The SZ effect: Big black holes can block new stars

Elliptical galaxy NGC 1132, as seen by NASA's Chandra X-Ray Observatory; the blue/purple in the image is the X-ray glow from hot, diffuse gas that is not forming into stars. 

Credit: NASA, ESA, M. West (ESO, Chile), and CXC /Penn State University /G. Garmire, et al.

Massive black holes spewing out radio-frequency-emitting particles at near-light speed can block formation of new stars in aging galaxies, a study has found.

The research provides crucial new evidence that it is these jets of "radio-frequency feedback" streaming from mature galaxies' central black holes that prevent hot free gas from cooling and collapsing into baby stars.

"When you look into the past history of the universe, you see these galaxies building stars," said Tobias Marriage, assistant professor of physics and astronomy at Johns Hopkins and co-lead author of the study.

"At some point, they stop forming stars and the question is: Why? Basically, these active black holes give a reason for why stars stop forming in the universe."

The findings have been published in the journal Monthly Notices of the Royal Astronomical Society.

They were made possible by adaptation of a well-known research technique for use in solving a new problem.

Johns Hopkins postdoctoral fellow Megan Gralla found that the Sunyaev–Zel'dovich effect signature, typically used to study large galaxy clusters, can also be used to learn a great deal about smaller formations.

The SZ effect occurs when high-energy electrons in hot gas interact with faint light in the cosmic microwave background, light left over from earliest times when the universe was a thousand times hotter and a billion times denser than today.

"The SZ is usually used to study clusters of hundreds of galaxies but the galaxies we're looking for are much smaller and have just a companion or two," Gralla said.

"What we're doing is asking a different question than what has been previously asked," Gralla said.

"We're using a technique that's been around for some time and that researchers have been very successful with, and we're using it to answer a totally different question in a totally different subfield of astronomy."

"I was stunned when I saw this paper, because I've never thought that detecting the SZ effect from active galactic nuclei was possible," said Eiichiro Komatsu, director of the Max Planck Institute for Astrophysics in Germany and an expert in the field who was not involved in the research.

"I was wrong. ... It makes those of us who work on the SZ effect from galaxy clusters feel old; research on the SZ effect has entered a new era."

In space, hot gas drawn into a galaxy can cool and condense, forming stars. Some gas also funnels down into the galaxy's black hole, which grows together with the stellar population.

This cycle can repeat continuously; more gas is pulled in to cool and condense, more stars begin to shine and the central black hole grows more massive.

But in nearly all mature galaxies, the big galaxies called "elliptical" because of their shape – that gas doesn't cool any more. "If gas is kept hot, it can't collapse," Marriage said. When that happens: No new stars.

Marriage, Gralla and their collaborators found that the elliptical galaxies with radio-frequency feedback, relativistic radio-frequency-emitting particles shooting from the massive central black holes at their center at close to the speed of light, all contain hot gas and a dearth of infant stars.

That provides crucial evidence for their hypothesis that this radio-frequency feedback is the "off switch" for star-making in mature galaxies.

Marriage said, however, that it is still not known just why black holes in mature elliptical galaxies begin to emit radio-frequency feedback.

"The exact mechanism behind this is not fully understood and there are still debates," he said.

Komatsu said that the new Johns Hopkins-led study, combined with others detecting SZ signals from more ordinary galaxies, "pose new challenges to the theory of galaxy formation, as there were hardly any data which told us how much hot gas there is around galaxies."

More information: Monthly Notices of the Royal Astronomical Society, mnras.oxfordjournals.org/content/445/1/460.full

HZDR Research: Cosmic jets of young stars formed by magnetic fields

This is an artist's rendering showing the birth of a star: A dust and gas cloud is forming a spiraling disk around a massive baby star while jets of material shoot from its core. 

Credit: ESO/L. Calada

Astrophysical jets are counted among our Universe's most spectacular phenomena: From the centers of black holes, quasars, or protostars, these rays of matter sometimes protrude several light years into space.

Now, for the first time ever, an international team of researchers has successfully tested a new model that explains how magnetic fields form these emissions in young stars.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) were part of this research.

Their findings have been published in the journal Science. The insights gleaned from this research may even apply to cancer therapy.

