Tag Archive: Black Holes

Buckle up, there may be some turbulence... or fractals <i>(Image: DR Fred Espenak/SPL)</i>

Feeding black holes develop a fractal skin as they grow. That’s the conclusion of simulations that take advantage of a correlation between fluid dynamics and gravity.

“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,” says Allan Adams at the Massachusetts Institute of Technology. “More precisely, the horizon itself becomes a fractal.”

Fractals are mathematical sets that show self-similar patterns: zoom in on one part of a fractal drawing, like the famous Mandelbrot set, and the smaller portion will look nearly the same as the original image. Objects with fractal geometries show up all over nature, from clouds to the coast of England.

Adams and his colleagues have now found evidence that fractal behaviour occurs in an unexpected place: on the surface of a feeding black hole. Black holes grow by devouring matter that falls into them; the black hole at the centre of our galaxy is due to feast on a gas cloud later this year. But the details of how feeding black holes grow, and how this might affect their host galaxies, are still unknown.

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Chasing the black holes of the ocean

Chasing the black holes of the ocean

According to researchers from ETH Zurich and the University of Miami, some of the largest ocean eddies on Earth are mathematically equivalent to the mysterious black holes of space. These eddies are so tightly shielded by circular water paths that nothing caught up in them escapes.

The mild winters experienced in Northern Europe are thanks to the Gulf Stream, which makes up part of those ocean currents spanning the globe that impact on the climate. However, our climate is also influenced by huge eddies of over 150 kilometres in diameter that rotate and drift across the ocean. Their number is reportedly on the rise in the Southern Ocean, increasing the northward transport of warm and salty water. Intriguingly, this could moderate the negative impact of melting sea ice in a warming climate.

However, scientists have been unable to quantify this impact so far, because the exact boundaries of these swirling water bodies have remained undetectable. George Haller, Professor of Nonlinear Dynamics at ETH Zurich, and Francisco Beron-Vera, Research Professor of Oceanography at the University of Miami, have now come up with a solution to this problem. In a paper just published in the Journal of Fluid Mechanics, they develop a new mathematical technique to find water-transporting eddies with coherent boundaries.

The challenge in finding such eddies is to pinpoint coherent water islands in a turbulent ocean. The rotating and drifting fluid motion appears chaotic to the observer both inside and outside an eddy. Haller and Beron-Vera were able to restore order in this chaos by isolating coherent water islands from a sequence of satellite observations. To their surprise, such coherent eddies turned out to be mathematically equivalent to black holes.

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Falling into a black hole may not be as final as it seems. Apply a quantum theory of gravity to these bizarre objects and the all-crushing singularity at their core disappears.

In its place is something that looks a lot like an entry point to another universe. Most immediately, that could help resolve the nagging information loss paradox that dogs black holes.

Though no human is likely to fall into a black hole anytime soon, imagining what would happen if they did is a great way to probe some of the biggest mysteries in the universe. Most recently this has led to something known as the black hole firewall paradox – but black holes have long been a source of cosmic puzzles.

According to Albert Einstein’s theory of general relativity, if a black hole swallows you, your chances of survival are nil. You’ll first be torn apart by the black hole’s tidal forces, a process whimsically named spaghettification.

Eventually, you’ll reach the singularity, where the gravitational field is infinitely strong. At that point, you’ll be crushed to an infinite density. Unfortunately, general relativity provides no basis for working out what happens next. “When you reach the singularity in general relativity, physics just stops, the equations break down,” says Abhay Ashtekar of Pennsylvania State University.

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Existing theories on the relationship between the size of a galaxy and its central black hole are wrong according to a new Australian study.

The discovery by Dr Nicholas Scott and Professor Alister Graham, from Melbourne’s Swinburne University of Technology, found smaller galaxies have far smaller black holes than previously estimated.

Central black holes, millions to billions of times larger than the Sun, reside in the core of most galaxies, and are thought to be integral to galactic formation and evolution.

However astronomers are still trying to understand this relationship.

Scott and Graham combined data from observatories in Chile, Hawaii and the Hubble Space Telescope, to develop a data base listing the masses of 77 galaxies and their central supermassive black holes.

The astronomers determined the mass of each central black hole by measuring how fast stars are orbiting it.

Existing theories suggest a direct ratio between the mass of a galaxy and that of its central black hole.

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Black holes are surrounded by many mysteries, but now researchers from the Niels Bohr Institute, among others, have come up with new groundbreaking theories that can explain several of their properties. The research shows that black holes have properties that resemble the dynamics of both solids and liquids.

Black holes are extremely compact objects in the universe. They are so compact that they generate an incredibly strong gravitational pull and everything that comes near them is swallowed up. Not even light can escape, so light that hits a black hole will not be reflected, but will be entirely absorbed, as a result, they cannot be seen and we call them black holes.

“But black holes are not completely black, because we know that they emit radiation and there are indications that the radiation is thermal, i.e. it has a temperature,” explains Niels Obers, a professor of theoretical particle physics and cosmology at the Niels Bohr Institute at the University of Copenhagen.

