CASTRO Simulations reveal an unusual death for ancient stars

This image is a slice through the interior of a supermassive star of 55,500 solar masses along the axis of symmetry. 

It shows the inner helium core in which nuclear burning is converting helium to oxygen, powering various fluid instabilities (swirling lines). 

This "snapshot" from a CASTRO simulation shows one moment a day after the onset of the explosion, when the radius of the outer circle would be slightly larger than that of the orbit of the Earth around the sun. 

Visualizations were done in VisIT. 

Credit: Ken Chen, University of California at Santa Cruz

Certain primordial stars, those 55,000 and 56,000 times the mass of our Sun, or solar masses, may have died unusually.

In death, these objects, among the Universe's first-generation of stars, would have exploded as supernovae and burned completely, leaving no remnant black hole behind.

Astrophysicists at the University of California, Santa Cruz (UCSC) and the University of Minnesota came to this conclusion after running a number of supercomputer simulations at the US Department of Energy's (DOE's) National Energy Research Scientific Computing Center (NERSC) and Minnesota Supercomputing Institute at the University of Minnesota.

They relied extensively on CASTRO, a compressible astrophysics code developed at DOE's Lawrence Berkeley National Laboratory's (Berkeley Lab's) Computational Research Division (CRD).

Their findings were recently published in Astrophysical Journal (ApJ).

First-generation stars are especially interesting because they produced the first heavy elements, or chemical elements other than hydrogen and helium.

In death, they sent their chemical creations into outer space, paving the way for subsequent generations of stars, solar systems and galaxies.

With a greater understanding of how these first stars died, scientists hope to glean some insights about how the Universe, as we know it today, came to be.

"We found that there is a narrow window where supermassive stars could explode completely instead of becoming a supermassive black hole, no one has ever found this mechanism before," says Ke-Jung Chen, a postdoctoral researcher at UCSC and lead author of the ApJ paper.

"Without NERSC resources, it would have taken us a lot longer to reach this result."

"From a user perspective, the facility is run very efficiently and it is an extremely convenient place to do science."

More information: Astrophysical Journal, iopscience.iop.org/0004-637X/790/2/162

Monster Black Hole discovered in centre of Dwarf Galaxy

Astronomers have just discovered the smallest known galaxy that harbours a huge, supermassive black hole at its core.

The relatively nearby dwarf galaxy may house a supermassive black hole at its heart equal in mass to about 21 million suns.

The discovery suggests that supermassive black holes may be far more common than previously thought.

A supermassive black hole millions to billions of times the mass of the sun lies at the heart of nearly every large galaxy like the Milky Way.

These monstrously huge black holes have existed since the infancy of the universe, some 800 million years or so after the Big Bang.

Scientists are uncertain whether dwarf galaxies might also harbour supermassive black holes.

"Dwarf galaxies usually refer to any galaxy less than roughly one-fiftieth the brightness of the Milky Way," said lead study author Anil Seth, an astronomer at the University of Utah in Salt Lake City.

These galaxies span only several hundreds to thousands of light-years across, much smaller than the Milky Way's 100,000-light-year diameter, and they "are much more abundant than galaxies like the Milky Way," Seth said.

The researchers investigated a rarer kind of dwarf galaxy known as an ultra-compact dwarf galaxy; such galaxies are among the densest collections of stars in the universe.

"These are found primarily in galaxy clusters, the cities of the universe," Seth told reporters

This image shows a huge galaxy, M60, with the small dwarf galaxy that is expected to eventually merge with it.

Credit: NASA /Space Telescope Science Institute /European Space Agency

Now, Seth and his colleagues have discovered that an ultra-compact dwarf galaxy may possess a supermassive black hole, which would make it the smallest galaxy known to contain such a giant.

The astronomers investigated M60-UCD1, the brightest ultra-compact dwarf galaxy currently known, using the Gemini North 8-meter optical-and-infrared telescope on Hawaii's Mauna Kea volcano and NASA's Hubble Space Telescope. M60-UCD1 lies about 54 million light-years away from Earth.

The dwarf galaxy orbits M60, one of the largest galaxies near the Milky Way, at a distance of only about 22,000 light-years from the larger galaxy's center, "closer than the sun is to the center of the Milky Way," Seth said.

The scientists calculated the size of the supermassive black hole that may lurk inside M60-UCD1 by analyzing the motions of the stars in that galaxy, which helped the researchers deduce the amount of mass needed to exert the gravitational field seen pulling on those stars.

For instance, the stars at the center of M60-UCD1 zip at speeds of about 230,000 mph (370,000 km/h), much faster than stars would be expected to move in the absence of such a black hole.

This illustration depicts the supermassive black hole located at the center of the very dense galaxy M60-UCD1. 

It may weigh 21 million times the mass of our sun.

Credit: NASA, ESA, D. Coe, G. Bacon (STScI)

The supermassive black hole at the core of the Milky Way has a mass of about 4 million suns, taking up less than 0.01 percent of the galaxy's estimated total mass, which is about 50 billion suns.

