̽��ֱ�� of Cambridge - Einstein

First detection of gravitational waves and light produced by colliding neutron stars

sc604 — Mon, 16 Oct 2017 13:17:01 +0000

It could be a scenario from science fiction, but it really happened 130 million years ago -- in the NGC 4993 galaxy in the Hydra constellation, at a time here on Earth when dinosaurs still ruled, and flowering plants were only just evolving.

Today, dozens of UK scientists – including researchers from the ̽��ֱ�� of Cambridge – and their international collaborators representing 70 observatories worldwide announced the detection of this event and the significant scientific firsts it has revealed about our Universe.

Those ripples in space finally reached Earth at 1.41pm UK time, on Thursday 17 August 2017, and were recorded by the twin detectors of the US-based Laser Interferometer Gravitational-wave Observatory (LIGO) and its European counterpart Virgo.

A few seconds later, the gamma-ray burst from the collision was recorded by two specialist space telescopes, and over following weeks, other space- and ground-based telescopes recorded the afterglow of the massive explosion. UK developed engineering and technology is at the heart of many of the instruments used for the detection and analysis.

Studying the data confirmed scientists’ initial conclusion that the event was the collision of a pair of neutron stars – the remnants of once gigantic stars, but collapsed down into approximately the size of a city. “These objects are made of matter in its most extreme, dense state, standing on the verge of total gravitational collapse,” said Michalis Agathos, from Cambridge’s Department of Applied Mathematics and Theoretical Physics. “By studying subtle effects of matter on the gravitational wave signal, such as the effects of tides that deform the neutron stars, we can infer the properties of matter in these extreme conditions.”

There are a number of “firsts” associated with this event, including the first detection of both gravitational waves and electromagnetic radiation (EM) - while existing astronomical observatories “see” EM across different frequencies (eg, optical, infra-red, gamma ray etc), gravitational waves are not EM but instead ripples in the fabric of space requiring completely different detection techniques. An analogy is that LIGO and Virgo “hear” the Universe.

̽��ֱ��announcement also confirmed the first direct evidence that short gamma ray bursts are linked to colliding neutron stars. ̽��ֱ��shape of the gravitational waveform also provided a direct measure of the distance to the source, and it was the first confirmation and observation of the previously theoretical cataclysmic aftermaths of this kind of merger - a kilonova.

Additional research papers on the aftermath of the event have also produced a new understanding of how heavy elements such as gold and platinum are created by supernova and stellar collisions and then spread through the Universe. More such original science results are still under current analysis.

By combining gravitational-wave and electromagnetic signals together, researchers also used for the first time a new and novel technique to measure the expansion rate of the Universe.

While binary black holes produce “chirps” lasting a fraction of a second in the LIGO detector’s sensitive band, the August 17 chirp lasted approximately 100 seconds and was seen through the entire frequency range of LIGO — about the same range as common musical instruments. Scientists could identify the chirp source as objects that were much less massive than the black holes seen to date. In fact, “these long chirping signals from inspiralling neutron stars are really what many scientists expected LIGO and Virgo to see first,” said Christopher Moore, researcher at CENTRA, IST, Lisbon and member of the DAMTP/Cambridge LIGO group. “ ̽��ֱ��shorter signals produced by the heavier black holes were a spectacular surprise that led to the awarding of the 2017 Nobel prize in physics.”

UK astronomers using the VISTA telescope in Chile were among the first to locate the new source. “We were really excited when we first got notification that a neutron star merger had been detected by LIGO,” said Professor Nial Tanvir from the ̽��ֱ�� of Leicester, who leads a paper in Astrophysical Journal Letters today. “We immediately triggered observations on several telescopes in Chile to search for the explosion that we expected it to produce. In the end, we stayed up all night analysing the images as they came in, and it was remarkable how well the observations matched the theoretical predictions that had been made.”

“It is incredible to think that all the gold in the Earth was probably produced by merging neutron stars, similar to this event that exploded as kilonovae billions of years ago.”

“Not only is this the first time we have seen the light from the aftermath of an event that caused a gravitational wave, but we had never before caught two merging neutron stars in the act, so it will help us to figure out where some of the more exotic chemical elements on Earth come from,” said Dr Carlos Gonzalez-Fernandez of Cambridge’s Institute of Astronomy, who processed the follow-up images taken with the VISTA telescope.

“This is a spectacular discovery, and one of the first of many that we expect to come from combining together information from gravitational wave and electromagnetic observations,” said Nathan Johnson-McDaniel, researcher at DAMTP, who contributed to predictions of the amount of ejected matter using the gravitational wave measurements of the properties of the binary.

