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Entries in Buraco Negro (5)

Saturday
Mar022013

Researchers Discovered the Mysterious Structure of a Black Hole Seen Edge On

Edge-on view of the accretion disc, as seen from the Earth. A raised structure (like a donut), seen in the interior, causes the light from the inner parts of the disc (those closest to the black hole) to be eclipsed. This 'donut' gyrates around the black hole in a few minutes and produces eclipses over more or less regular intervals. Copyright: Gabriel Pérez Díaz, Servicio MultiMedia (IAC)

Swift J1357.2-0933 is a black hole obscured by a disc of gas with a vertical structure (rather like a donut) that continues to expand

This is the first time a black hole has been seen with this inclination and it's the first time that eclipses in brightness have been detected in this kind of system

The structure described in the study could be present in many other systems, which would make Swift J1357.2-0933 the prototype of a hitherto veiled population with a high inclination"

Like an immense donut (or toroid) that expands daily. That's how Jesús Corral-Santana, a researcher at the Instituto de Astrofísica de Canarias (IAC), describes the odd - hitherto unknown - structure of the binary system Swift J1357.2-0933, consisting of a 'normal' star and a stellar-mass black hole (which feeds off its companion star). The investigation, just published in Science journal with Corral as first author, follows the stages of the outburst of the system, an event that occurs only once in decades or centuries.

The team observed strange eclipses in the system that lasted and were repeated every few minutes. This finding led them to two conclusions: they had to be viewing the black hole edge on (it had an inclination of at least 75 degrees) and it presented an odd vertical structure within the accretion disc of the system. In other words, the matter being drawn from the companion star formed an outflow in the shape of a whirlpool, rather like water flowing down a plughole.

As Jorge Casares, also an IAC researcher, coauthor of the paper and Principal investigator (PI), explains, 'this kind of structure is possibly present in many - or all - X-ray binaries, the class of systems to which Swift J1357.2-0933 belongs. So the object we've observed could be the prototype of a hitherto hidden population of highly inclined systems in which the black hole is obscured.' Statistically, around 20% of systems could be of this type.

Black holes are formed following the death of very massive stars, and their detection is complicated. 'Since they don't emit any light, they're nearly impossible to find if they are alone,' says Casares. 'In cases where they have a companion star, their probability of detection is much higher, since their presence is betrayed by the "cannibalization" of the companion star by the black hole.' This explains why, since the first detection of such a system in 1964, only 18 other black holes have been found in our Galaxy. Swift J1357.2-0933, discovered by the Swift X-ray satellite and studied by the IAC team, is the latest one in the list. There are a further 32 black-hole candidates, but these haven't yet been confirmed.

Many X-ray binaries are characterized by decades-long - even centuries-long - periods of quiescence, and it is easy to confuse them with normal stars when in this state. But, with no prior warning, these system can erupt, brightening dramatically (by as much as a million times their normal brilliance), in any part of the Galaxy. This enables them to be detected by satellites scanning the sky in X-rays. The system fades back to quiescence after a few months.

It's then, adds Corral-Santana, that the scientific community can analyse its structure: a 'normal' star and a compact object (either a black hole, as in this case, or a neutron star). The star transfers material to its companion, forming an accretion disc.

In the case of Swift J1357.2-0933, the IAC researcher continues, more data have been gathered owing to its relative proximity, estimated at 5000 light years and its great distance above the plane of the Milky Way, where most of the matter of the Galaxy is concentrated, meaning that light from the binary system is not dimmed by interstellar dust or glare from nearby stars.

The scientists found that the system has a very short period, a mere 2.8 hours. In that time the companion star completes an orbit around the black hole. They also measured the mass of the black hole to be three times that of the Sun. 'That's a lower limit. In fact, the mass could be very much greater than that. Further observations during the period of quiescence would enable us to get a more accurate value,' Corral-Santana explains.

However, the most unusual find concerns the eclipses of the system. From images taken with various telescopes at the Teide and Roque de los Muchachos Observatories (the IAC-80, Liverpool, Mercator and INT), it was found that eclipses occurred in which the brightness of the system dropped by 30% in only seven seconds, and that they were repeated at longer intervals after a few days. 'It's the first time a phenomenon with these characteristics has been observed. None of the 50 known transitory X-ray binaries (18 with confirmed black holes and 32 candidates)
produces eclipses by the companion star,' the IAC astrophysicist points out.

What could be causing the eclipses? The researchers are clear that they aren't produced by the companion star since these have orbital periods of 2.8 hours and the eclipses are produced every few minutes and are of extremely short duration. Corral-Santana further adds, 'The period in which the eclipses are repeated gets progressively longer each day. This fact suggests that the eclipses are produced by a vertical structure that is initially located close to the black hole and gradually moves outwards like a wave from the inner part of the accretion disc.