In comparison, the supermassive black hole that may lie in the core of M60-UCD1 appears five times larger than the one in the Milky Way, and also seems to make up about 15 percent of the dwarf galaxy's mass, which is about 140 million suns.

"That is pretty amazing, given that the Milky Way is 500 times larger and more than 1,000 times heavier than the dwarf galaxy M60-UCD1," Seth said in a statement.

Mysterious quasar sequence explained

A growing black hole, called a Quasar, can be seen at the center of a faraway galaxy in this artist's concept. 

Credit: NASA/JPL-Caltech

Quasars are supermassive black holes that live at the center of distant massive galaxies.

They shine as the most luminous beacons in the sky across the entire electromagnetic spectrum by rapidly accreting matter into their gravitationally inescapable centers.

Yue Shen

New work from Carnegie's Hubble Fellow Yue Shen and Luis Ho of the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University solves a quasar mystery that astronomers have been puzzling over for 20 years.

Their work, published in the September 11 issue of Nature, shows that most observed quasar phenomena can be unified with two simple quantities: one that describes how efficiently the hole is being fed, and the other that reflects the viewing orientation of the astronomer.

Luis Ho

Quasars display a broad range of outward appearances when viewed by astronomers, reflecting the diversity in the conditions of the regions close to their centers, but despite this variety, quasars have a surprising amount of regularity in their quantifiable physical properties, which follow well-defined trends (referred to as the "main sequence" of quasars) discovered more than 20 years ago.

Shen and Ho solved a two-decade puzzle in quasar research: What unifies these properties into this main sequence?

Using the largest and most-homogeneous sample to date of over 20,000 quasars from the Sloan Digital Sky Survey (SDSS), combined with several novel statistical tests, Shen and Ho were able to demonstrate that one particular property related to the accretion of the hole, called the Eddington ratio, is the driving force behind the so-called main sequence.

The Eddington Ratio

The Eddington ratio describes the efficiency of matter fueling the black hole, the competition between the gravitational force pulling matter inward and the luminosity driving radiation outward.

This push and pull between gravity and luminosity has long been suspected to be the primary driver behind the so-called main sequence, and their work at long last confirms this hypothesis.

Of additional importance, they found that the orientation of an astronomer's line-of-sight when looking down into the black hole's inner region plays a significant role in the observation of the fast-moving gas innermost to the hole, which produces the broad emission lines in quasar spectra.

This changes scientists' understanding of the geometry of the line-emitting region closest to the black hole, a place called the broad-line region: the gas is distributed in a flattened, pancake-like configuration.

Going forward, this will help astronomers improve their measurements of black hole masses for quasars.

New work solves a quasar mystery that astronomers have been puzzling over for 20 years. 

It shows that most observed quasar phenomena can be unified with two simple quantities: one that describes how efficiently the hole is being fed, and the other that reflects the viewing orientation of the astronomer.

This graph shows the distribution of about 20,000 luminous Sloan Digital Sky Survey (SDSS) quasars in the two-dimensional space of broad line width versus FeII strength, colour-coded by the strength of the narrow [OIII] line emission.

The strong horizontal trend is the main sequence of quasars driven by the efficiency of the black hole accretion, while the vertical spread of broad line width is largely due to our viewing angle to the inner region of the quasar. 

Credit: Yue Shen

"Our findings have profound implications for quasar research. This simple unification scheme presents a pathway to better understand how supermassive black holes accrete matter and interplay with their environments," Shen said.

"And better black hole mass measurements will benefit a variety of applications in understanding the cosmic growth of supermassive black holes and their place in galaxy formation," Ho added.

More information: The diversity of quasars unified by accretion and orientation, Nature, dx.doi.org/10.1038/nature13712

NASA NuSTAR: Rare blurring of Black Hole X-Ray light

An artist’s impression of a supermassive black hole and its surroundings. 

The regions around supermassive black holes shine brightly in X-rays. 

Some of this radiation comes from a surrounding disk, and most comes from the corona, pictured here as the white light at the base of a jet. 

This is one possible configuration for the Mrk 335 corona, as its actual shape is unclear. 

Credit: NASA-JPL / Caltech

NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) has captured an extreme and rare event in the regions immediately surrounding a supermassive black hole.

A compact source of X-rays that sits near the black hole, called the corona, has moved closer to the black hole over a period of just days.

"The corona recently collapsed in toward the black hole, with the result that the black hole's intense gravity pulled all the light down onto its surrounding disk, where material is spiraling inward," said Michael Parker of the Institute of Astronomy in Cambridge, United Kingdom, lead author of a new paper on the findings appearing in the Monthly Notices of the Royal Astronomical Society.

As the corona shifted closer to the black hole, the gravity of the black hole exerted a stronger tug on the X-rays emitted by it.

The result was an extreme blurring and stretching of the X-ray light. Such events had been observed previously, but never to this degree and in such detail.

Supermassive black holes are thought to reside in the centers of all galaxies. Some are more massive and rotate faster than others.

The black hole in this new study, referred to as Markarian 335, or Mrk 335, is about 324 million light-years from Earth in the direction of the Pegasus constellation.

