The origins of a torus in a Galactic Nucleus

An artist's conception of a quasar, with a Chandra X-ray Observatory image of the quasar GB1508+5714 inset.

The data reveal a jet of high-energy particles that extends more than 100,000 light years from the supermassive black hole powering the quasar.

A new study shows for the first time that a torus of gas and dust will naturally form around the nuclear black hole as material falls in toward the nucleus.

Credit: NASA/Chandra

Quasars are among the most energetic objects in the universe, with some of them as luminous as ten thousand Milky Way galaxies.

Quasars are thought to have massive black holes at their cores, and astronomers also think that the regions around the black holes actively accrete matter, a process that releases vast amounts of energy and often ejects a powerful, narrow jet of material.

Quasars can be seen even when they are very far away, because they are so bright, and this combination of being both highly energetic and located at cosmological distances makes them appealing to astronomers trying to figure out the nature of galactic center black holes (our own Milky Way has one) and the conditions in the early universe that prompt these monsters to form.

The situation may be about to change. The violent activity around a black hole is very difficult to analyze with just pen and paper, and so for years researchers have tried to use computer simulations to identify what happens.

These simulations have faced a major challenge: tracing the detailed flow of material from galaxy-wide scales of hundreds of thousands of light-years down into the central tenth of a light-year around the black hole.

It has just been too hard to keep track of everything at such a fine scale across such a large one.

CfA astronomers Chris Hayward and Lars Hernquist, together with ex-CfA member Phil Hopkins and a fourth colleague, have figured out a way to deal with the computational dilemma.

They use a clever scheme of multi-scale "zoom-ins" which allows them to track and model, in a physically consistent way, selected parcels of gas as they move inward towards the torus.

Their simulations lead them to reach two very significant conclusions. First, they show that a dusty torus is likely to be produced around the black hole - in the past it had been postulated in order to explain the various morphologies but had never been demonstrated, even in a simulation.

Secondly, the scientists show that the torus is not just a passive screen: it plays an active role in feeding gas and dust into the accretion disk around the black hole itself.

Provided by Harvard-Smithsonian Center for Astrophysics

Fermi telescope: Gamma-ray bursts' highest power side unveiled

Detectable for only a few seconds but possessing enormous energy, gamma-ray bursts are difficult to capture because their energy does not penetrate the Earth's atmosphere.

Now, thanks to an orbiting telescope, astrophysicists are filling in the unknowns surrounding these bursts and uncovering new questions.

The Fermi Gamma-Ray Space Telescope, formerly called the Gamma-Ray Large Area Space Telescope, launched on June 11, 2008. As part of its mission, the telescope records any gamma-ray bursts within its viewing area.

"Fermi is lucky to measure the highest energy portion of the gamma-ray burst emission, which last for hundreds to thousands of seconds -- maybe 20 minutes," said Péter Mészáros, Eberly Chair Professor of Astronomy and Astrophysics and Physics, Penn State.

Most gamma-ray bursts occur when stars that are more than 25 times larger than our sun come to the end of their lives. When the internal nuclear reaction in these stars ends, the star collapses in on itself and forms a black hole. The outer envelope of the star is ejected forming a supernova.

"The black hole is rotating rapidly and as it is swallowing the matter from the star, the rotation ejects a jet of material through the supernova envelope," said Mészáros.

This jet causes the gamma-ray burst, which briefly becomes the brightest thing in the sky. However, unlike supernovas that radiate in all directions, gamma-ray bursts radiate in a very narrow area, and Fermi sees only jets ejecting in its direction.

This, however, is the direction in which they send their highest energy photons. Any gamma-ray bursts on the other side of the black hole or even off at an angle are invisible to the telescope.

"We actually miss about 500 gamma-ray bursts for every one we detect," Mészáros told attendees today at the annual meeting of the American Association for the Advancement of Science in Vancouver, British Columbia.

