̽��ֱ�� of Cambridge - relativity

Astronomers observe light bending around an isolated white dwarf

sc604 — Thu, 02 Feb 2023 08:08:58 +0000

Astronomers have directly measured the mass of a dead star using an effect known as gravitational microlensing, first predicted by Einstein in his General Theory of Relativity, and first observed by two Cambridge astronomers 100 years ago.

LIGO detects gravitational waves for third time

sc604 — Thu, 01 Jun 2017 16:09:44 +0000

̽��ֱ��Laser Interferometer Gravitational-wave Observatory (LIGO) has made a third detection of gravitational waves, ripples in space and time, demonstrating that a new window in astronomy has been firmly opened. As was the case with the first two detections, the waves were generated when two black holes collided to form a larger black hole.

̽��ֱ��newfound black hole formed by the merger has a mass about 49 times that of our sun. “With this third confirmed detection we are uncovering the population of black holes in the Universe for the first time,” said Christopher Moore from the ̽��ֱ�� of Cambridge’s Department of Applied Mathematics and Theoretical Physics (DAMTP), who is part of the LIGO Scientific Collaboration.

̽��ֱ��new detection occurred during LIGO’s current observing run, which began November 30, 2016, and will continue through the summer. LIGO is an international collaboration with members around the globe. Its observations are carried out by twin detectors—one in Hanford, Washington, and the other in Livingston, Louisiana—operated by Caltech and MIT with funding from the United States National Science Foundation (NSF).

̽��ֱ��LIGO group in Cambridge consists of seven researchers spread across DAMTP, the Cavendish Laboratory and the Institute of Astronomy.

“Answering key questions about the formation history of astrophysical black holes and their role in the evolution of the universe critically relies on applying a statistical analysis to a sufficiently large sample of observations,” said Dr Ulrich Sperhake, head of the group in DAMTP. “Each new detection not only strengthens our confidence in the theoretical modelling, but enables us to explore new phenomena of these mysterious and fascinating objects.”

One of the interests of the Cambridge group is testing Einstein’s theory of general relativity. “This particular source of gravitational waves is the furthest detected so far. This allows us to test our understanding of the propagation of gravitational waves across cosmological distances, by means of which we constrained any signs of wave dispersion to unprecedented precision,” said Dr Michalis Agathos, a postdoctoral researcher at DAMTP.

̽��ֱ��LIGO-Virgo team is continuing to search the latest LIGO data for signs of space-time ripples from the far reaches of the cosmos. They are also working on technical upgrades for LIGO’s next run, scheduled to begin in late 2018, during which the detectors’ sensitivity will be further improved.

“With the third confirmed detection of gravitational waves from the collision of two black holes, LIGO is establishing itself as a powerful observatory for revealing the dark side of the universe,” said David Reitze of Caltech, executive director of the LIGO Laboratory. “While LIGO is uniquely suited to observing these types of events, we hope to see other types of astrophysical events soon, such as the violent collision of two neutron stars.”

LIGO is funded by the National Science Foundation (NSF), and operated by MIT and Caltech, which conceived and built the project. Financial support for the Advanced LIGO project was led by NSF with Germany (Max Planck Society), the UK (Science and Technology Facilities Council) and Australia (Australian Research Council) making significant commitments and contributions to the project. More than 1,000 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. LIGO partners with the Virgo Collaboration, a consortium including 280 additional scientists throughout Europe supported by the Centre National de la Recherche Scientifique (CNRS), the Istituto Nazionale di Fisica Nucleare (INFN), and Nikhef, as well as Virgo’s host institution, the European Gravitational Observatory. Additional partners are listed at: http://ligo.org/partners.php.

Results confirm new population of black holes.

Each new detection enables us to explore new phenomena of these mysterious and fascinating objects.