It is one of the most extreme of the systems for which the mass and spin rate have ever been measured. The black hole squeezes about 10 million times the mass of our Sun into a region only 30 times the diameter of the Sun, and it spins so rapidly that space and time are dragged around with it.

This plot of data captured by NASA's Nuclear Spectroscopic Telescope Array (NuSTAR), shows X-ray light streaming from regions near a supermassive black hole known as Markarian 335. 

Credit: NASA

Even though some light falls into a supermassive black hole never to be seen again, other high-energy light emanates from both the corona and the surrounding accretion disk of superheated material.

Though astronomers are uncertain of the shape and temperature of coronas, they know that they contain particles that move close to the speed of light.

NASA's Swift satellite has monitored Mrk 335 for years, and recently noted a dramatic change in its X-ray brightness.

In what is called a target-of-opportunity observation, NuSTAR was redirected to take a look at high-energy X-rays from this source in the range of 3 to 79 kiloelectron volts.

This particular energy range offers astronomers a detailed look at what is happening near the event horizon, the region around a black hole from which light can no longer escape gravity's grasp.

Follow-up observations indicate that the corona is still in this close configuration, months after it moved.

Researchers don't know whether and when the corona will shift back. What's more, the NuSTAR observations reveal that the grip of the black hole's gravity pulled the corona's light onto the inner portion of its superheated disk, better illuminating it.

Almost as if somebody had shone a flashlight for the astronomers, the shifting corona lit up the precise region they wanted to study.

The new data could ultimately help determine more about the mysterious nature of black hole coronas. In addition, the observations have provided better measurements of Mrk 335's furious relativistic spin rate.

Relativistic speeds are those approaching the speed of light, as described by Albert Einstein's theory of relativity.

"We still don't understand exactly how the corona is produced or why it changes its shape, but we see it lighting up material around the black hole, enabling us to study the regions so close in that effects described by Einstein's theory of general relativity become prominent," said NuSTAR Principal Investigator Fiona Harrison of the California Institute of Technology (Caltech) in Pasadena.

"NuSTAR's unprecedented capability for observing this and similar events allows us to study the most extreme light-bending effects of general relativity."

More information: "Black hole spin and size of the X-ray-emitting region(s) in the Seyfert 1.5 galaxy ESO 362-G18," B. Agís-González, G. Miniutti, E. Kara, A. C. Fabian, M. Sanfrutos, G. Risaliti, S. Bianchi, N. L. Strotjohann, R. D. Saxton and M. L. Parker, Monthly Notices of the Royal Astronomical Society, Oxford University Press, in press: mnras.oxfordjournals.org/content/443/4/2862

Fermi bubbles defy explanation, Despite extensive analysis

This artist's representation shows the Fermi bubbles towering above and below the galaxy. 

Credit: NASA's Goddard Space Flight Center

Scientists from Stanford University and the Department of Energy's SLAC National Accelerator Laboratory have analyzed more than four years of data from NASA's Fermi Gamma-ray Space Telescope, along with data from other experiments, to create the most detailed portrait yet of two towering bubbles that stretch tens of thousands of light-years above and below our galaxy.

The bubbles, which shine most brightly in energetic gamma rays, were discovered almost four years ago by a team of Harvard astrophysicists led by Douglas Finkbeiner who combed through data from Fermi's main instrument, the Large Area Telescope (FGST).

The new portrait, described in a paper that has been accepted for publication in The Astrophysical Journal, reveals several puzzling features, said Dmitry Malyshev, a postdoctoral researcher at the Kavli Institute for Particle Astrophysics and Cosmology who co-led on the analysis.

For example, the outlines of the bubbles are quite sharp, and the bubbles themselves glow in nearly uniform gamma rays over their colossal surfaces, like two 30,000-light-year-tall incandescent bulbs screwed into the center of the galaxy.

Their size is another puzzle. The farthest reaches of the Fermi bubbles boast some of the highest energy gamma rays, but there's no discernible cause for them that far from the galaxy.

Finally, although the parts of the bubbles closest to the galactic plane shine in microwaves as well as gamma rays, about two-thirds of the way out the microwaves fade and only gamma rays are detectable.

Not only is this different from other galactic bubbles, but it makes the researchers' work that much more challenging, said Malyshev's co-lead, KIPAC postdoctoral researcher Anna Franckowiak.

"Since the Fermi bubbles have no known counterparts in other wavelengths in areas high above the galactic plane, all we have to go on for clues are the gamma rays themselves," she said.

What Made The Bubbles?
Soon after the initial discovery theorists jumped in, offering several explanations for the bubbles' origins.

For example, they could have been created by huge jets of accelerated matter blasting out from the supermassive black hole at the center of our galaxy.

Or they could have been formed by a population of giant stars, born from the plentiful gas surrounding the black hole, all exploding as supernovae at roughly the same time.

"There are several models that explain them, but none of the models is perfect," Malyshev said. "The bubbles are rather mysterious."

Creating the portrait wasn't easy.