The gamma-ray bursts that Fermi has seen have allowed astrophysicists to clarify previous theories about gamma-ray bursts.

"We have been able to rule out the simplest version of theories which combine quantum mechanics with gravity, although others remain to be tested," said Mészáros.

Mészáros notes that Fermi and other programs like the SWIFT telescope have shown that gamma-ray bursts last longer than we thought they did and that there are long and short gamma-ray bursts.

Read more about the SWIFT Telescope discovery here

NASA ESA Hubble Image: Spiral Galaxy and Quasars

The Hubble space telescope captured an amazing view of spiral galaxy NGC 1073 and three quasars that are right outside its galactic neighbourhood.

Located in the constellation of Cetus, the galaxy has a bar structure in the centre, similar to our own Milky Way.

Rice lab mimics Jupiter's Trojan asteroids inside a single atom - YouTube

Rice University physicists have built an accurate model of part of the solar system inside a single atom.

In a new paper in Physical Review Letters, Rice's team and collaborators from Oak Ridge National Laboratory and the Vienna University of Technology showed they could make an electron orbit the atomic nucleus in the same way that Jupiter's Trojan asteroids orbit the sun.

The findings uphold a 1920 prediction by physicist Niels Bohr.

"Bohr predicted that quantum mechanical descriptions of the physical world would, for systems of sufficient size, match the classical descriptions provided by Newtonian mechanics," said lead researcher Barry Dunning, Rice's Sam and Helen Worden Professor of Physics and chair of the Department of Physics and Astronomy.

"Bohr also described the conditions under which this correspondence could be observed. In particular, he said it should be seen in atoms with very high principal quantum numbers, which are exactly what we study in our laboratory."

Bohr was a pioneer of quantum physics. His 1913 atomic model, which is still widely invoked today, postulated a small nucleus surrounded by electrons moving in well-defined orbits and shells.

The word "quantum" in quantum mechanics derives from the fact that these orbits can have only certain well-defined energies.

Jumps between these orbits lead to absorption or emission of specific amounts of energy termed quanta.

As an electron gains energy, its quantum number increases, and it jumps to higher orbits that circle ever farther from the nucleus.

In the new experiments, Rice graduate students Brendan Wyker and Shuzhen Ye began by using an ultraviolet laser to create a Rydberg atom.

Rydberg atoms contain a highly excited electron with a very large quantum number. In the Rice experiments, potassium atoms with quantum numbers between 300 and 600 were studied.

Graphene, Space, Chess boards and Electron Spin

Physicists at UCLA set out to design a better transistor and ended up discovering a new way to think about the structure of space.

 

Space is usually considered infinitely divisible — given any two positions, there is always a position halfway between.

 

But in a recent study aimed at developing ultra-fast transistors using graphene, researchers from the UCLA Department of Physics and Astronomy and the California NanoSystems Institute show that dividing space into discrete locations, like a chessboard, may explain how point-like electrons, which have no finite radius, manage to carry their intrinsic angular momentum, or “spin.”

 

While studying graphene’s electronic properties, professor Chris Regan and graduate student Matthew Mecklenburg found that a particle can acquire spin by living in a space with two types of positions — dark tiles and light tiles. The particle seems to spin if the tiles are so close together that their separation cannot be detected.

 

“An electron’s spin might arise because space at very small distances is not smooth, but rather segmented, like a chessboard,” Regan said.

 

Their findings are published in the March 18 edition of the journal Physical Review Letters.

 

In quantum mechanics, “spin up” and “spin down” refer to the two types of states that can be assigned to an electron. That the electron’s spin can have only two values — not one, three or an infinite number — helps explain the stability of matter, the nature of the chemical bond and many other fundamental phenomena.

 

However, it is not clear how the electron manages the rotational motion implied by its spin. If the electron had a radius, the implied surface would have to be moving faster than the speed of light, violating the theory of relativity. And experiments show that the electron does not have a radius; it is thought to be a pure point particle with no surface or substructure that could possibly spin.

