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Posted (IP: Staff) ·
NASA Achieves Breakthrough in Black Hole Simulation


The user posted image press release is reproduced below:

April 18, 2006
Grey Hautaluoma
Headquarters, Washington
(202) 358-0668

Susan Hendrix
Goddard Space Flight Center, Greenbelt, Md.
(301) 286-7745

RELEASE: 06-188


NASA Achieves Breakthrough in Black Hole Simulation


NASA scientists have reached a breakthrough in computer modeling that allows them to simulate what gravitational waves from merging black holes look like. The three-dimensional simulations, the largest astrophysical calculations ever performed on a NASA supercomputer, provide the foundation to explore the universe in an entirely new way.

According to Einstein's math, when two massive black holes merge, all of space jiggles like a bowl of Jell-O as gravitational waves race out from the collision at light speed.

Previous simulations had been plagued by computer crashes. The necessary equations, based on Einstein's theory of general relativity, were far too complex. But scientists at NASA's Goddard Space Flight Center in Greenbelt, Md., have found a method to translate Einstein's math in a way that computers can understand.

"These mergers are by far the most powerful events occurring in the universe, with each one generating more energy than all of the stars in the universe combined. Now we have realistic simulations to guide gravitational wave detectors coming online," said Joan Centrella, head of the Gravitational Astrophysics Laboratory at Goddard.

The simulations were performed on the Columbia supercomputer at NASA's Ames Research Center near Mountain View, Calif. This work appears in the March 26 issue of Physical Review Letters and will appear in an upcoming issue of Physical Review D. The lead author is John Baker of Goddard.

Similar to ripples on a pond, gravitational waves are ripples in space and time, a four-dimensional concept that Einstein called spacetime. They haven't yet been directly detected.

Gravitational waves hardly interact with matter and thus can penetrate the dust and gas that blocks our view of black holes and other objects. They offer a new window to explore the universe and provide a precise test for Einstein's theory of general relativity. The National Science Foundation's ground-based Laser Interferometer Gravitational-Wave Observatory and the proposed Laser Interferometer Space Antenna, a joint NASA - European Space Agency project, hope to detect these subtle waves, which would alter the shape of a human from head to toe by far less than the width of an atom.

Black hole mergers produce copious gravitational waves, sometimes for years, as the black holes approach each other and collide. Black holes are regions where gravity is so extreme that nothing, not even light, can escape their pull. They alter spacetime. Therein lies the difficulty in creating black hole models: space and time shift, density becomes infinite and time can come to a standstill. Such variables cause computer simulations to crash.

These massive, colliding objects produce gravitational waves of differing wavelengths and strengths, depending on the masses involved. The Goddard team has perfected the simulation of merging, equal-mass, non-spinning black holes starting at various positions corresponding to the last two to five orbits before their merger.

With each simulation run, regardless of the starting point, the black holes orbited stably and produced identical waveforms during the collision and its aftermath. This unprecedented combination of stability and reproducibility assured the scientists that the simulations were true to Einstein's equations. The team has since moved on to simulating mergers of non-equal-mass black holes.

Einstein's theory of general relativity employs a type of mathematics called tensor calculus, which cannot easily be turned into computer instructions. The equations need to be translated, which greatly expands them. The simplest tensor calculus equations require thousands of lines of computer code. The expansions, called formulations, can be written in many ways. Through mathematical intuition, the Goddard team found the appropriate formulations that led to suitable simulations.

Progress also has been made independently by several groups, including researchers at the Center for Gravitational Wave Astronomy at the University of Texas, Brownsville, which is supported by the NASA Minority University Research and Education Program.

To see two black holes collide, visit:
http://www.nasa.gov/centers/goddard/universe/gwave.html

- end -

--------------------------------------------------------------------------------


Source: NASA Press Release 06-188
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Posted (IP: Staff) ·
NASA's Chandra Finds Black Holes Are 'Green'


The user posted image press release is reproduced below:

April 24, 2006
Erica Hupp/Grey Hautaluoma
Headquarters, Washington
(202) 358-1237/0668

Steve Roy
Marshall Space Flight Center, Huntsville, Ala.
(256) 544-6535

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
(617) 496-7998

RELEASE: 06-192


NASA's Chandra Finds Black Holes Are 'Green'


Black holes are the most fuel efficient engines in the universe, according to a new study using NASA's Chandra X-ray Observatory. By making the first direct estimate of how efficient or "green" black holes are, this work gives insight into how black holes generate energy and affect their environment.

The new Chandra finding shows most of the energy released by matter falling toward a supermassive black hole is in the form of high-energy jets traveling at near the speed of light away from the black hole. This is an important step in understanding how such jets can be launched from magnetized disks of gas near the black hole's event horizon, the distance from a black hole within which nothing, even light, can escape.

"Just as with cars, it's critical to know the fuel efficiency of black holes," said lead author Steve Allen of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University and the Stanford Linear Accelerator Center, Stanford, Calif. "Without this information, we cannot figure out what is going on under the hood, so to speak, or what the engine can do."

Allen and his team used Chandra to study nine supermassive black holes at the centers of elliptical galaxies. These black holes ― from .2 to 3 billion times the mass of our sun ― are relatively old and generate much less radiation than quasars, the rapidly growing supermassive black holes seen in the early universe.

The surprise came when the Chandra results showed these "quiet" black holes are all producing much more energy in jets of high-energy particles than in visible light or X-rays. These jets create huge bubbles, or cavities, in the hot gas in the galaxies.

The efficiency of black hole energy-production was calculated in two steps. First, Chandra images of the galaxies' inner regions were used to estimate how much fuel is available for the black hole. Then, Chandra images were used to estimate the power required to produce the cavities. The galaxies were found to produce a lot of jet power with a surprisingly small amount of fuel.

"If a car was as fuel-efficient as these black holes, it could theoretically travel over a billion miles on a gallon of gas," said co-author Christopher Reynolds of the University of Maryland, College Park.

The findings explain how black hole engines achieve this extreme efficiency. Some of the gas first attracted to the black holes may be blown away by the energetic activity before it gets too near the black hole, but a significant fraction must eventually approach the event horizon, where it is used with high efficiency to power the jets. The study also implies that matter flows towards the black holes at a steady rate for several million years.

"These black holes are very efficient, but it also takes a very long time to refuel them," Allen said.

This new study also shows the energy transferred to the hot gas by the jets should keep hot gas from cooling, thereby preventing billions of new stars from forming. This would place limits on the growth of the largest galaxies.

These results will appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center, Cambridge, Mass.

For additional information and images from the research, visit:

or

For information about NASA and agency programs, visit:
http://www.nasa.gov/home

- end -

--------------------------------------------------------------------------------


Source: NASA Press Release 06-192
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So does this mean that black holes may expell matter in the form of energy and that in their own way black holes will eventually "burn" themselves out into nothing?

