius is zero, which means its density is infinite. In other words, it is a naked singularity. Lehner showed this will happen any time you have a black string.

Planets Could Orbit Singularities Inside Black Holes - Technology Review

Planets Could Orbit Singularities Inside Black Holes - Technology Review: It's well known that a traveller passing through a black hole's event horizon arrives in a region in which the radial dimension becomes time-like, rather than space-like. Conventional orbits are clearly impossible here.

But travel further in and there is another horizon where the dimensions switch back again (at least, inside charged and rotating black holes). This is the inner Cauchy horizon and it's beyond here that Dokuchaev says the interesting orbits for massive planets exist.

He calculates that the stable orbits are nonequatorial and have a rich structure...

Physicists create sonic black hole in the lab

Physicists create sonic black hole in the lab: The researchers created the sonic black hole in a Bose-Einstein condensate made of 100,000 rubidium atoms slowed to their lowest quantum state in a magnetic trap. This cold cluster of atoms acts like a single, large quantum mechanical object. In order to transform this condensate into a sonic black hole, the scientists had to find a way to accelerate some of the condensate to supersonic speeds so that the condensate would contain some regions of supersonic flow and some regions of subsonic flow.

The scientists achieved this acceleration by shining a large-diameter laser on the condensate in such a way as to create a steplike potential and a harmonic potential. When the condensate crosses the “step” in the steplike potential, the condensate accelerates to supersonic speeds. The scientists demonstrated that the condensate could accelerate to more than an order of magnitude faster than the speed of sound.

Black Holes In The Bathtub - Science News

Black Holes In The Bathtub - Science News: "The Canadian team with the water-based black hole analog now sees the radiation in the form of water waves. Another team observes photons emitted from a black hole analog in glass. Yet another has created a black hole in ultracold gas that could be probed for the signal in the form of sound. These lab-made emitters of Hawking radiation share one required feature with their astrophysical counterparts — a point of no return, analogous to the black hole’s outer boundary, or event horizon...
These and other analog systems may help solve a lingering problem in Hawking’s original proposal. His model suggested that radiating light could have wavelengths shorter than the Planck length, supposedly the shortest length allowed by quantum mechanics. If light could have such short wavelengths, and thus really high frequencies, one photon could carry more energy than contained in the entire universe — clearly fishy. Hawking had wanted to eliminate this possibility, but he couldn’t make his equations work without it."

Video - Black hole trip - New Scientist

Video - Black hole trip - New Scientist

New Scientist TV: Darkness visible: Five big black hole puzzles solved

New Scientist TV: Darkness visible: Five big black hole puzzles solved: "How do we know black holes exist? Would you like to know what it would be like to fall into one? Recent simulations and cutting-edge visuals are giving new insight into these strange objects and have helped us answer five big questions about them (see video above).

If you enjoyed this video, you may also like to travel into a black hole. Or how about a black-hole light show? Sounds impossible, so have a look to find out more."

Kitchen sink experiment simulates exotic white holes - New Scientist - New Scientist

Kitchen sink experiment simulates exotic white holes : When water hits the bottom of a sink, it flows outwards in all directions. At a certain distance from the point where the water hits the sink, the outgoing liquid rapidly decelerates and piles up before continuing its outward flow, creating a ring-like ridge.

Physicists have previously suspected that any ripples that might arise beyond the ridge and travel towards it should not be able to get past the ridge. This is because at the ridge the water flows outwards at the maximum speed that ripples could travel inwards, so the ripples would make no forward progress, like a runner on a treadmill. This makes the ridge behave like a white hole event horizon.

Hawking radiation glimpsed in artificial black hole - physics-math - 28 September 2010 - New Scientist

Hawking radiation glimpsed in artificial black hole: To create their lab-scale event horizon, Daniele Faccio of Heriot-Watt University in Edinburgh, UK, Francesco Belgiorno of the University of Milan, Italy, and their colleagues focused ultrashort pulses of infrared laser light at a wavelength of 1055 nanometres into a piece of glass. The extremely high intensity of these pulses – trillions of times that of sunlight – temporarily skews the properties of the glass. In particular, it boosts the glass's refractive index, the extent to which the glass slows down light travelling through it.

The result is a moving point of very high refractive index, equivalent to a physical hill, which acts as a horizon. Photons entering the glass behind this "hill", including ones that are part of a virtual pair, slow as they climb the hill and are unable to pass through it. Relative to the slow-moving pulse, they have come to a stop and remain behind the pulse until it has passed through the glass's length.

Technology Review: Blogs: arXiv blog: First Observation of Hawking Radiation

Technology Review: Blogs: arXiv blog: First Observation of Hawking Radiation: Today, Franco Belgiorno at the University of Milan and a few buddies say they've produced Hawking radiation by firing an intense laser pulse through a so-called nonlinear material, that is one in which the light itself changes the refractive index of the medium.

As the pulse moves through the material, so too does the change in refractive index, creating a kind of bow wave in which the refractive index is much higher than the surrounding material.

This increase in refractive index causes any light heading into it to slow down. "By choosing appropriate conditions, it is possible to bring the light waves to a standstill," say Belgiono and co. This creates a horizon beyond which light cannot penetrate, what physicists call a white hole event horizon, the inverse of a black hole.