"It's very tricky to model," said Franckowiak. "We had to remove all the foreground gamma-ray emissions from the data before we could clearly see the bubbles."

From the vantage point of most Earth-bound telescopes, all but the highest-energy gamma rays are completely screened out by our atmosphere.

It wasn't until the era of orbiting gamma-ray observatories like Fermi that scientists discovered how common extra-terrestrial gamma rays really are.

Pulsars, supermassive black holes in other galaxies and supernovae are all gamma rays point sources, like distant stars are point sources of visible light, and all those gamma rays had to be scrubbed from the Fermi data.

Hardest to remove were the galactic diffuse emissions, a gamma ray fog that fills the galaxy from cosmic rays interacting with interstellar particles.

"Subtracting all those contributions didn't subtract the bubbles," Franckowiak said. "The bubbles do exist and their properties are robust."

In other words, the bubbles don't disappear when other gamma-ray sources are pulled out of the Fermi data, in fact, they stand out quite clearly.

Franckowiak says more data is necessary before they can narrow down the origin of the bubbles any further.

"What would be very interesting would be to get a better view of them closer to the galactic center," she said, "but the galactic gamma ray emissions are so bright we'd need to get a lot better at being able to subtract them."

Fermi is continuing to gather the data Franckowiak wants, but for now, both researchers said, there are a lot of open questions.

NASA NuSTAR: Celebrating two years of science in space

Artist's concept of NuSTAR on orbit.

NuSTAR has a 10-m (30') mast that deploys after launch to separate the optics modules (right) from the detectors in the focal plane (left). 

The spacecraft, which controls NuSTAR's pointings, and the solar panels are with the focal plane. 

NuSTAR has two identical optics modules to increase sensitivity. The background is an image of the Galactic center obtained with the Chandra X-ray Observatory. 

Credit: NASA/JPL-Caltech

NASA's Nuclear Spectroscopic Telescope Array (NuSTAR), a premier black-hole hunter among other talents, has finished up its two-year prime mission, and will be moving onto its next phase, a two-year extension.

"It's hard to believe it's been two years since NuSTAR launched," said Fiona Harrison, the mission's principal investigator at the California Institute of Technology in Pasadena.

"We achieved all the mission science objectives and made some amazing discoveries I never would have predicted two years ago."

In this new chapter of NuSTAR's life, it will continue to examine the most energetic objects in space, such as black holes and the pulsating remains of dead stars.

In addition, outside observers, astronomers not on the NuSTAR team, will be invited to compete for time on the telescope.

"NuSTAR will initiate a general observer program, which will start execution next spring and will take 50 percent of the observatory time," said Suzanne Dodd, the NuSTAR project manager at NASA's Jet Propulsion Laboratory in Pasadena, California.

"We are very excited to see what new science the community will propose to execute with NuSTAR."

NuSTAR blasted into space above the Pacific Ocean on June 13, 2012, with the help of a plane that boosted the observatory and its rocket to high altitudes.

After a 48-day checkout period, the telescope began collecting X-rays from black holes, supernova remnants, galaxy clusters and other exotic objects.

With its long mast - the length of a school bus, NuSTAR has a unique design that allows it to capture detailed data in the highest-energy range of X-rays, the same type used by dentists.

It is the most sensitive high-energy X-ray mission every flown.

In its prime mission, NuSTAR made the most robust measurements yet of the mind-bending spin rate of black holes and provided new insight into how massive stars slosh around before exploding.

Other observations include: the discovery of a highly magnetized neutron star near the center of our Milky Way galaxy, measurements of luminous active black holes enshrouded in dust, and serendipitous discoveries of supermassive black holes.

How much of the universe is black holes?

Supermassive black holes are enormously dense objects buried at the hearts of galaxies. 

Credit: NASA/JPL-Caltech

We all fear black holes, but how many of them are there out there, really?

Between the stellar mass black holes and the supermassive ones, just how much of our Universe is black holes?

There are two kinds of black holes in the Universe that we know of: There's stellar mass black holes, formed from massive stars, and a supermassive black holes which lives at the hearts of galaxies.

About 1 in a 1000 stars have enough mass to become a black hole when they die. Our Milky Way has 100 billion stars, this means it could have up to 100 million stellar mass black holes.

As there are hundreds of billions of galaxies in the observable Universe, there are lots, lots more out there.

In fact, the math suggests there's a new black hole forming every second or so. So just to recap, the entire Universe is about 1/1000th "regular flavor" stellar mass black holes.

Supermassive black holes are a slightly different story. Our central galactic black hole is about 26,000 light years away from us.

Formally, it's called Sagittarius A-star, but for our purposes I'm going to call it Kevin. Just so you know they don't throw that term "supermassive" around for no reason, Kevin contains 4.1 million times the mass of the Sun.

Kevin is gigantic and horrible. We can only imagine what it's like to be in the region of space near Kevin. What percentage of the galaxy do you think Kevin makes up, mass wise?



Kevin, whilst absolutely super-massive, is a tiny, tiny 1/10,000 of a percent of the Milky Way galaxy's mass.