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Posted (IP: Staff) ·

So does this mean that black holes may expell matter in the form of energy and that in their own way black holes will eventually "burn" themselves out into nothing?

Actually that probably does happen. It's known as Hawking Radiation and is due to Quantum Mechanics effects near a Black Hole. It is not something I fully understand so I won't try to explain it.

As far as I understand it this is not what is being said in this article. This is about radiation from material before it falls into the black hole.

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Posted (IP: Staff) ·
NGC 4696 in the Centaurus Galaxy Cluster:
Black Holes Found To Be Green By NASA's Chandra


user posted image
Credit: X-ray: NASA/CXC/KIPAC/S.Allen et al; Radio: NRAO/VLA/G.Taylor; Infrared: NASA/ESA/McMaster Univ./W.Harris

By studying the inner regions of nine elliptical galaxies with Chandra, scientists can now estimate the rate at which gas is falling toward the galaxies' supermassive black holes. These images also allowed them to estimate the power required to produce radio emitting bubbles in the hot X-ray gas.

The composite image of NGC 4696 shows a vast cloud of hot gas (red), surrounding high-energy bubbles 10,000 light years across (blue) on either side of the bright white area around the supermassive black hole. Images of the other galaxies in the study show a similar structure. (The green dots in the image show infrared radiation from star clusters on the outer edges of the galaxy).

user posted image

user posted image

user posted image

Illustration of Black Hole Engine
The first artist's illustration shows a close-up view of a supermassive black hole in a galaxy's center. Gas becomes hotter as it approaches the black hole, turning from red to yellow to white. Most of the gas is swallowed by the black hole, but some is launched in jets away from the black hole at almost the speed of light. The next illustration shows a larger area where gas is first attracted to the black hole, a region about a million times larger than the black hole's event horizon. The final illustration shows enormous cavities -- a hundred times larger -- that have been created in the galaxy's hot gas by jets from the black hole.
(Credit: NASA/CXC/M.Weiss)


Surprisingly, the results indicate that most of the energy released by the infalling gas goes, not into an outpouring of light as is observed in many active galactic nuclei,
Animation of Black Hole in Elliptical Galaxy
but into jets of high-energy particles. Such jets can be launched from a magnetized gaseous disk around the central black hole, and blast away at near the speed of light to create huge bubbles.

An important implication of this work is that the conversion of energy by matter falling toward a black hole is much more efficient than nuclear or fossil fuels. For example, it is estimated that if a car was as fuel-efficient as these black holes, it could theoretically travel more than a billion miles on a gallon of gas!

Source: Chandra Web Site
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Posted (IP: Staff) ·
VLBA Reveals Closest Pair of Supermassive Black Holes


The National Radio Astronomy Observatory press release is reproduced below:

Astronomers using the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope have found the closest pair of supermassive black holes ever discovered in the Universe -- a duo of monsters that together are more than 150 million times more massive than the Sun and closer together than the Earth and the bright star Vega.

user posted image
The VLBA
CREDIT: NRAO/AUI/NSF


"These two giant black holes are only about 24 light-years apart, and that's more than 100 times closer than any pair found before," said Cristina Rodriguez, of the University of New Mexico (UNM) and Simon Bolivar University in Venezuela. Black holes are concentrations of mass with gravity so strong that not even light can escape them.

The black hole pair is in the center of a galaxy called 0402+379, some 750 million light-years from Earth. Astronomers presume that each of the supermassive black holes was once at the core of a separate galaxy, then the two galaxies collided, leaving the black holes orbiting each other. The black holes orbit each other about once every 150,000 years, the scientists say.

"If two black holes like these were to collide, that event would create the type of strong gravitational waves that physicists hope to detect with instruments now under construction," said Gregory Taylor, of UNM. The physicists will need to wait, though: the astronomers calculate that the black holes in 0402+379 won't collide for about a billion billion years.

"There are some things that might speed that up a little bit," Taylor remarked.

An earlier VLBA study of 0402+379, an elliptical galaxy, showed the pair of radio-wave-emitting objects near its core. Further studies using the VLBA and the Hobby-Eberly Telescope in Texas, revealed that the pair of objects is indeed a pair of supermassive black holes.

"We needed the ultra-sharp radio 'vision' of the VLBA, particularly at the high radio frequencies of 22 and 43 GigaHertz, to get the detail needed to show that those objects are a pair of black holes," Taylor said. The VLBA is a continent-wide system of ten radio-telescope antennas. It provides the greatest ability to see fine detail, called resolving power, of any telescope in astronomy.

"Astronomers have thought for a long time that close pairs of black holes should result from galaxy collisions," Rodriguez said. Still, finding them has proven difficult. Until now, the closest confirmed pairs of supermassive black holes were at least 4,500 light-years apart. Pairs of smaller black holes, each only a few times the mass of the Sun, have been found in our own Milky Way Galaxy, but 0402+379 harbors the pair of supermassive black holes that are the closest to each other yet found.

Galactic collisions are common throughout the Universe, and astronomers think that the binary pairs of supermassive black holes that result can have important effects on the subsequent evolution of the galaxies. In a number of predicted scenarios, such giant pairs of black holes will themselves collide, sending gravitational waves out through the Universe. Such gravitational waves could be detected with a proposed joint space mission between NASA and the European Space Agency, the Laser Interferometer Space Antenna.

"Such black-hole collisions undoubtedly are important processes, and we need to understand them. Finding ever-closer pairs of supermassive black holes is the first step in that process. Even finding one such system has dramatically changed our expectations, and informed us about what to look for," Taylor said. Taylor and his collaborators are currently using the VLBA to carry out the largest survey of compact radio-emitting objects ever undertaken, in the hope of finding more such pairs.

Rodriguez and Taylor worked with Robert Zavala of the U.S. Naval Observatory, Allison Peck of the SubMillimeter Array of the Harvard- Smithsonian Center for Astrophysics, Lindsey Pollack of the University of California at Santa Cruz, and Roger Romani of Stanford University. Their results have been accepted for publication in the Astrophysical Journal.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.


Source: NRAO Press Release
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Posted (IP: Staff) ·
Spitzer Reveals Jets Around a Dead Star


Written by Linda Vu, Spitzer Science Center
May 22, 2006


user posted image
NASA/JPL-Caltech/R. Hurt (SSC)

Stellar Jets

This artist concept illustrates jets of material shooting out from the neutron star in the binary system 4U 0614+091. Astronomers using the Spitzer Space Telescope found these remarkable jets, which are streaming into space at nearly the speed of light. Until this observation, astronomers thought that the ability to shoot such continuous jets into space was unique to black holes.

The 4U 0614+091 system contains two stellar corpses, remnants of long-dead stars. The larger one (upper left) is the surviving core of a sun-like star, known as a "white dwarf." The smaller neutron star (lower right, at center of disk) is the dead core of a much more massive star that once exploded in a supernova. Even though the neutron star is tiny compared to the white dwarf it is incredibly dense and is actually about 14 times more massive!

