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TOPIC: Black Holes
Blobrana


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Massive Black Holes
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Title: The Most Massive Black Holes in the Universe: Effects of Mergers in Massive Galaxy Clusters
Authors: Jaiyul Yoo, Jordi Miralda-Escude, David H. Weinberg, Zheng Zheng, Christopher W. Morgan
(Version v2)

Recent observations support the idea that nuclear black holes grew by gas accretion while shining as luminous quasars at high redshift, and they establish a relation of the black hole mass with the host galaxy's spheroidal stellar system. We develop an analytic model to calculate the expected impact of mergers on the masses of black holes in massive clusters of galaxies. We use the extended Press-Schechter formalism to generate Monte Carlo merger histories of halos with a mass 10^{15} h^{-1} Msun. We assume that the black hole mass function at z=2 is similar to that inferred from observations at z=0 (since quasar activity declines markedly at z<2), and we assign black holes to the progenitor halos assuming a monotonic relation between halo mass and black hole mass. We follow the dynamical evolution of subhalos within larger halos, allowing for tidal stripping, the loss of orbital energy by dynamical friction, and random orbital perturbations in gravitational encounters with subhalos, and we assume that mergers of subhalos are followed by mergers of their central black holes. Our analytic model reproduces numerical estimates of the subhalo mass function. We find that the most massive black holes in massive clusters typically grow by a factor ~ 2 by mergers after gas accretion has stopped. In our ten realizations of 10^{15} h^{-1} Msun clusters, the highest initial (z=2) black hole masses are 5-7 x 10^9 Msun, but four of the clusters contain black holes in the range 1-1.5 x 10^{10} Msun at z=0. Satellite galaxies may host black holes whose mass is comparable to, or even greater than, that of the central galaxy. Thus, black hole mergers can significantly extend the very high end of the black hole mass function.

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Blobrana


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Do black holes really exist?
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Black holes might not exist or at least not as scientists have imagined, cloaked by an impenetrable "event horizon". A controversial new calculation could abolish the horizon, and so solve a troubling paradox in physics.
The event horizon is supposed to mark a boundary beyond which nothing can escape a black hole's gravity. According to the general theory of relativity, even light is trapped inside the horizon, and no information about what fell into the hole can ever escape. Information seems to have fallen out of the universe.
That contradicts the equations of quantum mechanics, which always preserve information. How to resolve this conflict?
One possibility researchers have proposed in the past is that the information does leak back out again slowly. It may be encoded in a hypothetical flow of particles called Hawking radiation, which is thought to result from the black holes' event horizons messing with the quantum froth that is ever-present in space.
But other researchers argue the information may never have been cut off in the first place. Tanmay Vachaspati and his colleagues at Case Western Reserve University in Cleveland, Ohio, US, have tried to calculate what happens as a black hole is forming. Using an unusual mathematical approach called the functional Schrodinger equation, they follow a sphere of stuff as it collapses inwards, and predict what a distant observer would see.

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Blobrana


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Posts: 131433
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Primordial black holes
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Title: Primordial black holes from monopoles connected by strings
Authors: Tomohiro Matsuda
(Version v5)

Primordial black holes (PBHs) are known to be produced from collapsing cosmic defects such as domain walls and strings. In this paper we show how PBHs are produced in monopole-string networks.

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Blobrana


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Posts: 131433
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CFHQS 1641+3755
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Astronomers have used the 9.2-meter Hobby-Eberly Telescope ( HET ) at McDonald Observatory to confirm one of the most distant known objects in the universe. The object is a quasar -- an extremely bright galaxy nucleus powered by matter falling into a supermassive black hole at its heart -- that is 12.7 billion light-years away. Because light travels at a finite speed, we are seeing this quasar as it appeared 12.7 billion years ago, when the universe was just 7 percent of its present age.
The object was discovered by the Canada-France High-z Quasar Survey, which has been undertaken by an international group using the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii. The survey team, headed by Chris Willott of the University of Ottawa, presented their results on four extremely distant quasars, including this one, this week at the annual conference of the Canadian Astronomical Society in Kingston, Ontario.

