Caltech Scientists Create Tiny Photon Clock

PASADENA--In a new development that could be useful for future electronic devices, applied physicists at the California Institute of Technology have created a tiny disk that vibrates steadily like a tuning fork while it is pumped with light. This is the first micro-mechanical device that has been operated at a steady frequency by the action of photons alone.

Reporting in recently published issues of the journals Optics Express (July 11) and Physical Review Letters (June 10 and July 11), Kerry Vahala and group members Hossein Rokhsari, Tal Carmon, and Tobias Kippenberg, explain how the tiny, disk-shaped resonator made of silica can be made to vibrate mechanically when hit by laser light. The disk, which is less than the width of a human hair, vibrates about 80 million times per second when its rim is pumped with light.

According to Vahala, who is the Jenkins Professor of Information Science and Technology and Professor of Applied Physics, the effect is due to properties of the disk that allow it to store light very efficiently, and also to the fact that light exerts "radiation pressure." In much the same way that NASA's solar sails will catch photons from the sun to power spaceships to other worlds, the disk builds up light energy so that the disk itself swells.

"The light makes hundreds of thousands of orbits around the rim of the disk," Vahala explains. "This causes the disk to literally stretch, owing to the radiation pressure of the photons."

Once the disk has inflated, its physical properties change so that the light energy is lost, and the disk then deflates. The cycle then repeats itself, and this repetition continues in a very orderly fashion as long as the light is pumped into the disk.

In effect, this repetitive process makes the disk a very efficient clock, somewhat similar to the quartz crystal that is made to vibrate from electrical current for the regulation of a battery-powered wristwatch. The differences between the optically driven clock and the traditional electrical one, however, create a design element that could provide new electro-optic functions within the context of integrated circuits.

The researchers also note that whereas the basic operation of the device can be understood at the classical level, such a device could be used to study interactions between radiation and macroscopic mechanical motion at the quantum level. Several groups have already proposed theoretically using radiation pressure as a mechanism to investigate such interactions.

Also, the device could be of help in designing the next-generation Laser Interferometer Gravitational-Wave Observatory (LIGO). A National Science Foundation-funded project operated by Caltech and MIT, LIGO and has been created to detect the phenomenon known as gravitational waves, predicted by Einstein decades ago.

LIGO is designed in such a way that laser light bounces between mirrors along a five-mile right-angle circuit. The light is allowed to build up in the two arms of the detector so as to increase the possibility that gravitational waves will eventually be detected from exotic astrophysical objects such as colliding black holes and supernovae.

But designers have been concerned to ensure that the same radiation-pressure-driven instability does not appear in the LIGO system as its sensitivity is boosted. The work by the Vahala group, though at a vastly smaller size scale, therefore could be of help in the current plans for improvement of the LIGO detectors in Hanford, Washington and Livingston, Louisiana.

"This work demonstrates a mechanism that needs to be understood better," Vahala explains. "It has moved from theory to existence, and that is always exciting."

The paper, "Radiation-pressure-driven micro-mechanical oscillator," appearing in the July 11 issue of the journal Optics Express, is available on-line at http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-14-5293.

 

 

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KamLAND Detector Provides New Way to Study Heat from Radioactive Materials Within Earth

PASADENA, Calif.--Much of the heat within our planet is caused by the radioactive decay of the elements uranium and thorium. Now, an international team of particle physicists using a special detector in Japan has demonstrated a novel method of measuring that radioactive heat.

In the July 28 issue of the journal Nature, the physicists report on measurements of electron antineutrinos they have detected from within Earth by using KamLAND, the Kamioka Liquid Scintillator Anti-Neutrino Detector. These data indicate that Earth itself generates about 20 billion kilowatts (or terawatts) of power from underground radioactive decays.

According to Robert McKeown, a physicist at the California Institute of Technology and one of the authors of the paper, the results show that this novel approach to geophysical research is feasible. "Neutrinos and their corresponding antiparticles, antineutrinos, are remarkable for their ability to pass unhindered through large bodies of matter like the entire Earth, and so can give geophysicists a powerful method to access the composition of the planet's interior."

