A Thing and Its Opposite

English
 
Here is a tangled tale of four research paths that intersected in a surprising way in the Weizmann Institute’s Braun Center for Submicron Research. It combines high drama with subatomic physics, things with their opposites and, above all, the never-ceasing struggle to understand the basic nature of our world.
Majorana
 
The first part of the story took place in 1937. In that year, Ettore Majorana, a 31-year-old Sicilian theoretical physicist, published a paper in which he expanded on an idea of another physicist, Paul Dirac. Just four years older than Majorana, Dirac had already received a Nobel Prize in physics in 1933. Among other things, he predicted the existence of antiparticles – for instance, the positron, which is identical to the electron but with an opposite, positive charge. Antimatter particles, which have since been observed in the lab, were at that time a radical idea. But it was an idea that changed the way physicists thought about the structure of matter in the universe.

In his 1937 paper, Majorana took Dirac’s formula one step further, proposing that it is possible, in theory, to have an elementary particle that carries no electric charge; such a particle would, in fact, be its own antiparticle. This theoretical particle became known as Majorana’s fermion (a fermion being a particle of matter, rather than a force-carrying particle such as a photon).

Majorana’s personal life adds intrigue to the story: Although a gifted scientist who published his first scientific paper as an undergraduate, he was mentally unstable. His mentor, Enrico Fermi, called him a “genius of Newton’s rank.” But even as Fermi managed to convince him to publish his antiparticle paper, Majorana was becoming increasingly reclusive. Finally, in 1938, he boarded a ship in Palermo bound for Napoli. But he never disembarked. Although it is fairly certain that Majorana committed suicide, rumors of his having escaped to a monastery helped fuel the mystery surrounding the theory of a particle that is its own antiparticle.
 
 

Imaginary particles


The story picks up in 1982 with Robert Laughlin, an American physicist. Laughlin, in proposing an explanation for a quantum phenomenon called the Fractional Quantum Hall Effect, which occurs in semiconductors, made the claim that in certain circumstances imaginary particles – arising through the collective behavior of electrons – are formed and that these carry electric charges. Interestingly, the proposed charges were fractions of the basic charge of an electron.
 
Robert Laughlin
 

 

Such imaginary particles were expected to appear in Quantum Hall systems – systems in which electrons moving in a two-dimensional layer are exposed to a strong magnetic field. The proposed charges were odd fractions – one-third, one-fifth, etc. – of an electron’s charge.

This prediction was first proven experimentally in 1997 by the Weizmann Institute’s Prof. Moty Heiblum and his research group – an achievement that contributed to the decision to award Laughlin, Stormer and Tsui the Nobel Prize in Physics in 1998. But before long, other research into quantum phenomena began to hint at the existence of imaginary particles with completely different characteristics, those with fractional charges that were even – one-half, one-quarter, etc. Heiblum and his group succeeded in proving the existence of these charges, as well, a feat that depended on the growth of ultra-pure semiconductor crystals by the Institute’s Dr. Vladimir Umansky in the Braun Submicron Center.
 

Quantum switches


Imaginary particles come in two types: Abelian and non-Abelian. These mathematical terms, from the field of topology, refer to what happens when two particles in a system change places. Unlike the Abelian type, in the non-Abelian system (in which the particles have even denominators), this exchange moves the system from one quantum state to another. These quantum states are sensitive only to the topology of the path taken by the two particles in the exchange process.
 
Prof. Moty Heiblum
 
Because their quantum state is modified only when they switch positions, such exchanges of non-Abelian particles (often called “braiding”) should be resistant to local perturbation.  They could thus form the basis of a robust type of quantum computing known as topological quantum computation. Though abstract and theoretical, these findings have lately begun to garner interest, including a recent sizable contribution by software giant Microsoft to further the research.
 
 

Small Is beautiful


Another research path, which opened in 2007, began with an insight more common to sculpture than quantum physics: The level of detail that sculptors can achieve in their artwork is limited by the width of their finest carving tool. Past a certain physical point, the only way to introduce greater detail into the sculpture is to shape it from bottom up, by piecing together very tiny bits of stone. The dimensions of the smallest details will thus be determined by the size of the smallest stones.
 