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Title: Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey
Authors: Chris J. Willott, Philippe Delorme, Alain Omont, Jacqueline Bergeron, Xavier Delfosse, Thierry Forveille, Loic Albert, Celine Reyle, Gary J. Hill, Michael Gully-Santiago, Phillip Vinten, David Crampton, John B. Hutchings, David Schade, Luc Simard, Marcin Sawicki, Alexandre Beelen, Pierre Cox

The Canada-France High-z Quasar Survey (CFHQS) is an optical survey designed to locate quasars during the epoch of reionisation. In this paper we present the discovery of the first four CFHQS quasars at redshift greater than 6, including the most distant known quasar, CFHQS J2329-0301 at z=6.43. We describe the observational method used to identify the quasars and present optical, infrared, and millimetre photometry and optical and near-infrared spectroscopy. We investigate the dust properties of these quasars finding an unusual dust extinction curve for one quasar and a high far-infrared luminosity due to dust emission for another. The mean millimetre continuum flux for CFHQS quasars is substantially lower than that for SDSS quasars at the same redshift, likely due to a correlation with quasar UV luminosity. For two quasars with sufficiently high signal-to-noise optical spectra, we use the spectra to investigate the ionisation state of hydrogen at z>5. For CFHQS J1509-1749 at z=6.12, we find significant evolution (beyond a simple extrapolation of lower redshift data) in the Gunn-Peterson optical depth at z>5.4. The line-of-sight to this quasar has one of the highest known optical depths at z~5.8. An analysis of the sizes of the highly-ionised near-zones in the spectra of two quasars at z=6.12 and z=6.43 suggest the IGM surrounding these quasars was substantially ionised before these quasars turned on. Together, these observations point towards an extended reionisation process, but we caution that cosmic variance is still a major limitation in z>6 quasar observations.

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Blobrana


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RE: Black Holes
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Black holes have been aggravating physicists for some time.
The mere suggestion that stars could gravitationally collapse triggered one of the most bitter physics feuds of the last century. Eventual Nobel-Prize winner Subrahmanyan Chandrasekhar held that they could, but the United Kingdom's then-eminent Arthur Eddington so strongly disagreed that Chandrasekhar changed his area of research to escape the dispute.
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Blobrana


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Scientists reveal how supermassive black holes bind into pairs during galaxy mergers
Picture the Milky Way galaxya disk of stars and gas, a stellar spheroid and an enormous halo of dark matter. It spirals around a black hole that is supermassiveabout three million solar masses. The Milky Way's total mass is about 100 billion solar massesenormous to us but average among galaxies.
Then imagine that galaxy encountering its identical twin. The first galaxy merges with the second to produce a galaxy that's even grander and greater. Cosmologists think that's how galaxies growthrough a complex process of continuous mergers.
Now, using supercomputers to simulate galaxy mergers, scientists at Stanford and elsewhere have seen the formation of a new type of structurea central disk of gas that can be from a hundred to a few thousand light years wide and from a few hundred million to a billion solar masses. They report the first simulated formation of a supermassive black hole (SMBH) pair in the June 7 edition of Science Express, an online version of Science magazine.

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Blobrana


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Most distant BlackHole
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A team of astronomers using the Canada-France-Hawaii Telescope on Mauna Kea has found the most distant -- and therefore oldest -- black hole so far discovered in the universe.
The team announced their find yesterday at the annual conference of the Canadian Astronomical Society in Ontario.

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Blobrana


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Posts: 131433
Date:
Most distant quasar
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A team of astronomers from Canada, France and the United States is announcing the discovery of a record-breaking black hole located nearly 13 billion light years from the Earth. Details of the discovery, made with the Canada-France-Hawaii Telescope, are being presented today by Dr Chris Willott, of the University of Ottawa, to astronomers and astrophysicists during the annual conference of the Canadian Astronomical Society (CASCA 2007) in Kingston, Ontario. Future observations of this black hole will shed light on the early evolution of the Universe.
The black hole was discovered because when a black hole sucks gas towards it, the gas heats up and glows very brightly, allowing it to be seen at vast distances from the Earth. This type of black hole is known as a quasar.
The record-breaking black hole was found from a new survey for distant quasars called the Canada-France High-z Quasar Survey (CFHQS), which uses the MegaCam imager on the MegaPrime focus of the Canada-France-Hawaii Telescope (CFHT). The impressive set of data from MegaCam contains over 10 million stars and galaxies. Astronomers had to search the data carefully to discover the four distant quasars from amongst the ordinary stars and galaxies. The most distant quasar has been named CFHQS J2329-0301 after the survey name and its coordinate position in the sky, which is in the constellation Pisces.