This discovery is closely linked with another: 'The simple fact of detecting the eclipses indicates that the system is viewed at a high inclination, even greater than 75 degrees. In effect, we're looking at it edge on,' says the scientist, who further describes the structure as, 'probably like a donut, with the black hole permanently hidden in the middle.'

Source:

http://www.iac.es/divulgacion.php?op1=16&id=790&lang=en

Sunday
Feb172013

New research sheds light on black hole growth

The black hole that has grown the most can be found in the Sombrero galaxy . The researchers estimate that this black hole has been swallowing the equivalent of one Sun every twenty years and is now over 500 million times as heavy as the Sun. Credit: ESO Public Image Release

In a new study led by University of Central Lancashire astronomer Dr. Victor Debattista, researchers are looking into the mystery of how black holes grow and evolve. For many years, astronomers surmised black holes took on mass when their host galaxies merged, but now new modeling techniques show that black holes in spiral galaxies are forced to take on mass.

"Recent Hubble Space Telescope (HST) observations have revealed that a majority of active galactic nuclei (AGN) are resident in isolated disk galaxies, contrary to the usual expectation that AGN are triggered by mergers." says Debattista. "Here we develop a new test of the cosmic evolution of supermassive black holes (SMBHs) in disk galaxies by considering the local population of SMBHs. We show that substantial SMBH growth in spiral galaxies is required as disks assemble."

Weighing in a range of one million to one billion times that of the Sun, the black holes located at the core of most galaxies would appear to be gaining at much quicker rates than expected. These are not just exceptions – more like rules. Even the Milky Way's quiescent black hole might be gaining as much mass as the Sun every 3,000 years. Past observations have shown growth during collision events, when huge amounts of gas around the black hole become intensely hot and shine as an active galactic nucleus. This is a process which can be spotted as far back as the first formations in our Universe. However, these new simulations are giving insight into large scale growth without the need for violence.

"The X-ray-selected sample of moderate luminosity AGN consists of more than 50% disk galaxies, with ongoing mergers evident no more frequently than in nonactive galaxies." explains the research team. "Some show that even heavily obscured quasars are hosted largely by disks, not by mergers. Studies of star-formation using Herschel find that the specific star formation rates of X-ray selected AGN hosts are no different from those of inactive galaxies, also indicating that AGN hosts are not undergoing fundamentally different behaviors"

These modeling techniques, combined with current observations done with the Hubble Space Telescope, give credence to the theory that black holes can gain significant mass even in "quiet" spiral galaxies. As a matter of fact, there is a strong possibility that AGNs present in some spiral galaxies may even outnumber galaxy mergers. To make this concept even more exciting, astronomers are anticipating an event later this year in our own galaxy – an event where a gas cloud near the Milky Way's nucleus will encounter our own central black hole. According to predictions, our black hole may take on as much as 15 Earth masses in a period of 10 years from this cloud.

This concept of black hole growth isn't entirely new, though. According to other research done with the Hubble Space Telescope and led by Dr. Stelios Kazantzidis of Ohio State University and Professor Frank C. van den Bosch of Yale University, they had previously pinpointed mass properties of black holes – making size predictions which utilized the speed of stars residing in the galaxies. In this instance, the team disproved previous assumptions that black holes were unable to grow while the host galaxy grew. Their comparison of spiral and elliptical galaxies "found there is no mismatch between how big their black holes are." This means black holes would be gaining in mass – growing along at the same rate as the galaxy itself.

"These simulations show that it is no longer possible to argue that black holes in spiral galaxies do not grow efficiently. " comments Debattista on this new research. " Our simulations will allow us to refine our understanding of how black holes grew in different types of galaxies."

Source: http://phys.org/news/2013-02-black-hole-growth.html

Monday
Jan142013

"Black Holes Create their Host Galaxies" --An Odd Quasar Provides the Clues

The answer may have been found to the question of whether a galaxy or its black hole comes first -one of the most debated subjects in astrophysics today. A recent study suggests that supermassive black holes can trigger the formation of stars, thus 'building' their own host galaxies. 

This 2011 finding could also explain why galaxies hosting larger black holes have more stars. To reach such an extraordinary conclusion, the team of astronomers conducted extensive observations of a peculiar object, the quasar HE0450-2958, also called the "naked quasar" and the "quasar without a home," because it the only one for which a host galaxyhas not yet been detected.
Until recently, it was speculated that the quasar's host galaxy was hidden behind large amounts of dust, and so the astronomers used amid-infrared instrument on ESO's Very Large Telescope for the observations . At such wavelengths, dust clouds shine very brightly, and are readily detected.

"Observing at these wavelengths would allow us to trace dust that might hide the host galaxy," says Knud Jahnke, who led the observations performed at the VLT. "However, we did not find any. Instead we discovered that an apparently unrelated galaxy in the quasar's immediate neighborhood is producing stars at a frantic rate."