Researchers know that the black holes are very compact, but they do not know what their quantum properties are. Niels Obers works with theoretical modelling to better understand the physics of black holes. He explains that you can look at a black hole like a particle. A particle has in principle no dimensions. It is a point. If you give a particle an extra dimension, it becomes a string. If you give the string an extra dimension, it becomes a plane. Physicists call such a plane a ‘brane’ (the word ‘brane’ is related to ‘membrane’ from the biological world).

“In string theory, you can have different branes, including planes that behave like black holes, which we call black branes. The black branes are thermal, that is to say, they have a temperature and are dynamical objects. When black branes are folded into multiple dimensions, they form a ‘blackfold’,” explains Niels Obers, who worked out this new way of looking at black branes with associate professor in theoretical physics at the Niels Bohr Institute, Troels Harmark, back in 2009.

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Astronomers have discovered a new, enormous black hole that could change our understanding of how galaxies evolve.

Holding the mass of 17 billion suns, the black hole at the centre of the NGC 1277 galaxy may be the largest discovered to date. It is 250 million light-years from the Earth.

Most supermassive black holes are contained within very large galaxies. But the NGC 1277 galaxy is remarkably small compared to the black hole at its centre.

The researchers, who reported their findings in Nature today, say black holes usually take up 0.1% of a galaxy’s “stellar bulge” (the collection of stars at its centre). It’s thought this black hole comprises 59% of its galaxy’s stellar bulge mass, and 14% of the galaxy’s mass overall.

For this reason, the black hole has been described as “overmassive” rather than simply supermassive.

In its entirety, it is thought to be 11 times wider than Neptune’s orbit of the sun.

“This is a really oddball galaxy,” team member Karl Gebhardt of The University of Texas said in a statement. “It’s almost all black hole.”

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British scientists are to mimic black holes in the laboratory as part of a £2.35 million project looking at how matter and energy interact.

The team from Heriot-Watt University in Edinburgh will produce laser pulses whose energy is measured in trillions of watts.

They will be used to simulate conditions found around a black hole, a place where gravity is so strong that light cannot escape and the normal laws of physics break down.

Lead scientist Daniele Faccio said: “What we are creating is the same space-time structure which characterises a black hole. But we’re doing this with a light pulse, so we don’t actually have the mass which is associated with black holes.

“Gravitational black holes are generated by a collapsing star. We don’t actually have this collapsing star, so there’s no danger of being sucked into the black holes we’re generating here.”

The university has been awarded a three million euro (£2.35 million) grant by the European Research Council to investigate new areas of quantum physics.

Another study will look at how single photons and electrons interact with each other in computer chips.

Because black holes are impossible to see, one of scientists’ best hopes to study them is to look for the ripples in space-time, called gravitational waves, that they are thought to create.

Gravitational waves would be distortions propagating through space and time caused by violent events such as the collision of two black holes. They were first predicted by Einstein’s general theory of relativity; however, scientists have yet to find one.

That could change when the latest version of a gravitational wave-hunting facility gets up and running. The Laser Interferometer Gravitational Wave Observatory (LIGO) is actually a pair of observatories, in Louisiana and Washington state, that began operating in 2002. Newly sensitized detectors are being added to both.

“The advanced LIGO detectors that are now being installed will see out through a substantial part of the universe,” said California Institute of Technology emeritus professor of physics Kip Thorne, a leading proponent of LIGO. “We expect to see black holes colliding at a rate of perhaps somewhere between once an hour and once a year.”

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Our universe may exist inside a black hole. This may sound strange, but it could actually be the best explanation of how the universe began, and what we observe today. It’s a theory that has been explored over the past few decades by a small group of physicists including myself.

Successful as it is, there are notable unsolved questions with the standard big bang theory, which suggests that the universe began as a seemingly impossible “singularity,” an infinitely small point containing an infinitely high concentration of matter, expanding in size to what we observe today. The theory of inflation, a super-fast expansion of space proposed in recent decades, fills in many important details, such as why slight lumps in the concentration of matter in the early universe coalesced into large celestial bodies such as galaxies and clusters of galaxies.

But these theories leave major questions unresolved. For example: What started the big bang? What caused inflation to end? What is the source of the mysterious dark energy that is apparently causing the universe to speed up its expansion?

The idea that our universe is entirely contained within a black hole provides answers to these problems and many more. It eliminates the notion of physically impossible singularities in our universe. And it draws upon two central theories in physics.

The first is general relativity, the modern theory of gravity. It describes the universe at the largest scales. Any event in the universe occurs as a point in space and time, or spacetime. A massive object such as the Sun distorts or “curves” spacetime, like a bowling ball sitting on a canvas. The Sun’s gravitational dent alters the motion of Earth and the other planets orbiting it. The sun’s pull of the planets appears to us as the force of gravity.

The second is quantum mechanics, which describes the universe at the smallest scales, such as the level of the atom. However, quantum mechanics and general relativity are currently separate theories; physicists have been striving to combine the two successfully into a single theory of “quantum gravity” to adequately describe important phenomena, including the behavior of subatomic particles in black holes.