The white dwarf orbits the neutron star similar to the way the Earth orbits the sun. Like a cosmic vacuum cleaner, the neutron star's intense gravity picks up material leaving the white dwarf's atmosphere and collects it into a disk around itself. Known as an "accretion disk," the collected material orbits the neutron star similar to the way rings circle Saturn. The accretion disk is much denser than Saturn's rings, however, and under the influence of the neutron star's immense gravity the inner portions are heated to incredible temperatures.

How the jets around the neutron star are created remains a mystery, but scientists note that accretion disks and intense gravitational fields are characteristics that both neutron stars in binary systems like this one and black holes share. They believe that these traits may be all that is needed to form and fuel the continuous jets of matter.



One of the most mysterious aspects of black holes is their ability to shoot small, steady jets of matter into space near the speed of light. Until the sensitive infrared eyes of NASA's Spitzer Space Telescope recently spotted one of these jets around a nearby neutron star, or super-dense dead star, black holes were the only known objects in the universe with this "talent."

"For years, scientists suspected that something unique to black holes must be fueling the continuous compact jets because we only saw them coming from black hole systems. Now that Spitzer has revealed a steady jet coming from a neutron star in an X-ray binary system, we know that the jets must be fueled by something that both systems share," said Dr. Simone Migliari of the University of California at San Diego. Migliari is the lead author of a paper that was published in the May 20, 2006 issue of Astrophysical Journal Letters.

A neutron star X-ray binary system occurs when a companion star orbits a dead star that is so dense all of its atoms have collapsed into neutrons, hence the name "neutron star." The partner circles the neutron star the same way Earth orbits the Sun. Migliari used Spitzer to study a jet in one such system called 4U 0614+091. In this system, the neutron star is more than 14 times the mass of its orbiting companion.

As the smaller object travels around its massive partner, the neutron star's intense gravity collects the material leaving its stellar companion's atmosphere and creates a disk around itself. The disk of matter, or accretion disk, circles the neutron star similar to the way rings circle Saturn. According to Migliari, accretion disks and intense gravitational fields are characteristics that black holes and neutron stars in X-ray binaries share.

"Our data shows that the presence of an accretion disk and an intense gravitational field may be all we need to form and fuel a compact jet," he said.

Typically, radio telescopes are the tool of choice for observing compact jets around black holes. At radio wavelengths, astronomers can isolate the jet from everything else in the system. However, because the compact jets of a neutron star can be more than 10 times fainter than those of a black hole, using a radio telescope to observe a neutron star's jet would take many hours.

With Spitzer's super-sensitive infrared eyes, Migliari's team detected 4U 0614+091's faint jet in minutes. The infrared telescope also helped astronomers infer details about the jet's geometry. System 4U 0614+091 is located approximately 10,000 light-years away in the constellation Orion.

Other co-authors of this research include: John Tomsick of the University of California at San Diego; Elena Gallo University of California at Santa Barbra, Santa Barbra, Calif.; Gijs Nelemans of the University of Nijmegen in the Netherlands; and Thomas Maccarone, David Russell, and Rob Fender of the University of Southampton in the United Kingdom.

Source: NASA/CalTech - Spitzer- Happenings
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Posted (IP: Staff) ·

Clues to Black Hole Growth Beginning to Add Up

Up to one quarter of the light brightening the universe comes from the massive crush of matter succumbing to the extreme gravity of black holes. Scientists have long understood that amount of light means black holes have the colossal appetite to ingest whole stars and huge amounts of gas. But a critical question has always remained: how they can continue to devour so much?

IPB Image

Image above: Black holes grow by drawing gas from nearby objects such as stars into an accretion disk.

Credit: NASA/CXC/M.Weiss

+ View Larger Image

For the first time, a team of scientists with NASA's Chandra X-ray Observatory led by Jon Miller has uncovered the answer. It's based on the notion that what comes in, must go out.

The In and Out of It

Black holes swell by attracting matter from stars and other nearby objects in a snowballing process called "accretion." The sticky wicket is that generally everything in space is to some degree spinning away from the black hole. The hole's gravity may be strong enough to start peeling off, say, gas from a close star, but the gas still has a slight tendency to travel in the same rotating spin and orbit as the star. The result is that the gas begins to head indirectly toward the black hole; it's always curving just a bit. This penchant to spin is a property called "angular momentum" and means that the black hole is always receiving a healthy supply of it. The curving causes the hot gas to swirl around the hole, forming a glowing, momentum-rich accretion disk.

For the gas to continue spinning into the black hole, the disk needs to shed existing angular momentum to make room for the incoming momentum. Think of it as a sort of cosmic waterwheel driving matter into a hole. This means that the black hole must receive and shed angular momentum in equal amounts just like a waterwheel fills and empties with water to keep turning.

Friction from bumping and rubbing molecules together is one way the gas dissipates angular momentum. But some astrophysicists wonder if friction is really working alone. Figuring out the answer is the challenge that caught the interest of Miller and fellow astrophysicists John Raymond and Danny Steeghs.

"By understanding what makes material fall onto a black hole, we may also learn how it falls onto other important objects," said Steeghs.

The team suspected that friction has a thieving accomplice: magnetic field winds.

The theory is that coiled magnetic fields corkscrew into the spinning accretion disk and whip up a wind blowing at 300 miles per second. The wind provides angular momentum out-flowing into space. The Chandra team thinks momentum lost to both friction and wind balances out the incoming angular momentum, sending gas into the black hole and lighting up the night.

Model Behavior

To prove their theory, the scientists used Chandra to compare the characteristics of a peculiar wind coming from a Milky Way black hole with computer models of the hypothetical magnetic field wind. When Miller began receiving the array of data back from Chandra, he and Raymond were excited by the caliber of what they saw.

IPB Image

Image above: Coiled magnetic fields churn into an accretion disk and produce strong winds.

Credit: NASA/CXC/M.Weiss

+ View Larger Image

"The quality of the data was a big surprise," said Miller. "I met with John Raymond and we looked at a large, printed version of the spectrum in a hallway. We spent the afternoon identifying features and soon realized that we had something very special on our hands."

The information streaming back from Chandra showed that wind from the black hole behaves exactly as the computer models predicted.

This powerful discovery not only proved the scientists right, but also disproved two competing theories and validated three decades of previous scientific speculation in the process.

"In 1973, theorists came up with the idea that magnetic fields could drive the generation of light by black holes," said Raymond. "Now, over 30 years later, we finally may have proof."

For Miller and his cohorts, proving the magnetic field winds exist is an inspiring early step in understanding how black holes grow. "It is certainly not the endpoint," finalized Miller. "There is much work left to do."