McKeown credits the discovery with the unique KamLAND experimental apparatus. The antineutrino detector was primarily built to study antineutrinos emitted by Japanese nuclear power plants. The KamLAND experiment has already resulted in several breakthroughs in experimental particle physics, including the 2002 discovery that antineutrinos emitted by the power plants do indeed change flavor as they travel through space. This result helped solve a longstanding mystery related to the fact that the number of neutrinos from the sun was apparently too small to be reconciled with our current understanding of nuclear fusion. The new results turn from nuclear reactors and the sun to the Earth below. To detect geoneutrinos (or antineutrinos arising from radioactive decays within the planet), the researchers carefully shielded the detector from background radiation and cosmic sources, and also compensated for the antineutrinos that have come from Japan's 53 nuclear power reactors.

The decays of both uranium and thorium have been well understood for decades, with both decays eventually resulting in stable isotopes of lead. KamLAND is the first detector built with the capability to detect the antineutrinos from these radioactive decays.

The researchers plan to continue running the KamLAND experiments for several years. By reducing the trace residual radioactivity in the detector, they hope to increase the sensitivity of the experiment to geoneutrinos and neutrinos from the sun. The additional data will also allow them to better constrain the oscillation of neutrinos as they change their flavors, and perhaps to catch neutrinos from interstellar space if any supernovae occur in our galaxy.

Other members of McKeown's team at Caltech's Kellogg Radiation Lab are Christopher Mauger, a postdoctoral scholar in physics, and Petr Vogel, a senior research associate emeritus in physics. Other partners in the study include the Research Center for Neutrino Science at Tohuku University in Japan, the University of Alabama, the University of California at Berkeley and the Lawrence Berkeley National Laboratory, Drexel University, the University of Hawaii, the University of New Mexico, the University of North Carolina, Kansas State University, Louisiana State University, Stanford University, Duke University, North Carolina State University, the University of Tennessee, the Institute of High Energy Physics in Beijing, and the University of Bordeaux in France.

The project is supported in part by the U.S. Department of Energy.

 

 

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Researchers devise plasma experiment that shows how astrophysical jets are formed

PASADENA, Calif.--Applied physicists at the California Institute of Technology have devised a plasma experiment that shows how huge long, thin jets of material shoot out from exotic astrophysical objects such as young stars, black holes, and galactic nuclei.

Reporting in an upcoming issue of the journal Physical Review Letters, applied physics professor Paul Bellan, his graduate student Gunsu Yun, and postdoctoral scholar Setthivoine You describe how they create jets of plasma at will in an experimental device known as a "planar spheromak gun." The researchers form the jets by sending an intense electric current through a gas to form a plasma, after applying a background magnetic field to the whole system. The magnetized plasma then naturally tends to shoot out of the gun in the form of a long collimated filament.

According to Bellan, his research group is the first to achieve an experimental result showing how astrophysical jets are formed. Theorists have done mathematical modeling and computer simulations to show how known magnetohydrodynamic effects could explain the jet phenomenon, but the Bellan experiment actually creates similar jets in a lab device.

"We're not claiming to make scale models, but I think we've captured the essence of astrophysical jets," says Bellan, who has been working on this and related projects at Caltech since the late 1990s.

Although there are differences between astrophysical jets and the ones created in the spheromak gun, Bellan says there are also important similarities that link the 13-inch-long plasma jets created in the lab to the enormous jets in outer space. The similarity is primarily in the way that the magnetic flux tubes are straightened through a sort of squeezing effect that points to a common collimation process.

Astrophysical jets are accelerated by magnetic forces, but also carry along magnetic fields, the researchers explain. These magnetic fields are frozen into the plasma that makes up the jet and wrapped around the jet like rubber bands around a paper tube. The flowing plasma piles up, much like fast traffic coming up on slower traffic on a freeway, and this pile-up increases the plasma density just like the density of cars increases in a traffic jam.