Dr. Hadas Shtrikman
 
Dr. Hadas Shtrikman used this insight in her Weizmann Institute lab, moving from growing two-dimensional crystals that were further miniaturized to nanowires that can be used directly in electronic devices. Working with Dr. Ronit Popovitz-Biro over several years, she managed to grow nanowires with perfect crystal structure and so thin that, for all practical purposes, electrons flow through them in one dimension.

 

 

States


The final path in this story began in 2001, with Prof. Alexei Kitaev, a former visiting scientist at the Weizmann Institute. Kitaev suggested that quantum topological memory could be created using a new version of non-Abelian imaginary particles – particles without any charge that would have the properties of Majorana particles. These would not be true Majorana’s fermions, which are particles of matter, but complex imaginary particles in which the lack of charge would be both a “state” and its own “anti-state.”
 
Nanowires from the lab of Dr. Hadas Shtrikman
 
A few years later, in 2010, the Institute’s Prof. Yuval Oreg and his colleagues Prof. Felix von Oppen of the Open University Berlin and Prof. Gil Refael of the California Institute of Technology described the possibility of creating quantum states containing complex imaginary particles that behave like Majorana particles. To do this, they proposed a relatively simple experimental system, based on one-dimensional semiconductor nanowires placed near a superconductor, with a weak magnetic field applied along the axis of the nanowires.
 

The paths converge


Oreg and his research student Yonatan Most had suggested that if Shtrikman’s nanowires were placed next to the superconductor, complex imaginary Majorana-like particles would appear at the ends of the wires. Heiblum, postdoctoral fellow Dr. Anindya Das and research student Yuval Ronen planned and built an experimental apparatus to test this theory, and within a few months they managed to find evidence for quantum states that fit the expected profile for the proposed Majorana states.
 
Just a short time before they completed their experiment, Dutch physicist Leo Kouwenhoven of Delft University announced a similar finding, supporting Oreg and his colleagues’ proposed realization of the experiment. If these results do point to a Majorana state, say Heiblum and Oreg, “they will get us a step closer to realizing the principles of quantum computing.”
 
Prof. Yuval Oreg
 

Open question


The quantum states seen at the Weizmann Institute and Delft via observations of the imaginary particles aroused much excitement. However, as noted, they are not true Majorana particles, which, as fermions, must be real matter particles to qualify.  In other words, the question is still open: Do the particles that Majorana predicted actually exist in nature?

Some think that neutrinos could be Majorana particles, and if this is the case it might help solve one of the biggest mysteries in physics. In the Big Bang, equal amounts of matter and antimatter should have been produced, yet we observe only matter in our universe. How did matter survive in the world when all antimatter disappeared? If neutrinos were Majorana particles, this might imply an as-yet-undetected force in the universe that prefers matter over antimatter.

 
Prof. Moty Heiblum’s research is supported by the Dan and Herman Mayer Fund for Submicron Research; the Willner Family Leadership Institute for the Weizmann Institute of Science; the Joseph H. and Belle R. Braun Center for Submicron Research, which he heads; the Maurice and Gabriela Goldschleger Center for Nanophysics, which he heads; the Wolfson Family Charitable Trust; the estate of Olga Klein Astrachan; and the European Research Council. Prof. Heiblum is the incumbent of the Alex and Ida Sussman Professorial Chair of Submicron Electronics.
 
Prof. Yuval Oreg’s research is supported by the Yeda-Sela Center for Basic Research.