Whenever an object in space forms a rotating disc of matter, chances are that it gives rise to a "jet" – a thin, straight emission of matter which emanates from the disc's center and that looks like a spintop.

These structures can be observed especially during the formation of new stars, but understanding how such thin beams are able to form within the disc is something that continues to elude scientists.

Now, HZDR researchers, along with their European, American, and Asian colleagues, have investigated this process in the lab.

At the Laboratoire pour l'Utilisation des Lasers Intenses (LULI), in France, scientists hit a plastic sample with laser light which set the electrons at the target's core in motion, transforming the solid plastic object into conductive plasma.

"Think of it as a sort of rapidly expanding hot cloud of electrons and ions. On a small scale, the plasma represents a young star's accumulation of matter," explains Professor Thomas Cowan, the study's co-author and Director of the HZDR Institute of Radiation Physics.

Miniature versions of young stars for the lab
What made the experiment special was the fact that the plasma was exposed to a very powerful pulsed magnetic field.

The idea behind it: under a magnetic field's influence, the normally widely scattered plasma begins to focus, forming a hollow center.

This ultimately produces a shockwave, from which a very thin beam starts to project, a jet.

The experiment was set up in such a way as to allow for extrapolation to conditions as they would be encountered in the Universe: within as little as 20 nanoseconds, over 100,000 times faster than a fly flapping its wings, the lab plasma forms structures similar to a young star's jet in approximately six years.

This allowed the researchers to test their model with astronomical observations, which were made possible through space telescopes, in the last two decades.

The data were in good agreement. In a jet, for instance, a crossing over of particle streams can occur, which in turn results in the formation of very hot spots.

"X-ray measurements of actual jets show these features at the exact same points as our true-to-scale plasma model in the lab," says Cowan.

With its help, the researchers were able to offer a model that, for the first time ever, is capable of explaining the formation of jets solely by way of magnetic fields.

Previous approaches had considered the rotation of matter about the young star another influencing factor.

The realisation that plasma can be focused in this way may prove a real practical boon in the field of medical engineering.

According to Cowan, it's conceivable that with the help of pulsed magnetic fields, a particularly thin proton beam could be produced for use in radiation therapy.

It's what Florian Kroll, Ph.D. student at the HZDR and one of the study's co-authors, is investigating.

Special pulse generator designed at the Dresden High Magnetic Field Lab

To produce strong pulsed magnetic fields for the experiment, the researchers drew on the expertise at the HZDR's Dresden High Magnetic Field Lab: "We developed a special pulse generator which allowed our French colleagues to set up powerful magnetic fields within a small, enclosed lab space," says Dr. Thomas Herrmannsdörfer, head of division at the High Magnetic Field Lab.

The generator, just about the size of a wardrobe, is capable of generating currents of up to 300 kiloampere.

According to Herrmannsdörfer, building such a compact facility was a real technical challenge: "Our electrical engineers came up with some very innovative solutions."

"This is also helping us now with developing these types of generators for application in industry and medical technology."

Currently, the pulse generator is still located at the French laser lab at Palaiseau near Paris, because beginning in December the Dresden scientists are planning on once again working together with their LULI colleagues.

More information: Science DOI: 10.1126/science.1259694

Researcher shows that black holes do not exist

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

Black holes have long captured the public imagination and been the subject of popular culture, from Star Trek to Hollywood.

They are the ultimate unknown, the blackest and most dense objects in the universe that do not even let light escape, and as if they weren't bizarre enough to begin with, now add this to the mix: they don't exist.

By merging two seemingly conflicting theories, Laura Mersini-Houghton, a physics professor at UNC-Chapel Hill in the College of Arts and Sciences, has proven, mathematically, that black holes can never come into being in the first place.

The work not only forces scientists to reimagine the fabric of space-time, but also rethink the origins of the universe.

"I'm still not over the shock," said Mersini-Houghton. "We've been studying this problem for a more than 50 years and this solution gives us a lot to think about."

For decades, black holes were thought to form when a massive star collapses under its own gravity to a single point in space, imagine the Earth being squished into a ball the size of a peanut, called a singularity.