Ulrich Sperhake

LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)

Artist's conception shows two merging black holes similar to those detected by LIGO.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Gravitational vortex provides new way to study matter close to a black hole

Anonymous — Tue, 12 Jul 2016 15:01:00 +0000

Matter falling into a black hole heats up as it plunges to its doom. Before it passes into the black hole and is lost from view forever, it can reach millions of degrees. At that temperature it shines x-rays into space.

In the 1980s, astronomers discovered that the x-rays coming from black holes vary on a range of timescales and can even follow a repeating pattern with a dimming and re-brightening taking 10 seconds to complete. As the days, weeks and then months progress, the pattern’s period shortens until the oscillation takes place 10 times every second. Then it suddenly stops altogether.

This phenomenon was dubbed a Quasi Periodic Oscillation (QPO). During the 1990s, astronomers began to suspect that the QPO was associated with a gravitational effect predicted by Einstein’s general relativity which suggested that a spinning object will create a kind of gravitational vortex. ̽��ֱ��effect is similar to twisting a spoon in honey: anything embedded in the honey will be ‘dragged’ around by the twisting spoon. In reality, this means that anything orbiting around a spinning object will have its motion affected. If an object is orbiting at an angle, its orbit will ‘precess’ – in other words, the whole orbit will change orientation around the central object. ̽��ֱ��time for the orbit to return to its initial condition is known as a precession cycle.

In 2004, NASA launched Gravity Probe B to measure this so-called Lense-Thirring effect around Earth. By analysing the resulting data, scientists confirmed that the spacecraft would turn through a complete precession cycle once every 33 million years. Around a black hole, however, the effect would be much stronger because of the stronger gravitational field: the precession cycle would take just a matter of seconds to complete, close to the periods of the QPOs.

An international team of researchers, including Dr Matt Middleton from the Institute of Astronomy at the ̽��ֱ�� of Cambridge, has used the European Space Agency’s XMM-Newton and NASA’s NuSTAR, both x-ray observatories, to study the effect of black hole H1743-322 on a surrounding flat disc of matter known as an ‘accretion disk’.

Close to a black hole, the accretion disc puffs up into a hot plasma, a state of matter in which electrons are stripped from their host atoms – the precession of this puffed up disc has been suspected to drive the QPO. This can also explain why the period changes - the place where the disc puffs up gets closer to the black hole over weeks and months, and, as it gets closer to the black hole, the faster its Lense-Thirring precession becomes.

̽��ֱ��plasma releases high energy radiation that strikes the matter in the surrounding accretion disc, making the iron atoms in the disc shine like a fluorescent light tube. Instead of visible light, the iron releases X-rays of a single wavelength – referred to as ‘a line’. Because the accretion disc is rotating, the iron line has its wavelength distorted by the Doppler effect: line emission from the approaching side of the disc is squashed – blue shifted – and line emission from the receding disc material is stretched – red shifted. If the plasma really is precessing, it will sometimes shine on the approaching disc material and sometimes on the receding material, making the line wobble back and forth over the course of a precession cycle.

It is this ‘wobble’ that has been observed by the researchers.

“Just as general relativity predicts, we’ve seen the iron line wobble as the accretion disk orbits the black hole,” says Dr Middleton. “This is what we’d expect from matter moving in a strong gravitational field such as that produced by a black hole.”

This is the first time that the Lense-Thirring effect has been measured in a strong gravitational field. ̽��ֱ��technique will allow astronomers to map matter in the inner regions of accretion discs around back holes. It also hints at a powerful new tool with which to test general relativity. Einstein’s theory is largely untested in such strong gravitational fields. If astronomers can understand the physics of the matter that is flowing into the black hole, they can use it to test the predictions of general relativity as never before - but only if the movement of the matter in the accretion disc can be completely understood.

“We need to test Einstein’s general theory of relativity to breaking point,” adds Dr Adam Ingram, the lead author at the ̽��ֱ�� of Amsterdam. “That’s the only way that we can tell whether it is correct or, as many physicists suspect, an approximation – albeit an extremely accurate one.”