 
 
 
 
Majorana
Space & Physics
English
  • Condensed Matter Physics
  • Moty Heiblum›Moty Heiblum
  • Nanowire
  • Quantum Hall effect
  • Quasiparticle
  • Submicron
  • Yuval Oreg

Through the Window of Opportunity

English

 

(l-r) Michal Dagan, Dr. Barry Brunner, Hadas Soifer, Oren Pedatzur, Dr. Nirit Dudovich and Dr. Dror Shafir
 

 

This summer in London, competitors vied to see who could claim the title of fastest in the world – their speeds often measured down to hundredths of seconds. But for truly record-breaking speed measurements, one needs to look in a modest lab at the end of a basement hallway in a Weizmann Institute physics building. That is where Dr. Nirit Dudovich has her lab. Here, Dudovich recently succeeded in measuring the amount of time it takes for an electron to briefly pop out of its home in the atom. The results appeared in Nature.

Normally, an electron is like a ping-pong ball sitting inside an upright ice-cream cone. As long as nothing changes, there is no reason for the ball to suddenly leave the cone. And yet, in certain situations, an electron can occasionally escape its snug hole. When it does so, the electron passes, ghost-like, through the barrier – a quantum phenomenon known as tunneling, which arises from the fact that such quantum particles as electrons can also act as waves. This is one of the most basic principles of quantum physics, but because it has no parallel in the everyday world, it still challenges the imagination of laypeople and physicists, alike.

The type of quantum tunneling Dudovich researches takes place when a strong laser field is applied to a material. Such laser fields make tunneling a bit easier for electrons by “bending” the rim of the cone. Tunneling electrons must move swiftly. The bending grants them an incredibly narrow window of opportunity, opening for just 200 attoseconds, give or take – about the amount of time a light wave remains at its peak. An attosecond is a billionth of a billionth of a second. And that tiny window has, until now, been much too small for scientists to measure directly.
 
 
Different electron trajectories are separated along the time axis. Only a narrow region in time is selected by the kicking mechanism (shaded red)
 
It’s not just that electrons prefer to stay put. They are also loyal to their home bases, so that even when one takes a brief “trip,” it may return straight home. Scientists can observe the instant that an electron gets back home because as it flies into place, a photon is emitted. Measurements of these emitted photons enabled Dudovich to trace tunneling dynamics.

Dudovich essentially played a trick on the tunneling electrons, which pop out and back again in a straight line. She devised a way of “kicking” the electron (with another laser) so that it could not be absorbed back into place – and thus no photon emitted. With these measurements, she was able to trace the electron's movements back to the moment when it left the atom.

But just like Olympic runners, electrons can have different energy levels, and thus some take longer than others to pass beyond the rim of the cone. Dudovich wanted to accurately measure this time difference.  To find out, she again made use of the phenomenon of wave-particle duality. When electrons return home, they can appear as waves; such waves interfere with one another, and the patterns of that interference can be observed. When the interference is destructive – that is, the waves are opposite and cancel one another out – their absence reveals the time difference between the two events. Dudovich succeeded in measuring this difference – around 50 attoseconds. This is apparently among the shortest periods of time ever measured.

On one the hand, this research has shed new light on some very basic phenomena in atomic physics. On the other, it may give rise to new knowledge that will, in the future, be used to create new technologies.
 
 
Dr. Nirit Dudovich’s research is supported by the Jay Smith and Laura Rapp Laboratory for Research in the Physics of Complex Systems; the Jacques and Charlotte Wolf Research Fund; the Enoch Foundation; and the Crown Photonics Center.
 
(l-r) Michal Dagan, Dr. Barry Brunner, Hadas Soifer, Oren Pedatzur, Dr. Nirit Dudovich and Dr. Dror Shafir
Space & Physics
English
  • Electron
  • Laser
  • Nirit Dudovich

Proof of Inequality

English

(l-r) Dr. Zohar Komargodski, Prof. Adam Schwimmer and visiting Prof. Alexander Zamolodchikov. Extra dimensions

 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The LHC particle accelerator in CERN – the European Laboratory for Particle Physics – near Geneva, is expecting big discoveries in the near future. By big, of course, they mean very, very small. The accelerator has the capacity to reveal the existence of forces and particles that have been beyond the reach of science until now: particles so small that they are dwarfed by the protons and neutrons in the nucleus of an atom. If protons and neutrons measure a millionth of a billionth of a meter, the particles scientists hope to observe in the LHC are sized around a billionth of a billionth of a meter – an atto-meter. Inside the LHC, immensely powerful forces are exerted on these minuscule particles, bringing science into uncharted regions. What will be found there?  