So the story went, an invisible membrane known as the event horizon surrounds the singularity and crossing this horizon means that you could never cross back.

It's the point where a black hole's gravitational pull is so strong that nothing can escape it.

The reason black holes are so bizarre is that it pits two fundamental theories of the universe against each other.

Einstein's theory of gravity predicts the formation of black holes but a fundamental law of quantum theory states that no information from the universe can ever disappear.

Efforts to combine these two theories lead to mathematical nonsense, and became known as the information loss paradox.

In 1974, Stephen Hawking used quantum mechanics to show that black holes emit radiation.

Since then, scientists have detected fingerprints in the cosmos that are consistent with this radiation, identifying an ever-increasing list of the universe's black holes.

But now Mersini-Houghton describes an entirely new scenario. She and Hawking both agree that as a star collapses under its own gravity, it produces Hawking radiation.

However, in her new work, Mersini-Houghton shows that by giving off this radiation, the star also sheds mass. So much so that as it shrinks it no longer has the density to become a black hole.

Before a black hole can form, the dying star swells one last time and then explodes. A singularity never forms and neither does an event horizon.

The take home message of her work is clear: there is no such thing as a black hole.

The paper, which was recently submitted to ArXiv, an online repository of physics papers that is not peer-reviewed, offers exact numerical solutions to this problem and was done in collaboration with Harald Peiffer, an expert on numerical relativity at the University of Toronto.

An earlier paper, by Mersini-Houghton, originally submitted to ArXiv in June, was published in the journal Physics Letters B, and offers approximate solutions to the problem.

Experimental evidence may one day provide physical proof as to whether or not black holes exist in the universe, but for now, Mersini-Houghton says the mathematics are conclusive.

Many physicists and astronomers believe that our universe originated from a singularity that began expanding with the Big Bang.

However, if singularities do not exist, then physicists have to rethink their ideas of the Big Bang and whether it ever happened.

"Physicists have been trying to merge these two theories, Einstein's theory of gravity and quantum mechanics, for decades, but this scenario brings these two theories together, into harmony," said Mersini-Houghton. "And that's a big deal."

More information: Mersini-Houghton's ArXiv papers: Approximate solutions: arxiv.org/abs/arXiv:1406.1525 Exact solutions: arxiv.org/abs/arXiv:1409.1837

Hints of gravitational waves found in the stars

Energetic events, such as this artist’s rendition of a binary-star merger, are thought to create gravitational waves that cause ripples in space and time. 

 Credit: NASA

Scientists have shown how gravitational waves, invisible ripples in the fabric of space and time that propagate through the universe, might be "seen" by looking at the stars.

The new model proposes that a star that oscillates at the same frequency as a gravitational wave will absorb energy from that wave and brighten, an overlooked prediction of Einstein's 1916 theory of general relativity.

The study, which was published today in the Monthly Notices of the Royal Astronomical Society: Letters, contradicts previous assumptions about the behavior of gravitational waves.

"It's pretty cool that a hundred years after Einstein proposed this theory, we're still finding hidden gems," said Barry McKernan, a research associate in the Museum's Department of Astrophysics, who is also a professor at CUNY's Borough of Manhattan Community College; a faculty member at CUNY's Graduate Center; and a Kavli Scholar at the Kavli Institute for Theoretical Physics.

Gravitational waves can be thought of like the sound waves emitted after an earthquake, but the source of the "tremors" in space are energetic events like supernovae (exploding stars), binary neutron stars (pairs of burned-out cores left behind when stars explode), or the mergers of black holes and neutron stars.

Although scientists have long known about the existence of gravitational waves, they've never made direct observations but are attempting to do so through experiments on the ground and in space.

Part of the reason why detection is difficult is because the waves interact so weakly with matter but McKernan and his colleagues from CUNY, the Harvard-Smithsonian Center for Astrophysics, the Institute for Advanced Study, and Columbia University, suggest that gravitational waves could have more of an effect on matter than previously thought.

The new model shows that stars with oscillations, vibrations, that match the frequency of gravitational waves passing through them can resonate and absorb a large amount of energy from the ripples.