Larger X-ray telescopes in the future could help in the search because they could collect the X-rays faster. This would allow astronomers to investigate the QPO phenomenon in more detail. But for now, astronomers can be content with having seen Einstein’s gravity at play around a black hole.

Adapted from a press release by the European Space Agency.

Image: ESA/ATG medialab.

An international team of astronomers has proved the existence of a ‘gravitational vortex’ around a black hole, solving a mystery that has eluded astronomers for more than 30 years. ̽��ֱ��discovery will allow astronomers to map the behaviour of matter very close to black holes. It could also open the door to future investigation of Albert Einstein’s general relativity.

We need to test Einstein’s general theory of relativity to breaking point

Adam Ingram, ̽��ֱ�� of Amsterdam

ESA/ATG medialab

Illustration of gravitational vortex

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Licence type:

Attribution

Five-dimensional black hole could ‘break’ general relativity

sc604 — Fri, 19 Feb 2016 06:00:00 +0000

Researchers have shown how a bizarrely shaped black hole could cause Einstein’s general theory of relativity, a foundation of modern physics, to break down. However, such an object could only exist in a universe with five or more dimensions.

̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge and Queen Mary ̽��ֱ�� of London, have successfully simulated a black hole shaped like a very thin ring, which gives rise to a series of ‘bulges’ connected by strings that become thinner over time. These strings eventually become so thin that they pinch off into a series of miniature black holes, similar to how a thin stream of water from a tap breaks up into droplets.

Ring-shaped black holes were ‘discovered’ by theoretical physicists in 2002, but this is the first time that their dynamics have been successfully simulated using supercomputers. Should this type of black hole form, it would lead to the appearance of a ‘naked singularity’, which would cause the equations behind general relativity to break down. ̽��ֱ��results are published in the journal Physical Review Letters.

View post on imgur.com

General relativity underpins our current understanding of gravity: everything from the estimation of the age of the stars in the universe, to the GPS signals we rely on to help us navigate, is based on Einstein’s equations. In part, the theory tells us that matter warps its surrounding spacetime, and what we call gravity is the effect of that warp. In the 100 years since it was published, general relativity has passed every test that has been thrown at it, but one of its limitations is the existence of singularities.

A singularity is a point where gravity is so intense that space, time, and the laws of physics, break down. General relativity predicts that singularities exist at the centre of black holes, and that they are surrounded by an event horizon – the ‘point of no return’, where the gravitational pull becomes so strong that escape is impossible, meaning that they cannot be observed from the outside.

“As long as singularities stay hidden behind an event horizon, they do not cause trouble and general relativity holds - the ‘cosmic censorship conjecture’ says that this is always the case,” said study co-author Markus Kunesch, a PhD student at Cambridge’s Department of Applied Mathematics and Theoretical Physics (DAMTP). “As long as the cosmic censorship conjecture is valid, we can safely predict the future outside of black holes. Because ultimately, what we’re trying to do in physics is to predict the future given knowledge about the state of the universe now.”

But what if a singularity existed outside of an event horizon? If it did, not only would it be visible from the outside, but it would represent an object that has collapsed to an infinite density, a state which causes the laws of physics to break down. Theoretical physicists have hypothesised that such a thing, called a naked singularity, might exist in higher dimensions.

“If naked singularities exist, general relativity breaks down,” said co-author Saran Tunyasuvunakool, also a PhD student from DAMTP. “And if general relativity breaks down, it would throw everything upside down, because it would no longer have any predictive power – it could no longer be considered as a standalone theory to explain the universe.”

We think of the universe as existing in three dimensions, plus the fourth dimension of time, which together are referred to as spacetime. But, in branches of theoretical physics such as string theory, the universe could be made up of as many as 11 dimensions. Additional dimensions could be large and expansive, or they could be curled up, tiny, and hard to detect. Since humans can only directly perceive three dimensions, the existence of extra dimensions can only be inferred through very high energy experiments, such as those conducted at the Large Hadron Collider.