Learn more about black holes:

+ World Book Encyclopedia introduces black holes

Charlie Plain

NASA's Chandra X-ray Observatory and John F. Kennedy Space Center

Source: NASA - Exploring the Universe - Stars and Galaxies

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I imagine the basics of black holes are pretty well-known around here. Singularities are the infinitesimal points inside where the mass is concentrated. Event horizons are the point of no return where the gravitational pull becomes too strong for even light to escape. By the no hair theorem black holes are featureless except for three properties: mass, charge, and angular momentum. Of course all black holes have mass but the other two properties may or may not be present. Since angular momentum is conserved and the objects that collapse to form black holes ought to have possessed it, it stands to reason most physical black holes would be rotating. Such black holes are known as Kerr black holes and are a little different than stationary (Schwarschild) black holes. They have singularities that get pulled into a ring shape and they have a spinning elliptical region outside the event horizon called the ergosphere which an enterprising civilization could use to extract energy from the black hole.

But I should get to the point. There's an interesting rapid communication in the current Physical Review D that concerns some interesting possibilities about black holes. You may have heard of a naked singularity--a singularity that isn't hidden from the universe behind an event horizon. Black holes, of course, are singularities surrounded by an event horizon so they don't qualify. It turns out, however, there are solutions to the equations of general relativity that yield what're called axial singularities. The authors calculate that such singularities would actually break up the event horizon of a Kerr black hole, meaning there would be a hole in the horizon that connects the inside and outside of the black hole. Since the Kerr singularity wouldn't be completely shielded from the outside universe by an event horizon, they refer to it as being "half dressed" (i.e. not quite naked but certainly not clothed). These axial singularities would appear as a result of gravitational and/or electromagnetic excitations of the black hole; they would be unstable and the authors suggest that they would be associated with some sort of jet or burst (perhaps the origin of the jet formation associated with black holes).

In other words, this raises the possibility that ephemeral gateways in the event horizons of black holes could form, connecting interior and exterior. Interesting ideas.

astro-ph

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:P I cant say I understand any of the work from the link , but I did read it. The idea of the Axial "SEMI-INFINITE" Singular Lines did not sound like an accurate description of the Theoretical Phenomenon. Smaller thinkers such as my self may require a better depiction.

Now I will go to the Joke section to remove the Squirrel Food from my mind! :wacko:

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Hard going. I cant say anything as I am braindead.

Will read again and hope others come to argue for and against the ideas.

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Posted (IP: Staff) ·
Black Hole Spills Kaleidoscope of Color


Shoes may not come in every color, but space objects do. All objects in space, everything from dust to distant galaxies, give off a rainbow of light - including light our eyes can't see. That's where NASA's Great Observatories come in. Together, they help astronomers see all the shades of the cosmos.

user posted image
Image above: A new false-colored image from NASA's Hubble, Chandra and Spitzer space telescopes shows a giant jet of particles that has been shot out from the vicinity of
a type of supermassive black hole called a quasar.
Image credit: NASA/JPL-Caltech/Yale Univ.


A new false-colored image from NASA's Hubble, Chandra and Spitzer space telescopes demonstrates this principle beautifully. The multi-hued portrait shows a giant jet of particles that has been shot out from the vicinity of a type of supermassive black hole called a quasar. The jet is enormous, stretching across more than 100,000 light-years of space - a size comparable to our own Milky Way galaxy!

Quasars are among the brightest objects in the universe. They consist of supermassive black holes surrounded by turbulent material, which is being heated up as it is dragged toward the black hole. This hot material glows brilliantly, and some of it gets blown off into space in the form of powerful jets.

The jet pictured here is streaming out from the first known quasar, called 3C273, discovered in 1963. A kaleidoscope of colors represents the jet's assorted light waves. X-rays, the highest-energy light in the image, are shown at the far left in blue (the black hole itself is well to the left of the image). The X-rays were captured by Chandra. As you move from left to right, the light diminishes in energy, and wavelengths increase in size. Visible light recorded by Hubble is displayed in green, while infrared light caught by Spitzer is red. Areas where visible and infrared light overlap appear yellow.

Astronomers were able to use these data to solve the mystery of how light is produced is quasar jets. Light is created in a few, very different ways. For example, our sun generates most of its light via a process called fusion, in which hydrogen atoms are combined, causing an explosion of light. In the case of this jet, even the most energetic light was unexpectedly found to be the result of charged particles spiraling through a magnetic field, a process known as synchrotron radiation.

Media contact: Whitney Clavin/JPL
(818) 354-4673


Source: NASA - Exploring the Universe - Stars and Galaxies
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Posted (IP: Staff) ·

Would these lights represent a defined edge of the black holes event horizon?

No, these show material being jetted away from the blackhole. The event horizo would be a tiny object at the centre of the image and at this ditance would be far too small to resolve.

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I saw this and decided to mention about it, this morning. Waspie tries to inform us on many interesting projects, but this one caught my eye. I noticed the angulation in the image, and realized it was a twisting, one-sided jet, left to right.

I quote from Time Magazine, 1966, and it is a lot to read. But not near as time-consuming as my images- 34 of them.

First, I want to mention the term Kelvin-Helmholz instabillity. I looked through Waspie's Cassini thread (wowy), but did not find what I wanted. But, NASA has an image of Saturn, showing curling tracts of cloud material. Also, a wicki picture shows regular clouds doing the same thing.

I also have 34 images of this quasar not clearly the same, but at least similar. The quasi-stellar object issues forth from the AGN of an excited elliptical galaxy. The furthest, outer, distal portion of the jet looks to me like box cars in a pile, with over-turned segments.

Onward-

Quasar 3C 273 is one of the closest, and most luminous active galactic nuclei. Its outflow has been studied in gamma, X-ray, optical, near infrared and radio wavebands. The jet moves at a relativistic speed of 10 % C, and is evidently "one-sided".

Its apparent relativistic boosting may occur as a side-by-side, "galactic bar" type outflow, from near a black hole accretion disk. Such an outflow may involve shock waves and

"Kelvin-Helmholtz" instability, when a material flows in different densities and at different speeds.

A quasar jet may extend hundreds of kiloparsecs from its nucleus, and often radiate mostly X-rays. However, this one has most of its emmision in the near and mid-infrared. The jet column also contains about ten sections, and has a twisting shape. The so-called "inner knots", A and B1, radiate strongly in X-ray, and are more proximal to the core, or nucleus of the quasar. The "outer knots" C1, C2, D1, D2, and H3 radiate mostly in near and mid-infrared. The outer or more distal regions at the end of the jet are areas of slower radio frequencies.

The first observations of 3C 273 in the early 1960s, resulted in the spectra being obtained using the 200 inch Palomar optical telescope. The astronomer, Maartin Schmidt, pondered for several months over the combination of 15% redshifted Balmer series lines of hydrogen, with unusual brightness. It was the extreme luminosity of what was then considered the most disatant object in the known universe, which eventually brought out several different theories.