So, to be precise, if we add Kevin's mass to the mass of all the stellar mass black holes aka. "mini-Kevins", we get a very minor 11/10000s of a %.

As it turns out this ratio holds up on a Universal scale and is approximately the same for all the mass in the Universe. So, 11 ten thousandths of a percent is the answer to the question. As far as we know.

Unless… dark matter is black holes. Dark matter accounts for more than ¾ of the mass of the Universe. It doesn't absorb light or interact with matter in any way. We're only aware of its presence through its gravitational influence.

As it turns out, Astronomers think that one explanation for dark matter might be primordial black holes.

These microscopic black holes would have the mass of an asteroid or more and could only form in the high pressure, high temperature conditions after the Big Bang.

Experiments to search for primordial black holes have yet to turn up any evidence, and most scientists don't think they're a viable explanation. But if they were, then the Universe is almost entirely composed of the physics inspired nightmare that are black holes.

Fluid Turbulence in Gravitational Fields around Black Holes

This artist's concept depicts a supermassive black hole at the center of a galaxy. 

The blue colour here represents radiation pouring out from material very close to the black hole. 

The grayish structure surrounding the black hole, called a torus, is made up of gas and dust. 

Credit: NASA/JPL-Caltech

Fasten your seatbelts, gravity is about to get bumpy. Of course, if you're flying in the vicinity of a black hole, a bit of extra bumpiness is the least of your worries. But it's still surprising.

The accepted wisdom among gravitational researchers has been that spacetime cannot become turbulent. New research from Perimeter, though, shows that the accepted wisdom might be wrong.

The researchers followed this line of thought: Gravity, it's thought, can behave as a fluid. One of the characteristic behaviours of fluids is turbulence, that is, under certain conditions, they don't move smoothly, but eddy and swirl. Can gravity do that too?

Perimeter Faculty member Luis Lehner explains why it might make sense to treat gravity as a fluid. "There's a conjecture in physics, the holographic conjecture, which says gravity can be described as a field theory," he says.

"And we also know that at high energies, field theories can be described with the mathematical tools we use to describe fluids."

"So it's a two-step dance: gravity equals field theory, and field theory equals fluids, so gravity equals fields equals fluids. That's called the gravity/fluids duality."

The gravity/fluids duality is not new work, it's been developing over the past six years but hidden at the heart of it is a tension. If gravity can be treated as a fluid, then what about turbulence?

"For many years, the folklore among physicists was that gravity could not be turbulent," notes Lehner.

The belief was that gravity is described by a set of equations that are sufficiently different from fluid dynamics equations, such that there would not be turbulence under any circumstances.

Lehner highlights the emerging paradox: "Either there was a problem with the duality and gravity really can't be fully captured by a fluid description, or there was a new phenomenon in gravity and turbulent gravity really can exist."

A team of researchers; Lehner, Huan Yang (Perimeter and the Institute for Quantum Computing), and Aaron Zimmerman (Canadian Institute for Theoretical Astrophysics), set out to find out which.

They had hints about what directions to go. Previous simulations at Perimeter, and independent work out of MIT, had hinted that there could be turbulence around the non-realistic case of black holes confined in anti-de Sitter space.

"There might be turbulence if you confine gravity in a box, essentially," says Lehner. "The deeper question is whether this can happen in a realistic situation."

More information: Read the original paper on arXiv: arxiv.org/abs/1402.4859

Very Strong magnetic fields challenge the pull of supermassive black holes

This is a computer simulation of gas (in yellow) falling into a black hole (too small to be seen). 

Twin jets are also shown with magnetic field lines. 

Credit: Alexander Tchekhovskoy, Berkeley Lab

A new study of supermassive black holes at the centers of galaxies has found magnetic fields play an impressive role in the systems' dynamics.

In fact, in dozens of black holes surveyed, the magnetic field strength matched the force produced by the black holes' powerful gravitational pull, says a team of scientists from the U.S. Department of Energy's Lawrence Berkeley National Laboratory (LBNL) and Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany.

The findings "Dynamically important magnetic fields near accreting supermassive black holes" are published in this week's issue of Nature.

"This paper for the first time systematically measures the strength of magnetic fields near black holes," says Alexander Tchekhovskoy, the Berkeley Lab researcher who helped interpret the observational data within the context of existing computational models.

"This is important because we had no idea, and now we have evidence from not just one, not just two, but from 76 black holes."

Previously, Tchekhovskoy, who is also a postdoctoral fellow at the University of California, Berkeley, had developed computational models of black holes that included magnetic fields.

His models suggested a black hole could sustain a magnetic field that was as strong as its gravity, but there was not yet observational evidence to support this prediction.

With the two forces balancing out, a cloud of gas caught on top of the magnetic field would be spared the pull of gravity and instead levitate in place.

The magnetic field strength was confirmed by evidence from jets of gas that shoot away from supermassive black holes.

Formed by magnetic fields, these jets produce a radio emission. "We realized that the radio emission from black holes' jets can be used to measure the magnetic field strength near the black hold itself," says Mohammad Zamaninasab, the lead author of the study, who did the work while at MPIfR.