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Blobrana


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RE: Black Holes
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In a study of more than 1,000 void galaxies, using data from the Sloan Digital Sky Survey, astronomers from Drexel and Widener Universities found that the growth of monster black holes with masses millions to hundreds of millions times that of our sun are found where galaxies are sparse and interact very little with each other.
These findings shed light on the black hole formation and evolution process by showing that the environment does affect how quickly galaxies proceed through their evolutionary cycle.
The simple presence of growing supermassive black holes in the rural outposts of the universe challenges the current theoretical models of galaxy and structure formation and evolution, explained Anca Constantin of Drexel University, lead author of the paper delivered today at the American Astronomical Society meeting in Honolulu.

Interestingly, we see actively accreting galactic black holes in all phases of evolution in these sparse regions. This means that the black hole growth process is quite similar in what could be compared to the most reclusive countrysides and in the crowded urban regions of the universe - Anca Constantin.

The void regions, nearly empty, three-dimensional fields hundreds of millions of light-years across, fill half of the universe. Only five percent of all galaxies live in these bubble-like regions. The other 95 percent of galaxies live together in communities, crowded into clusters, filaments, and walls: the cities and suburbs of the universe.
Studying a 700-million light year wide slice of the universe, the researchers found that spectra of the centres of void galaxies show hot gases ionised by light emitted from matter swirling around supermassive black holes.

 The more isolated accreting black holes are however not as active as the ones in more populous environs, and the fuel seems less available for accretion in voids than in urban galaxies - Anca Constantin.

 This is strange given that these reclusive galaxies are forming stars at higher rates than their counterparts in denser regions; this means there is plenty of fuel, but it is not efficiently channelled toward the central engine - Astronomer Fiona Hoyle, a member of the discovery team from Widener University

Star formation requires the presence of large amounts of gas and so there must be more than enough gas in the void galaxies if their star forming rates are high. The smaller accretion rate observed in void galaxies means that this gas is just not getting down to the nuclear region where accretion happens. Interactions with other galaxies are thought to disturb the gravitational potential, which drives some gas into the nuclear region.

These interactions are not as frequent in voids, so the 'feeding' of the black hole is slower.

These rugged individuals in voids do not need to compete with their neighbours for fuel, and their life cycle is rarely bothered. In contrast, life is more hectic in crowded regions where galaxy interactions are frequent. As a consequence, galaxies are either stripped of their gas or more material is funnelled toward the central engine. This means that there are many more chances the accretion onto black holes is enhanced or turned off in more 'urban environments.'

On the other hand, the void galaxy black holes might take longer to reach the mature, low accretion rate phase, which might explain why the most massive, lazy black holes are less frequent in voids - Anca Constantin.

The data studied by Constantin may also show that active black holes appear to be more common in voids but only among small (less massive) galaxies, while less common among massive galaxies. This is also a clue that the life cycle of black hole growth in voids is delayed or slower compared to that in denser regions.
Discovery team member Michael Vogeley of Drexel said that it's particularly puzzling that the few most massive and sluggishly accreting void systems live within the most secluded sub-regions, while their "urban" counterparts are found in the most populated neighbourhoods.

Perhaps because massive objects are prone to accreting material around them, such a 'cleaning' process would contribute to emptying the already rarefied neighbouring space in voids. This would leave little or insufficient material for future formation of other nearby massive, bright galaxies  - Michael Vogeley.

In contrast, within galaxy clusters where there is plenty of stuff around, accretion of surrounding material would make a small difference.
These results have been possible only because of the sheer number of void regions and void galaxies found in the SDSS-II data, the most ambitious survey of the universe ever undertaken, the researchers said. The sample used in the analysis announced today comprises more than 1,000 void galaxies. Previously, the black hole accretion in centres of void galaxies had been studied in only a handful of objects contained in only one void region, the Bootes Void.

The results are described in the paper "Active Galactic Nuclei in Void Regions" submitted for publication in The Astrophysical Journal.

Source: Drexel University    

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Blobrana


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Black holes appear to be intimately connected with the formation of massive spherical bulges in galaxies. Astronomers have found a direct relationship between the mass of the black hole in such a galaxy and the mass of its central bulge. However, it is unclear whether small galaxies contain smaller black holes, and their discovery may lead to new insights about the impact of black holes on galaxy formation.

"In recent years, we have been detecting black holes with masses between 100,000 and a few million times the mass of the Sun, but less massive objects have been exceptionally difficult to find" - Jenny Greene,  Princeton University.
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