 

In 1928, British physicist Paul Dirac showed that the spin of the electron is intimately related to the structure of space-time. His elegant argument combined quantum mechanics with special relativity, Einstein’s theory of space-time (famously represented by the equation E=mc²).

 

Dirac’s equation, far from merely accommodating spin, actually demands it. But while showing that relativistic quantum mechanics requires spin, the equation does not give a mechanical picture explaining how a point particle manages to carry angular momentum, nor why this spin is two-valued.

 

Unveiling a concept that is at once novel and deceptively simple, Regan and Mecklenburg found that electrons’ two-valued spin can arise from having two types of tiles — light and dark — in a chessboard-like space. And they developed this quantum mechanical model while working on the surprisingly practical problem of how to make better transistors out of a new material called graphene.

 

Graphene, a single sheet of graphite, is an atomically-thin layer of carbon atoms arranged in a honeycomb structure. First isolated in 2004 by Andre Geim and Kostya Novoselov, graphene has a wealth of extraordinary electronic properties, such as high electron mobility and current capacity.

 

In fact, these properties hold such promise for revolutionary advances that Geim and Novoselov were awarded the 2010 Nobel Prize a mere six years after their achievement.

 

Regan and Mecklenburg are part of a UCLA effort to develop extremely fast transistors using this new material.

 

“We wanted to calculate the amplification of a graphene transistor,” Mecklenburg said. “Our collaboration was building them and needed to know how well they were going to work.”

 

This calculation involved understanding how light interacts with the electrons in graphene.

 

The electrons in graphene move by hopping from carbon atom to carbon atom, as if hopping on a chessboard. The graphene chessboard tiles are triangular, with the dark tiles pointing “up” and light ones pointing “down.”  When an electron in graphene absorbs a photon, it hops from light tiles to dark ones. 

 

Mecklenburg and Regan showed that this transition is equivalent to flipping a spin from “up” to “down.”

In other words, confining the electrons in graphene to specific, discrete positions in space gives them spin. 

 

This spin, which derives from the special geometry of graphene’s honeycomb lattice, is in addition to and distinct from the usual spin carried by the electron. In graphene the additional spin reflects the unresolved chessboard-like structure to the space that the electron occupies.

 

“My adviser [Regan] spent his Ph.D. studying the structure of the electron,” Mecklenburg said. “So he was very excited to see that spin can emerge from a lattice. It makes you wonder if the usual electron spin could be generated in the same way.”

 

“It’s not yet clear if this work will be more useful in particle or condensed matter physics,” Regan said, “but it would be odd if graphene’s honeycomb structure was the only lattice capable of generating spin.”

 

The California NanoSystems Institute at UCLA is an integrated research facility located at UCLA and UC Santa Barbara.

Dead quasar illuminates black holes

The green Voorwerp in the foreground remains illuminated by light emitted up to 70,000 years ago by a quasar in the center of the background galaxy, which has since died out. (Credit: William Keel, Anna Manning/WIYN Observatory)

Scientists say the object, known as Hanny’s Voorwerp and discovered by Dutch schoolteacher Hanny von Arkel as part of the Galaxy Zoo citizen science project, is a large cloud of glowing gas illuminated by the light from a quasar—an extremely energetic galaxy with a supermassive black hole at its centre.

The twist, described online in the Astrophysical Journal Letters, is that the quasar lighting up the gas has since burned out almost entirely, even though the light it emitted in the past continues to travel through space, illuminating the gas cloud and producing a sort of “light echo” of the dead quasar.

“This system really is like the Rosetta Stone of quasars,” says Kevin Schawinski, an astronomer at Yale University, co-founder of Galaxy Zoo, and lead author of the study.

“The amazing thing is that if it wasn’t for the Voorwerp being illuminated nearby, the galaxy never would have piqued anyone’s interest.”