"It's like if you have a spring that's vibrating at a particular frequency and you hit it at the same frequency, you'll make the oscillation stronger," McKernan said. "The same thing applies with gravitational waves."

If these stars absorb a large pulse of energy, they can be "pumped up" temporarily and made brighter than normal while they discharge the energy over time.

This could provide scientists with another way to detect gravitational waves indirectly.

"You can think of stars as bars on a xylophone, they all have a different natural oscillation frequency," said co-author Saavik Ford, who is a research associate in the Museum's Department of Astrophysics as well as a professor at the Borough of Manhattan Community College, CUNY; a faculty member at CUNY's Graduate Center; and a Kavli Scholar at the Kavli Institute for Theoretical Physics.

"If you have two black holes merging with each other and emitting gravitational waves at a certain frequency, you're only going to hit one of the bars on the xylophone at a time but because the black holes decay as they come closer together, the frequency of the gravitational waves changes and you'll hit a sequence of notes. So you'll likely see the big stars lighting up first followed by smaller and smaller ones."

The work also presents a different way to indirectly detect gravitational waves. From the perspective of a gravitational wave detector on Earth or in space, when a star at the right frequency passes in front of an energetic source such as merging black holes, the detector will see a drop in the intensity of gravitational waves measured."

"In other words, stars, including our own Sun, can eclipse background sources of gravitational waves.

"You usually think of stars as being eclipsed by something, not the other way around," McKernan said.

The researchers will continue to study these predictions and try to determine how long it would take to observe these effects from a telescope or detector.

More Information:
B. McKernan, K.E.S. Ford, B. Kocsis, Z. Haiman. "Stars as resonant absorbers of gravitational waves." Monthly Notices of the Royal Astronomical Society: Letters, 2014 - arxiv.org/abs/1405.1414

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.

Black holes exploding into 'white holes'

The collapse of a star into a black hole could be a temporary effect that leads to the formation of a 'white hole', suggests a new model based on a theory known as loop quantum gravity.

A new scientific theory suggests that when black holes reach the end of their lifespan, they explode into "white holes" and release all of their matter into space.

If true, the theory could help put to rest the debate over whether or not black holes actually destroy the matter they end up devouring.

As noted by Albert Einstein's theory of relativity, when a dying star ends up collapsing under its own weight, at some point the collapse becomes irreversible, resulting in a black hole that consumes light and anything else within its surrounding area.

Although black holes do slowly leak radiation over time, ultimately draining the black hole completely, this doesn't account for all the other matter that the dying star has consumed.

Since quantum theory does not allow for the possibility that information can be lost, though, two researchers from France's Aix-Marseille University believe they've discovered an explanation for this so-called "information paradox."

Carlo Rovelli

According to physicists Carlo Rovelli and Hal Haggard, a black hole eventually reaches a point where it cannot collapse any further and the internal pressure begins to push outwards.

This essentially turns the black hole inside out and expels everything it once consumed back into space.

Notably, the scientists believe that these white holes are created not long after the black hole's original formation, and we humans can't see it because gravity dilates time and makes the black hole's lifespan seem to last for billions or trillions of years.

Their current calculation is that it only takes a few thousandths of a second for a black hole to turn into a white hole.

Hal Haggard

Importantly, the process is very long seen from the outside, but is very short for a local observer at a small radius," the researchers wrote in a paper on the subject.

Ron Cowen, a science writer at Nature, explained further.

If the authors are correct, tiny black holes that formed during the very early history of the Universe would now be ready to pop off like firecrackers and might be detected as high-energy cosmic rays or other radiation.

In fact, they say, their work could imply that some of the dramatic flares commonly considered to be supernova explosions could in fact be the dying throes of tiny black holes that formed shortly after the Big Bang.

Although Rovelli and Haggard aren't completely dismissing the idea that black holes leak radiation, they said the trickles of energy would not be sufficient enough to deplete the dying stars of all the energy they've consumed.

Radiation may very well seep out, but their work is primarily concerned with discovering what happens inside a black hole.

Both Rovelli and Haggard admitted that their theory needs to be tested further with more comprehensive calculations.