From Time Magazine, 1966-

"By now, much of the scientific community accepts Astronomer Maarten Schmidt's contention that the faint stars called quasars are the most distant objects ever observed. But challengers remain, and they have by no means given up. Schmidt's colleague, Halton Arp of the Mount Wilson and Palomar observatories, for example, believes that quasars were ejected from odd-looking galaxies that are, by cosmological standards, virtual neighbors to the earth.

Arp worked out his novel theory after compiling an atlas of the "peculiar galaxies" that appear to have been distorted by cataclysmic explosions. Many of these distorted galaxies, he noted, were located at just about the midpoint of a line joining a pair of nearby radio sources. Most of these sources are radio galaxies, but eight have been identified as quasars. Furthermore, filaments of matter from several of the peculiar central galaxies appear to extend out in the direction of the radio sources.

Unknown Cause. It is more than coincidence, says Arp in an article in Science, that so many of the quasars and radio galaxies appear to lie so close to the peculiar galaxies in the sky. The explanation, he believes, is that they were formed from great masses of matter expelled from exploding central galaxies between 10 million and one billion years ago. If they were formed in this manner, he concludes, they must still be relatively close to their parent galaxies, which are located only 30 million to 300 million light-years from the earth. They would not have reached the cosmological distances suggested by Schmidt.

Arp acknowledges that light from the quasars shows a substantially greater red shift than light from the galaxies that he thinks gave them birth. But he is not bothered by the problem; unlike most astronomers he does not believe that the red shift is caused by the speed with which quasars are receding from the earth-a speed that would indicate they are billions of light-years away. Instead, says Arp, the red shift could be caused by an immense quasar gravitational field, by the high velocity of material falling toward the center of quasars that are suffering catastrophic collapse, or by "some as yet unknown cause."

Back to the Drawing Board. Such speculations have caused a stir among astronomers, who are impressed by Arp's statistics. But many are equally impressed by his failure to account for the energy needed to expel quasars and radio galaxies from his collection of "peculiar galaxies." And most point out that he has offered only informed guesses, no scientific evidence that the red shift of quasar light is caused by anything other than their speed of recession. "If Arp is right," says one astronomer, "we have to abandon most of our work of the past 30 years, drop the general theory of relativity and go back to our drawing boards"-something few of Arp's colleagues are yet ready to do."

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Astronomers have looked under the hoods of quasars, the brightest objects in the universe, and found some of the best evidence yet for the black holes that are thought to power them.

The new study, presented today at the meeting of the American Astronomical Society (AAS) High Energy Astrophysics Division in San Francisco, lends further confirmation to the idea that quasars are anchored by supermassive black holes and the flattened disks of material spiraling into them.

Astronomers have puzzled over quasars for decades before deciding each is a very active and developing galaxy most likely containing supermassive black holes that formed billions of years ago. This cosmic yin-yang between the darkest and brightest space objects has made understanding quasars difficult.

Black holes are so dense that nothing, not even light, can escape their gravitational clutches, making them impossible to observe directly. And even though quasars, or quasi-stellar radio sources, are the universe’s most powerful sources of constant light, they are billions of light-years away. So even with the most powerful telescopes they appear as pinpoints of light. On top of that, the dust and gas lit up by a quasar makes seeing inside one a great challenge.

The researchers led by Xinyu Dai and Christopher Kochanek of Ohio State University were only able to view the interior structures of the two quasars, named RXJ1131-1231 and Q2237+0305, when a galaxy lined up between them and the Earth, magnifying their light—a phenomenon called gravitational microlensing. Like a Sumo wrestler rolling over and deforming a soft mat, the weighty galaxy dented, or curved, the fabric of space-time, rerouting and in this case focusing light from the quasars behind it.

The magnification allows astronomers to see quasars that would otherwise have remained invisible.

"Luckily for us, sometimes stars and galaxies act as very high-resolution telescopes," Kochanek said. "Now we're not just looking at a quasar, we're probing the very inside of a quasar and getting down to where the black hole is."

With NASA's Chandra X-Ray Observatory, coupled with measurements from optical telescopes, the astronomers were able to measure the size of the so-called accretion disk inside each quasar, one of which spanned about 14 astronomical units (AU), where one AU is the distance from Earth to the sun.

“It's the first time anyone has measured the size of the disk around one of these black holes,” Kochanek told SPACE.com.

The disks each surrounded an area that was emitting X-rays, a telltale sign that the material at the disk’s center is being heated up as it speeds up prior to falling into the black hole.

The astronomers are currently studying 20 such lensed quasars, and they hope to gather X-ray data on all of them

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Neat how they are getting closer to the black hole itself. Also amazing that now they can detect materials heating up before entering.

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Posted (IP: Staff) ·
Hidden Mass Concentration Near the Center of Starbursting Galaxy M83


The Gemini Observatory press release is reproduced below:

Friday, 13 October 2006

user posted image
Figure 1.

CIRPASS integral field is depicted and superposed on a HST pseudo color optical image of the center of
Messier 83. The rotation center of the galaxy (intruder nucleus) is at the youngest end of the partial ellipse
that describes the positions of the main star forming regions of the giant arc.


user posted image
Figure 2.
Left: radial velocity of the ionized gas, corresponding to the main integral field observed. Note the position
of the optical nucleus at the upper right of the CIRPASS field, the bulge center, and the intruder nucleus inside
the yellow circle. Right: image generated from the continuum in the spectral region of 1.28 microns. The
achieved resolution is 0.6 arcseconds.


Using the near infrared integral field spectrograph CIRPASS at Gemini South, Ruben Diaz and an international team of astronomers, have discovered a previously unknown hidden mass concentration that looks like a second nucleus in the starburst galaxy M83. The mass concentration is located at the youngest end of a giant star forming arc near the galaxy's center (Figure 1). This concentration probably represents the wreckage of the nucleus of the smaller galaxy which is being "swallowed" by M83.

This double nucleus arrangement is also associated with complex kinematics near the galaxy center (Figure 2). The masses of the objects were derived from the kinematics of the ionized gas. The nucleus of the intruder body has an estimated mass of about 16 million times the mass of the Sun, compared to 2 million solar masses for the optical "main" nucleus. The two nuclei are about 100 parsecs apart and are probably harboring black holes. Numerical modeling conducted by the team suggest that the two nuclei would coalesce to form a single massive core in about 60 million years.

Located at about 12 million light-years (3.7 megaparsecs) away, Messier 83 is a nearby grand design galaxy displaying intense star forming activity. This activity is likely the result of a recent merger of an accreted satellite galaxy.

See more details in the paper "Hidden Trigger for the Giant Starburst Arc in M83" by Ruben Diaz et al., The Astrophysical Journal, 2006, in press.