The team calculated that the light from the dead quasar, which is the nearest known galaxy to have hosted a quasar, took up to 70,000 years to travel through space and illuminate the Voorwerp—meaning the quasar must have shut down sometime within the past 70,000 years.

Until now, it was assumed that supermassive black holes took millions of years to die down after reaching their peak energy output. The Voorwerp suggests, however, that the supermassive black holes that fuel quasars shut down much more quickly than previously thought.

“This has huge implications for our understanding of how galaxies and black holes co-evolve,” Schawinski says.

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Einstein and the end of space-time

Physicists struggling to reconcile gravity with quantum mechanics have hailed a theory – inspired by pencil lead – that could make it all very simple

IT WAS a speech that changed the way we think of space and time. The year was 1908, and the German mathematician Hermann Minkowski had been trying to make sense of Albert Einstein's hot new idea - what we now know as special relativity - describing how things shrink as they move faster and time becomes distorted.

"Henceforth space by itself and time by itself are doomed to fade into the mere shadows," Minkowski proclaimed, "and only a union of the two will preserve an independent reality."

And so space-time - the malleable fabric whose geometry can be changed by the gravity of stars, planets and matter - was born. It is a concept that has served us well, but if physicist Petr Horava is right, it may be no more than a mirage.

Horava, who is at the University of California, Berkeley, wants to rip this fabric apart and set time and space free from one another in order to come up with a unified theory that reconciles the disparate worlds of quantum mechanics and gravity - one the most pressing challenges to modern physics.

Since Horava published his work in January 2009, it has received an astonishing amount of attention. Already, more than 250 papers have been written about it. Some researchers have started using it to explain away the twin cosmological mysteries of dark matter and dark energy.

Others are finding that black holes might not behave as we thought. If Horava's idea is right, it could forever change our conception of space and time and lead us to a "theory of everything", applicable to all matter and the forces that act on it.

For decades now, physicists have been stymied in their efforts to reconcile Einstein's general theory of relativity, which describes gravity, and quantum mechanics, which describes particles and forces (except gravity) on the smallest scales.

The stumbling block lies with their conflicting views of space and time. As seen by quantum theory, space and time are a static backdrop against which particles move. In Einstein's theories, by contrast, not only are space and time inextricably linked, but the resulting space-time is moulded by the bodies within it.

Part of the motivation behind the quest to marry relativity and quantum theory - to produce a theory of quantum gravity - is an aesthetic desire to unite all the forces of nature. But there is much more to it than that.

We also need such a theory to understand what happened immediately after the big bang or what's going on near black holes, where the gravitational fields are immense.

One area where the conflict between quantum theory and relativity comes to the fore is in the gravitational constant, G, the quantity that describes the strength of gravity. On large scales - at the scale of the solar system or of the universe itself - the equations of general relativity yield a value of G that tallies with observed behaviour.

But when you zoom in to very small distances, general relativity cannot ignore quantum fluctuations of space-time. Take them into account and any calculation of G gives ridiculous answers, making predictions impossible.

To read the full article Click Here

Chinese Scientists Seek Support For Dark Matter Mission In Space

Chinese Scientists Seek Support For Dark Matter Mission In Space

Chinese scientists are lobbying for greater government support for a groundbreaking project that would see the launch of a satellite to investigate mysterious dark matter in space.

The Center for Space Science and Applied Research (CSSAR) of the Chinese Academy of Sciences was focusing on developing China's first astronomical satellite to prove the existence of dark matter.

"This would be a major breakthrough in the field of basic science which has been dormant for decades since Einstein's Theory of Relativity," said center director Wu Ji.

Dark matter and dark energy represent the vast majority of the mass in the observable universe, but their presence is only inferred from their gravitational effects on visible matter. Dark matter is believed to play a central role in galaxy evolution and the formation of universe.

Explained: The 10 Dimensions that make up our Universe

This is an excellent, clear and concise description of the 10 Dimensions that make up our perceived Universe. To connect with the 10 Dimensions CLICK HERE