Though the LIGO detectors first picked up the gravitational wave in the United States, Virgo, in Italy, played a key role in the story. Due to its orientation with respect to the source at the time of detection, Virgo recovered a small signal; combined with the signal sizes and timing in the LIGO detectors, this allowed scientists to precisely triangulate the position in the sky. After performing a thorough vetting to make sure the signals were not an artefact of instrumentation, scientists concluded that a gravitational wave came from a relatively small patch of the southern sky.

“This event has the most precise sky localisation of all detected gravitational waves so far,” says Jo van den Brand of Nikhef (the Dutch National Institute for Subatomic Physics) and VU ̽��ֱ�� Amsterdam, who is the spokesperson for the Virgo collaboration. “This record precision enabled astronomers to perform follow-up observations that led to a plethora of breath-taking results.”

Fermi was able to provide a localisation that was later confirmed and greatly refined with the coordinates provided by the combined LIGO-Virgo detection. With these coordinates, a handful of observatories around the world were able, hours later, to start searching the region of the sky where the signal was thought to originate. A new point of light, resembling a new star, was first found by optical telescopes. Ultimately, about 70 observatories on the ground and in space observed the event at their representative wavelengths. “What I am most excited about, personally, is a completely new way of measuring distances across the universe through combining the gravitational wave and electromagnetic signals. Obviously, this new cartography of the cosmos has just started with this first event, but I just wonder whether this is where we will see major surprises in the future,” said Ulrich Sperhake, Head of Cambridge’s gravitational wave group in LIGO.

In the weeks and months ahead, telescopes around the world will continue to observe the afterglow of the neutron star merger and gather further evidence about its various stages, its interaction with its surroundings, and the processes that produce the heaviest elements in the universe.

Reference:
Physical Review Letters
"GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral."

Science
"A Radio Counterpart to a Neutron Star Merger."
"Swift and NuSTAR observations of GW170817: detection of a blue kilonova."
"Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger."

Astrophysical Journal Letters
"Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A."
"Multi-Messenger Observations of a Binary Neutron Star Merger."

Nature
"A gravitational-wave standard siren measurement of the Hubble constant."

Adapted from STFC and LIGO press releases.

In a galaxy far away, two dead stars begin a final spiral into a massive collision. ̽��ֱ��resulting explosion unleashes a huge burst of energy, sending ripples across the very fabric of space. In the nuclear cauldron of the collision, atoms are ripped apart to form entirely new elements and scattered outward across the Universe.

What I am most excited about, personally, is a completely new way of measuring distances across the universe.

Ulrich Sperhake

ESO/L. Calçada/M. Kornmesser

Artist’s impression of merging neutron stars

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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

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Understanding gravity - from Newton to Hawking

sjr81 — Fri, 29 Apr 2016 14:12:30 +0000

As part of its 600th anniversary, the ̽��ֱ�� Library has put on display some of its greatest treasures in the blockbuster exhibition Lines of Thought: Discoveries that Changed the World.

To celebrate the anniversary and the exhibition, which runs until September 30, 2016, the ̽��ֱ�� Library has made a series of six short films, each examining one of the six key themes of Lines of Thought.

On the Shoulders of Giants – Understanding Gravity covers three centuries of development in human understanding of how and why gravity operates.

Beginning with Copernicus and a first-edition copy of his iconic De Revolutionibus, Understanding Gravity looks at his first formative ideas of a sun-centred (heliocentric) universe.

Adam Perkins, Curator of Scientific Manuscripts at the ̽��ֱ�� Library, said: “It’s essential to have Copernicus’ idea to create what we know today about the solar system. But we also have on display other, later objects in the exhibition – such as Tyco Brahe’s De Nova Stella – which tried to keep the Earth at the centre of the solar system. However, Johannes Kepler, Brahe’s pupil, immediately rejected the ideas in De Nova Stella and went back to Copernicus’ sun-centred solar system.”

Perhaps the star of Understanding Gravity, and Lines of Thought as a whole, is Newton’s copy of Principia.

Although earlier minds had challenged the view that the earth was the centre of the solar system, it was the work of Sir Isaac Newton, second Lucasian Professor of Mathematics at the ̽��ֱ�� of Cambridge, which firmly established that the planets revolved around the sun, and that gravity was the force which controlled this.

