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Scooped by Dr. Stefan Gruenwald!

Shedding light on the growth of stars and black holes

Shedding light on the growth of stars and black holes | Amazing Science |
A Southampton astronomer is among a team of international researchers whose work has revealed a surprising similarity between the way in which astronomical objects grow including black holes, white dwarfs and young stars.

Christian Knigge, Professor in Physics and Astronomy, worked with colleagues from around the world to study one of the most important, but least understood processes in astronomy – accretion, where the mass of an object grows by gravitationally collecting material from nearby.

The article Accretion-induced variability links young stellar objects, white dwarfs, and black holes has been published in the latest edition of the journal Science AdvancesThe paper reveals a close relationship between the way in which different types of accreting objects vary in brightness over time. Their results connect proto-stars resembling our Sun at the time of its birth, to accreting white dwarfs, to supermassive black holes with a billion times the mass of the Sun, located in galaxies millions of light years away.

The team found that the two most important properties of the object are its physical size, scale and the rate at which it is accreting matter. They discuss a unified scenario for understanding brightness variations from accretion discs around different types of stars and compact objects. Previous work had unified the variability in discs around black holes of different mass ranges, but by considering not just the mass of the object, but also its size, scientists can now add accreting white dwarfs and proto-stars to this unified picture.

Prof Knigge said: “This is a really exciting result. It suggests that the process by which astronomical objects grow is fundamentally the same, regardless of the type, mass or size of the object.”

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Mysterious ripples found racing through planet-forming disc: Unique structures spotted around nearby star

Mysterious ripples found racing through planet-forming disc: Unique structures spotted around nearby star | Amazing Science |

sing images from the NASA/ESA Hubble Space Telescope and ESO's Very Large Telescope, astronomers have discovered never-before-seen structures within a dusty disc surrounding a nearby star. The fast-moving wave-like features in the disc of the star AU Microscopii are unlike anything ever observed, or even predicted, before now. The origin and nature of these features present a new mystery for astronomers to explore. The results are published in the journal Nature on 8 October 2015.

AU Microscopii, or AU Mic for short, is a young, nearby star surrounded by a large disc of dust [1]. Studies of such debris discs can provide valuable clues about how planets, which form from these discs, are created.

Astronomers have been searching AU Mic's disc for any signs of clumpy or warped features, as such signs might give away the location of possible planets. And in 2014 they used the powerful high-contrast imaging capabilities of ESO's newly installed SPHERE instrument, mounted on the Very Large Telescope for their search -- and discovered something very unusual.

"Our observations have shown something unexpected," explains Anthony Boccaletti of the Observatoire de Paris, France, lead author on the paper. "The images from SPHERE show a set of unexplained features in the disc which have an arch-like, or wave-like, structure, unlike anything that has ever been observed before."

Five wave-like arches at different distances from the star show up in the new images, reminiscent of ripples in water. After spotting the features in the SPHERE data the team turned to earlier images of the disc taken by the NASA/ESA Hubble Space Telescope in 2010 and 2011 to see whether the features were also visible in these [2]. They were not only able to identify the features on the earlier Hubble images -- but they also discovered that they had changed over time. It turns out that these ripples are moving -- and very fast!

"We reprocessed images from the Hubble data and ended up with enough information to track the movement of these strange features over a four-year period," explains team member Christian Thalmann (ETH Zürich, Switzerland). "By doing this, we found that the arches are racing away from the star at speeds of up to about 40,000 kilometers/hour!"

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Old enigma cracked: What's Driving the Brightest Galaxies in the Universe

Old enigma cracked: What's Driving the Brightest Galaxies in the Universe | Amazing Science |

Astronomers may have finally cracked the enigma of why the universe's brightest galaxies are so incredibly luminous. 

Over the past 50 years or so, astronomers have observed certain galaxies in our universe—called submillimeter galaxies (SMGs)—that outshine other galaxies by hundreds of times over. These rabid, glowing galaxies also give birth to stars thousands of times faster than our own Milky Way does. But ever since their discovery, exactly what exactly causes these ultra-bright galaxies to become so radiant has been a longstanding mystery.

One prevailing theory is that SMGs are cosmic car crashes—the fiery result of two disc galaxies like the Milky Way colliding. But in simulation after simulation, nobody's ever been able to plug in the physics and explain what we see in real life. But today, a team of astronomers—led by Desika Narayanan at Haverford College—has announced the first working model of SMGs and the first conclusive answer of why they're so radiant. They published their work today in the journal Nature.

Based on Narayanan's new model, SMGs are not the result of spectacular crashes. Rather, something much more interesting is going on: SMG galaxies are strange, long-lived convection ovens driven by gravity.

Narayanan's new model shows that despite their ample reservoirs of gas and dust, SMGs don't leak gas (what astronomers call galactic outflow) at all the way Milky Way-type galaxies do. Instead, because of the tight grip of gravity in these hugely massive galaxies, as stars die and go nova the stellar gas is recycled back inward, continually fueling the formation of new stars and future supernova. That recycling process forms a feedback loop that jets out crazy amounts of light while keeping the mass trapped inside the galaxy.

According to Narayanan and his team, their model owes its accuracy to a newly developed computer code that describes how light escapes the complex maze of dust and gas in an SMG. Romeel Davé, an astronomer at the University of the Western Cape who specializes in supercomputer galactic models (and was not involved in the research), says that thanks to this breakthrough, Narayanan and his team have "presented the first impressively viable model of SMG formation, allowing us a tantalizing glimpse behind the mask of these behemoths of deep space."

According to Davé, Narayanan's new model "offer[s] unprecedented clarity in understanding the origins of such deep-space monsters."

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SpARCS1049+56 contains at least 27 galaxies and has a total mass of 400 trillion suns.

SpARCS1049+56 contains at least 27 galaxies and has a total mass of 400 trillion suns. | Amazing Science |

A team of international astronomers has discovered a rare and colossal cluster of galaxies that is turning preconceived notions on their head -- and giving scientists plenty of fodder for inventive metaphors. According to a release, the discovery shows a "beast of a galaxy cluster whose heart is bursting with new stars."

SpARCS1049+56 -- as the cluster has been tagged -- is 9.8 billion light years from Earth, contains at least 27 individual galaxies and has a total mass equal to about 400 trillion suns. Scientists say the dominant galaxy at the cluster's heart is stealing gas from a neighbor galaxy as it spits out an incredible 860 stars per year. For contrast, our Milky Way galaxy gives birth to only one or two new stars per year.

The discovery -- originally made with telescopes atop Mauna Kea on Hawaii's Big Island -- is the first to show that gigantic galaxies at the center of massive clusters can grow significantly by feeding off gas stolen from other galaxies.

Tracy Webb of McGill University in Montreal, the lead author of the study, said in a statement that usually stars at the centers of galaxy clusters are old and dead, essentially fossils. "But we think the giant galaxy at the center of this cluster is furiously making new stars after merging with a smaller galaxy," she said.

Via Jocelyn Stoller
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A new approach towards solving mysteries of the interstellar 'empty' space

A new approach towards solving mysteries of the interstellar 'empty' space | Amazing Science |

It is one of the most intriguing questions in astrochemistry: the mystery of the diffuse interstellar bands (DIBs), a collection of about 400 absorption bands that show up in spectra of light that reaches the earth after having traversed the interstellar medium. Despite intense research efforts over the last few decades, an assignment of the DIBs has remained elusive, although indications exist that they may arise from the presence of large hydrocarbon molecules in interstellar space. Recent experiments at the Max Born Institute lend novel credibility to this hypothesis.