The frozen-in bandlike magnetic field lines also become squeezed together in this "traffic jam," and so, just like rubber bands piling up on a paper tube, pinch down the diameter of the plasma jet, making it thin and even more dense.

Why do the researchers think this is an accurate portrayal of astrophysical jets? Because this is precisely how they make similar but smaller jets in their experiment.

"Very dense, fast, thin plasma jets observed in our laboratory experiments have been shown to be in good agreement with this picture," explains You.

Bellan says that the research stems from work he and his group have done for years in the formidable and longstanding effort to make fusion power an eventual reality. The current results have implications for the goal of containing the extremely hot plasma required for fusion, as well as for explaining certain exotic events in the cosmos.

 

 

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Andromeda Galaxy Three Times Bigger in Diameter Than Previously Thought

MINNEAPOLIS--The lovely Andromeda galaxy appeared as a warm fuzzy blob to the ancients. To modern astronomers millennia later, it appeared as an excellent opportunity to better understand the universe. In the latter regard, our nearest galactic neighbor is a gift that keeps on giving.

Scott Chapman, from the California Institute of Technology, and Rodrigo Ibata, from the Observatoire Astronomique de Strasbourg in France, have led a team of astronomers in a project to map out the detailed motions of stars in the outskirts of the Andromeda galaxy. Their recent observations with the Keck telescopes show that the tenuous sprinkle of stars extending outward from the galaxy are actually part of the main disk itself. This means that the spiral disk of stars in Andromeda is three times larger in diameter than previously estimated.

At the annual summer meeting of the American Astronomical Society today, Chapman will outline the evidence that there is a vast, extended stellar disk that makes the galaxy more than 220,000 light-years in diameter. Previously, astronomers looking at the visible evidence thought Andromeda was about 70,000 to 80,000 light-years across. Andromeda itself is about 2 million light-years from Earth.

The new dimensional measure is based on the motions of about 3,000 of the stars some distance from the disk that were once thought to be merely the "halo" of stars in the region and not part of the disk itself. By taking very careful measurements of the "radial velocities," the researchers were able to determine precisely how each star was moving in relation to the galaxy.

The results showed that the outlying stars are sitting in the plane of the Andromeda disk itself and, moreover, are moving at a velocity that shows them to be in orbit around the center of the galaxy. In essence, this means that the disk of stars is vastly larger than previously known.

Further, the researchers have determined that the nature of the "inhomogeneous rotating disk"-in other words, the clumpy and blobby outer fringes of the disk-shows that Andromeda must be the result of satellite galaxies long ago slamming together. If that were not the case, the stars would be more evenly spaced.

Ibata says, "This giant disk discovery will be very hard to reconcile with computer simulations of forming galaxies. You just don't get giant rotating disks from the accretion of small galaxy fragments."

The current results, which are the subject of two papers already available and a third yet to be published, are made possible by technological advances in astrophysics. In this case, the Keck/DEIMOS multi-object spectrograph affixed to the Keck II Telescope possesses the mirror size and light-gathering capacity to image stars that are very faint, as well as the spectrographic sensitivity to obtain highly accurate radial velocities.

A spectrograph is necessary for the work because the motion of stars in a faraway galaxy can only be detected within reasonable human time spans by inferring whether the star is moving toward us or away from us. This can be accomplished because the light comes toward us in discrete frequencies due to the elements that make up the star.

If the star is moving toward us, then the light tends to cram together, so to speak, making the light higher in frequency and "bluer." If the star is moving away from us, the light has more breathing room and becomes lower in frequency and "redder."

If stars on one side of Andromeda appear to be coming toward us, while stars on the opposite side appear to be going away from us, then the stars can be assumed to orbit the central object.

The extended stellar disk has gone undetected in the past because stars that appear in the region of the disk could not be known to be a part of the disk until their motions were calculated. In addition, the inhomogeneous "fuzz" that makes up the extended disk does not look like a disk, but rather appears to be a fragmented, messy halo built up from many previous galaxies' crashing into Andromeda, and it was assumed that stars in this region would be going every which way.