Source: Gemini Observatory press release
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Hidden Mass Concentration Near the Center of Starbursting Galaxy M83

The Gemini Observatory press release is reproduced below:

Friday, 13 October 2006

user posted image

Figure 1.

CIRPASS integral field is depicted and superposed on a HST pseudo color optical image of the center of

Messier 83. The rotation center of the galaxy (intruder nucleus) is at the youngest end of the partial ellipse

that describes the positions of the main star forming regions of the giant arc.

user posted image

Figure 2.

Left: radial velocity of the ionized gas, corresponding to the main integral field observed. Note the position

of the optical nucleus at the upper right of the CIRPASS field, the bulge center, and the intruder nucleus inside

the yellow circle. Right: image generated from the continuum in the spectral region of 1.28 microns. The

achieved resolution is 0.6 arcseconds.

Using the near infrared integral field spectrograph CIRPASS at Gemini South, Ruben Diaz and an international team of astronomers, have discovered a previously unknown hidden mass concentration that looks like a second nucleus in the starburst galaxy M83. The mass concentration is located at the youngest end of a giant star forming arc near the galaxy's center (Figure 1). This concentration probably represents the wreckage of the nucleus of the smaller galaxy which is being "swallowed" by M83.

This double nucleus arrangement is also associated with complex kinematics near the galaxy center (Figure 2). The masses of the objects were derived from the kinematics of the ionized gas. The nucleus of the intruder body has an estimated mass of about 16 million times the mass of the Sun, compared to 2 million solar masses for the optical "main" nucleus. The two nuclei are about 100 parsecs apart and are probably harboring black holes. Numerical modeling conducted by the team suggest that the two nuclei would coalesce to form a single massive core in about 60 million years.

Located at about 12 million light-years (3.7 megaparsecs) away, Messier 83 is a nearby grand design galaxy displaying intense star forming activity. This activity is likely the result of a recent merger of an accreted satellite galaxy.

See more details in the paper "Hidden Trigger for the Giant Starburst Arc in M83" by Ruben Diaz et al., The Astrophysical Journal, 2006, in press.

Source: Gemini Observatory press release

If this section of space, and I mean it's a small section really in the grand scheme of thing shows us just how powerful gravity is, well. When we look at an anomaly that has 16 times the greater mass of our star, that becomes huge! To be within a community of blackholes would deffinitly suggest a build up of mass. That would lead to a lack of mass in a near region, due to the increased mass in another close by. Hense "sucking" more mase to potentialy eject it, to create another galaxy. Maybe created by blackholes. A life and death yet life again cycle. Given the vast amounts of time it would take, but then again what do we truely know about time.

Time for a beer :blink:

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If this section of space, and I mean it's a small section really in the grand scheme of thing shows us just how powerful gravity is, well. When we look at an anomaly that has 16 times the greater mass of our star, that becomes huge! To be within a community of blackholes would deffinitly suggest a build up of mass. That would lead to a lack of mass in a near region, due to the increased mass in another close by. Hense "sucking" more mase to potentialy eject it, to create another galaxy. Maybe created by blackholes. A life and death yet life again cycle. Given the vast amounts of time it would take, but then again what do we truely know about time.

Time for a beer :blink:

the Andomeda galaxy; is actually merging with the milky way galaxy as we speak...nice article ... :tu:

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Posted (IP: Staff) ·

the Andomeda galaxy; is actually merging with the milky way galaxy as we speak...nice article ... :tu:

Not yet it isn't.

Andromeda and the Milky Way are heading towards each other but we have a few billion years before they collide. There is a thread on that here: Collision Course, When galaxies collide

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Posted (IP: Staff) ·
Belching Black Holes


Written by Linda Vu, Spitzer Science Center
October 24, 2006


user posted image
A quasar detected by Spitzer may be about
to expel matter
NASA/JPL-Caltech/M. Polletta (UCSD)


Astronomers using NASA's Spitzer Space Telescope have recently identified two quasars, or supermassive black holes, that may be on the verge of a colossal cosmic "belch."

Scientists have long suspected that when galaxies collide, the supermassive black holes that reside within them gorge on a magnificent "buffet" of dust, gas, and stars. The cosmic feast is provided by violent episodes of star formation triggered in the great galactic clash. Most telescopes cannot detect these feasting black holes because dense clouds of dust and gas kicked up in the galactic collision shroud the objects from view.

However, at some point astronomers suspect that these celestial gluttons do get "full." Once this happens, scientists believe that the black holes let out an enormous belch of energy, strong enough to destroy much of its obscuring surrounding material. Some supermassive black hole belches may even destroy enough material to stop star formation in its host galaxy.

According to Dr. Maria del Carmen Polletta of the University of California at San Diego, in La Jolla, Calif., the recently identified supermassive black holes are heavily cloaked in dense dust clouds, and may be on the verge of such a cosmic burp. Polletta is the lead author of a paper on the topic. Her research was published in the May 2006 issue of Astrophysical Journal.

"Black holes always release a lot of energy as they accrete [or gobble up] matter," she says.

As matter falls into a black hole, energy is emitted. The more a black hole eats, the more energy is released. Astronomers suspect that at some point black holes will emit so much energy that the surrounding dust will be blown away or destroyed. Scientists measure this emitted energy in "luminosity." Polletta notes that the most luminous black hole in her study is about three billion times more massive than our Sun, and can gobble up about 68 solar masses of material per year, or more than the mass of one Sun per week.

"The dust surrounding an obscured black hole can complicate calculations of luminosity because dust actually absorbs some of the emitted energy and reradiates it in the infrared," says Polletta.

Using Spitzer's infrared eyes, Polletta and her team were able to measure the amount of energy being absorbed by dust, and thus accurately predict the black hole's luminosity. With NASA's Chandra X-ray Observatory, team members were also able to discern the amount of dust surrounding the object.

"The luminosity of the sources in my research are so high that dust should not survive," says Polletta. This is why she suspects that the black holes in her study are about to belch.

Although this type of phenomena has been predicted in astronomical models, Polletta is careful to note that there is still a lot that astronomers don't know about character of heavily obscured black holes.

"Black holes that are this heavily obscured and with this luminosity are very difficult to find and have not been extensively studied," says Polletta. "The belch of a black hole has never been verified with observations, so the explosion may not happen."

"The role that supermassive black holes play in the development of a galaxy is still unclear, there are still a lot of missing pieces. What we are seeing here is a very specific moment in the life of a black hole," she adds. "According to astronomical models, black holes at this luminosity should destroy their surrounding material pretty soon."

The sources were detected in observations obtained by the Spitzer Wide area Infrared Extragalactic (SWIRE) Legacy project. The SWIRE Legacy project uses Spitzer's super sensitive infrared eyes to understand how material from the big bang developed into our modern galactic neighbors.

According to Polletta, who is a member of the SWIRE team, out of the millions of supermassive black holes detected by SWIRE, the objects in her study are the most luminous. She adds that her sources are among the most dust-obscured black holes ever studied.