Einstein’s theory itself does not state how many dimensions there are in the universe, so theoretical physicists have been studying general relativity in higher dimensions to see if cosmic censorship still holds. ̽��ֱ��discovery of ring-shaped black holes in five dimensions led researchers to hypothesise that they could break up and give rise to a naked singularity.

What the Cambridge researchers, along with their co-author Pau Figueras from Queen Mary ̽��ֱ�� of London, have found is that if the ring is thin enough, it can lead to the formation of naked singularities.

Using the COSMOS supercomputer, the researchers were able to perform a full simulation of Einstein’s complete theory in higher dimensions, allowing them to not only confirm that these ‘black rings’ are unstable, but to also identify their eventual fate. Most of the time, a black ring collapses back into a sphere, so that the singularity would stay contained within the event horizon. Only a very thin black ring becomes sufficiently unstable as to form bulges connected by thinner and thinner strings, eventually breaking off and forming a naked singularity. New simulation techniques and computer code were required to handle these extreme shapes.

“ ̽��ֱ��better we get at simulating Einstein’s theory of gravity in higher dimensions, the easier it will be for us to help with advancing new computational techniques – we’re pushing the limits of what you can do on a computer when it comes to Einstein’s theory,” said Tunyasuvunakool. “But if cosmic censorship doesn’t hold in higher dimensions, then maybe we need to look at what’s so special about a four-dimensional universe that means it does hold.”

̽��ֱ��cosmic censorship conjecture is widely expected to be true in our four-dimensional universe, but should it be disproved, an alternative way of explaining the universe would then need to be identified. One possibility is quantum gravity, which approximates Einstein’s equations far away from a singularity, but also provides a description of new physics close to the singularity.

̽��ֱ��COSMOS supercomputer at the ̽��ֱ�� of Cambridge is part of the Science and Technology Facilities Council (STFC) DiRAC HPC Facility.

Inset image: A video of a very thin black ring starting to break up into droplets. In this process a naked singularity is created and weak cosmic censorship is violated. Credit: Pau Figueras, Markus Kunesch, and Saran Tunyasuvunakool

Reference:
Pau Figueras, Markus Kunesch, and Saran Tunyasuvunakool ‘End Point of Black Ring Instabilities and the Weak Cosmic Censorship Conjecture.’ Physical Review Letters (2016). DOI: 10.1103/PhysRevLett.116.071102

Researchers have successfully simulated how a ring-shaped black hole could cause general relativity to break down: assuming the universe contains at least five dimensions, that is.

As long as singularities stay hidden behind an event horizon, they do not cause trouble and general relativity holds

Markus Kunesch

Marc Van Norden

Star field - 4

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Licence type:

Attribution

Gravitational waves detected 100 years after Einstein’s prediction

sc604 — Thu, 11 Feb 2016 15:30:00 +0000

An international team of scientists have observed ripples in the fabric of spacetime called gravitational waves, arriving at the earth from a cataclysmic event in the distant universe. This confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window onto the cosmos.

̽��ֱ��gravitational waves were detected on 14 September 2015 at 09:51 UK time by both LIGO (Laser Interferometer Gravitational-wave Observatory) detectors in Louisiana and Washington State in the US. They originated from two black holes, each around 30 times the mass of the Sun and located more than 1.3 billion light years from Earth, coalescing to form a single, even more massive black hole.

̽��ֱ��LIGO Observatories are funded by the National Science Foundation (NSF), and were conceived, built, and are operated by Caltech and MIT. ̽��ֱ��discovery, published in the journal Physical Review Letters, was made by the LIGO Scientific Collaboration (which includes the GEO Collaboration and the Australian Consortium for Interferometric Gravitational Astronomy) and the Virgo Collaboration using data from the two LIGO detectors.