"Finding all these stars in an orderly rotation was the last explanation anyone would think of," says Chapman.

On the flip side, finding that the bulk of the complex structure in Andromeda's outer region is rotating with the disk is a blessing for studying the true underlying stellar halo of the galaxy. Using this new information, the researchers have been able to carefully measure the random motions of stars in the stellar halo, probing its mass and the form of the elusive dark matter that surrounds it.

Although the main work was done at the Keck Observatory, the original images that posed the possibility of an extended disk were taken with the Isaac Newton Telescope's Wide-Field Camera. The telescope, located in the Canary Islands, is intended for surveys, and in the case of this study, served well as a companion instrument.

Chapman says that further work will be needed to determine whether the extended disk is merely a quirk of the Andromeda galaxy, or is perhaps typical of other galaxies.

The main paper with which today's AAS news conference is concerned will be published this year in The Astrophysical Journal with the title "On the Accretion Origin of a Vast Extended Stellar Disk Around the Andromeda Galaxy." In addition to Chapman and Ibata, the other authors are Annette Ferguson, University of Edinburgh; Geraint Lewis, University of Sydney; Mike Irwin, Cambridge University; and Nial Tanvir, University of Hertfordshire.

 

 

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Four from Caltech Named to National Academy of Sciences

PASADENA-Three members at the California Institute of Technology faculty and one former faculty who is now a visiting associate are among the 72 new members and 18 foreign associates being named to the National Academy of Sciences today. The election was announced during the 142nd annual meeting of the Academy in Washington, D.C.

Caltech's newest members are Richard Andersen, the Boswell Professor of Neuroscience; James Eisenstein, the Roshek Professor of Physics; and Wallace Sargent, the Bowen Professor of Astronomy. Roger Blandford, a former Caltech faculty member and current visiting associate in physics, is also among the electees.

Membership in the National Academy of Sciences is considered one of the most important honors that a scientist can achieve. In addition to the 1,976 active members of the academy following today's election, 360 foreign associates are also listed in the organization's roster as nonvoting members.

The National Academy of Sciences is a private organization of scientists and engineers dedicated to the furtherance of science and its use for the general welfare. It was established in 1863 by a congressional act of incorporation signed by Abraham Lincoln that calls on the Academy to act as an official adviser to the federal government, upon request, in any matter of science or technology.

Andersen is a neuroscientist who has garnered considerable attention in recent years for his progress toward the goal of controlling prosthetic devices with brain signals. Much of his current work focuses on severely paralyzed human patients who can think about making movements, but due to brain lesions from trauma, stroke, or peripheral neuropathies, can no longer make movements. His approach is to create brain-implant technology that will act as an interface between a patient's thoughts for movement and artificial limbs, computers, or other devices, that would "read out" the patient's desires.

Eisenstein is a specialist in condensed-matter physics, which involves the exploration of the fundamental laws of nature as they apply to atoms and molecules that comprise solid matter. His most significant research accomplishment in the last year has been his demonstration that unusual particles known as "excitons" can inhabit solid semiconductor materials in such a way that each exciton loses its individual identity and, in certain ways, a large collection of excitons becomes a single quantum entity.

Sargent is particularly well-known in the astrophysical community for his work in spectroscopy. His research in extragalactic spectroscopy provided the first evidence for a black hole in galaxy M87, and his work on intergalactic gas has led to new insights on the primeval materials of the early universe. His work in the stellar spectroscopy of A-type stars led to the discovery of the He3 isotope in the star 3 Centauri.

Blandford is a former faculty member in the Division of Physics, Mathematics and Astronomy at Caltech. He is currently a visiting associate in physics at Caltech and the Pehong and Adele Chen Professor of Physics and Stanford Linear Accelerator Center at Stanford University, where he is also director of the Kavli Institute for Astrophysics and Cosmology.

Today's election brings the total number of Caltech faculty members of the National Academy of Sciences to 70.