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Astronomers have found the best evidence yet that the dormant gravitational monster that lies at the centre of the Milky Way — a supermassive black hole known as Sagittarius A* — recently emitted a pair of γ-ray jets.

As they feed on stars and clouds of gas that stray too close, black holes at the centres of other galaxies create bright jets that can be seen across cosmic distances. But the Milky Way’s black hole shows no signs of such activity. Now, the Fermi Gamma-ray Space Telescope has picked up some faint γ-ray signals that suggest that Sagittarius A* has not always been so tranquil. The black hole could even have been active as recently as 20,000 years ago, after gulping down a gas cloud with a mass about 100 times that of the Sun, says Douglas Finkbeiner of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

“If these features truly are γ-ray jets from Sagittarius A*, it would tell us that our Galactic supermassive black hole has not always been as feeble as we currently observe it to be,” says Fred Baganoff of the Massachusetts Institute of Technology in Cambridge. And that would solve an enduring puzzle, he notes. Sagittarius A* is growing about 1,000 times too slowly for it to have reached its current mass of about four million solar masses since the Galaxy formed about 13.2 billion years ago. “If confirmed, the existence of γ-ray jets would provide the strongest evidence to date for the existence of higher activity in the past,” he says.

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Astronomers have found a black hole that behaves like one of those batting cages that automatically spits baseballs.

The stellar mass black hole ejects glowing cannon balls of plasma simultaneously in opposite directions that blaze though space at one-quarter the speed of light. That’s fast enough to travel from the sun to Earth in half an hour!

Astronomers don’t have any idea how the ultra-fast bullets are launched, but they do know that the fuel supply for these fireworks comes from a companion star to the black hole.

Material from the companion spills into an ultra hot accretion disk encircling the black hole. Something happens during this feeding process that causes the disk to grow very hot every eight months and glow fiercely in X-rays, and then subside and begin the process all over again.

The black hole and companion star, called H1742, is 28,000 light-years away near the galactic center. NASA’s High Energy Optical Observatory first saw the X-ray sputtering in the late 1970s.

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Scientists may have found the smallest black hole yet by listening to its X-ray “heartbeat.”

The black hole, if it truly exists, would weigh less than three times the mass of the sun, putting it near the theoretical minimum mass required for a black hole to be stable.

The researchers can’t directly observe the black hole, but they measured a rise and fall in X-ray light coming from a binary star system in our Milky Way galaxy that they think signals the presence of a black hole.

Until now, this X-ray pattern, which is similar to a heartbeat registered on an electrocardiogram, has been seen in only one other black hole system.

NASA’s Rossi X-ray Timing Explorer (RXTE) spacecraft measured this X-ray heartbeat in a star system in the direction of the constellation Scorpius, at a distance between 16,000 and 65,000 light-years away (a light-year is the distance light travels in a single year, about 6 trillion miles (10 trillion kilometers).

Researchers think the system, officially called IGR J17091-3624, includes one normal star with a companion black hole. Mass would stream off this normal star and fall toward the black hole, forming a flattened disk around it. As friction in the disk heats the gas to millions of degrees, the disk would emit high-energy X-rays that can be seen across the galaxy.

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Scientists have discovered the largest black holes yet, and they’re far bigger than researchers expected based on the galaxies in which they were found.

The discovery suggests we have much to learn about how monster black holes grow, scientists said.

All large galaxies are thought to harbor super-massive black holes at their hearts that contain millions to billions of times the mass of our sun. Until now, the largest black hole known was a mammoth dwelling in the giant elliptical galaxy Messier 87. This black hole has a mass 6.3 billion times that of the sun.

Now research suggests black holes in two nearby galaxies are even bigger.

The scientists used the Gemini and Keck observatories in Hawaii and the McDonald Observatory in Texas to monitor the velocities of stars orbiting around the centers of a pair of galaxies. These velocities reveal the strength of the gravitational pull on those stars, which in turn is linked with the masses of the black holes lurking there.

The new findings suggest that one galaxy, known as NGC 3842, the brightest galaxy in the Leo cluster of galaxies nearly 320 million light years distant, has a central black hole 9.7 billion solar masses large. The other, named NGC 4889, the brightest galaxy in the Coma cluster more than 335 million light years away, has a black hole of comparable or larger mass. Both encompass regions or “event horizons” about five times the distance from the sun to Pluto.

Image of the center of our Galaxy from laser-guide-star adaptive optics on the Keck Telescope. This is an HKL-band color mosaic, where H(1.8 microns) = blue, K(2.2 microns) = green, and L(3.8 microns) = red. More massive black holes have larger event horizons, the region within which even light cannot escape. If a 10 billion solar mass black hole resided at the Galactic center, its immense event horizon would be visible (illustrated by the central black disk). The actual black hole at the Galactic center is 2,500 times smaller.

“For comparison, these black holes are 2,500 times as massive as the black hole at the center of the Milky Way galaxy, whose event horizon is one-fifth the orbit of Mercury,” said study lead author Nicholas McConnell at the University of California, Berkeley.

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