Among the hydrocarbons that are possible carriers of the DIBs, polycyclic aromatic hydrocarbons (PAHs) are considered to be particularly promising. The presence of PAH molecules was previously inferred in many astronomical objects, as well as in the interstellar medium of the Milky Way. However, within the astronomical community, the linewidths of the DIBs, which are indicative of the lifetimes of the excited states that are involved in the absorption process, are often considered as an argument that speaks against the PAHs. The new experiment was performed in collaboration with scientists from the university of Lyon and aided by theoretical input from scientists at the universities of Heidelberg, Hyderabad and Leiden. It has been shown that the lifetimes of excited states of small to medium-size PAHs are consistent with the linewidths that are observed for the DIBs.

In the experiments, a series of small to medium-size PAH molecules (naphthalene, anthracene, pyrene and tetracene, containing 2-4 benzene-like aromatic rings), were ionized by an ultrashort extreme-ultraviolet (XUV) laser pulse. As a result of electron correlation, the absorption of an XUV photon not only led to removal of one of the electrons, but furthermore to electronic excitation of the molecular ion left behind. The lifetimes of these excited cationic electronic states were monitored by probing the ions with a moderately strong, time-delayed infrared (IR) laser pulse. When the ions are formed, the electronic excitation is at its highest, and only one or a few IR photons are needed to remove a second electron. However, a little later, when the ion relaxes and energy is transferred from the electronic to the vibrational degrees of freedom, more IR photons are needed to remove the second electron. In other words, monitoring the formation of doubly-charged ions as a function of the time delay between the XUV and IR laser pulses allowed extraction of the lifetimes of the states formed by the XUV ionization process. As it turned out, and as was further supported by high-level calculations, these lifetimes of a few 10s of femtoseconds are well within the range of what is required for potential carriers of the DIBs. 

Beyond the implications for the DIBs, the new experiments have implications for the further development of attosecond science. One of the most sought-after goals in attosecond science at the moment, is the observation of charge migration, i.e. ultrafast (attosecond to few-femtosecond) motion of an electron or hole through a molecular structure. It has been proposed that charge migration may provide new opportunities for control of chemical reactivity, a goal that is as old as the chemical research itself. First indications that attosecond to few-femtosecond time-scale dynamics can be observed in polyatomic molecules were obtained by researchers at the university of Milano last year. The PAH molecules that were investigated in the experiments at MBI represent the largest molecular species yet to which ultrafast XUV-IR pump-probe spectroscopy has been applied. Besides the insights into ultrafast electronic relaxation obtained from the current work, the theoretical work performed in order to interpret the experiments suggests that PAH molecules are also ideal candidates for observing attosecond to few-femtosecond timescale charge migration. Such experiments will therefore be attempted next.

Abb.: Schematic of the experiment. (a) Schematic of the XUV-induced dynamics in PAH molecules studied in this paper. Excited states are created in the valence shell of the cation through one of two possibilities, namely the formation of a single-hole configuration or the formation of a 2hole-1particle configuration (involving a shake-up process) (left) (IP stands for Ionization potential). The cation can be further ionized by the IR probe laser, provided that non-adiabatic relaxation has not taken place yet (middle). After relaxation, the IR probe cannot ionize the cation anymore (right). (b) Two-colour XUV-IR ion signals measured in the case of anthracene, as a function of the detected mass-to-charge ratio and the XUV-IR delay. XUV-only and IR-only signals have been subtracted. The XUV pump and IR probe pulses overlap at zero delay (black dashed line). A red colour corresponds to a signal increase, while a blue colour signifies depletion. For positive XUV-IR delays, a very fast dynamics is observed for the doubly charged anthracene ion (A2+, m/q=89). As explained in the text, the measurement reflects non-adiabatic relaxation in the anthracene cation (A+). The dynamics observed in the first fragment (A-C2H2+) is not discussed in this article.

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The Universe is Slowly Fading, Astronomers Discovered

The Universe is Slowly Fading, Astronomers Discovered | Amazing Science |
A group of astronomers studying 221,000 galaxies has measured the energy generated within a large portion of space more precisely than ever before.

Their study, which is part of the Galaxy And Mass Assembly (GAMA) project, the largest multi-wavelength survey ever put together, involved many of the world’s most powerful telescopes, including ESO’s VISTA and VST survey telescopes at the Paranal Observatory in Chile, NASA’s orbiting telescopes GALEX and WISE, and ESA’s Herschel Space Observatory.

“We used as many space and ground-based telescopes as we could get our hands on to measure the energy output of over 200,000 galaxies across as broad a wavelength range as possible,” said team leader Prof Simon Driver from the University of St Andrews, UK, and ICRAR.

The survey data, released to scientists around the world today, includes measurements of the energy output of each galaxy at 21 wavelengths, from the ultraviolet (UV) to the far infrared (IR). This dataset will help them to better understand how different types of galaxies form and evolve.

All energy in the Universe was created in the Big Bang with some portion locked up as mass. Stars shine by converting this mass into energy as described by Einstein’s famous equation E=mc2.

The GAMA study sets out to map and model all of the energy generated within a large volume of space today and at different times in the past.

“While most of the energy sloshing around was created in the aftermath of the Big Bang, additional energy is constantly being released by stars as they fuse elements like hydrogen and helium together,” said Prof Driver, who is the first author of a paper submitted for publication in the Monthly Notices of the Royal Astronomical Society.

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Assembly of galaxies in the early universe witnessed for the first time

Assembly of galaxies in the early universe witnessed for the first time | Amazing Science |
The Atacama Large Millimeter/submillimeter Array (ALMA) has been used to detect the most distant clouds of star-forming gas yet found in normal galaxies in the early universe. The new observations allow astronomers to start to see how the first galaxies were built up and how they cleared the cosmic fog during the era of reionization. This is the first time that such galaxies are seen as more than just faint blobs.

When the first galaxies started to form a few hundred million years after the Big Bang, the Universe was full of a fog of hydrogen gas. But as more and more brilliant sources -- both stars and quasars powered by huge black holes -- started to shine they cleared away the mist and made the Universe transparent to ultraviolet light. Astronomers call this the epoch of reionisation, but little is known about these first galaxies, and up to now they have just been seen as very faint blobs. But now new observations using the power of ALMA are starting to change this.

A team of astronomers led by Roberto Maiolino (Cavendish Laboratory and Kavli Institute for Cosmology, University of Cambridge , United Kingdom) trained ALMA on galaxies that were known to be seen only about 800 million years after the Big Bang. The astronomers were not looking for the light from stars, but instead for the faint glow of ionised carbon [3] coming from the clouds of gas from which the stars were forming. They wanted to study the interaction between a young generation of stars and the cold clumps that were assembling into these first galaxies.

They were also not looking for the extremely brilliant rare objects -- such as quasars and galaxies with very high rates of star formation -- that had been seen up to now. Instead they concentrated on rather less dramatic, but much more common, galaxies that reionised the Universe and went on to turn into the bulk of the galaxies that we see around us now.