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Five from Caltech Faculty Elected to American Academy of Arts and Sciences

PASADENA, Calif.-Five faculty members at the California Institute of Technology are among this year's newly elected fellows of the American Academy of Arts and Sciences. They join 191 other Americans and 17 foreign honorees as the 225th class of fellows of the prestigious institution that was cofounded in 1780 by John Adams.

This year's new Caltech inductees are Barry Barish, the Linde Professor of Physics and director of the Laser Interferometer Gravitational-Wave Observatory (LIGO); Andrew Lange, the Goldberger Professor of Physics; Barry Simon, the IBM Professor of Mathematics and Theoretical Physics; David Tirrell, chair of the Division of Chemistry and Chemical Engineering and McCollum-Corcoran Professor and professor of chemistry and chemical engineering; and William Bridges, the Braun Professor of Engineering, Emeritus.

The five from Caltech join an illustrious list of fellows, both past and present. Other inductees in the 225th class include Supreme Court Chief Justice William Rehnquist, Angels in America author Tony Kushner, Academy Award-winning actor Sidney Poitier, former NBC Nightly News anchor Tom Brokaw, Washington Post CEO Donald Graham, and Pulitzer Prize-winning cartoonist Art Spiegelman. Past fellows have included George Washington, Benjamin Franklin, Ralph Waldo Emerson, Albert Einstein, and Winston Churchill.

According to the academy's president, Patricia Meyer Spacks, the fellows were chosen "through a highly competitive process that recognizes individuals who have made preeminent contributions to their disciplines and to society at large."

"Throughout its history, the Academy has convened the leading thinkers of the day, from diverse perspectives, to participate in projects and studies that advance the public good," said Executive Officer Leslie Berlowitz.

The academy is an independent policy research center that focuses on complex and emerging problems such as scientific issues, global security, social policy, the humanities and culture, and education.

The new fellows and foreign honorary members will be formally recognized at the annual induction ceremony on October 8 at the academy's headquarters in Cambridge, Massachusetts.

 

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Caltech Physicist Kip ThorneWins 2005 Common Wealth Award

PASADENA, Calif.--Kip Thorne, a physicist who is famed for his work on the cosmic consequences of relativity, is one of five winners of the 2005 Common Wealth Award.

This year's other winners are former secretary of state Colin Powell, Pulitzer Prize-winning playwright David Mamet, World Wide Web inventor Tim Berners-Lee, and novelist Amy Tan.

Thorne, who has been a faculty member at the California Institute of Technology since 1966, is currently the Feynman Professor of Theoretical Physics. The Common Wealth Trust cited him for his longtime efforts toward "opening new windows on the universe for scientists and lay audiences alike."

Thorne is a cofounder of and intellectual force in the Laser Interferometer Gravitational-Wave Observatory (LIGO), an NSF-funded project to detect gravitational waves and use them to probe the "dark side" of the universe. Gravitational waves were predicted almost 90 years ago by Einstein, but have not yet been detected. They are theorized to come from exotic astrophysical phenomena such as colliding black holes and neutron stars being torn apart by black holes.

LIGO is now a collaboration of 500 scientists in eight nations, headquartered at Caltech and directed by Caltech's Barry Barish and Stan Whitcomb.

Thorne earned his bachelor's degree from Caltech in 1962 and his doctorate in physics from Princeton University in 1965. He returned to his alma mater the following year and quickly rose through the faculty ranks, becoming a full professor of theoretical physics in 1970.

He was elected to the American Academy of Arts and Sciences in 1972 and the National Academy of Sciences in 1973. He has been awarded the Lilienfeld Prize of the American Physical Society (1996), the Karl Schwarzschild Medal of the German Astronomical Society (1996), the American Institute of Physics Science Writing Award in Physics and Astronomy (1969 and 1994), and the Phi Beta Kappa Science Writing Award (1994).