“Its publication in 1687 inspired a scientific revolution and laid the foundations of modern physics,” said Perkins. “ ̽��ֱ��bulk of Newton’s scientific manuscripts came to Cambridge in 1872, where they continue to be the focus of global scholarly activity.”

Although Newton was able to posit the existence of gravity, he was unable to explain how it functioned and it fell to Einstein’s Theory of Relativity to suggest a solution, with proof coming from Trinity College mathematicians Frank Dyson and Arthur Eddington.

Cambridge physicists and mathematicians including Stephen Hawking and Jocelyn Bell have continued to grapple with the implications of Newton and Einstein’s work in order to explain better the universe around us.

To celebrate Lines of Thought, Cambridge ̽��ֱ�� Library commissioned a once-in-a-lifetime photo of Professor Stephen Hawking and Newton’s copy of Principia, shot in Professor Hawking’s office at the Department of Applied Mathematics and Theoretical Physics in Cambridge. Lines of Thought has also put on display Hawking’s typescript draft of A Brief History of Time – the worldwide bestseller which was first published in 1988.

Added Perkins: “Hawking sees his own theoretical work as part of a continuum of the ideas going back across the great founding fathers of modern science, many of whom we have on display at the moment.

“Well over 200 scientists have deposited their papers in Cambridge which has given us a world-class treasure. Lines of Thought has given us the opportunity to share these treasures with people around the world as we celebrate 600 years of Cambridge ̽��ֱ�� Library.”

̽��ֱ��most important publication in the history of science – Isaac Newton’s own annotated copy of Principia Mathematica – and other seminal works by Copernicus, Einstein and Stephen Hawking, feature in a new film, released today, celebrating 600 years of Cambridge ̽��ֱ�� Library.

Principia's publication in 1687 inspired a scientific revolution and laid the foundations of modern physics.

Adam Perkins

Lines of Thought: Understanding Gravity

Priceless treasures: in a shot commissioned to celebrate Cambridge ̽��ֱ�� Library’s 600th anniversary, Professor Stephen Hawking is pictured with Newton’s annotated first edition of Principia Mathematica. Credit: Graham CopeKoga

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Born identity revealed in newly-opened archive

sjr81 — Fri, 07 Oct 2011 00:10:27 +0000

̽��ֱ��Centre, nestled in the grounds of Churchill College, already houses some of the most important political, military and scientific papers of the 20^th century, including those of Winston Churchill, Margaret Thatcher, John Cockcroft and James Chadwick.

But the story contained within Born’s archive, who fled Nazi Germany in 1933, opposed the dawn of atomic weapons and corresponded with all the major physicists of his age, draws a compelling portrait of the man who helped formulate quantum mechanics with his assistant Werner Heisenberg and who is renowned for his many major contributions to 20^th century physics.

Not only was Born, who came to Cambridge ̽��ֱ�� after fleeing Germany, a close and lifelong friend of Einstein, he also taught nine Nobel-winning physicists including Heisenberg, during a period often referred to as the ‘golden age of physics’.

Others that received their Ph.D. degrees under Born at Göttingen ̽��ֱ��, before Hitler ordered the expulsion of Jews from universities in 1933, included J. Robert Oppenheimer, father of the atomic bomb, Max Delbrück, Walter Elsasser, Friedrich Hund, Pascual Jordan and Maria Goeppert-Mayer.

Lynsey Robertson, who has worked on the collection, said: “Born’s story is an incredible one. Although a pacifist, he was the teacher of the inventors of the atomic bomb. He was forced to flee Nazi Germany and was a friend of Einstein’s for 40 years. He provided the first self-consistent mathematical formulation of quantum mechanics and developed the concept that, at the atomic level, physical processes are determined by probabilities, a completely different perspective from that of classical physics.”

Allen Packwood, Director of the Churchill Archives Centre, said: “ ̽��ֱ��archive provides a wonderful window on the personal development and private life of one of the twentieth century’s greatest scientists. It is appropriate that his papers should sit alongside those of many of his contemporaries, including John Cockcroft, James Chadwick and Lise Meitner who, like Born, fled Nazi persecution.”

Included in the archive, which amounts to some 84 boxes of material, is original correspondence that illuminates Born’s complex relationship with 1932 Nobel Prize winner Heisenberg, who worked on Germany’s nuclear weapons research during the Second World War.

They met again after the war and in correspondence with his son, Gustav, in 1947, Born said Heisenberg had become ‘somewhat infected by Nazi ideas…but in spite of all that we liked him immensely’.