“ ̽��ֱ��discovery of gravitational waves by the LIGO team is an incredible achievement,” said Professor Stephen Hawking, the Dennis Stanton Avery and Sally Tsui Wong-Avery Director of Research at the Department of Applied Mathematics and Theoretical Physics at the ̽��ֱ�� of Cambridge. “It is the first observation of gravitational waves as predicted by Einstein and will allow us new insights into our universe. ̽��ֱ��gravitational waves were released from the collision of two black holes, the properties of which are consistent with predictions I made in Cambridge in the 1970s, such as the black hole area and uniqueness theorems. We can expect this observation to be the first of many as LIGO sensitivity increases, keeping us all busy with many further surprises.”

Gravitational waves carry unique information about the origins of our Universe and studying them is expected to provide important insights into the evolution of stars, supernovae, gamma-ray bursts, neutron stars and black holes. However, they interact very weakly with particles and require incredibly sensitive equipment to detect. British and German teams, including researchers from the ̽��ֱ�� of Cambridge, working with US, Australian, Italian and French colleagues as part of the LIGO Scientific Collaboration and the Virgo Collaboration, are using a technique called laser interferometry.

Each LIGO site comprises two tubes, each four kilometres long, arranged in an L-shape. A laser is beamed down each tube to very precisely monitor the distance between mirrors at each end. According to Einstein’s theory, the distance between the mirrors will change by a tiny amount when a gravitational wave passes by the detector. A change in the lengths of the arms of close to 10^-19 metres (just one-ten-thousandth the diameter of a proton) can be detected.

According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years, and then much more quickly in the final minutes. During the final fraction of a second, the two black holes collide into each other at nearly one-half the speed of light and form a single more massive black hole, converting a portion of the combined black holes’ mass to energy, according to Einstein’s formula E=mc². This energy is emitted as a final strong burst of gravitational waves. It is these gravitational waves that LIGO has observed.

Independent and widely separated observatories are necessary to verify the direction of the event causing the gravitational waves, and also to determine that the signals come from space and are not from some other local phenomenon.

To ensure absolute accuracy, the consortium of nearly 1,000 scientists from 16 countries spent several months carefully checking and re-checking the data before submitting their findings for publication.

Christopher Moore, a PhD student from Cambridge’s Institute of Astronomy, was part of the discovery team who worked on the data analysis.

“Since September, we’ve known that something was detected, but it took months of checking to confirm that it was actually gravitational waves,” he said. “This team has been looking for evidence of gravitational waves for decades – a huge amount of work has gone into it, and I feel incredibly lucky to be part of the team. This discovery will change the way we do astronomy.”

Over coming years, the Advanced LIGO detectors will be ramped up to full power, increasing their sensitivity to gravitational waves, and in particular allowing more distant events to be measured. With the addition of further detectors, initially in Italy and later in other locations around the world, this first detection is surely just the beginning. UK scientists continue to contribute to the design and development of future generations of gravitational wave detectors.

̽��ֱ��UK Minister for Universities and Science, Jo Johnson MP, said: “Einstein’s theories from over a century ago are still helping us to understand our universe. Now that we have the technological capability to test his theories with the LIGO detectors his scientific brilliance becomes all the more apparent. ̽��ֱ��Government is increasing support for international research collaborations, and these scientists from across the UK have played a vital part in this discovery.”

LIGO was originally proposed as a means of detecting these gravitational waves in the 1980s by Kip Thorne, Caltech’s Richard P. Feynman Professor of Theoretical Physics, Emeritus; Ronald Drever, professor of physics, emeritus also from Caltech; and Rainer Weiss, professor of physics, emeritus, from MIT.

“ ̽��ֱ��description of this observation is beautifully described in the Einstein theory of General Relativity formulated 100 years ago and comprises the first test of the theory in strong gravitation. It would have been wonderful to watch Einstein’s face had we been able to tell him,” said Weiss.

“With this discovery, we humans are embarking on a marvelous new quest: the quest to explore the warped side of the universe—objects and phenomena that are made from warped spacetime. Colliding black holes and gravitational waves are our first beautiful examples,” said Thorne.