These observations have provided a surprising new take on the system. While no trace of stars is revealed around the black hole, its companion galaxy is extremely rich in bright and very young stars. It is forming stars at a rate equivalent to about 350 Suns per year, one hundred times more than rates for typical galaxies in the local Universe.

Earlier observations had shown that the companion galaxy is, in fact, under fire: the quasar is spewing a jet of highly energetic particles towards its companion, accompanied by a stream of fast-moving gas. The injection of matter and energy into the galaxy indicates that the quasar itself might be inducing the formation of stars and thereby creating its own host galaxy; in such a scenario, galaxies would have evolved from clouds of gas hit by the energetic jets emerging fromquasars.

"The two objects are bound to merge in the future: the quasar is moving at a speed of only a few tens of thousands of km/h with respect to the companion galaxy and their separation is only about 22 000 light-years," says Elbaz. "Although the quasar is still 'naked', it will eventually be 'dressed' when it merges with its star-rich companion. It will then finally reside inside a host galaxy like all other quasars."

The team identified black hole jets as a possible driver of galaxy formation, which may also represent the long-sought missing link to understanding why the mass of black holes is larger in galaxies that contain more stars. "A natural extension of our work is to search for similar objects in other systems," says Jahnke.

The image at top of page shows quasar HE0450-2958, which is the only one for which no sign of a host galaxy has yet been detected. The team of astronomers has identified black hole jets as a possible driver of galaxy formation, which may also represent the long-sought missing link to understanding why the mass of black holes is larger in galaxies that contain more stars. The mid-infrared part of this image was obtained with the VISIR instrument on ESO’s Very Large Telescope, while the visible image comes courtesy of the Hubble Space Telescope and theAdvanced Camera for Surveys.

Source: http://www.dailygalaxy.com/my_weblog/2013/01/black-holes-create-their-host-galaxies-a-strange-quasar-provides-clues.html

Monday
Dec312012

Colossal Black Hole Equal to 17 Billion Suns Discovered

A group of astronomers led by Remco van den Bosch from the Max Planck Institute for Astronomy (MPIA) have discovered a black hole that could shake the foundations of current models of galaxy evolution. The Hubble image above shows the small, flattened disk galaxy NGC 1277, which contains one of the biggest central super-massive black holes ever found in its center. With the mass of 17 billion Suns, the black hole weighs in at an extraordinary 14% of the total galaxy mass --a mass much greater than current models predict — in particular in relation to the mass of its host galaxy. This could be the most massive black hole found to date. Astronomers would have expected a black hole of this size inside blob-like (“elliptical”) galaxies ten times larger. Instead, this black hole sits inside a fairly small disk galaxy.

If the additional candidates are confirmed, astronomers will need to rethink fundamentally their models of galaxy evolution. In particular, they will need to look at the early universe: The galaxy hosting the new black hole appears to have formed more than 8 billion years ago, and does not appear to have changed much since then. Whatever created this giant black hole must have happened a long time ago.

To the best of our astronomical knowledge, almost every galaxy should contain in its central region what is called a supermassive black hole: a black hole with a mass between that of hundreds of thousands and billions of Suns. The best-studied super-massive black hole sits in the center of our home galaxy, the Milky Way, with a mass of about four million Suns.

NGC 1277 is embedded in the nearby Perseus galaxy cluster, at a distance of 250 million light-years from Earth. All the ellipticals and round yellow galaxies in the image below are galaxies located in this cluster. Compared to all the other galaxies around it, NGC 1277 is a relatively compact. (Credit: David W. Hogg, Michael Blanton, and the SDSS Collaboration)

For the masses of galaxies and their central black holes, an intriguing trend has emerged: a direct relationship between the mass of a galaxy’s black hole and that of the galaxy’s stars.Typically, the black hole mass is a tiny fraction of the galaxy’s total mass. But now a search led by the Dutch astronomer Remco van den Bosch (MPIA) has discovered a massive black hole that could upset the accepted relationship between black hole mass and galaxy mass, which plays a key role in all current theories of galaxy evolution.

With a mass 17 billion times that of the Sun, the newly discovered black hole in the center of the disk galaxy NGC 1277 might even be the biggest known black hole of all: the mass of the current record holder is estimated to lie between 6 and 37 billion solar masses. The big surprise is that the black hole mass for NGC 1277 amounts to 14% of the total galaxy mass, instead of usual values around 0.1%.

Is this surprisingly massive black hole a freak accident? Preliminary analysis of additional data suggests otherwise — so far, the search has uncovered five additional galaxies that are comparatively small, yet, going by first estimates, seemed to harbor unusually large black holes too. More definite conclusions have to await detailed images of these galaxies.