If research confirms their ideas, however, theoretical physicist Steven Giddings of the University of California Santa Barbara says, "It would be important. Understanding how information escapes from a black hole is the key question for the quantum mechanics of black holes, and possibly for quantum gravity itself."

Theoretical physicist Stephen Hawking of the University of Cambridge, UK, has recently suggested that true event horizons would be incompatible with quantum physics.

More Information: Black hole fireworks: quantum-gravity effects outside the horizon spark black to white hole tunneling - Authors: Hal M. Haggard, Carlo Rovelli - arXiv:1407.0989

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

Chandra Sagittarius A*: Black holes at centre of galaxies are wormholes

Credit: X-ray: NASA /UMass /D.Wang et al., IR: NASA/STScI

Zilong Li and Cosimo Bambi with Fudan University in Shanghai have come up with a very novel idea, those black holes that are believed to exist at the center of a lot of galaxies, may instead by wormholes.

They've written a paper, uploaded to the preprint server arXiv, describing their idea and how what they've imagined could be proved right (or wrong) by a new instrument soon to be added to an observatory in Chile.

Sagittarius A*: NASA's Chandra Finds Milky Way's Black Hole may be Grazing on Asteroids

Back in 1974, space scientists discovered Sagittarius A* (SgrA ∗), a bright source of radio waves emanating from what appeared to be near the center of the Milky Way galaxy.

Subsequent study of the object led scientists to believe that it was (and is) a black hole, the behaviour of stars nearby, for example, suggested it was something massive and extremely dense.

What we're able to see when we look at SgrA ∗ are plasma gasses near the event horizon, not the object itself as light cannot escape.

That should be true for wormholes too, of course, which have also been theorized to exist by the Theory of General Relativity. Einstein even noted the possibility of their existence.

GRAVITY overview. The beam combiner instrument (bottom right) is located in the VLTI laboratory. 

The infrared wavefront-sensors (bottom left) are mounted to each of the four UTs. 

The laser metrology is launched from the beam-combiner and is detected at each UT/AT (top middle).

Unfortunately, no one has ever come close to proving the existence of wormholes, which are believed to be channels between different parts of the universe, or even between two universes in multi-universe theories.

In their paper, Li and Bambi suggest that there is compelling evidence suggesting that many of the objects we believe to be black holes at the center of galaxies, may in fact be wormholes.

Plasma gases orbiting a black hole versus a wormhole should look different to us, the pair suggest, because wormholes should be a lot smaller.

Plus, the presence of wormholes would help explain how it is that even new galaxies have what are now believed to be black holes, such large black holes would presumably take a long time to become so large, so how can they exist in a new galaxy?

They can't Li and Bambi conclude, instead those objects are actually wormholes, which theory suggests could spring up in an instant, and would have, following the Big Bang.

Making the two's speculation more exciting is the soon to be installed piece of equipment known as GRAVITY, it will be added to the European Space Observatory (ESO) in Chile, giving researchers there an unprecedented view of SgrA ∗ (and other black holes).

In just a couple of years, it should be possible to prove whether Li and Bambi's idea is correct or not, the photon capture sphere of the wormhole should be much smaller than that for a black hole, they note, if that's the case with SgrA ∗, space scientists will have to do some serious rethinking of wormholes and how they might fit in to current theories describing the universe.

More information: Distinguishing black holes and wormholes with orbiting hot spots, arXiv:1405.1883

Red stars and big bulges: How black holes shape galaxies

Images of a small fraction of the galaxies analysed in the new study. 

The galaxies are ordered by total mass of stars (rising from bottom to top) and by ‘bulge to total stellar mass ratio’ (rising from left to right). 

Galaxies that appear redder have high values for both of these measurements, meaning that the mass of the bulge –and central black hole – determines their colour. 

Credit: A. Bluck.

The universe we can see is made up of billions of galaxies, each containing anywhere from hundreds of thousands to hundreds of billions of stars.

Large numbers of galaxies are elliptical in shape, red and mostly made up of old stars.

Another (more familiar) type is the spiral, where arms wind out in a blue thin disk from a central red bulge. On average stars in spiral galaxies tend to be much younger than those in ellipticals.