Physicists, in truth, do not know what to expect. Nevertheless, they try to plan for all possibilities, using the tools they have at hand to endeavor to make sense of any new phenomena, particles or forces they might encounter. Can such key tools as quantum field theory describe this new region in physics, in which such tiny particles exist on extremely small-distance scales and with enormously high energies? Quantum field theory provides the framework for particle physics, and it is, in a very real sense, the basis of everything we know about the physical world. This theory is the unavoidable result of attempts to reconcile the field of quantum mechanics founded by Bohr and Heisenberg with Einstein’s Theory of Special Relativity.

One such attempt to formulate a general principle for quantum field theory was put forward by the British physicist John Cardy in 1988. According to his theorem, inequalities arise in systems with known “rules” that involve large numbers of factors. The states of these systems cannot be explained just through knowing the rules and the various players. Examples of such systems include stock markets, traffic patterns and weather. The inequalities transpire between degrees of freedom: the degrees of freedom existing at short-distance scales (for example the scales of the new particles that LHC researchers hope to discover) versus those at longer-distance scales (for instance in the forms of matter we know today).
equations
 
If Cardy’s theory proves correct, it might provide an explanation of how we arrive at the Standard Model – the main theory of particle physics in use today – when a system of infinitesimally small particles at small-distance scales and very high energies cools down. We might even begin to understand how the world as we know it arises out of a complex universe of subatomic particles and powerful forces.

In 1986, about two years before Cardy presented his theory, another physicist, Alexander Zamolodchikov, had shown that this inequality between degrees of freedom on short-distance scales exists in two-dimensional systems (one dimension of space and one of time). Cardy took the idea one step further, theorizing a similar inequality in a four-dimensional system (three of space and one of time). But the theory remained open for the next 23 years, until one evening a few months ago, when two Weizmann Institute theoretical physicists were relaxing on a beach on an Aegean island. The two were Prof. Adam Schwimmer of the Physics of Complex Systems Department and Dr. Zohar Komargodski, a recent addition to the Particle Physics and Astrophysics faculty and an Institute alumnus who recently completed postdoctoral work at the Institute for Advanced Study, Princeton.  

For the last few years, Schwimmer and Komargodski had been looking for a way to prove Cardy’s theorem and turn it into an accepted axiom. They had traded ideas and explored a number of different avenues, but none had really panned out. But that evening, sitting on the Aegean sands and relaxing between lectures in a scientific conference they were attending, the two began to discuss their old problem. As the sun set over the blue water, the solution seem to float up to them: Although none of the methods they had applied to the problem had yielded the long-awaited proof, they realized that four or five of their beginnings might be combined into a framework on which they could erect that proof.

So far, a number of physicists have checked the proof and announced that it stands up to various challenges. The Institute scientists say that it must be shown to withstand a number of further challenges before it can be completely accepted. Even so, physicists in a number of different fields have begun to envision new applications of the theorem, now that it appears to stand on somewhat solid ground. In particular, it could prove to be a valuable tool in interpreting LHC results in which scientists are not only searching for new particles, but for evidence for such models as supersymmetry that will help to explain the physical world.
 

Dr. Zohar Komargodski’s research is supported by the Peter and Patricia Gruber Awards.