(NGC 1277 is a compact disk galaxy with one of the biggest black holes known to date. Its black hole weighs 17 billion times the mass of the Sun, which amounts to a remarkable 14% of this galaxy’s total mass. Most of the stars in the galaxy are strongly affected by the gravitational pull of this black hole. The black hole was found by van den Bosch and collaborators and published in Nature on 29 November 2012.

The animation above shows representative orbits of the galaxy’s stars in this, taken from the dynamical model that was used to measure the black hole mass. The green orbit shows the orbit of the stars in the disk. The red orbit shows the strong gravitational pull near the black hole. The blue orbit is strongly influenced by the (round) dark matter halo. One second in this animation represents 22 million years of simulated time, and the horizontal size of this image amounts to 41 million lightyears (36 arcsec).

Remco C. E. van den Bosch et al., An over-massive black hole in the compact lenticular galaxy NGC 1277, Nature, 2012, DOI: 10.1038/nature11592

Source: http://www.dailygalaxy.com/my_weblog/2012/12/colossal-black-hole-equal-to-17-billion-suns-discovered-may-overturn-existing-models-2012-most-popul.html

Tuesday
Oct092012

Rapidly Growing Giant Black Holes Found

Markarian 231 is an example of a galaxy with a dusty rapidly growing supermassive black hole located 600 million light years from Earth. The black hole is the very bright source at the centre of the galaxy. Rings of gas and dust can be seen around it as well as “tidal tails” left over from a recent impact with another galaxy. Image Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

Scientists at the University of Cambridge have used cutting-edge infrared surveys of the sky to discover a new population of enormous, rapidly growing supermassive black holes in the early Universe. The black holes were previously undetected because they sit cocooned within thick layers of dust. The new study has shown however that they are emitting vast amounts of radiation through violent interactions with their host galaxies. The team publish their results in the journal Monthly Notices of the Royal Astronomical Society.

The most extreme object in the study is a supermassive black hole called ULASJ1234+0907. This object, located in the direction of the constellation of Virgo, is so far away that the light from it has taken 11 billion years to reach us, so we see it as it appeared in the early universe. The monster black hole has more than 10 billion times the mass of the Sun and 10,000 times the mass of the supermassive black hole in our own Milky Way, making it one of the most massive black holes ever seen.

The research indicates that that there may be as many as 400 such giant black holes in the part of the Universe that we can observe. “These results could have a significant impact on studies of supermassive black holes” said Dr Manda Banerji, lead author of the paper. “Most black holes of this kind are seen through the matter they drag in. As the neighbouring material spirals in towards the black holes, it heats up. Astronomers are able to see this radiation and observe these systems.”

“Although these black holes have been studied for some time, the new results indicate that some of the most massive ones may have so far been hidden from our view.” The newly discovered black holes, devouring the equivalent of several hundred Suns every year, will shed light on the physical processes governing the growth of all supermassive black holes.

Supermassive black holes are now known to reside at the centres of all galaxies. In the most massive galaxies in the Universe, they are predicted to grow through violent collisions with other galaxies, which trigger the formation of stars and provides food for the black holes to devour. These violent collisions also produce dust within the galaxies therefore embedding the black hole in a dusty envelope for a short period of time as it is being fed.

In comparison with remote objects like ULASJ1234+0907, the most spectacular example of a dusty, growing black hole in the local Universe is the well-studied galaxy Markarian 231 located a mere 600 million light years away. Detailed studies with the Hubble Space Telescope have shown evidence that Markarian 231 underwent a violent impact with another galaxy in the recent past. ULASJ1234+0907 is a more extreme version of this nearby galaxy, indicating that conditions in the early Universe were much more turbulent and inhospitable than they are today.

In the new study, the team from Cambridge used infrared surveys being carried out on the UK Infrared Telescope (UKIRT) to peer through the dust and locate the giant black holes for the first time. Prof. Richard McMahon, co-author of the study, who is also leading the largest infrared survey of the sky, said: “These results are particularly exciting because they show that our new infrared surveys are finding super massive black holes that are invisible in optical surveys. These new quasars are important because we may be catching them as they are being fed through collisions with other galaxies. Observations with the new Atacama Large Millimeter Array (ALMA) telescope in Chile will allow us to directly test this picture by detecting the microwave frequency radiation emitted by the vast amounts of gas in the colliding galaxies.”

Infrared colour image of ULASJ1234+0907 located 11 billion light years from Earth and one of the reddest objects in the sky. This red colour is caused by the enormous amounts of dust within this system. The dust preferentially absorbs bluer light and is responsible for obscuring this supermassive black hole in the visible wavelengths. Image Credit: image created using data from UKIDSS and the Wide-field Infrared Survey Explorer (WISE) observator

Source: Royal Astronomical Society (RAS)

Source: http://annesastronomynews.com/rapidly-growing-giant-black-holes-found/