From one of the galaxies -- given the label BDF 3299 -- ALMA could pick up a faint but clear signal from the glowing carbon. However, this glow wasn't coming from the centre of the galaxy, but rather from one side. Co-author Andrea Ferrara (Scuola Normale Superiore, Pisa, Italy) explains the significance of the new findings: "This is the most distant detection ever of this kind of emission from a 'normal' galaxy, seen less than one billion years after the Big Bang. It gives us the opportunity to watch the build-up of the first galaxies. For the first time we are seeing early galaxies not merely as tiny blobs, but as objects with internal structure!"

The astronomers think that the off-centre location of the glow is because the central clouds are being disrupted by the harsh environment created by the newly formed stars -- both their intense radiation and the effects of supernova explosions -- while the carbon glow is tracing fresh cold gas that is being accreted from the intergalactic medium.

By combining the new ALMA observations with computer simulations, it has been possible to understand in detail key processes occurring within the first galaxies. The effects of the radiation from stars, the survival of molecular clouds, the escape of ionising radiation and the complex structure of the interstellar medium can now be calculated and compared with observation. BDF 3299 is likely to be a typical example of the galaxies responsible for reionisation.

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What happens when Cosmic Giants meet Galactic Dwarfs?

What happens when Cosmic Giants meet Galactic Dwarfs? | Amazing Science |

When two different sized galaxies smash together, the larger galaxy stops the smaller one making new stars, according to a study of more than 20,000 merging galaxies.

The research, published today, also found that when two galaxies of the same size collide, both galaxies produce stars at a much faster rate. Astrophysicist Luke Davies, from The University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR), says our nearest major galactic neighbour, Andromeda, is hurtling on a collision course with the Milky Way at about 400,000 kilometres per hour.

“Don’t panic yet, the two won’t smash into each other for another four billion years or so,” he says. “But investigating such cosmic collisions lets us better understand how galaxies grow and evolve.”

Previously, astronomers thought that when two galaxies smash into each other their gas clouds—where stars are born—get churned up and seed the birth of new stars much faster than if they remained separate.

However Dr Davies’ research, using the Galaxy and Mass Assembly (GAMA) survey observed using the Anglo-Australian Telescope in regional New South Wales, suggests this idea is too simplistic. He says whether a galaxy forms stars more rapidly in a collision, or forms any new stars at all, depends on if it is the big guy or the little guy in this galactic car crash.

“When two galaxies of similar mass collide, they both increase their stellar birth rate,” Dr Davies says. “However when one galaxy significantly outweighs the other, we have found that star formation rates are affected for both, just in different ways.

“The more massive galaxy begins rapidly forming new stars, whereas the smaller galaxy suddenly struggles to make any at all. “This might be because the bigger galaxy strips away its smaller companion’s gas, leaving it without star-forming fuel or because it stops the smaller galaxy obtaining the new gas required to form more stars.”

The study was released today in the journal Monthly Notices of the Royal Astronomical Society, published by Oxford University Press.

So what will happen in four billion years to the Milky Way and Andromeda? Dr Davies says the pair are like “cosmic tanks”—both relatively large and with similar mass. “As they get closer together they will begin to affect each other’s star formation, and will continue to do so until they eventually merge to become a new galaxy, which some call ‘Milkdromeda’,” he says.

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Falling into a black hole may convert you into a hologram or you will hit a firewall of doom

Falling into a black hole may convert you into a hologram or you will hit a firewall of doom | Amazing Science |

In the movie Interstellar, the main character Cooper escapes from a black hole in time to see his daughter Murph in her final days. Some have argued that the movie is so scientific that it should be taught in schools. In reality, many scientists believe that anything sent into a black hole would probably be destroyed. But a new study suggests that this might not be the case after all. The research says that, rather than being devoured, a person falling into a black hole would actually be absorbed into a hologram — without even noticing. The paper challenges a rival theory stating that anybody falling into a black hole hits a “firewall” and is immediately destroyed.

Forty years ago, Stephen Hawking shocked the scientific establishment with his discovery that black holes aren’t really black. Classical physics implies that anything falling through the horizon of a black hole can never escape. But Hawking showed that black holes continually emit radiation once quantum effects are taken into account. Unfortunately, for typical astrophysical black holes, the temperature of this radiation is far lower than that of the cosmic microwave background, meaning detecting them is beyond current technology.

Hawking’s calculations are perplexing. If a black hole continually emits radiation, it will continually lose mass—eventually evaporating. Hawking realised that this implied a paradox: if a black hole can evaporate, the information about it will be lost forever. This means that even if we could measure the radiation from a black hole we could never figure out it was originally formed. This violates an important rule of quantum mechanics that states information cannot be lost or created.

Another way to look at this is that Hawking radiation poses a problem with determinism for black holes. Determinism implies that the state of the universe at any given time is uniquely determined from its state at any other time. This is how we can trace its evolution both astronomically and mathematically though quantum mechanics.

This means that the loss of determinism would have to arise from reconciling quantum mechanics with Einstein’s theory of gravity – a notoriously hard problem and ultimate goal for many physicists. Black hole physics provides a test for any potential quantum gravity theory. Whatever your theory is, it must explain what happens to the information recording a black hole’s history.

It took two decades for scientists to come up with a solution. They suggested that the information stored in a black hole is proportional to its surface area (in two dimensions) rather than its volume (in three dimensions). This could be explained by quantum gravity, where the three dimensions of space could be reconstructed from a two-dimensional world without gravity – much like a hologram. Shortly afterwards, string theory, the most studied theory of quantum gravity, was shown to be holographic in this way.

Using holography we can describe the evaporation of the black hole in the two-dimensional world without gravity, for which the usual rules of quantum mechanics apply. This process is deterministic, with small imperfections in the radiation encoding the history of the black hole. So holography tells us that information is not lost in black holes, but tracking down the flaw in Hawking’s original arguments has been surprisingly hard.

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Researchers characterize mysterious ultraluminous X-ray sources

Researchers characterize mysterious ultraluminous X-ray sources | Amazing Science |

Many black holes are believed to have surrounding accretion disks of matter trapped by gravity and spiraling toward the event horizon. Supercritical accretion disks (SCADs) are those with mass accretion rates exceeding the Eddington limit—this describes the maximum possible luminosity of an energetic body when the outward force of radiation is in equilibrium with gravitation. Masses that exceed the Eddington luminosity to produce SCADs emit extremely intense stellar winds from their outer layers.

The only known supercritical accretor in the Milky Way galaxy is SS 433, a highly exotic eclipsing binary star system. Its primary object is likely a black hole. Its secondary companion is believed to be a late A-type star based on its light spectrum. The secondary in SS 433 is losing mass into an accretion disk as it spirals in toward the primary, which is slowly consuming it. In turn, as the accretion disc spirals in toward the primary, it becomes super-heated and emits intense X-rays.

Physicists are fascinated by the exotic nature of SS 433, but also by its strong resemblance to ultraluminous X-ray sources (ULXs), which are astronomical sources of X-rays that are less luminous than the nuclei of active galaxies, but are more luminous than any known stellar process. These are sources of X-rays that exceed the Eddington luminosities of neutron stars and stellar black holes. Recently, a group of researchers from Russia and Japan have compared the optical spectra of ULXs to SS 433 and have determined that ULXs with X-ray luminosities of ~1040 erg S-1 must constitute a homogenous class of objects that most likely have SCADs. They have published their results in Nature Physics.