He has been a Woodrow Wilson Fellow, a Danforth Foundation Fellow, a Fulbright Lecturer, and a Guggenheim Fellow, and has served on the International Committee on General Relativity and Gravitation, the Committee on US-USSR Cooperation in Physics, and the National Academy of Sciences' Space Science Board.

The Common Wealth Awards of Distinguished Service were first presented in 1979 by the Common Wealth Trust, created under the will of the late Ralph Hayes, an influential business executive and philanthropist. Hayes conceived the awards to reward and encourage the best of human performance worldwide.

Now in their 26th year, the awards have conferred more than $3.5 million in prize money on 153 honorees of international renown. Past award winners include archbishop and human rights leader Desmond Tutu, the late actor Christopher Reeve, primatologist Jane Goodall, former CBS anchorman Walter Cronkite, and Nobel Prize-winning novelist Toni Morrison. In addition to Tutu, Morrison, and former secretary of state Henry Kissinger, eight other Nobel laureates have also won the award.

 

 

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Caltech Physics Team Invents DeviceFor Weighing Individual Molecules

PASADENA, Calif.-Physicists at the California Institute of Technology have created the first nanodevices capable of weighing individual biological molecules. This technology may lead to new forms of molecular identification that are cheaper and faster than existing methods, as well as revolutionary new instruments for proteomics.

According to Michael Roukes, professor of physics, applied physics, and bioengineering at Caltech and the founding director of Caltech's Kavli Nanoscience Institute, the technology his group has announced this week shows the immense potential of nanotechnology for creating transformational new instrumentation for the medical and life sciences. The new devices are at the nanoscale, he explains, since their principal component is significantly less than a millionth of a meter in width.

The Caltech devices are "nanoelectromechanical resonators"--essentially tiny tuning forks about a micron in length and a hundred or so nanometers wide that have a very specific frequency at which they vibrate when excited. Just as a bronze bell rings at a certain frequency based on its size, shape, and composition, these tiny tuning forks ring at their own fundamental frequency of mechanical vibration, although at such a high pitch that the "notes" are nearly as high in frequency as microwaves.

The researchers set up electronic circuitry to continually excite and monitor the frequency of the vibrating bar. Intermittently, a shutter is opened to expose the nanodevice to an atomic or molecular beam, in this case a very fine "spray" of xenon atoms or nitrogen molecules. Because the nanodevice is cooled, the molecules condense on the bar and add their mass to it, thereby lowering its frequency. In other words, the mechanical vibrations of the now slightly-more-massive nanodevice become slightly lower in frequency--just as thicker, heavier strings on an instrument sound notes that are lower than lighter ones.

Because frequency can be measured so precisely in physics labs, the researchers are then able to evaluate extremely subtle changes in mass of the nanodevice, and therefore, the weight of the added atoms or molecules.

Roukes says that their current generation of devices is sensitive to added mass at the level of a few zeptograms, which is few billionths of a trillionth of a gram. In their experiments this represents about thirty xenon atoms-- and it is the typical mass of an individual protein molecule.

"We hope to transform this chip-based technology into systems that are useful for picking out and identifying specific molecules, one-by-one--for example certain types of proteins secreted in the very early stages of cancer," Roukes says.

"The fundamental problem with identifying these proteins is that one must sort through millions of molecules to make the measurement. You need to be able to pick out the 'needle' from the 'haystack,' and that's hard to do, among other reasons because 95 percent of the proteins in the blood have nothing to do with cancer."

The new method might ultimately permit the creation of microchips, each possessing arrays of miniature mass spectrometers, which are devices for identifying molecules based on their weight. Today, high-throughput proteomics searches are often done at facilities possessing arrays of conventional mass spectrometers that fill an entire laboratory and can cost upwards of a million dollars each, Roukes adds. By contrast, future nanodevice-based systems should cost a small fraction of today's technology, and an entire massively-parallel nanodevice system will probably ultimately fit on a desktop.

Roukes says his group has technology in hand to push mass-sensing technology to even more sensitive levels, probably to the point that individual hydrogen atoms can be weighed. Such an intricately accurate method of determining atomic-scale masses would be quite useful in areas such as quantum optics, in which individual atoms are manipulated.