̽��ֱ��discovery was made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared to the first generation LIGO detectors, enabling a large increase in the volume of the universe probed—and the discovery of gravitational waves during its first observation run.

̽��ֱ��US National Science Foundation leads in financial support for Advanced LIGO. Funding organisations in Germany (Max Planck Society), the UK (Science and Technology Facilities Council, STFC) and Australia (Australian Research Council) also have made significant commitments to the project.

Several of the key technologies that made Advanced LIGO so much more sensitive have been developed and tested by the German UK GEO collaboration. Significant computer resources have been contributed by the AEI Hannover Atlas Cluster, the LIGO Laboratory, Syracuse ̽��ֱ��, and the ̽��ֱ�� of Wisconsin-Milwaukee.

Several universities designed, built, and tested key components for Advanced LIGO: ̽��ֱ��Australian National ̽��ֱ��, the ̽��ֱ�� of Adelaide, the ̽��ֱ�� of Florida, Stanford ̽��ֱ��, Columbia ̽��ֱ�� of New York, and Louisiana State ̽��ֱ��.

Cambridge has a long-standing involvement in the field of gravitational wave science, and specifically with the LIGO experiment. Until recently these efforts were spearheaded by Dr Jonathan Gair, who left last year for a post at the ̽��ֱ�� of Edinburgh and who has made significant contributions to a wide range of gravitational wave and LIGO science; he is one of the authors on the new paper. Several scientists in Cambridge are current members of the collaboration, including PhD students Christopher Moore and Alvin Chua from the Institute of Astronomy; Professor Anthony Lasenby and PhD student Sonke Hee from the Cavendish Laboratory and the Kavli Institute of Cosmology; and Professor Mike Hobson from the Cavendish Laboratory.

Further members of the collaboration until recently based at Cambridge, include Dr Philip Graff (author on the detection paper) and Dr Farhan Feroz, who, jointly with Mike Hobson and Anthony Lasenby, developed a machine learning method of analysis used currently within LIGO, as well as Dr Christopher Berry (author) and Dr Priscilla Canizares.

These findings will be discussed at next month's Cambridge Science Festival during the open afternoon at the Institute of Astronomy.

Reference:
B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration) 'Observation of Gravitational Waves from a Binary Black Hole Merger.' Physical Review Letters (2016). DOI: 10.1103/PhysRevLett.116.061102.

New window on the universe is opened with the observation of gravitational waves – ripples in spacetime – caused by the collision of two black holes.

I feel incredibly lucky to be part of the team - this discovery will change the way we do astronomy.

Christopher Moore

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

New insights found in black hole collisions

sc604 — Fri, 27 Mar 2015 08:00:00 +0000

An international team of astronomers, including from the ̽��ֱ�� of Cambridge, have found solutions to decades-old equations describing what happens as two spinning black holes in a binary system orbit each other and spiral in toward a collision.

̽��ֱ��results, published in the journal Physical Review Letters, should significantly impact not only the study of black holes, but also the search for elusive gravitational waves – a type of radiation predicted by Einstein’s theory of general relativity – in the cosmos.

Unlike planets, whose average distance from the sun does not change over time, general relativity predicts that two black holes orbiting around each other will move closer together as the system emits gravitational waves.

“An accelerating charge, like an electron, produces electromagnetic radiation, including visible light waves,” said Dr Michael Kesden of the ̽��ֱ�� of Texas at Dallas, the paper’s lead author. “Similarly, any time you have an accelerating mass, you can produce gravitational waves.”

̽��ֱ��energy lost to gravitational waves causes the black holes to spiral closer and closer together until they merge, which is the most energetic event in the universe, after the big bang. That energy, rather than going out as visible light, which is easy to see, goes out as gravitational waves, which are much more difficult to detect.