The most popular models for ULXs have either intermediate mass black holes with standard accretion disks or stellar-mass black holes with accretion disk luminosity exceeding the Eddington limit. Based on X-ray data alone, it is not possible to distinguish these models, so the researchers have turned to optical spectroscopy to find unique information about ULXs. Using the 8.2 meter Subaru Telescope of the National Astronomical Observatory of Japan, located at the Mauna Kea Observatory on Hawaii, they obtained high-quality spectroscopic data from a number of ULX sources.

They have determined that ULX spectra are quite similar to late nitrogen Wolf-Rayet stars (WNLs), which exhibit broad emissions of ionized nitrogen and helium or carbon. They have very high surface temperatures and produce intense stellar winds. The spectra from ULXs also resemble those of luminous blue variable stars (LBVs) in the compact stages of stellar development. Because the physical conditions of its disk wind may be similar to WNL stars, SS 433 also bears a strong resemblance to ULXs. The authors write, "Such spectra of high luminosities with prominent He II emission lines have never been observed from any stellar-mass black hole X-ray binaries, except for SS 433 and those having WNL donors [secondaries losing mass to the accretion disks of primaries in binary systems]."

They exclude a number of stellar cases, including ULXs with WNL donors that exhibit stellar winds with the observed spectra. Wind terminal velocity is determined by surface gravity, making it difficult to explain the rapid variability of the He II line width in the recorded spectra. The authors conclude that SS 433 is intrinsically the same as ULXs, but is an extreme case with a particularly high mass accretion rate from its secondary, which accounts for the presence of its persistent jet outflows.

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A group of unusual black holes is consuming excessive amounts of matter at a rapid rate

A group of unusual black holes is consuming excessive amounts of matter at a rapid rate | Amazing Science |
Astronomers have known for some time that supermassive black holes − with masses ranging from millions to billions of times the mass of the Sun and residing at the centers of galaxies − can gobble up huge quantities of gas and dust that have fallen into their gravitational pull. As the matter falls towards these black holes, it glows with such brilliance that they can be seen billions of light years away. Astronomers call these extremely ravenous black holes "quasars."

This new result suggests that some quasars are even more adept at devouring material than scientists previously knew.

"Even for famously prodigious consumers of material, these huge black holes appear to be dining at enormous rates, at least five to ten times faster than typical quasars," said Bin Luo of Penn State University in State College, Pennsylvania, who led the study.

Luo and his colleagues examined data from Chandra for 51 quasars that are located at a distance between about 5 billion and 11.5 billion light years from Earth. These quasars were selected because they had unusually weak emission from certain atoms, especially carbon, at ultraviolet wavelengths. About 65% of the quasars in this new study were found to be much fainter in X-rays, by about 40 times on average, than typical quasars.

The weak ultraviolet atomic emission and X-ray fluxes from these objects could be an important clue to the question of how a supermassive black hole pulls in matter. Computer simulations show that, at low inflow rates, matter swirls toward the black hole in a thin disk. However, if the rate of inflow is high, the disk can puff up dramatically, because of pressure from the high radiation, into a torus or donut that surrounds the inner part of the disk.

"This picture fits with our data," said co-author Jianfeng Wu of the Harvard-Smithsonian Center for Astrophysics, in Cambridge, Massachusetts. "If a quasar is embedded in a thick donut-shaped structure of gas and dust, the donut will absorb much of the radiation produced closer to the black hole and prevent it from striking gas located further out, resulting in weaker ultraviolet atomic emission and X-ray emission."
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Earth-Size Event Horizon Telescope Will Explore Black Hole In Center Of Our Galaxy

Earth-Size Event Horizon Telescope Will Explore Black Hole In Center Of Our Galaxy | Amazing Science |

Looking into the galactic center is hard. Too much dust and gas lies between Earth and the center of the Milky Way that very little of the visible light emitted there makes it to us. We can peek through that dust and gas by collecting x-rays, infrared radiation, and radio waves. Even then, however, resolving the tiny speck of sky that contains the Milky Way’s central black hole, with enough clarity to see the black hole’s shadow, is extremely difficult. You need a very special telescope roughly the size of the Earth to do it. This might sound impractical. Fortunately, it’s possible to mimic the performance of an Earth-size telescope by coordinating existing radio telescopes scattered around the world.

That’s the idea behind the Event Horizon Telescope (EHT). If all goes well, by the end of next year the EHT will be a coordinated array of radio telescopes stretching from the South Pole to Hawaii to Chile to Mexico, plus many points in between. The astronomers behind the EHT have been already been observing for years using a smaller telescope array. In 2007, a three-station version of the EHT resolved Sagittarius A*, the black hole at the center of the Milky Way, with unprecedented clarity, detecting something (“structure” is the proper term) on the scale that we would expect from the black hole’s event horizon. It was a big deal, the farthest into the inner sanctum of a black hole that anyone had ever seen. The goal now is to make the EHT powerful enough to take the black hole’s picture.

Shep Doeleman, an astronomer with joint appointments at the Massachusetts Institute of Technology and the Harvard-Smithsonian Center for Astrophysics, leads the international group of researchers who are working to make this happen. Scientists from the U.S., Japan, Taiwan, Chile, Mexico, and several European countries are involved in the project.

The EHT uses the technique of Very Long Baseline Interferometry (VLBI) to synthesize an Earth-sized telescope in order to achieve the highest resolution possible using ground-based instrumentation. The target source is observed simultaneously at all telescopes. The data are recorded at each of the sites and later brought back to a processing facility where they are passed through a special purpose supercomputer known as a correlator. More information about radio astronomy and the technique of interferometry is available here.

Key science results so far
  • Sgr A* is a black hole: Material is falling into the Sgr A* system. If Sgr A* had a surface no bigger than the size measured by the EHT, it would be a very bright source at infrared wavelengths. However, Sgr A* is a faint infrared source, indicating that energy is disappearing through an event horizon, the existence of which defines a black hole.
  • The accretion disc in Sgr A* is inclined to the line of sight: The material orbiting and falling into the black hole is confined to a region called the accretion disk. The size obtained from the EHT indicates that we are viewing this disk closer to edge-on than face-on. EHT data also place constraints on other parameters, such as the spin of the black hole.
  • The millimeter emission in Sgr A* is offset from the black hole: As an object gets close to a black hole, it appears bigger than it actually is. The apparent size measured by the EHT is smaller than the minimum size allowed by gravitational lensing. The emission must therefore be offset from the black hole. Models indicate that we are seeing the portion of the accretion disk that is moving toward us.
  • The variability in Sgr A* occurs near the black hole: The emission we detect from Sgr A* changes in brightness, but its apparent size does not change. While the mechanism that produces this variability is not well understood, EHT data indicate that the changes occur in the accretion flow very near the black hole.
  • The black hole in M87 is spinning: Like any other object, black holes can rotate. The small size of the emission around M87 implies that the black hole is rotating rapidly and that the accreting material is orbiting the black hole in the same direction.