 
 
(l-r) Dr. Zohar Komargodski, Prof. Adam Schwimmer and visiting Prof. Alexander Zamolodchikov. Extra dimensions
Space & Physics
English
  • Adam Schwimmer
  • Particle Physics and Astrophysics
  • Physics of Complex Systems
  • Quantum physics
  • Theoretical physics
  • Zohar Komargodski

Divine Secrets of the Ant Sisterhood

English
 
 
ant communcations
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
“In the long history of humankind (and animal kind, too) those who learned to collaborate and improvise most effectively have prevailed,” wrote Darwin. Ants, a family that has inhabited the earth for about 100 million years, must be one of the most magnificent manifestations of such biological cooperation. Thousands of female ants pull together in a coordinated effort to ensure that all the needs are met for the proper functioning of the entire colony. (The males’ only role is to mate with the queen, and once this is completed, they die). While some ants forage, others stay behind to tend the brood, or to build, maintain or defend the colony’s living quarters; and there are even those whose task it is to bury the dead. But the thing that makes their behavior so remarkable is that they have no leader – no boss or governing body to allocate and manage their activities.  How exactly do ants collaborate and divide the labor among themselves so successfully and altruistically?

In his new lab in the Physics of Complex Systems Department, Dr. Ofer Feinerman and his team are hoping to reveal some of the ants’ secrets in a collaborative effort of their own, using tools from such fields as information theory, statistical and theoretical physics, computer science, systems biology, neuroscience and, of course biology. “Biology is rife with complex systems consisting of individual components – proteins, cells, organisms – organizing themselves into networks to coordinate their activity. While biology is able to identify and describe the individual components, the interactions between them can get very messy and analyzing such data can become overwhelming. By borrowing tools from physics and math, more quantitative measurements can be used to discern the rules that govern such complex collective behaviors,” says Feinerman.
Dr. Ofer Feinerman. Complex communications
 

Social networking


Ants primarily “speak” to one another in the language of chemicals: If an ant finds a rich food source, for example, it will deposit a trail of pheromones that tells the other ants where to find it. Social networks are formed between the ants during such communication, and it is these networks that Feinerman wants to understand.

In a setup reminiscent of Big Brother, Feinerman has handpicked a number of native Israeli ants to enter an artificial, nest-like structure that has cameras dotted around, enabling his team to eavesdrop on the ants’ “conversations.” Each ant is identified by a barcode glued to its back, enabling the scientists to track and record its activities. The scientists are hoping to answer such questions as: Who “speaks” to whom? Do ants form cliques and only interact with those in the same group, or are they indiscriminate? Do they employ far-reaching social networking tools akin to, say, Twitter or Facebook, relying on others to “retweet” and “share” their messages? Do messages get passed down a line of ants, or would an ant prefer to wander far and wide to make sure the message is relayed accurately?

Feinerman: “Ants use different communication strategies, ranging from one extreme to the other, depending on the setting. For example, in ‘piggybacking,’ one ant rides on top of another; though slow, this is a very reliable and direct method of communication, appropriate, for example, for ensuring the second ant arrives at the exact food location without getting lost along the way. Other situations may warrant less focused, but faster, forms of communication. For example, if a colony comes under attack, the ants spray pheromones into the air. This alarm system rapidly warns other, distant colonies of potentially imminent danger.”

Slow and reliable or fast with some compromise: Understanding ant communication and social networking strategies will do more than help reveal the intricate workings of an ant colony; they also assist in the long term goal of using this rich cooperative system to develop a theory of collective information processing. Ultimately, the researchers would like to develop the tools needed to answer fundamental questions about other complex biological systems: for instance, how immune system cells work together to fight infection. Such tools could also have practical applications in the design of so-called distributed systems, including cellular communication antennae, wireless sensor networks or even groups of robots engaged in rescue operations.
 

Empire of the Ants


At the head of each ant colony is a queen; but, though “royalty,” she does not possess any sovereign power over the worker ants – her sole duty is to lay eggs. With no ruler, how do ants divide labor? Do some ants belong to “elite” units, with others relegated to more “lower-class” duties? Or are they all equal?

In previous research, Dr. Feinerman investigated whether certain factors – previous experience, age, body weight, spatial location – determine how tasks are allocated. One way to test this is to see how ants respond to increased demands in certain tasks. For example, when food stores are running low, which ants take it upon themselves to aid in the foraging effort? Or offer a helping hand to nurse an extra brood in the colony?