Source: NASA/CalTech - Spitzer- Happenings
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Posted (IP: Staff) ·
Host Galaxy Cluster to Largest Known Radio Eruption


News Release Number: STScI-2006-51

user posted image


This is a composite image of galaxy cluster MS0735.6+7421, located about 2.6 billion light-years away in the constellation Camelopardus. The image represents three views of the region that astronomers have combined into one photograph. The optical view of the galaxy cluster, taken by the Hubble Space Telescope's Advanced Camera for Surveys in February 2006, shows dozens of galaxies bound together by gravity. Diffuse, hot gas with a temperature of nearly 50 million degrees permeates the space between the galaxies. The gas emits X-rays, seen as blue in the image taken with the Chandra X-ray Observatory in November 2003. The X-ray portion of the image shows enormous holes or cavities in the gas, each roughly 640 light-years in diameter — nearly seven times the diameter of the Milky Way. The cavities are filled with charged particles gyrating around magnetic field lines and emitting radio waves shown in the red portion of image taken with the Very Large Array telescope in New Mexico in October 2004. The cavities were created by jets of charged particles ejected at nearly light speed from a supermassive black hole weighing nearly a billion times the mass of our Sun lurking in the nucleus of the bright central galaxy. The jets displaced more than one trillion solar masses worth of gas. The power required to displace the gas exceeded the power output of the Sun by nearly ten trillion times in the past 100 million years.

Object Name: MS 0735.6+7421

Image Type: Astronomical/Illustration

Hubble and Chandra Image Credit: NASA, ESA, CXC, STScI, and B. McNamara (University of Waterloo)

Very Large Array Telescope Image Credit: NRAO, and L. Birzan and team (Ohio University)

Source: HubbleSite - Newsdesk
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Spinning Black Hole Pushes the Limit


The Harvard-Smithsonian Center for Astrophysics press release is reproduced below:

Release No.: 06-30
For Release: 9:30 a.m. EST, Monday, November 20, 2006

Spinning Black Hole Pushes the Limit


IPB Image

This illustration shows a swirling disk of accreting gas orbiting a black hole, with the bulk of the X-rays pouring out of the inner, white-shaded region of the disk. One remarkable prediction of Einstein's relativity theory is the existence of a smallest radius for the disk, inside of which the gas suddenly plunges into the hole with no time to radiate away its energy.

For the non-spinning black hole shown at left, this inner radius is large, which leaves a big dark hole cut out of the center of the hot disk of gas. For the fast-spinning black hole shown at right, the gas can orbit very near the event horizon, and thus only a small portion of the inner disk is missing. Therefore, the radius of the hole is a direct measure of the spin.
Credit: NASA/NASA/CXC/M.Weiss


IPB Image

This illustration shows a swirling disk of accreting gas orbiting a fast-spinning black hole, with the bulk of the X-rays pouring out of the inner, white-shaded region of the disk. One remarkable prediction of Einstein's relativity theory is the existence of a smallest radius for the disk, inside of which the gas suddenly plunges into the hole with no time to radiate away its energy. The distance from this innermost stable orbit to the black hole center depends on spin. The greater the spin, the closer the matter can orbit "safely." Because the inner edge of the disk is so close in the case of the fast-spinning black hole, the gas there is extraordinarily hot and bright. The radius of the hole -- which is a direct measure of the spin -- is determined by fitting the continuous X-ray spectrum recorded by an X-ray spectrometer (which is completely analogous to the spectrum of sunlight dispersed by a prism) to a model of the hot disk that includes all the effects of relativity.
Credit: David A. Aguilar (CfA)


Cambridge, MA - The existence of black holes is perhaps the most fascinating prediction of Einstein's General Theory of Relativity. When any mass, such as a star, becomes more compact than a certain limit, its own gravity becomes so strong that the object collapses to a singular point, a black hole. In the popular mind, this immense gravity well is a place where strange things happen. And now, a Center for Astrophysics-led team has measured a stellar-mass black hole spinning so rapidly - turning more than 950 times per second - that it pushes the predicted speed limit for rotation.

"I would say that this regime of gravity is as far from direct experience and knowing as the subatomic world itself," says CfA astronomer Jeffrey McClintock.

Applying a technique to measure spin developed jointly by McClintock and CfA astrophysicist Ramesh Narayan, the team used NASA's Rossi X-ray Timing Explorer satellite data to provide the most direct determination yet of black hole spin.

McClintock and Narayan led an international group consisting of Rebecca Shafee, Harvard University Physics Department; Ronald Remillard, Kavli Center for Astrophysics and Space Research, MIT; Shane Davis, University of California, Santa Barbara, and Li-Xin Li, Max-Planck Institute for Astrophysics, Germany, in this research. The results are published in today's issue of the Astrophysical Journal.

"We now have accurate values for the spin rates of three black holes," says McClintock. "The most exciting is our result for the microquasar GRS1915+105, which has a spin that is between 82% and 100% of the theoretical maximum value."

"This result has major implications for explaining how black holes emit jets, for modeling possible sources of gamma-ray bursts, and for the detection of gravitational waves," says theorist Narayan.

Why do astronomers care about spin?

"In astronomy, a black hole is completely described by just two numbers that specify its mass and how rapidly it is rotating," says McClintock. "We know of nothing else this simple except for a fundamental particle like an electron or a quark."

Although astronomers have been successful at measuring black hole mass, they have found it much more difficult to measure the second fundamental parameter of a black hole, its spin.

"Indeed, until this year, there was no credible estimate of spin for any black hole," says Narayan.

A black hole's gravity is so strong that, as the black hole spins, it drags the surrounding space along. The edge of this spinning hole is called the event horizon. Any material crossing the event horizon is pulled into the black hole.

"The black hole spin frequency we measured is the rate at which space-time is spinning, or is being dragged, right at the black hole's event horizon," says Narayan.

The high-speed black hole, GRS 1915, is the most massive of the 20 X-ray binary black holes for which masses are presently known, weighing about 14 times as much as the Sun. It is well known for unique properties such as ejecting jets of matter at nearly the speed of light and rapid variations in its X-ray emission.

Over the last few decades, dozens of black holes have been discovered in X-ray binary systems. An X-ray binary is a system in which two objects orbit around each other, with gas from one - a normal star like the Sun - being transferred steadily to the other - in this case, a black hole. The gas spirals onto the black hole by a process called accretion. As it spirals in, it heats up to millions of degrees and radiates X-rays. The team used the X-ray spectrum of the black hole's accretion disk to determine its spin.