The next step for Roukes' team at Caltech is to engineer the interfaces so that individual biological molecules can be weighed. For this, the team will likely collaborate with various proteomics labs for side-by-side comparisons of already known information on the mass of biological molecules with results obtained with the new method.

Roukes announced the technology in Los Angeles on Wednesday, March 24, at a news conference during the annual American Physical Society convention. Further results will be published in the near future.

The Caltech team behind the zepto result included Dr. Ya-Tang Yang, former graduate student in applied physics, now at Applied Materials; Dr. Carlo Callegari, former postdoctoral associate, now a professor at the University of Graz, Austria; Xiaoli Feng, current graduate student in electrical engineering; and Dr. Kamil Ekinci former postdoctoral associate, now a professor at Boston University.

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Hard X-Ray telescope up for final NASA review; project will be led by Caltech's Fiona Harrison

PASADENA, Calif.--If all goes well with a technical study approved by NASA for this year, an innovative telescope should be orbiting Earth by the end of the decade and taking the first focused high-energy X-ray pictures of matter falling into black holes and shooting out of exploding stars. Not only will the telescope be 1,000 times more capable of finding new black holes than anything previously launched into space, but it will also give us an unprecedented look at the origins of the heavy elements we're all made of.

Named the Nuclear Spectroscopic Telescope Array--or NuSTAR, for short--the project has just been pegged by NASA for detailed study in the competitive Small Explorer Program (SMEX), which seeks out new technologies and new proposals for space missions that can be launched at low cost. NASA announced earlier this week that an unrelated mission called the Interstellar Boundary Explorer will be launched by 2008, and that NuSTAR will be given an up-or-down decision by next year for launch in 2009.

According to California Institute of Technology astrophysicist Fiona Harrison, the principal investigator of the NuSTAR project, an April high-altitude balloon flight in New Mexico should help to demonstrate whether the advanced sensors invented and built at Caltech are ready for space.

The balloon phase of the project sports the intuitive acronym HEFT (for High-Energy Focusing Telescope), and will mark the first time that focused pictures at "hard X-ray" wavelengths will have been returned from high altitudes. In fact, the HEFT data from the balloon is expected to be superior to any data returned so far from satellites at high X-ray energies.

NuSTAR will be much better than the balloon experiment, Harrison explains, because it's necessary to get above Earth's atmosphere for extended periods to get a good view of the X-ray sky. NuSTAR will orbit Earth at an altitude of about 300 miles or so for at least three years.

The reason that the new technology will be superior to that employed by existing X-ray satellites for certain observations is that high-energy, or hard, X rays, tend to penetrate the gas and dust of galaxies much better than the soft X rays observed by NuSTAR's forerunners. Thus, NuSTAR will get the first focused hard X-ray images for three basic science goals:

--The taking of a census of black holes at all scales. NuSTAR will not only count them, but will also measure the "accretion rate" at which material has fallen into them over time, and the rate supermassive black holes have grown.

--The detecting and measuring of radioactive stuff in recently exploded stars. These remnants of supernovae will provide a better idea of how elements are formed in supernova explosions and then mixed in the interstellar medium, which is the space between stars. NuSTAR will be especially good at observing the decay of titanium to calcium, which tends to be produced in the region of a supernova where material either is ejected forever from the explosion or falls back inward to form a compact remnant of some sort. NuSTAR will thus be an especially good probe of this region, and the data returned will contribute directly to NASA's "Cycles of Matter and Energy" program.

--The observing and imaging of the highly energetic jets that stream out of certain black holes at nearly the speed of light. Coupled with observations from the Gamma-Ray Large-Area Space Telescope (GLAST), NuSTAR will provide data to help scientists explain this still-enigmatic but powerful phenomenon.

