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Posts Tagged ‘BLACK HOLES

Soft Hair on Black Holes

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Stephen W. Hawking, Malcolm J. Perry, and Andrew Strominger
It has recently been shown that BMS supertranslation symmetries imply an infinite number of conservation laws for all gravitational theories in asymptotically Minkowskian spacetimes. These laws require black holes to carry a large amount of soft (i.e. zero-energy) supertranslation hair. The presence of a Maxwell field similarly implies soft electric hair. This paper gives an explicit description of soft hair in terms of soft gravitons or photons on the black hole horizon, and shows that complete information about their quantum state is stored on a holographic plate at the future boundary of the horizon. Charge conservation is used to give an infinite number of exact relations between the evaporation products of black holes which have different soft hair but are otherwise identical. It is further argued that soft hair which is spatially localized to much less than a Planck length cannot be excited in a physically realizable process, giving an effective number of soft degrees of freedom proportional to the horizon area in Planck units.
Read more at https://arxiv.org/pdf/1601.00921v1.pdf

Read also: “Gary T. Horowitz, Black Holes Have Soft Quantum Hair

Written by physicsgg

June 7, 2016 at 11:12 am

Posted in COSMOLOGY

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The black-hole collision that reshaped physics

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A momentous signal from space has confirmed decades of theorizing on black holes — and launched a new era of gravitational-wave astronomy.gravafter-LIGO-feature-onlineRead more at www.nature.com

Written by physicsgg

March 24, 2016 at 10:49 am

Posted in RELATIVITY

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Testing General Relativity in a Black Hole’s Shadow

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Deviations in the shadow of our Galaxy’s supermassive black hole could reveal violations of general relativity.
PhysRevLett.116

The Event Horizon Telescope (EHT), a planet-wide network of radio telescopes, is compiling the first direct image of the giant black hole in the center of our Galaxy. The trapping of light by the hole will produce a dark shadow surrounded by a bright circular ring. A new analysis shows that the EHT could potentially detect small deviations in the shadow size, which are predicted by alternative theories of gravity.

Like most galaxies, our Milky Way has a supermassive black hole, called Sagittarius A* (Sgr A*). Observations of stars orbiting Sgr A* have provided estimates of its mass (about 4 million solar masses) and its distance from us (roughly 27,000 light years). The radius of the black hole, defined by its event horizon, is just 17 times that of the Sun. To image this compact object, astronomers formed the EHT project, which performs interferometry on data from several radio telescopes from around the globe. The group expects to have the first snapshot of Sgr A* in the next few years.

According to general relativity, the warping of space around Sgr A* creates a shadow with an apparent radius of exactly 50 microarcseconds. By contrast, many alternative gravity theories predict a larger or smaller shadow. Tim Johannsen from the Perimeter Institute for Theoretical Physics, Canada, and colleagues analyzed a previously constructed simulation of EHT data for Sgr A*. They first showed that the EHT will dramatically reduce the uncertainties in the mass and distance measurements. They also describe in detail how the EHT will test general relativity by measuring certain spacetime deviation parameters that have nonzero values in alternative gravity theories.

This research is published in Physical Review Letters.

–Michael Schirber – http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.116.031101

Written by physicsgg

January 19, 2016 at 6:50 pm

Posted in ASTROPHYSICS, RELATIVITY

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Einstein’s Amazing Theory of Gravity: Black Holes and Novel Ideas in Cosmology

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Sir Roger Penrose giving his talk ‘Einstein’s Amazing Theory of Gravity: Black Holes and Novel Ideas in Cosmology’ at ‘What’s Your Angle?’ – a mathematics festival organised in collaboration between the London Mathematical Society and the Science Museum in November 2015

Written by physicsgg

January 6, 2016 at 10:30 am

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Soft Hair on Black Holes

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Stephen W. Hawking, Malcolm J. Perry, Andrew Strominger
It has recently been shown that BMS supertranslation symmetries imply an infinite number of conservation laws for all gravitational theories in asymptotically Minkowskian spacetimes. These laws require black holes to carry a large amount of soft (i.e. zero-energy) supertranslation hair. The presence of a Maxwell field similarly implies soft electric hair. This paper gives an explicit description of soft hair in terms of soft gravitons or photons on the black hole horizon, and shows that complete information about their quantum state is stored on a holographic plate at the future boundary of the horizon. Charge conservation is used to give an infinite number of exact relations between the evaporation products of black holes which have different soft hair but are otherwise identical. It is further argued that soft hair which is spatially localized to much less than a Planck length cannot be excited in a physically realizable process, giving an effective number of soft degrees of freedom proportional to the horizon area in Planck units.
Read more at http://arxiv.org/pdf/1601.00921v1.pdf

Written by physicsgg

January 6, 2016 at 8:25 am

Posted in COSMOLOGY, High Energy Physics

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How Do Black Holes Really Evaporate?