Asa Bluck

Now a group of astronomers led by Asa Bluck of the University of Victoria in Canada have found a (relatively) simple relationship between the colour of a galaxy and the size of its bulge – the more massive the bulge the redder the galaxy.

The researchers publish their results in the Oxford University Press journal Monthly Notices of the Royal Astronomical Society.

Asa and his team used data from the Sloan Digital Sky Survey (SDSS) to group together over half a million galaxies of all different colours, shapes, and masses.

They then used pattern recognition software to measure the shape of each one, to see how the proportion of red stars in a galaxy varies with its other properties.

They found that the mass in the central bulge (regardless of how big the disk surrounding it may be) is the key to knowing the colour of the whole galaxy.

Above a given bulge mass, galaxies are red and have no new young stars. Almost all galaxies have supermassive black holes at their centres.

The mass of the bulge is closely related to the mass of the black hole; the more massive the black hole the more energy is released into the surrounding galaxy in the form of powerful jets and X-ray emission.

This can blow away and heat up gas, stopping new stars from forming.

Asa comments: "A relatively simple result, that large galaxy bulges mean red galaxies, has profound consequences. Big bulges mean big black holes and these can put an end to star formation."

Journal Reference: Asa F. L. Bluck, J. Trevor Mendel, Sara L. Ellison, Jorge Moreno, Luc Simard, David R. Patton, Else Starkenburg. Bulge mass is king: The dominant role of the bulge in determining the fraction of passive galaxies in the Sloan Digital Sky Survey. Monthly Notices of the Royal Astronomical Society, 2014

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)

Pushy black holes stop elliptical galaxies from forming stars

Multi-wavelength view of the elliptical galaxy NGC 5044. Credit: Digitised Sky Survey /NASA Chandra /Southern Observatory for Astrophysical Research/Very Large Array. 

Contradicting past theories, cold gas has been found in abundance in some elliptical galaxies—showing that there must be some other explanation why these types of galaxies don't form new stars.

Astronomers believe that the jets from supermassive black holes in these galaxies' center must push around the gas and prevent stars from forming.

Researchers spotted the gas for the first time using old data from the recently retired Herschel space observatory, which was able to peer well into the infrared—where it spotted carbon ions and oxygen atoms.

This find stands against the previous belief that these galaxies were "red and dead", referring to their physical appearance and the fact that they form no new stars.

"We looked at eight giant elliptical galaxies that nobody had looked at with Herschel before and we were delighted to find that, contrary to previous belief, six out of eight abound with cold gas", stated Norbert Werner, a researcher at Stanford University in California who led the study.

"These galaxies are red, but with the giant black holes pumping in their hearts, they are definitely not dead," added Werner.

Previously, scientists thought that the galaxies got rid of their cold gas or had used it all up during a burst of earlier star formation.

With cold gas found in the majority of the sample, researchers then used other observatories to try to find warmer gas up to tens of millions of Kelvin (or Fahrenheit or Celsius).

NGC 1399, an elliptical galaxy about 65 million light years from Earth. Credit: NASA, Chandra

X-ray information from NASA's Chandra X-ray Observatory revealed that there is hot gas cooling in six of the eight galaxies, but not in the remaining two of the sample.

"This is consistent with theoretical expectations: once cooled, the hot gas would become the warm and cold gas that are observed at longer wavelengths.

However, in these galaxies the cooling process somehow stopped, and the cold gas failed to condense and form stars," the European Space Agency stated.

"While the six galaxies with plenty of cold gas harbour moderately active black holes at their centres," ESA added, "the other two show a marked difference."

"In the two galaxies without cold gas, the central black holes are accreting matter at frenzied pace, as confirmed by radio observations showing powerful jets of highly energetic particles that stem from their cores."

More information: N. Werner, J. B. R. Oonk, M. Sun, P. E. J. Nulsen, S. W. Allen, R. E. A. Canning, A. Simionescu, A. Hoffer, T. Connor, M. Donahue, A. C. Edge, A. C. Fabian, A. von der Linden, C. S. Reynolds, and M. Ruszkowski. "The origin of cold gas in giant elliptical galaxies and its role in fuelling radio-mode AGN feedback." MNRAS first published online February 24, 2014 DOI: 10.1093/mnras/stu006

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]