While Einstein’s theories predict the existence of gravitational waves, they have not been directly detected. But the ability to ‘see’ gravitational waves would open up a new window to view and study the universe.

Optical telescopes can capture photos of visible objects, such as stars and planets, and radio and infrared telescopes can reveal additional information about invisible energetic events. Gravitational waves would provide a qualitatively new medium through which to examine astrophysical phenomena.

“Using gravitational waves as an observational tool, you could learn about the characteristics of the black holes that were emitting those waves billions of years ago, information such as their masses and mass ratios, and the way they formed” said co-author and PhD student Davide Gerosa, of Cambridge’s Department of Applied Mathematics and Theoretical Physics. “That’s important data for more fully understanding the evolution and nature of the universe.”

Later this year, upgrades to the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US and VIRGO in Europe will be completed, and the first direct measurements of gravitational waves may be just around the corner. Around the same time, the LISA Pathfinder mission will be launched as a test mission for establishing a gravitational wave detector of unprecedented sensitivity in space.

“ ̽��ֱ��equations that we solved will help predict the characteristics of the gravitational waves that LIGO would expect to see from binary black hole mergers,” said co-author Dr Ulrich Sperhake, who, along with Gerosa, is also a member of Cambridge’s Centre for Theoretical Cosmology. “We’re looking forward to comparing our solutions to the data that LIGO collects.”

̽��ֱ��equations the researchers solved deal specifically with the spin angular momentum of binary black holes and a phenomenon called precession.

“Like a spinning top, black hole binaries change their direction of rotation over time, a phenomenon known as procession,” said Sperhake. “ ̽��ֱ��behaviour of these black hole spins is a key part of understanding their evolution.”

Just as Kepler studied the motion of the earth around the sun and found that orbits can be ellipses, parabola or hyperbolae, the researchers found that black hole binaries can be divided into three distinct phases according to their rotation properties.

̽��ֱ��researchers also derived equations that will allow statistical tracking of such spin phases, from black hole formation to merger, far more efficiently and quickly than was possible before.

“With these solutions, we can create computer simulations that follow black hole evolution over billions of years,” said Kesden. “A simulation that previously would have taken years can now be done in seconds. But it’s not just faster. There are things that we can learn from these simulations that we just couldn’t learn any other way.”

“With these tools, new insights into the dynamics of black holes will be unveiled,” said Gerosa. “Gravitational wave signals can now be better interpreted to unveil mysteries of the massive universe.”

Researchers from the Rochester Institute of Technology and the ̽��ֱ�� of Mississippi also contributed to the Physical Review Letters paper. ̽��ֱ��researchers were supported in part by the Science and Technology Facilities Council, the European Commission, the National Science Foundation, UT Dallas and the ̽��ֱ�� of Cambridge.

Inset image: Illustration of two rotating black holes in orbit. Both, the black hole spins (red arrows) and the orbital angular momentum (blue arrow) precess about the total angular momentum (grey arrow) in a manner that characterizes the black-hole binary system. Gravitational waves carry away energy and momentum from the system and the orbital plane (light blue) tilts and turns accordingly. Credit: Graphic by Midori Kitagawa

Adapted from ̽��ֱ�� of Texas at Dallas press release.

New research provides revelations about the most energetic event in the universe — the merging of two spinning, orbiting black holes into a much larger black hole.

̽��ֱ��behaviour of these black hole spins is a key part of understanding their evolution

Ulrich Sperhake

NASA's Marshall Space Flight Center

Black Holes Go 'Mano a Mano' (NASA, Chandra, 10/06/09)

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Licence type:

Attribution-Noncommerical

“Echo” of light augurs new era in study of black holes

bjb42 — Thu, 31 May 2012 21:00:24 +0000

̽��ֱ��findings open up new opportunities for scientists trying to map and understand what happens on the brink of “active galactic nuclei”, or AGNs; monster black holes that exist at the heart of most big galaxies.