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Is this ET? Mystery of strange radio bursts from space

Is this ET? Mystery of strange radio bursts from space | Amazing Science |

Mysterious radio wave flashes from far outside the galaxy are proving tough for astronomers to explain. Is it pulsars? A spy satellite? Or an alien message?

BURSTS of radio waves flashing across the sky seem to follow a mathematical pattern. If the pattern is real, either some strange celestial physics is going on, or the bursts are artificial, produced by human – or alien – technology. Telescopes have been picking up so-called fast radio bursts (FRBs) since 2001. They last just a few milliseconds and erupt with about as much energy as the sun releases in a month. Ten have been detected so far, most recently in 2014, when the Parkes Telescope in New South Wales, Australia, caught a burst in action for the first time. The others were found by sifting through data after the bursts had arrived at Earth. No one knows what causes them, but the brevity of the bursts means their source has to be small – hundreds of kilometres across at most – so they can't be from ordinary stars. And they seem to come from far outside the galaxy. The weird part is that they all fit a pattern that doesn't match what we know about cosmic physics.

To calculate how far the bursts have come, astronomers use a concept called the dispersion measure. Each burst covers a range of radio frequencies, as if the whole FM band were playing the same song. But electrons in space scatter and delay the radiation, so that higher frequency waves make it across space faster than lower frequency waves. The more space the signal crosses, the bigger the difference, or dispersion measure, between the arrival time of high and low frequencies – and the further the signal has travelled.

Michael Hippke of the Institute for Data Analysis in Neukirchen-Vluyn, Germany, and John Learned at the University of Hawaii in Manoa found that all 10 bursts' dispersion measures are multiples of a single number: 187.5 (see chart). This neat line-up, if taken at face value, would imply five sources for the bursts all at regularly spaced distances from Earth, billions of light-years away. A more likely explanation, Hippke and Lerned say, is that the FRBs all come from somewhere much closer to home, from a group of objects within the Milky Way that naturally emit shorter-frequency radio waves after higher-frequency ones, with a delay that is a multiple of 187.5 (

They claim there is a 5 in 10,000 probability that the line-up is coincidence. "If the pattern is real," says Learned, "it is very, very hard to explain." Cosmic objects might, by some natural but unknown process, produce dispersions in regular steps. Small, dense remnant stars called pulsars are known to emit bursts of radio waves, though not in regular arrangements or with as much power as FRBs. But maybe superdense stars are mathematical oddities because of underlying physics we don't understand.

It's also possible that the telescopes are picking up evidence of human technology, like an unmapped spy satellite, masquerading as signals from deep space. The most tantalising possibility is that the source of the bursts might be a who, not a what. If none of the natural explanations pan out, their paper concludes, "An artificial source (human or non-human) must be considered."

"Beacon from extraterrestrials" has always been on the list of weird possible origins for these bursts. "These have been intriguing as an engineered signal, or evidence of extraterrestrial technology, since the first was discovered," says Jill Tarter, former director of the SETI Institute in California. "I'm intrigued. Astronomers have long speculated that a mathematically clever message – broadcasts encoded with pi, or flashes that count out prime numbers, as sent by aliens in the film Contact – could give away aliens' existence. Perhaps extraterrestrial civilizations are flagging us down with basic multiplication. Stay tuned."

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Astronomers Create Pseudo-3D Maps of Milky Way's Interstellar Material

Astronomers Create Pseudo-3D Maps of Milky Way's Interstellar Material | Amazing Science |
A group of astronomers has produced pseudo-3D maps of the material located between the stars in our Milky Way Galaxy.

Analyzing bands of starlight that have passed through space gives scientists information about the makeup of the space materials that the light has encountered.

In 1922, U.S. astronomer Mary Lea Heger discovered dark lines indicating ‘missing’ starlight, which must have been absorbed by a yet unknown source. These mysterious features were called diffuse interstellar bands, or DIBsSince then, scientists have identified more than 400 DIBs, but the material that is causing these bands to appear and their precise location have remained a mystery.

In a new approach to understanding DIBs, Dr Kos and his co-authors combined information from nearly 500,000 stellar spectra obtained by theRAVE (Radial Velocity Experiment) survey to produce pseudo-3D maps of the DIB-material at 862 nm covering the nearest 9,800 light-years from our Solar System.

RAVE project used the UK Schmidt Telescope in Australia to collect spectroscopic information from the light of as many as 150 stars at once. The resulting maps are described as ‘pseudo-3D’ because a specific mathematical form was assumed for the distribution in the vertical dimension that provides the distances from the plane of the Milky Way, with the maps presented in the remaining two dimensions.

The maps showed the intriguing result that the complex molecules thought to be responsible for the DIBs are distributed differently than another known component of the interstellar medium – the solid particles known as dust – also traced by the RAVE survey.

“With the wide area coverage of the spectroscopic survey RAVE it was for the first time possible to map out the 3D distribution of the DIBs,” said Dr Matthias Steinmetz of the Leibniz Institute for Astrophysics Potsdam, who is a co-author of the paper reporting the results in the journal Science.

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New ‘stealth dark matter’ theory may explain mystery of the universe’s missing mass

New ‘stealth dark matter’ theory may explain mystery of the universe’s missing mass | Amazing Science |

A new theory that may explain why dark matter has evaded direct detection in Earth-based experiments has been developed by a team of Lawrence Livermore National Laboratory (LLNL) particle physicists known as the Lattice Strong Dynamics Collaboration.

The group has combined theoretical and computational physics techniques and used the Laboratory’s massively parallel 2-petaflop Vulcan supercomputer to devise a new model of dark matter. The model identifies today’s dark matter as naturally “stealthy.” But in the extremely high-temperature plasma conditions that pervaded the early universe, it would have been easy to see dark matter via interactions with ordinary matter, the model shows.

“These interactions in the early universe are important because ordinary and dark matter abundances today are strikingly similar in size, suggesting this occurred because of a balancing act performed between the two before the universe cooled,” said Pavlos Vranas of LLNL, one of the authors of a paper in an upcoming edition of the journal Physical Review Letters.

Dark matter makes up 83 percent of all matter in the universe and does not interact directly with electromagnetic or strong and weak nuclear forces. Light does not bounce off of it, and ordinary matter goes through it with only the feeblest of interactions. It is essentially invisible, yet its interactions with gravity produce striking effects on the movement of galaxies and galactic clusters, leaving little doubt of its existence.

The key to stealth dark matter’s split personality is its compositeness and the miracle of confinement. Like quarks in a neutron, at high temperatures these electrically charged constituents interact with nearly everything. But at lower temperatures, they bind together to form an electrically neutral composite particle. Unlike a neutron, which is bound by the ordinary strong interaction of quantum chromodynamics (QCD), the stealthy neutron would have to be bound by a new and yet-unobserved strong interaction, a dark form of QCD.