The ants were placed in an artificial, two-chambered nest, and the scientists manipulated the task load by withholding food or adding new members to a brood. Again, the ants were individually tagged – this time using radio-frequency identification (RFID) – to identify individuals that responded.

This study revealed that it is the leaner ants that are usually on the frontline: They are the first to respond to increased foraging needs, even when other factors (age, experience and spatial location) are taken into account. They also seem to be the ones who engage in transporting the newly planted brood members to the main brood pile. However, lean ants do not seem to actually help in tending the brood. In fact, Feinerman found that brood care seems to be random, not dependent on by age, experience or weight, but rather, by whoever happens to be passing by.
 
 
Barcoded ant in the lab of Dr. Ofer Feinerman
 

“With regard to foraging, sending out the leaner ants could boost colony survival, as they would be more expendable in the risky task of foraging, may attract fewer predators, and might even be more mobile than their heavier counterparts. Likewise, the fact that brood care seems to be open to all suggests that flexibility in general task allocation, and collaboration on the whole, is more valuable  than, say, expertise or experience, as it allows for a rapid response to a changing environment, thereby ensuring the survival of the colony,” says Feinerman.


ANT-thropologist


Dr. Ofer Feinerman was born in Rehovot, Israel, and he earned a B.Sc. in physics and mathematics summa cum laude (1996) and an M.Sc. in physics (1999), both from the Hebrew University of Jerusalem. As a Ph.D. student at the Weizmann Institute of Science, under the guidance of Prof. Elisha Moses, he grew the first artificial logic circuits made of nerve cells, earning his doctorate in 2006. He then conducted postdoctoral research for three years at the Memorial Sloan-Kettering Cancer Center in New York, investigating how the immune system's T-regulation cells work together to fight infection. Feinerman spent one year studying ants at Rockefeller University before joining the Department of Physics of Complex Systems at the Weizmann Institute of Science as a Senior Scientist in October 2010. “Coming back to the Weizmann Institute was a dream – not only did it give me the opportunity to return to Israel, but it also gave me the freedom to study ants – a somewhat unconventional subject. For this I am eternally grateful to and proud of the Weizmann Institute.”

Feinerman is married to Micka, a mosaic artist, and has three children: Matan (9), Shai (7) and Nomi (4).
 
Dr. Ofer Feinerman's research is supported by the Clore Foundation.
 
 


 

 
Barcoded ant in the lab of Dr. Ofer Feinerman
Space & Physics
English
  • Communication
  • Elisha Moses
  • Ofer Feinerman
  • Physics of Complex Systems
  • Social behavior›Social behavior
  • Systems biology

Fast Focus

English
 
 
(l-r) Ori Katz, Eran Small and Prof. Yaron Silberberg. Under the skin
 

 

 

 

 

 

 

 

 

 

 

 

 

A few well-known facts about lasers: These ultra-focused beams of light have been used for decades to cut metal cleanly and precisely. In the field of medicine they take the place of sharp surgical scalpels; they are also used in some kinds of medical imaging; and they are a part of today’s advanced optical microscopes. Many of these uses require the light to be focused tightly to a very narrow, highly intense point. One way of cutting cleanly without causing harm to the surrounding area – say, in biological tissue that is easily damaged by excess energy – is to zap the target point with very brief (less than a millionth of a millionth of a second) flashes of highly concentrated laser light.


This is all well and fine when the target point is on an exposed surface. But scientists and surgeons would like to be able to aim lasers under the skin as well – for instance at tumors inside the body. And herein lies the difficulty: A standard laser can’t focus even a millimeter under the skin. For one thing, biological tissue is simply not transparent – meaning the light entering it scatters in all directions. When it passes through tissue, a flash of laser beam that is extremely short and focused when it leaves its source tends to lengthen and spread out along the way. Its intensity weakened, the beam loses its scalpel-like ability to slice cleanly through living matter.
 