Other research teams had previously collected radio-emission data from "radio-loud" galaxies using the Very Long Baseline Array, a vast network of radio telescopes in the United States.

The researchers analyzed this pre-existing data to create radio-emission maps at different wavelengths. Shifts in jet features between different maps let them calculate the field strength near the black hole.

Based on the results, the team found not only that the measured magnetic fields can be as strong as a black hole's gravity, but that they are also comparable in strength to those produced inside MRI machines found in hospitals, roughly 10,000 times greater than the field of the Earth itself.

Tchekhovskoy says the new results mean theorists must re-evaluate their understanding of black-hole behaviour.

"The magnetic fields are strong enough to dramatically alter how gas falls into black holes and how gas produces outflows that we do observe, much stronger than what has usually been assumed," he says. "We need to go back and look at our models once again."

More information: Paper: Dynamically important magnetic fields near accreting supermassive black holes, DOI: 10.1038/nature13399

NASA WISE study challenges black hole 'doughnut' theory

Active, supermassive black holes at the hearts of galaxies tend to fall into two categories: those that are hidden by dust, and those that are exposed. 

Credit: NASA/JPL-Caltech

A survey of more than 170,000 supermassive black holes, using NASA's Wide-field Infrared Survey Explorer (WISE), has astronomers reexamining a decades-old theory about the varying appearances of these interstellar objects.

The unified theory of active, supermassive black holes, first developed in the late 1970s, was created to explain why black holes, though similar in nature, can look completely different.

Some appear to be shrouded in dust, while others are exposed and easy to see.

The unified model answers this question by proposing that every black hole is surrounded by a dusty, doughnut-shaped structure called a torus.

Depending on how these "doughnuts" are oriented in space, the black holes will take on various appearances.

For example, if the doughnut is positioned so that we see it edge-on, the black hole is hidden from view. If the doughnut is observed from above or below, face-on, the black hole is clearly visible.

However, the new WISE results do not corroborate this theory. The researchers found evidence that something other than a doughnut structure may, in some circumstances, determine whether a black hole is visible or hidden.

The team has not yet determined what this may be, but the results suggest the unified, or doughnut, model does not have all the answers.

"Our finding revealed a new feature about active black holes we never knew before, yet the details remain a mystery," said Lin Yan of NASA's Infrared Processing and Analysis Center (IPAC), based at the California Institute of Technology in Pasadena.

"We hope our work will inspire future studies to better understand these fascinating objects."

Yan is the second author of the research accepted for publication in the Astrophysical Journal.

The lead author is a post-doctoral researcher, Emilio Donoso, who worked with Yan at IPAC and has since moved to the Instituto de Ciencias Astronómicas, de la Tierra y del Espacio (ICATE) in Argentina.

The research also was co-authored by Daniel Stern at NASA's Jet Propulsion Laboratory in Pasadena, California, and Roberto Assef of Universidad Diego Portales in Chile and formerly of JPL.

Every galaxy has a massive black hole at its heart. The new study focuses on the "feeding" ones, called active, supermassive black holes, or active galactic nuclei. These black holes gorge on surrounding gas material that fuels their growth.

With the aid of computers, scientists were able to pick out more than 170,000 active supermassive black holes from the WISE data.

They then measured the clustering of the galaxies containing both hidden and exposed black holes—the degree to which the objects clump together across the sky.

More information: The Angular Clustering of WISE-Selected AGN: Different Haloes for Obscured and Unobscured AGN, arxiv.org/abs/1309.2277

ESA XMM-Newton: Unique pair of supermassive black holes discovered

Artist’s impression of a pair of black holes. 

One of them is accreting the 'debris' of the disrupted star, while the second is temporarily interrupting the stream of gas toward the other black hole. 

Credit: ESA /C. Carreau

A pair of supermassive black holes in orbit around one another have been discovered by an international research team including Stefanie Komossa from the Max Planck Institute for Radio Astronomy in Bonn, Germany. This is the first time such a pair could be found in an ordinary galaxy.

Stefanie Komossa

They were discovered because they ripped apart a star when ESA's space observatory XMM-Newton happened to be looking in their direction.

The findings are published in the May 10 issue of the Astrophysical Journal, and appeared online today at the astrophysics preprint server.

Most massive galaxies in the universe are thought to harbor at least one supermassive black hole at their center.

Two supermassive black holes are the smoking gun that the galaxy has merged with another.

Thus, finding binary supermassive black holes can tell astronomers about how galaxies evolved into their present-day shapes and sizes.

To date, only a few candidates for close binary supermassive black holes have been found. All are in active galaxies where they are constantly ripping gas clouds apart, in the prelude to crushing them out of existence.

In the process of destruction, the gas is heated so much that it shines at many wavelengths, including X-rays. This gives the galaxy an unusually bright center, and leads to it being called active.

Fukun Liu

The new discovery, reported by Fukun Liu from Peking University in China, and colleagues, is important because it is the first to be found in a galaxy that is not active.

"There might be a whole population of quiescent galaxies that host binary black holes in their centers," says co-author Stefanie Komossa, Max-Planck-Institut für Radioastronomie, Bonn, Germany.