“It is remarkable that a dark matter candidate just several hundred times heavier than the proton could be a composite of electrically charged constituents and yet have evaded direct detection so far,” Vranas said. Similar to protons, stealth dark matter is stable and does not decay over cosmic times. However, like QCD, it produces a large number of other nuclear particles that decay shortly after their creation. These particles can have net electric charge but would have decayed away a long time ago. In a particle collider with sufficiently high energy (such as the Large Hadron Collider in Switzerland), these particles can be produced again for the first time since the early universe. They could generate unique signatures in the particle detectors because they could be electrically charged.

malik matwi's comment, December 13, 2015 3:00 PM
neither dark matter nor energy
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Converging black holes in Virgo constellation: Crash expected in 100,000 years

Converging black holes in Virgo constellation: Crash expected in 100,000 years | Amazing Science |

Astronomers have provided additional evidence that a pair of closely orbiting black holes deep in the Virgo constellation is causing the rhythmic flashes of light coming from quasar PG 1302-102. Based on calculations of the pair's mass -- together, and relative to each other -- the researchers go on to predict a smashup 100,000 years from now, far sooner than previously predicted.

Earlier this year, astronomers discovered what appeared to be a pair of supermassive black holes circling toward a collision so powerful it would send a burst of gravitational waves surging through the fabric of space-time itself.

Now, in a study in the journal Nature, astronomers at Columbia University provide additional evidence that a pair of closely orbiting black holes is causing the rhythmic flashes of light coming from quasar PG 1302-102.

Based on calculations of the pair's mass--together, and relative to each other--the researchers go on to predict a smashup 100,000 years from now, an impossibly long time to humans but the blink of an eye to a star or black hole. Spiraling together 3.5 billion light-years away, deep in the Virgo constellation, the pair is separated by a mere light-week. By contrast, the closest previously confirmed black hole pair is separated by 20 light-years.

"This is the closest we've come to observing two black holes on their way to a massive collision," said the study's senior author, Zoltan Haiman, an astronomer at Columbia. "Watching this process reach its culmination can tell us whether black holes and galaxies grow at the same rate, and ultimately test a fundamental property of space-time: its ability to carry vibrations called gravitational waves, produced in the last, most violent, stage of the merger."

At the center of most giant galaxies, including our own Milky Way, lies a supermassive black hole so dense that not even light can escape. Over time, black holes grow bigger--millions to billions times more massive than the sun--by gobbling up stars, galaxies and even other black holes.

A supermassive black hole about to cannibalize its own can be detected by the mysterious flickering of a quasar--the beacon of light produced by black holes as they burn through gas and dust swirling around them. Normally, quasars brighten and dim randomly, but when two black holes are on the verge of uniting, the quasar appears to flicker at regular intervals, like a light bulb on timer.

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Researchers find 13.2 billion year-old galaxy in our 13.8 billion year old universe

Researchers find 13.2 billion year-old galaxy in our 13.8 billion year old universe | Amazing Science |
A team of Caltech researchers that has spent years searching for the earliest objects in the universe now reports the detection of what may be the most distant galaxy ever found. In an article published August 28, 2015 in Astrophysical Journal Letters, Adi Zitrin, a NASA Hubble Postdoctoral Scholar in Astronomy, and Richard Ellis—who recently retired after 15 years on the Caltech faculty and is now a professor of astrophysics at University College, London—describe evidence for a galaxy called EGS8p7 that is more than 13.2 billion years old. The universe itself is about 13.8 billion years old.

Earlier this year, EGS8p7 had been identified as a candidate for further investigation based on data gathered by NASA's Hubble Space Telescope and the Spitzer Space Telescope. Using the multi-object spectrometer for infrared exploration (MOSFIRE) at the W.M. Keck Observatory in Hawaii, the researchers performed a spectrographic analysis of the galaxy to determine its redshift. Redshift results from the Doppler effect, the same phenomenon that causes the siren on a fire truck to drop in pitch as the truck passes. With celestial objects, however, it is light that is being "stretched" rather than sound; instead of an audible drop in tone, there is a shift from the actual color to redder wavelengths.

Redshift is traditionally used to measure distance to galaxies, but is difficult to determine when looking at the universe's most distant—and thus earliest—objects. Immediately after the Big Bang, the universe was a soup of charged particles—electrons and protons—and light (photons). Because these photons were scattered by free electrons, the early universe could not transmit light. By 380,000 years after the Big Bang, the universe had cooled enough for free electrons and protons to combine into neutral hydrogen atoms that filled the universe, allowing light to travel through the cosmos. Then, when the universe was just a half-billion to a billion years old, the first galaxies turned on and reionized the neutral gas. The universe remains ionized today.
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For the First Time, Radio Astronomers Find a Link Between Gamma Ray Bursts (GRBs) and Two Galaxies Colliding

For the First Time, Radio Astronomers Find a Link Between Gamma Ray Bursts (GRBs) and Two Galaxies Colliding | Amazing Science |

Gamma ray bursts (GRBs) are among the most dramatically explosive events in the universe. They’re often dubbed the largest explosions since the Big Bang (it’s pretty hard to quantify how big the Big Bang was, but suffice it to say it was quite large). There are two classes of GRBs: long-duration and short-duration. Long-duration GRBs (which interest us today) are caused when extremely massive stars go bust.

The most massive stars burn through their fuel much faster, and die out much more quickly than smaller stars. Therefore, long-duration GRBs should only be seen in galaxies with a lot of recent star formation. All the massive stars will have already died in a galaxy which isn’t forming new stars. Lots of detailed observations have been required to confirm this connection between GRBs and their host galaxies. It’s, in fact, one of the main pieces of evidence for the massive-star explanation.

The authors of a recent paper studied the host galaxy of a long-duration GRB with an additional goal in mind. Rather than just show that this galaxy is forming lots of stars, they wanted to look at its gas to explainwhy it’s forming so many stars. So, they went looking for neutral hydrogen gas in the galaxy. Neutral gas is a galaxy’s fuel for forming new stars. Understanding the properties of the gas should tell us about the way in which the galaxy is forming stars.

Hot, ionized hydrogen is easy to observe, because it emits a lot of light in the UV and optical ranges. This ionized hydrogen is found right around young, star-forming regions, and so has been seen in GRB hosts before. But the cold, neutral hydrogen – which makes up most of a galaxy’s gas – is much harder to observe directly. It doesn’t emit much light on its own, but one of the main places it does emit is in the radio band: the 21-cm line. For more information on the physics involved, see this astrobite page, but suffice it to say that pretty much all neutral hydrogen emits weakly at 21 cm.

This signal is weak enough that it hasn’t been detected in the more distant GRB hosts. Today’s authors observed the host galaxy of the closest-yet-observed GRB (980425), which is only 100 million light-years away: about 50 times farther away than the Andromeda galaxy. This is practically just next-door, compared to most GRBs. This close proximity allowed them to make the first ever detection of 21-cm hydrogen emission from a GRB host galaxy.

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Monitoring a Waking Black Hole

Monitoring a Waking Black Hole | Amazing Science |
NASA's Swift satellite detected a rising tide of high-energy X-rays from the constellation Cygnus on June 15, just before 2:32 p.m. EDT. About 10 minutes later, the Japanese experiment on the International Space Station called the Monitor of All-sky X-ray Image (MAXI) also picked up the flare.

The outburst came from V404 Cygni, a binary system located about 8,000 light-years away that contains a black hole. Every couple of decades the black hole fires up in an outburst of high-energy light, becoming an X-ray nova. Until the Swift detection, it had been slumbering since 1989.