 
Fluorescence created by a flash of laser light passing through a ½ mm piece of bone before (l) and after (r) application of the algorithm to focus the beam to a single point
 
Prof. Yaron Silberberg and research students Ori Katz, Eran Small and Yaron Bromberg of the Physics of Complex Systems Department sought a way to focus rapid flashes of laser light as they pass through a scattering layer. The method they developed works on feedback: They created a system that can assess, in real time, how the light scatters. Using algorithms they developed, they created a beam that can “anticipate” the dispersal of its light and make the necessary corrections. This computerized system is able to tailor a laser beam to the tissue such that it is precisely and narrowly focused on the internal target.  

In this research, which appeared in Nature Photonics, the scientists employed a simple LCD screen, similar to those found in computer projectors, to correct the beams’ focus. While it was known that screens of this type could be used to correct spatial errors, Silberberg and his team succeeded in demonstrating that this simple system can also correct for errors in the dimension of time.

The scientists hope that this system will, in the future, aid in the development of applications, including new types of medical lasers and optical microscopes that will enable researchers in the life sciences to get under the skin and into the underlying tissue.
 
Prof. Yaron Silberberg’s research is supported by the Crown Photonics Center, which he heads; the Wolfson Family Charitable Trust; and the Cymerman - Jakubskind Prize. Prof. Silberberg is the incumbent of the Harry Weinrebe Professorial Chair of Laser Physics.
 
 
(l-r) Ori Katz, Eran Small and Prof. Yaron Silberberg. Under the skin
Space & Physics
English
  • Algorithm
  • Laser
  • Microscopy
  • Optical imaging
  • Physics of Complex Systems
  • Yaron Silberberg

A scientific first

English
A Supernova Explosion is Observed in Real Time Including a tell-tale flash of radiation preceding the event

An ordinary observation with NASA’s Swift research satellite recently led to the first real-time sighting of a star in the process of exploding. Astronomers have surveyed thousands of these supernova explosions in the past, but their observations have always begun some time after the main event is underway. The information gained from catching a supernova at the very onset is already being hailed as the 'Rosetta Stone' of star explosion, and it is helping scientists to form a detailed picture of the processes involved.

A typical supernova is preceded by the burn-out of a massive star. When the nuclear fuel at its core runs out, the star collapses under its own weight. The resulting body, now known as a neutron star, is so dense that one teaspoonful of its core material weighs as much as all the humans on earth. This extreme compression is followed by a rebound, creating a shock wave that bounces off the surface of the newly-formed neutron star and rips through its outer, gaseous layers. These layers are ejected, flying off the surface in rapidly expanding shells.

For the last four decades, astronomers have theorized that the explosion is preceded by a burst of x-ray radiation that lasts for several minutes. For the first time, that burst was actually seen – all previous observations had taken place when the star was already an expanding shell of debris, days or even weeks after the explosions’ start. Both luck and the Swift satellite’s unique design played a role in the discovery. In January of this year, Drs. Alicia Soderberg and Edo Berger of Princeton University, USA, were using the satellite, which measures gamma rays, X rays and ultraviolet light, to observe another supernova in a spiral galaxy in the Lynx constellation, 90 million light-years from Earth. At 9:33 EST, they spotted an extremely bright five-minute X-ray burst and realized it was coming from another location within the same galaxy.

The Princeton scientists immediately assembled a team of 15 research groups around the world to investigate, including Prof. Eli Waxman and Dr. Avishay Gal-Yam of the Weizmann Institute’s Physics Faculty. Gal-Yam performed measurements and calculations that enabled the scientific team to cancel out the various disturbances that affect astronomical data, such as radiation-absorbing interstellar dust, which skews observed measurements. The shock-wave eruption and X-ray generation of this supernova explosion went exactly according to the theoretical model that Waxman and Prof. Peter Meszaros of Penn State University had developed earlier. The data showed that the explosion – known as supernova 2008D – is a relatively common type of supernova, and not a rare supernova involving jets of gamma ray radiation.