But finding them is a difficult task because in quiescent galaxies, there are no gas clouds feeding the black holes, and so the cores of these galaxies are truly dark.

The only hope that the astronomers have is to be looking in the right direction at the moment one of the black holes goes to work, and rips a star to pieces. Such an occurrence is called a 'tidal disruption event.'

As the star is pulled apart by the gravity of the black hole, it gives out a flare of X-rays.

In an active galaxy, the black hole is continuously fed by gas clouds. In a quiescent galaxy, the black hole is fed by tidal disruption events that occur sporadically and are impossible to predict.

So, to increase the chances of catching such an event, researchers use ESA's X-ray observatory, XMM-Newton, in a novel way.

ESA's X-ray observatory, XMM-Newton

Artist's impression of XMM-Newton spacecraft in orbit around the Earth. 

The X-ray emission from galaxy SDSS J120136.02+300305.5 was detected in slew modus of the space observatory. 

Credit: ESA /D. Ducros

Usually, the observatory collects data from designated targets, one at a time.

Once it completes an observation, it slews to the next.

The trick is that during this movement, XMM-Newton keeps the instruments turned on and recording.

Effectively this surveys the sky in a random pattern, producing data that can be analyzed for unknown or unexpected sources of X-rays.

On 10 June 2010, a tidal disruption event was spotted by XMM-Newton in galaxy SDSS J120136.02+300305.5, approximately 2 billion light-years away.

NASA's Swift satellite

Komossa and her colleagues were scanning the data for such events and scheduled follow-up observations just days later with XMM-Newton and NASA's Swift satellite.

The galaxy was still spilling X-rays into space.

It looked exactly like a tidal disruption event caused by a supermassive black hole but as they tracked the slowly fading emission day after day something strange happened.

The X-rays fell below detectable levels between days 27 and 48 after the discovery. Then they re-appeared and continued to follow a more expected fading rate, as if nothing had happened.

Now, thanks to Fukun Liu, this behaviour can be explained. "This is exactly what you would expect from a pair of supermassive black holes orbiting one another," says Liu.

More information: "A milliparsec supermassive black hole binary candidate in the galaxy SDSS J120136.02+300305.5," by F. K. Liu, Shuo Li, and S. Komossa, 2014, Astrophysical Journal, Volume 786, Article 103 (May 10). DOI: 10.1088/0004-637X/786/2/103 . Preprint: arxiv.org/abs/1404.4933

Hubble Image: Observing the Heart of NGC 5793

This new Hubble image is centered on NGC 5793, a spiral galaxy over 150 million light-years away in the constellation of Libra. 

This galaxy has two particularly striking features: a beautiful dust lane and an intensely bright center. much brighter than that of our own galaxy, or indeed those of most spiral galaxies we observe.

NGC 5793 is a Seyfert galaxy. These galaxies have incredibly luminous centers that are thought to be caused by hungry supermassive black holes, black holes that can be billions of times the size of the sun, that pull in and devour gas and dust from their surroundings.

This galaxy is of great interest to astronomers for many reasons. For one, it appears to house objects known as masers.

Whereas lasers emit visible light, masers emit microwave radiation. The term "masers" comes from the acronym Microwave Amplification by Stimulated Emission of Radiation.

Maser emission is caused by particles that absorb energy from their surroundings and then re-emit this in the microwave part of the spectrum.

Naturally occurring masers, like those observed in NGC 5793, can tell us a lot about their environment; we see these kinds of masers in areas where stars are forming.

In NGC 5793 there are also intense mega-masers, which are thousands of times more luminous than the sun.

Credit: NASA, ESA, and E. Perlman (Florida Institute of Technology)

NASA RXTE: Clouds seen circling supermassive black holes - video

Credit: NASA

Astronomers see huge clouds of gas orbiting supermassive black holes at the centers of galaxies using NASA's Rossi X-Ray Timing Explorer satellite (RXTE).

Once thought to be a relatively uniform, fog-like ring, the accreting matter instead forms clumps dense enough to intermittently dim the intense radiation blazing forth as these enormous objects condense and consume matter, they report in a paper to be published in the Monthly Notices of the Royal Astronomical Society, available online now.

Evidence for the clouds comes from records collected over 16 years by NASA's Rossi X-Ray Timing Explorer satellite (RXTE), a satellite in low-earth orbit equipped with instruments that measured variations in X-ray sources.

Those sources include active galactic nuclei, brilliantly luminous objects powered by supermassive black holes as they gather and condense huge quantities of dust and gas.

By sifting through records for 55 active galactic nuclei Alex Markowitz, an astrophysicist at the University of California, San Diego and the Karl Remeis Observatory in Bamberg, Germany and colleagues found a dozen instances when the X-ray signal dimmed for periods of time ranging from hours to years, presumably when a cloud of dense gas passed between the source and satellite.

Mirko Krumpe

Mirko Krumpe of the European Southern Observatory in Garching, Germany and Robert Nikutta, of Andrés Bello University in Santiago, Chile co-authored the report, which confirms what recent models of these systems have predicted.