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Perhaps the greatest thing Stephen Hawking ever discovered — and the reason he’s so renowned among physicists — is that black holes don’t live forever.
Rather, they radiate their energy away over extraordinarily long timescales through a process discovered in 1974 that’s now known as Hawking radiation…
… Read more at forbes.com

Written by physicsgg

December 13, 2015 at 8:16 am

Posted in COSMOLOGY

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How Big Can a Black Hole Grow?

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blackhole1

The mass limit Mmax for accreting supermassive black holes, compared with the largest observed masses.

Andrew King
I show that there is a physical limit to the mass of a black hole, above which it cannot grow through luminous accretion of gas, and so cannot appear as a quasar or active galactic nucleus.
The limit is Mmax ~ 5×1010Msun for typical parameters, but can reach Mmax ~ 2.7×1011Msun in extreme cases (e.g. maximal prograde spin).
The largest black hole masses so far found are close to but below the limit. The Eddington luminosity ~6.5×1048 erg/s corresponding to Mmax is remarkably close to the largest AGN bolometric luminosity so far observed.
The mass and luminosity limits both rely on a reasonable but currently untestable hypothesis about AGN disc formation, so future observations of extreme SMBH masses can therefore probe fundamental disc physics. Black holes can in principle grow their masses above Mmax by non-luminous means such as mergers with other holes, but cannot become luminous accretors again.
They might nevertheless be detectable in other ways, for example through gravitational lensing. I show further that black holes with masses ~ Mmax can probably grow above the values specified by the black-hole — host-galaxy scaling relations, in agreement with observation…

Read more at http://arxiv.org/pdf/1511.08502v2.pdf

Read also: Black holes have a size limit of 50 billion suns

Written by physicsgg

December 12, 2015 at 1:51 pm

Posted in ASTROPHYSICS

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A supermassive black hole in action

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Copyright NASA, ESA, S. Baum & C. O’Dea (RIT), R. Perley & W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA)

Copyright NASA, ESA, S. Baum & C. O’Dea (RIT), R. Perley & W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA)

Scientists often use the combined power of multiple telescopes to reveal the secrets of the Universe – and this image is a prime example of when this technique is strikingly effective.

The yellow-hued object at the centre of the frame is an elliptical galaxy known as Hercules A, seen by the Earth-orbiting NASA/ESA Hubble Space Telescope. In normal light, an observer would only see this object floating in the inky blackness of space.

However, view Hercules A with a radio telescope, and the entire region is completely transformed. Stunning red–pink jets of material can be seen billowing outwards from the galaxy – jets that are completely invisible in visible light. They are shown here as seen by the Karl G. Jansky Very Large Array radio observatory in New Mexico, USA. These radio observations were combined with the Hubble visible-light data obtained with the Wide Field Camera 3 to create this striking composite.

The two jets are composed of hot, high-energy plasma that has been flung from the centre of Hercules A, a process that is driven by a supermassive black hole lurking at the galaxy’s heart. This black hole is some 2.5 billion times the mass of the Sun, and around a thousand times more massive than the black hole at the centre of our Milky Way galaxy.

Hercules A’s black hole heats material and accelerates it to nearly the speed of light, sending it flying out into space at phenomenally high speeds. These highly focused jets lose energy as they travel, eventually slowing down and spreading out to form the cloud-like lobes seen here.

The multiple bright rings and knots seen within these lobes suggest that the black hole has sent out numerous successive bursts of material over the course of its history. The jets stretch for around 1.5 million light-years – roughly 15 times the size of the Milky Way.

Hercules A, also known as 3C 348, lies around two billion light-years away. It is one of the brightest sources of radio emission outside our Galaxy.

This image was originally published in November 2012.

Read more at www.esa.int

Written by physicsgg

November 18, 2015 at 1:46 pm

Posted in ASTRONOMY, ASTROPHYSICS

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