Many, including Heisenberg himself, felt that Born should have shared the 1932 Nobel Prize. That he did not was a passing sadness to Born but he did not complain about it. Many years later, in a 1952 letter from Born to his son, he remarks that many of his discoveries had been wrongly attributed to Heisenberg.

However, Born did finally receive the Nobel Prize for Physics in 1954 for his work on the interpretation of Schrodinger’s wave function.

Also included in the archive are letters from Born to his wife and children recording his views on contemporary scientific work, his colleagues and international affairs -including the dropping of the atomic bomb and what he saw as man’s failings on the nuclear issue. He went on to become one of the founding members of Pugwash – the movement opposing such armed conflict – alongside Bertrand Russell.

Of particular note to those with an interest in the history of science, the archive also holds Born’s handwritten notes, including lectures to the Kapitza Club, as well as a volume of the young Born’s notes of the famous mathematician David Hilbert’s lectures.

Cambridge ̽��ֱ��’s Professor Malcolm Longair, who has studied the original Born scientific papers for a new book entitled Quantum Concepts in Physics, said: “Max Born was a brilliant mathematical physicist who made some of the most important technical advances which led to the first fully self-consistent theory of quantum mechanics.

“Born was also remarkably modest about his achievements, claiming he lacked the intuition of people like Niels Bohr and Heisenberg, but he had the mathematical and technical knowledge to convert Heisenberg’s revolutionary concepts into the first complete theory of non-relativistic quantum mechanics.”

Born, who lived from 1882-1970, was born into a Jewish family in Breslau (then Germany, now Poland) but converted to the Lutheran faith following his marriage to Hedwig Ehrenberg, a practicing Lutheran. He was educated and taught at some of the best German universities.

He went on to study at the ̽��ֱ�� of Breslau, Heidelberg ̽��ֱ��, the ̽��ֱ�� of Zurich, ̽��ֱ�� of Göttingen and, during 1908-1909, he studied at Gonville and Caius College, Cambridge.

He became a lecturer at Gottingen in 1909 and married Hedwig Ehrenberg in 1913, having three children together. It was in 1915, while Born was Professor of Theoretical Physics at the ̽��ֱ�� of Berlin, that he met Albert Einstein.Returning to Gottingen in 1921, following a stint in Frankfurt, Born created its School of Theoretical Physics, making Gottingen one of the most important international centres of the new ‘quantum mechanics’, which he named in 1924.

In 1925, he recognised the key concept of non-commutativity in quantum mechanics which had appeared in Heisenberg's revolutionary paper of 1925 and which caused Heisenberg great concern. Born showed that this phenomenon can be naturally described in terms of matrix calculus and this led to the formulation of matrix mechanics which he worked out with his assistants, Heisenberg and Pascual Jordan.

In 1926, Schrodinger showed how quantum mechanics could be formulated more transparently using wave functions and Born went on to demonstrate how this could be interpreted in terms of probabilities, the work for which he was belatedly awarded the Nobel prize in 1954.

Although a convert to Lutheranism, he was condemned as Jewish according to Nazi Germany’s anti-Semitic laws. Fleeing from Germany in 1933, Born accepted the position of Stokes Lecturer of Applied Mathematics at Cambridge before moving to Bangalore for a period of six months. In 1936 he accepted the post of Tait Professor of Natural Philosophy at the ̽��ֱ�� of Edinburgh where he remained until his retirement in 1953.

Following his retirement he returned to Germany where he lived until his death on January 5, 1970.

̽��ֱ��archive has been deposited by Max Born’s son, Professor Gustav Born FRS (etc), an eminent medical scientist, assisted by members of his family. His daughter, Max Born’s grand-daughter, Georgina Born, was responsible for initiating the connection with Churchill College when she was Professor of Sociology, Anthropology and Music at Cambridge ̽��ֱ�� (2006-10).

Other grandchildren include Sebastian Born, Associate Director of the National Theatre in London and Grammy-Award winning singer and actress Olivia Newton-John.

A Nobel Prize Medal, a postcard from Einstein and a Hitler-stamped letter of expulsion are among a fascinating archive of documents and other material belonging to Max Born – one of the fathers of quantum mechanics – being opened by Cambridge ̽��ֱ��’s Churchill Archives Centre.

Born’s story is an incredible one. Although a pacifist, he was the teacher of the inventors of the atomic bomb. He was forced to flee Nazi Germany and was a friend of Einstein’s for 40 years.

Lynsey Robertson

Churchill Archives Centre

Max Born

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