These black holes contain millions of times the sun’s mass. As matter streams towards them, the centre of the galaxy lights up, emitting billions of times more energy than the sun and illuminating the disk of matter that forms at the hole’s edge.

One of the most important tools for astronomers studying these black holes is something called the “iron K line”. This is a shape which appears as very distinctive X-rays created by iron atoms, which, when excited, emit energies of around 6,000 to 7,000 electron volts – several thousand times the energy in visible light.

̽��ֱ��line brightens as the result of a mysterious and intense X-ray source near to the black hole. This source shines on to the accumulated matter, causing the iron atoms to radiate their K-line energy. In effect, when the source flares, a light “echo” sweeps across the disk of matter and the iron K line lights up accordingly, after a delay corresponding to how long the X-rays took to reach the disk. ̽��ֱ��process is called relativistic reverberation.

Although observing this process carries the promise of a much better understanding of what is happening around supersized black holes, neither the European Space Agency, nor NASA, have telescopes powerful enough to spot the reverberations of single flares coming from the source.

To get round this problem, the researchers, from the Universities of Maryland and Cambridge, reasoned that it might be possible to detect the combined echoes from several flares, if a large amount of data from a particular object in space could be analysed.

This object turned out to be the galaxy NGC 4151, which is located about 45 million light-years away in the constellation Canes Venatici. ̽��ֱ��galaxy has one of the brightest AGNs in X-rays and astronomers think that it is powered by a black hole weighing 50 million solar masses. ̽��ֱ��sheer scale of this black hole suggests that it also has a large accretion disk of matter, capable of producing particularly long-lived and detectable echoes of light coming from the X-ray source.

̽��ֱ��data needed to identify the light echoes came from observations carried out using the European Space Agency’s XMM-Newton satellite. By analysing the data, the researchers were able to uncover numerous X-ray echoes, demonstrating the reality of relativistic reverberation for the first time. Their findings are published in the May 8 issue of the Monthly Notices of the Royal Astronomical Society.

̽��ֱ��study shows that the echoes lagged behind the original flares by a little more than 30 minutes. Moving at the speed of light, the X-rays associated with the echo must have travelled an additional 400 million miles – about four times the Earth’s average distance from the sun, to reach the accretion disk.

“This tells us that the mysterious X-ray source in the AGN hovers at some height above the accretion disk,” Chris Reynolds, a professor of astronomy at the ̽��ֱ�� of Maryland at College Park and a co-author on the study, said. Jets of accelerated particles are often found around AGNs, and the finding appears to endorse an idea which has already been postulated that whatever the X-ray source is, it may be located near to the bases of these jets.

“ ̽��ֱ��data show that the earliest echo comes from the most broadened iron line emission,” Andy Fabian, from the Institute of Astronomy at the ̽��ֱ�� of Cambridge, and another co-author, added. “This line originates from closest to the black hole, and fits well with what we were expecting.”

̽��ֱ��detection of X-ray echoes in the AGN opens up a new way of studying black holes and the disks of matter that accrete around them. Astronomers anticipate that the next generation of X-ray telescopes will have collecting areas large enough to detect the echo produced by a single flare from the X-ray source, giving them an even better tool for testing relativity and probing the immediate surroundings of massive black holes.

“Our analysis allows us to probe black holes through a different window,” Abderahmen Zoghbi, a postdoctoral research associate at the ̽��ֱ�� of Maryland at College Park and the report’s lead author, said. “It confirms some long-held ideas about AGN and gives us a sense of what we can expect when a new generation of space-based X-ray telescopes eventually becomes available.”

A long-sought “echo” of light that promises to reveal more about supersized black holes in distant galaxies has been identified by an international team of astronomers.

Our analysis allows us to probe black holes through a different window.

Abderahmen Zoghbi

NASA.

̽��ֱ��galaxy NGC 4151. Researchers were able to use this galaxy to accumulate data about flares coming from a mysterious X-ray source close to the giant black hole at its centre.

This work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page.

Yes