This animation shows an artist's rendition of the cloudy structure revealed by a study of data from NASA's Rossi X-Ray Timing Explorer satellite (RXTE). Credit: NASA

The clouds they observed orbit a few light-weeks to a few light-years from the center of the active galactic nuclei.

One, in a spiral galaxy in the direction of the constellation Centaurus designated NGC 3783, appeared to be in the midst of being torn apart by tidal forces.

More Information: 'First X-ray-Based Statistical Tests for Clumpy-Torus Models: Eclipse Events from 230 Years of Monitoring of Seyfert AGN': Alex Markowitz (Univ. Calif., San Diego and Karl Remeis Sternwarte/ECAP), Mirko Krumpe (European Southern Observatory and Univ. Calif., San Diego), Robert Nikutta (Univ. Andrés Bello): arXiv:1402.2779 [astro-ph.GA]

Dwarf galaxies provide clues to origin of supermassive black holes

Dwarf galaxy NGC 4395, about 13 million light-years from Earth, known to harbour a black hole some 300,000 times more massive than the Sun. 

It is a prototypical example of a small galaxy once thought to be too small to contain such a black hole. 

Credit: David W. Hogg, Michael R. Blanton, and the Sloan Digital Sky Survey Collaboration; NRAO/AUI/NSF.

Pouring through data from a large sky survey, astronomers have found more than 100 small, dwarf galaxies with characteristics indicating that they harbor massive black holes feeding on surrounding gas.

The discovery confounds a common assumption that only much larger galaxies hold such monsters and may help resolve the question of how such black holes originated and grew in the early universe.

Amy Reines

"We've shown that even small galaxies can have massive black holes and that they may be more common than previously thought," said Amy Reines, of the National Radio Astronomy Observatory (NRAO).

"This is really exciting because these little galaxies hold the clues to the origin of the first 'seeds' of supermassive black holes in the early universe," she said. Reines and her colleagues presented their findings to the American Astronomical Society's meeting in Washington, DC.

Black holes are concentrations of mass so dense that not even light can escape their gravitational pull.

Nearly all "full-sized" galaxies are known to have supermassive black holes, millions or billions of times more massive than the Sun, at their cores.

Until recently, however, smaller galaxies were thought not to harbor massive black holes.

Marla Geha

Reines, along with Jenny Greene of Princeton University and Marla Geha of Yale University, analyzed data from the Sloan Digital Sky Survey and found more than 100 dwarf galaxies whose patterns of light emission indicated the presence of massive black holes and their feeding process.

"The galaxies are comparable in size to the Magellanic Clouds, dwarf satellite galaxies of the Milky Way," Geha said.

"Previously, such galaxies were thought to be too small to have such massive black holes," she added.

In the nearby universe, astronomers have found a direct relationship between the mass of a galaxy's central black hole and a "bulge" in its center.

This indicates that the black holes and the bulges may have affected each others' growth.

ESA XMM-Newton: Taking the pulse of a supermassive black hole

This artist's concept depicts a supermassive black hole at the center of a galaxy. Image: NASA

Rare heartbeat-like pulsations detected from a supermassive black hole may grant scientists better insight into these exotic objects, according to two University of Alabama astronomers who co-authored a recent scientific article on the discovery.

Drs. Dacheng Lin, a post-doctoral researcher, and Jimmy Irwin, an assistant professor in UA's physics and astronomy department, co-wrote, along with three French scientists, an article about this black hole, with a mass about 100,000 times that of the sun, that published in a recent issue of Astrophysical Journal Letters.

"Such signals from supermassive black holes are very important for understanding the link between black holes across mass scale, but they have proved very difficult to find," Lin said.

"Only two cases were discovered before, and our signal is five times stronger than those two cases."

The scientists used data provided by the European Space Agency's XMM-Newton space observatory in their analysis.

This black hole is 1.7 billion light years away from Earth at the center of a distant galaxy, the UA scientists said.

The black hole, at the time of observation, was "eating" matter at near the maximum rate, Lin said. The UA scientists have requested additional observation time by XMM-Newton in an attempt to better understand why this black hole is eating so much matter.

"One interesting possibility is a nearby star happened to be wandering too closely to the black hole," Lin said, "so the star is torn apart by the black hole and a lot of gas becomes available to fall onto the black hole."

The origin of the pulsation, or "quasi-periodic X-ray oscillation" as scientists refer to it, is difficult to identify, Lin said. One explanation is that as the matter falls toward the black hole, a flattened disk forms.

The disk produces high-energy X-rays. As the disc structure changes cyclically due to eating so much matter, so does the intensity of the X-rays streaming from it.

"Such oscillations are common in black holes with masses less than 20 times that of the sun, but are rarely seen in supermassive black holes," Lin said.

"Black holes are one of the most exotic objects in the universe, and it is so compact and the gravity around it so strong that many interesting physical phenomena, such as the heartbeat-like X-ray signal discovered here, can happen."

The discovery published in the Oct. 10 edition of Astrophysical Letters.