Download video in HD formats from NASA Goddard's Scientific Visualization Studio

An X-ray nova is a bright, short-lived X-ray source that reaches peak intensity in a few days and then fades out over a period of weeks or months. The outburst occurs when stored gas abruptly rushes toward a neutron star or black hole. By studying the patterns of the X-rays produced, astronomers can determine the kind of object at the heart of the eruption.

"Relative to the lifetime of space observatories, these black hole eruptions are quite rare," said Neil Gehrels, Swift's principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "So when we see one of them flare up, we try to throw everything we have at it, monitoring across the spectrum, from radio waves to gamma rays."

Astronomers classify this type of system as a low-mass X-ray binary. In V404 Cygni, a star slightly smaller than the sun orbits a black hole 10 times its mass in only 6.5 days. The close orbit and strong gravity of the black hole produce tidal forces that pull a stream of gas from its partner. The gas travels to a storage disk around the black hole and heats up to millions of degrees, producing a steady stream of X-rays as it falls inward.

But the disk flips between two dramatically different conditions. In its cooler state, the gas resists inward flow and just collects in the outer part of the disk like water behind a dam. Inevitably the build-up of gas overwhelms the dam, and a tsunami of hot bright gas rushes toward the black hole.

Astronomers relish the opportunity to collect simultaneous multiwavelength data on black hole binaries, especially one as close as V404 Cygni. In 1938 and 1956, astronomers caught V404 Cygni undergoing outbursts in visible light. During its eruption in 1989, the system was observed by Ginga, an X-ray satellite operated by Japan, and instruments aboard Russia's Mir space station.

"Right now, V404 Cygni shows exceptional variation at all wavelengths, offering us a rare chance to add to this unique data set," said Eleonora Troja, a Swift team member at Goddard.

Ongoing or planned satellite observations of the outburst involve NASA’s Swift satellite, Chandra X-ray Observatory and Fermi Gamma-ray Space Telescope, as well as Japan’s MAXI, the European Space Agency's INTEGRAL satellite, and the Italian Space Agency's AGILE gamma-ray mission. Ground-based facilities following the eruption include the 10.4-meter Gran Telescopio Canarias operated by Spain in the Canary Islands, the University of Leicester's 0.5-meter telescope in Oadby, U.K., the Nasu radio telescope at Waseda University in Japan, and amateur observatories.

V404 Cygni has flared many times since the eruption began, with activity ranging from minutes to hours. "It repeatedly becomes the brightest object in the X-ray sky -- up to 50 times brighter than the Crab Nebula, which is normally one of the brightest sources," said Erik Kuulkers, the INTEGRAL project scientist at ESA's European Space Astronomy Centre in Madrid. "It is definitely a 'once in a professional lifetime' opportunity."

In a single week, flares from V404 Cygni generated more than 70 "triggers" of the Gamma-ray Burst Monitor (GBM) aboard Fermi. This is more than five times the number of triggers seen from all objects in the sky in a typical week. The GBM triggers when it detects a gamma-ray flare, then it sends numerous emails containing increasingly refined information about the event to scientists on duty.

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Magnetic Waves From Distant Black Hole Shake Like Whip Being Held by Giant Hand

Magnetic Waves From Distant Black Hole Shake Like Whip Being Held by Giant Hand | Amazing Science |

NASA scientists say fast-moving waves coming from a distant supermassive black hole undulate like a whip whose handle is being held by a giant hand. NASA released a series of slinky-like images that illustrate the undulating waves. The observation was made by scientists studying data from National Radio Astronomy Observatory's Very Long Baseline Array. The galaxy/black hole system is called BL Lacertae (BL Lac).

This is the first time Alfven waves have been identified in a black hole system. The waves are generated when magnetic field lines interact with charged particles or ions. They then become twisted or coiled. The ions from BL Lac are in the form of particle jets flung from opposite sides of the black hole at speeds about 98 percent the speed of light. The jet is a flow of charged particles, called a plasma. It has a helical magnetic field that permeates the plasma. 

David Meier, a retired astrophysicist from NASA's Jet Propulsion Laboratory and the California Institute of Technology, says in a statement, "The waves are excited by a shaking motion of the jet at its base. By analyzing these waves, we are able to determine the internal properties of the jet, and this will help us ultimately understand how jets are produced by black holes." 

Marshall Cohen, an astronomer at Caltech and first author of the study, says, "Imagine running a water hose through a slinky that has been stretched taut. A sideways disturbance at one end of the slinky will create a wave that travels to the other end, and if the slinky sways to and fro, the hose running through its center has no choice but to move with it." 

The researchers say it is common for black hole particle jets to bend but it typically takes place of thousands of millions of years. Cohen says what is happening with the BL Lacertae system takes place in a matter of weeks. 

He says, "We're taking pictures once a month, and the position of the waves is different each month." 

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AI algorithm learns to ‘see’ features in galaxy images

AI algorithm learns to ‘see’ features in galaxy images | Amazing Science |

A team of astronomers and computer scientists at the University of Hertfordshire have taught a machine to “see” astronomical images, using data from the Hubble Space Telescope Frontier Fields set of images of distant clusters of galaxies that contain several different types of galaxies. The technique, which uses a form of AI called unsupervised machine learning, allows galaxies to be automatically classified at high speed, something previously done by thousands of human volunteers in projects like Galaxy Zoo.

“We have not told the machine what to look for in the images, but instead taught it how to ‘see,’” said graduate student Alex Hocking. “Our aim is to deploy this tool on the next generation of giant imaging surveys where no human, or even group of humans, could closely inspect every piece of data. But this algorithm has a huge number of applications far beyond astronomy, and investigating these applications will be our next step,” said University of Hertfordshire Royal Society University Research Fellow James Geach, PhD.

The scientists are now looking for collaborators to make use of the technique in applications like medicine, where it could for example help doctors to spot tumors, and in security, to find suspicious items in airport scans.

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Does a black hole create a hologram copy of anything that touches it?

Does a black hole create a hologram copy of anything that touches it? | Amazing Science |

According to Samir Mathur. professor of physics at The Ohio State University, the recently proposed idea that black holes have “firewalls” that destroy all they touch is wrong. He believes that a black hole converts anything that touches it into a hologram — a near-perfect copy of itself that continues to exist just as before.

Mathur says he proves that in a open-access paper posted online to the arXiv preprint server. In fact, he says, our world could be captured by a black hole, and we wouldn’t even notice. The debate hinges on a principle called complementarity, proposed by Stanford University physicist Leonard Susskind. Complementarity requires that any such hologram created by a black hole be a perfect copy of the original.

But mathematically, physicists on both sides of this debate have concluded that strict complementarity is not possible; that is to say, a perfect hologram can’t form on the surface of a black hole. But Mathur and his colleagues are comfortable with the idea, because they have since developed a modified model of complementarity, in which they assume that an imperfect hologram forms.

The information paradox: Physicist Stephen Hawking has famously said that the universe was imperfect from the very first moments of its existence. Without an imperfect scattering of the material created in the Big Bang, gravity would not have been able to draw together the atoms that make up galaxies, stars, the planets—and us.

This new dispute about hinges on whether physicists can accept that black holes are imperfect, just like the rest of the universe. “There’s no such thing as a perfect black hole, because every black hole is different,” Mathur explained.