Already, the observation has provided scientists with valuable new information on supernovae, including the dimensions of the exploding star, the structure of its envelope and the properties of the shock wave that hurls off the star’s outer envelope. As they continue to analyze the data, the scientists believe it may help them to solve some of the outstanding puzzles surrounding these types of explosion. For instance, according to mathematical calculations of the forces involved in neutron star collapse, the bouncing shock wave should stall out before it manages to eject the stellar envelope. Clearly, this is not what happens in nature, but clues found in the Swift observations may help researchers to correct the model.

Now that they have observed a supernova from the pre-explosion stage, the scientists are not only gaining a better understanding of the little-understood processes that make these stars explode, they hope their knowledge of the x-ray emissions will enable them to catch more stars that are right on the brink of becoming supernovae.

Prof. Eli Waxman is Head of the Benoziyo Center for Astrophysics and the Albert Einstein Minerva Center for Theoretical Physics.

Dr. Avishai Gal-Yam's research is supported by the Nella and Leon Benoziyo Center for Astrophysics and the William Z. and Eda Bess Novick Young Scientist Fund.
 

The Weizmann Institute of Science in Rehovot, Israel, is one of the world's top-ranking multidisciplinary research institutions. Noted for its wide-ranging exploration of the natural and exact sciences, the Institute is home to 2,600 scientists, students, technicians and supporting staff. Institute research efforts include the search for new ways of fighting disease and hunger, examining leading questions in mathematics and computer science, probing the physics of matter and the universe, creating novel materials and developing new strategies for protecting the environment.
 

Weizmann Institute news releases are posted on the World Wide Web at

http://wis-wander.weizmann.ac.il, and are also available at http://www.eurekalert.org
 
Space & Physics
English
  • Astrophysics
  • Avishay Gal-Yam
  • Eli Waxman
  • Supernova

Radiation Detectors

English
 
Prof. Zeev Vager
 
Prof. Zeev Vager and his Weizmann colleagues developed innovative radiation detectors based on electron amplification and other technological principles.

 

Application

 
El-Mul Technologies, Ltd. was created on the basis of two Weizmann Institute technologies for the detection of charged particles and radiation. The company supplies particle detection solutions for semiconductor manufacturing tools, industrial electron microscopy and mass spectrometry.
 
Prof. Zeev Vager
Space & Physics
English
  • Electron microscopy
  • Particle detector
  • Semiconductor
  • Zeev Vager

Cutting Diamonds With Lasers

English
Prof. Yehiam Prior
 
Prof. Yehiam Prior developed an advanced method for cutting diamonds with lasers. The method practically halves the loss of material and makes it possible to cut stones into virtually any shape.
 

Application

 
The Institute’s method for laser cutting of diamonds has been incorporated into Israel’s diamond industry.
 
Prof. Yehiam Prior
Space & Physics
English
  • Laser
  • Optical science
  • Yehiam Prior

Advanced Radiation Detectors

English
Prof. Amos Breskin
 
Prof. Amos Breskin develops advanced radiation detectors, which have an important impact on many fields of research, such as particle, nuclear and atomic physics, medical diagnostics, biology and materials science.
 

Application

 
Together with colleagues at Weizmann and elsewhere, Breskin developed a minimally invasive electronic “finger” for the detection and diagnosis of prostate cancer. The technology is being tested in collaboration with urologists from the Kaplan Medical Center.
 
Prof. Amos Breskin
Space & Physics
English
  • Amos Breskin
  • Prostate cancer

Compact Head Displays for Pilots

English
Prof. Asher Friesem
 
Prof. Asher Friesem was among the first in the world to become involved in the technology of planar optics. In this technology, several diffractive optical components are combined on the surface of one substrate to enable the formation of a complete optical system mounted on a thin, single transparent plate.
 

Application

 
Elop, Electro-Optics Industries Ltd. in Kiryat Weizmann, develops compact head displays for pilots based on Friesem’s technology. Manufacture of head displays for doctors and for virtual reality systems are under consideration by other companies.
 
 
Prof. Asher Friesem
Space & Physics
English
  • Asher Friesem
  • Optical imaging
  • Physics of Complex Systems

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