The technique is based on a key prediction of relativity theory: gas that accretes onto a black hole radiates only down to a certain radius that lies outside the black hole - outside its event horizon. Inside this radius, the gas falls into the hole too quickly to produce much radiation. The critical radius depends on the black hole spin, so measuring this radius provides a direct estimate of the spin. The smaller the radius is, the hotter the X-rays which are emitted from the disk. The temperature of the X-rays, coupled with the X-ray brightness, gives the radius which, in turn, gives the black hole's spin rate.

"It is really cool to be able to measure something this fundamental," says Rebecca Shafee, who is a graduate student in the Physics Department at Harvard University. "Our method is very simple in concept and easy to understand. We are really lucky to have powerful X-ray observatories such as the Rossi X-ray Timing Explorer in space and telescopes on Earth to carry out the measurements we need."

The search for the cause of gamma-ray bursts, which can be, for a moment, the brightest flash in the universe, may be helped by the team's results. Theoretical astrophysicist Stan Woosley of the University of California, Santa Cruz, has modeled gamma-ray bursts based on the collapse of a massive star. These models, however, depend on the existence of black holes with very high spin, which until now had never been confirmed.

"This is extremely important," Woosley says. "I had no idea such measurements could be made."

The paper concludes that GRS 1915 and the other two black holes studied by the team were born with their high spins. That is, the collapsing core of the original massive star poured its angular momentum down into the black hole.

"Ever since the community figured out many years ago how to measure black hole mass, measuring spin has been the holy grail in this field," says McClintock. "The technique we used on GRS 1915 can be applied to a number of other black hole X-ray binaries. We cannot wait to see what we find!'"

"One of our fond hopes is that the black hole systems that we are studying will also be studied by other groups using their favorite methods of measuring spin," says Narayan. "Once these other methods are developed further and become more reliable, cross-comparison of results from the different methods would be most interesting."

More information is available at http://www.nasa.gov/vision/universe/starsg..._blackhole.html.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Source: CfA Press Release
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Posted (IP: Staff) ·
No matter their size black holes "feed" in the same way


The Particle Physics and Astronomy Research Council (PPARC) press release is reproduced below:

Research by UK astronomers, published today in Nature (7th December 2006) reveals that the processes at work in black holes of all sizes are the same and that supermassive black holes are simply scaled up versions of small Galactic black holes.

IPB Image
Image - An X-ray binary system consisting of an accreting black hole and a binary star.
Credit: R Hynes


For many years astronomers have been trying to understand the similarities between stellar-mass sized Galactic black hole systems and the supermassive black holes in active galactic nuclei (AGN). In particular, do they vary fundamentally in the same way, but perhaps with any characteristic timescales being scaled up in proportion to the mass of the black hole. If so, the researchers proposed, we could determine how AGN should behave on cosmological timescales by studying the brighter and much faster galactic systems.

Professor Ian McHardy, from the University of Southampton, heads up the research team whose findings are published today (along with colleagues Dr Elmar Koerding, Dr Christian Knigge, Professor Rob Fender and Dr Phil Uttley, currently working at the University of Amsterdam). Their observations were made using data from NASA's Rossi X-ray Timing Explorer and XMM Newton's X-ray Observatory.

Professor McHardy comments, "By studying the way in which the X-ray emission from black hole systems varies, we found that the accretion or 'feeding' process - where the black hole is pulling in material from its surroundings - is the same in black holes of all sizes and that AGN are just scaled-up Galactic black holes. We also found that the way in which the X-ray emission varies is strongly correlated with the width of optical emission lines from black hole systems."

He adds, "These observations have important implications for our understanding of the different types of AGN, as classified by the width of their emission lines. Thus narrow line Seyfert galaxies, which are often discussed as being unusual, are no different to other AGN; they just have a smaller ratio of mass to accretion rate."

IPB Image
Image - An Artist's impression of an intermediate sized black hole, which exist in the heart of spiral galaxies throughout the Universe.
Credit: NASA Goddard


The research shows that the characteristic timescale changes linearly with black hole mass, but inversely with the accretion rate (when measured relative to the maximum possible accretion rate). This result means that the accretion process is the same in black holes of all sizes. By measuring the characteristic timescale and the accretion rate, the team argues this simple relationship can help determine black hole masses where other methods are very difficult, for example in obscured AGN or in the much sought after intermediate mass black holes.

Professor McHardy continues: "Accretion of matter into a black hole produces strong X-ray emission from very close to the black hole itself. So, studying the way in which the X-ray emission varies with time, known as the X-ray lightcurves, provides one of the best ways of understanding the behaviour of black holes.

It has been known for over two decades that characteristic timescales can be seen in the X-ray lightcurves of Galactic black hole systems. The timescales are short (< second) and so can be found in short observations. However to find the equivalent timescales in AGN is much harder as we must observe for months or years."

Notes

The paper 'Active galactic nuclei as scaled-up Galactic black holes' by Professor Ian McHardy, Dr Elmar Koerding, Dr Christian Knigge, Professor Rob Fender of the University of Southampton (UK) and Dr Phil Uttley of the University of Amsterdam, is published in Nature today (7 December) pp 730-732.

Further information

Preliminary work by Professor McHardy in 1988 indicated that a similar characteristic timescale was present in the AGN NGC5506, but high-quality, long timescale monitoring observations, needed to measure the timescale accurately, were not possible until the launch of the NASA Rossi X-ray Timing Explorer in 1995. Since that time, a number of groups around the world, including one at the University of Southampton, have been making suitable observations. Combined with shorter timescale observations, for example with the ESA XMM-Newton X-ray Observatory, these observations have now enabled characteristic timescales to be found in over a dozen AGN.

A rough linear scaling of characteristic timescale with black hole mass was soon confirmed but it was clear that, for a given black hole mass, there was a large spread in characteristic timescale. The present paper shows that the spread is entirely accounted for by a spread in accretion rate rather than by any other parameter such as black hole spin. The origin of the characteristic timescale is not known, but it is suspected that it might be associated with the location of the inner edge of the accretion disc, close to the black hole. With higher accretion rates, this edge may be pushed closer towards the black hole, resulting in shorter characteristic timescales.

It has also been known for many years that the optical emission lines in AGN are narrower in AGN which are 'more variable'. However this observation has never previously been properly quantified or explained.

In their paper, the team show that the width of the lines is correlated very strongly with the characteristic X-ray timescales. "Using some basic physical assumptions about the gas which emits the emission lines, and some very simple mathematics, we showed that the observed relationship between line width and characteristic timescale is exactly what is expected, as long as the characteristic timescale is proportional to the ratio of the black hole mass and accretion rate,' says Professor McHardy. 'Our optical observations provide very strong confirmation that the characteristic timescale which links large and small black holes is just proportional to the ratio of the black hole mass to accretion rate. So AGN really are just scaled-up galactic black holes."

The work was supported by PPARC.

Dr Uttley, who obtained his PhD from the University of Southampton under the supervision of Professor McHardy, will be returning to the University of Southampton as a lecturer in February 2007.


About PPARC


Source: PPARC News Release
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