His comment refers to the resolution of the “information paradox,” a long-running physics debate in which Hawking eventually conceded that the material that falls into a black hole isn’t destroyed, but rather becomes part of the black hole. The black hole is permanently changed by the new addition. That means every black hole is a unique product of the material that happens to come across it.

Interestingly, one of the tenets of string theory is that our three-dimensional existence might actually be a hologram on a surface that exists in many more dimensions. “If the surface of a black hole is a firewall, then the idea of the universe as a hologram has to be wrong,” Mathur said.  “It’s a simple question, really. Do you accept the idea of imperfection, or do you not?”

Kit Newton's comment, June 17, 2015 3:22 PM
Does the idea of perfection even make sense in concrete terms?
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Driven by merging black holes, gas thrown off in galactic jets can reach nearly the speed of light

Driven by merging black holes, gas thrown off in galactic jets can reach nearly the speed of light | Amazing Science |

Gigantic jets of gas that leap out of galaxies at nearly the speed of light occur only after two galaxies merge, a survey of the distant Universe shows. The results suggest that the jets are powered by the collision of black holes at the galaxies’ centres and solve the puzzle of why only some galaxies emit these jets.

The link between mergers and galactic jets seems to be a “slam dunk”, says astronomer Sylvain Veilleux of the University of Maryland in College Park, who was not involved in the work. Most large galaxies are thought to host black holes at their centres, and these can be billions of times as massive as the Sun. Some black holes, including the one at the heart of our own Milky Way, are dormant and are mostly only noticeable from the gravitational pull that they exert on nearby stars. But other black holes are surrounded by a disk of matter, light years across, that shines more brightly than the rest of its galaxy combined as the matters spirals into the black hole.

Only a few of these ‘active galactic nuclei’ have been seen producing what are probably the most spectacular fireworks in the Universe: jets of matter accelerated to nearly the speed of light that stream out of the galaxy centres in opposite directions, at right angles to the disks. These jets shine brightly in the radio spectrum and their hosts are therefore known as radio galaxies.

But why some systems have jets and some do not has been a puzzle. Marco Chiaberge, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, and his collaborators stumbled on an explanation almost by chance in late 2013, during a survey of radio galaxies using the Wide Field Camera 3 on the Hubble Space Telescope. “We printed out the images of this new survey and put them on a table,” Chiaberge recalls. “We looked at them and we said, ‘These are all mergers!’”

The team followed up their initial intuition with more careful work on a larger sample of 19 radio galaxies, all of them at least 7.8 billion light years (2.4 billion parsecs) away. Nearly all had irregular shapes with regions of intense star formation, a sign that they were the result of a recent merger, on cosmic time scales. Not all galaxy mergers are seen producing jets because in some of them the central black holes are still falling towards each other and are not merging, Chiaberge suggests. The results are available on the preprint server arXiv1 and are due to be published in the Astrophysical Journal.

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Is the universe a hologram? New calculations show that this may be fundamental feature of space itself

Is the universe a hologram? New calculations show that this may be fundamental feature of space itself | Amazing Science |

At first glance, there is not the slightest doubt: to us, the universe looks three dimensional. But one of the most fruitful theories of theoretical physics in the last two decades is challenging this assumption. The "holographic principle" asserts that a mathematical description of the universe actually requires one fewer dimension than it seems. What we perceive as three dimensional may just be the image of two dimensional processes on a huge cosmic horizon.

Up until now, this principle has only been studied in exotic spaces with negative curvature. This is interesting from a theoretical point of view, but such spaces are quite different from the space in our own universe. Results obtained by scientists at TU Wien (Vienna) now suggest that the holographic principle even holds in a flat spacetime.

Gravitational phenomena are described in a theory with three spatial dimensions, the behavior of quantum particles is calculated in a theory with just two spatial dimensions - and the results of both calculations can be mapped onto each other. Such a correspondence is quite surprising. It is like finding out that equations from an astronomy textbook can also be used to repair a CD-player. But this method has proven to be very successful. More than ten thousand scientific papers about Maldacena's "AdS-CFT-correspondence" have been published to date.

For theoretical physics, this is extremely important, but it does not seem to have much to do with our own universe. Apparently, we do not live in such an anti-de-sitter-space. These spaces have quite peculiar properties. They are negatively curved, any object thrown away on a straight line will eventually return. "Our universe, in contrast, is quite flat - and on astronomic distances, it has positive curvature", says Daniel Grumiller.

However, Grumiller has suspected for quite some time that a correspondence principle could also hold true for our real universe. To test this hypothesis, gravitational theories have to be constructed, which do not require exotic anti-de-sitter spaces, but live in a flat space. For three years, he and his team at TU Wien (Vienna) have been working on that, in cooperation with the University of Edinburgh, Harvard, IISER Pune, the MIT and the University of Kyoto. Now Grumiller and colleagues from India and Japan have published an article in the journal Physical Review Letters, confirming the validity of the correspondence principle in a flat universe.

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Pulsing light may indicate a supermassive black hole binary

Pulsing light may indicate a supermassive black hole binary | Amazing Science |

As two galaxies enter the final stages of merging, scientists have theorized that the galaxies' supermassive black holes will form a "binary," or two black holes in such close orbit they are gravitationally bound to one another. In a new study, astronomers at the University of Maryland present direct evidence of a pulsing quasar, which may substantiate the existence of black hole binaries. "We believe we have observed two supermassive black holes in closer proximity than ever before," said Suvi Gezari, assistant professor of astronomy at the University of Maryland and a co-author of the study. "This pair of black holes may be so close together that they are emitting gravitational waves, which were predicted by Einstein's theory of general relativity."

The study was published online April 14, 2015, in the Astrophysical Journal Letters. The discovery could shed light on how often black holes get close enough to form a gravitationally bound binary and eventually merge together. Black holes typically gobble up matter, which accelerates and heats up, emitting electromagnetic energy and creating some of the most luminous beacons in the sky called quasars. When two black holes orbit as a binary, they absorb matter cyclically, leading theorists to predict that the binary's quasar would respond by periodically brightening and dimming.

The researchers conducted a systematic search for so-called variable quasars using the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) Medium Deep Survey. This Haleakala, Hawaii-based telescope imaged the same patch of sky once every three days and collected hundreds of data points for each object over four years. In that data, the astronomers found quasar PSO J334.2028+01.4075, which has a very large black hole of almost 10 billion solar masses and emits a periodic optical signal that repeats every 542 days. The quasar's signal was unusual because the light curves of most quasars are arrhythmic. To verify their finding, the research team performed rigorous calculations and simulations and examined additional data, including photometric data from the Catalina Real-Time Transient Survey and spectroscopic data from the FIRST Bright Quasar Survey.

"The discovery of a compact binary candidate supermassive black hole system like PSO J334.2028+01.4075, which appears to be at such close orbital separation, adds to our limited knowledge of the end stages of the merger between supermassive black holes," said UMD astronomy graduate student Tingting Liu, the paper's first author.

The researchers plan to continue searching for new variable quasars. Beginning in 2023, their search could be aided by the Large Synoptic Survey Telescope, which is expected to survey a much larger area and could potentially pinpoint the locations of thousands of these merging supermassive black holes in the night sky.

"These telescopes allow us to watch a movie of how these systems evolve," said Liu. "What's really cool is that we may be able to watch the orbital separation of these supermassive black holes get smaller and smaller until they merge."

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