The technical difficulties of obtaining hard X-ray images has been overcome with groundbreaking work in various Caltech labs, including that of famed inventor Carver Mead, who is the Moore Professor of Engineering and Applied Science, Emeritus, at Caltech. Both HEFT and NuSTAR will rely on an array of coaligned conical mirrors that will focus X rays from about 20 to 100 kilo-electron-volts on a pixel detector made of cadmium zinc telluride. The sensor is segmented into squares of about half a millimeter each, and these will take thousands of individual readings of X-ray photons and turn them into electronic signals.

"With this mission, we'll open the hard X-ray frontier and look at things never seen before," says Harrison, who is an associate professor of physics and astronomy at Caltech.

In addition to Caltech, the other participating organizations and universities are the Jet Propulsion Laboratory (managed by Caltech for NASA), Columbia University, the Stanford Linear Accelerator (SLAC), the Lawrence Livermore National Laboratory, Sonoma State University, the University of California at Santa Cruz, and the Danish Space Research Institute. NuSTAR's spacecraft will be built by General Dynamics Spectrum Astro.

JPL handles project management, the metrology system, and the extensible mast, and is involved in the mission's science. The mast is based on a previous JPL mission, the Shuttle Radar Topography Mission.

The selected proposals were among 29 SMEX and eight mission-of-opportunity proposals submitted to NASA in May 2003. They were in response to an Explorer Program Announcement of Opportunity issued in February 2003. NASA selected six proposals in November 2003 for detailed feasibility studies.

The Explorer Program is designed to provide frequent, low-cost access to space for physics and astronomy missions with small to mid-sized spacecraft. NASA has successfully launched six SMEX missions since 1992. The missions include the Reuven Ramaty High Energy Solar Spectroscopic Imager, launched in February 2002, and the Galaxy Evolution Explorer, launched in April 2003 and led by Caltech physics professor Chris Martin.

NASA's Goddard Space Flight Center, Greenbelt, Md., manages the Explorer Program for the Science Mission Directorate.

 

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Retired Caltech Physicist Robert Walker Dies; Worked on Manhattan Project as Grad Student

PASADENA, Calif.-Robert Walker, a retired physics professor at the California Institute of Technology, died January 4 in New Mexico. A graduate student who worked on the Manhattan Project during World War II, he was 85 years old at the time of his death.

Born June 29, 1919, in St. Louis, Walker earned his bachelor's degree at the University of Chicago and was a doctoral student at Cornell University when he joined the effort to produce the atomic bomb. While on the Manhattan Project he worked both at Los Alamos and the University of Chicago. He finished his doctorate in physics in 1948, and after an additional year at Cornell as a postdoctoral researcher he was hired as an assistant professor at Caltech.

Walker became an associate professor in 1953 and a full professor in 1959. During his time on the faculty he served as executive officer for physics. He retired in 1981 and moved to the Santa Fe area.

Walker's specialty was experimental high-energy physics, and for many years he worked on the Caltech synchrotron, first as one of the co-developers with colleagues Robert V. Langmuir and Bruce Rule, and as a researcher for the accelerator's entire 30-year lifetime. For many years, he was also the principal investigator of Caltech's contract with the Department of Energy and its predecessors to do experimental and theoretical research in elementary particle physics.

According to Charles Peck, a professor emeritus of physics at Caltech who earned his doctorate under Walker's tutelage, Walker's collaborative research utilizing the synchrotron helped lay the foundation work that led to what is now known as the Standard Model of elementary particle physics. In particular, Peck said, Walker's work involved pion photoproduction (in which a proton or neutron is bombarded with a high-energy photon which converts into a pi meson). His research was also useful to his longtime Caltech colleague Richard Feynman in his theoretical studies of the underlying mechanisms of particles.

"Bob was also a superb teacher," Peck said. "He taught a course in the mathematical methods of physics, and also courses in quantum mechanics and particle phenomena."

Walker also co-wrote a textbook, Mathematical Methods of Physics, with Jon Mathews.

After retiring from Caltech, Walker built harpsichords at his home near Santa Fe, Peck said.

He is survived by two children, Robert Craig Walker and Jan Walker Roenisch.

 

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