Caltech astronomer Jesse Greenstein dies; was early investigator of quasars, white dwarfs

Jesse L. Greenstein, an astrophysicist whose many accomplishments included seminal work on the nature of quasars, died Monday, October 21, 2002, three days after falling and breaking his hip. He was 93.

A native of New York City, Greenstein grew up in a family that actively encouraged his scientific interests. At the age of eight he received a brass telescope from his grandfather—not an unusual gift for an American child, but Greenstein soon was also experimenting in earnest with his own prism spectroscope, an arc, a rotary spark, a rectifier, and a radio transmitter. With the spectroscope he began his lifelong interest in identifying the composition of materials, a passion that would lead to his becoming a worldwide authority on the evolution and composition of stars.

Greenstein entered the Horace Mann School for Boys at the age of 11, and by 16 was a student at Harvard University. After earning his bachelor's degree in 1929 and his master's in 1930, he decided that it would be prudent, in the depths of the Great Depression, to join the family's real estate and finance business in New York. But by 1934 he was back at Harvard, earning his doctorate in 1937.

Greenstein won a National Research Council Fellowship in 1937, which allowed a certain amount of latitude in his place of employment. With the stipend, he chose to join the University of Chicago's Yerkes Observatory at Williams Bay, Wisconsin, remaining there for the duration of the two-year fellowship. In 1939 he joined the University of Chicago astrophysics faculty, and during the war years did military research in optical design at Yerkes. He also spent time at McDonald Observatory, then jointly operated by the University of Chicago and the University of Texas, before accepting an offer from the California Institute of Technology to organize a new graduate program in optical astronomy in conjunction with the new 200-inch Hale Telescope at Palomar Observatory.

The Caltech astronomy program quickly became the premier academic program of its kind in the world, with Greenstein serving as department head from 1948 to 1972. During the 24-year period, he spent more than 1,000 observing nights at Palomar and other major observatories, and also took up radio astronomy in 1955. He was a staff member at Mount Wilson and Palomar Observatories until 1979, when he retired from the Caltech faculty, and remained active in research for many years afterward. He stopped observing in 1983, but continued research on white dwarfs, M dwarfs, and the molecular composition of stars. Despite many chances to become an administrator, he remained a researcher for his entire life.

Greenstein's research interests largely centered on the physics of astronomical objects. In addition to stellar composition, he also worked on the synthesis of chemical elements in stellar interiors, studied the physical processes of radio-emitting sources, worked with Caltech colleague Maarten Schmidt on the high redshift of quasars in 1963, demonstrated that quasars are quite compact objects, and discovered and studied more than 500 white dwarfs. In later years, he studied the magnetic fields of white dwarfs, established their luminosities, and worked on ultraviolet spectroscopy with data obtained from the IUE satellite.

A common thread of his research endeavors, Greenstein wrote, "was that they were pioneering thrusts, attempts to provide first tests of a variety of physical laws under extreme conditions in the inaccessible but convenient experimental laboratories of the stars."

Greenstein was active in the establishment of the National Radio Astronomy Observatory, served as chair of the board of the Association of University Research in Astronomy, and was a former member of the Harvard Board of Overseers. He also played a pivotal role in organizing various national astronomical facilities, serving as chair of the 1970 decadal review of astronomy for the National Research Council (for which the Greenstein Report was issued), and served on the National Academy of Sciences' committee on science engineering and public policy.

He was elected to the National Academy of Sciences in 1957.

During his 72-year career in astrophysics, Greenstein was named California Scientist of the Year in 1964, was awarded the NASA Distinguished Public Service Medal in 1974, and the Gold Medal of the Royal Astronomical Society in 1975. He was presented the Centennial Medal by Harvard, and was named to the American Academy of Achievement in 1982.

He is survived by two sons, Peter Greenstein of Oakland, California, and George Greenstein of Amherst, Massachusetts. Naomi Kitay Greenstein, his wife of 68 years, whom he met as a 16-year-old Harvard undergraduate, died earlier this year. The Greensteins were often commended for the warmth and hospitality they extended to astronomers throughout the world. Naomi Greenstein also played a role in building the spirit of the astronomy group at Caltech.

Contact: Robert Tindol (626) 395-3631

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President Bush Nominates Caltech Physicist To National Science Board

Barry Barish, an experimental high-energy physicist at the California Institute of Technology, has been nominated to the National Science Board by President George W. Bush. The White House made the announcement Thursday, October 17.

Barish is the Linde Professor of Physics at Caltech, and since 1997 has been director of the Laser Interferometer Gravitational-Wave Observatory (LIGO) project, a National Science Foundation–funded collaboration between Caltech and MIT for detecting gravitational waves from exotic sources such as colliding black holes. He is a member of the National Academy of Sciences.

The eight new appointees must be approved by the U.S. Senate. If they are accepted, Barish will help oversee the National Science Foundation and advise the president and the congress on a broad range of policy issues related to science, engineering, and education. The 24-member board initiates and conducts studies, presents the results and board recommendations in reports and policy statements to the president and the congress, and makes these documents available to the research and educational communities and the general public.

The board meets in Washington, D.C., at least five times a year, with individual members also serving on committees. The board also publishes the biennial Science and Engineering Indicators.

As a high-energy physicist, Barish has been involved through the years with some of the highest-profile projects in the United States and abroad. A graduate of the University of California at Berkeley, Barish has been at Caltech since 1963. He was leader of one of the large detectors for the Superconducting Supercollider before the project was cancelled, searched for magnetic monopoles in the underground experiment below the Gran Sasso Mountain in Italy, performed several experiments at the Stanford Linear Accelerator Center, and is presently involved in the neutrino experiment inside the Soudan Underground Mine in Minnesota.

He was also responsible for the experiment at Fermilab that provided definitive evidence of the weak neutral current, the linchpin of the electroweak theory for which Sheldon Glashow, Abdus Salam, and Steven Weinberg won the Nobel Prize.

The project he currently leads, the Laser Interferometer Gravitational-Wave Observatory, recently began collecting data in the quest to study gravitational waves, which were predicted long ago by Einstein but thus far have been detected only indirectly. The LIGO project aims not only to demonstrate the existence of gravitational waves within the next few years, but also to pioneer a new type of astrophysical observation by studying exotic objects such as colliding black holes, supernovae, and neutron-star and black-hole interactions.

The National Science Board was created by an act of congress in 1950. Its official mission is to "promote the progress of science; advance the national health, prosperity, and welfare; and secure the national defense."

Contact: Robert Tindol (626) 395-3631

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Caltech researchers devisenew microdevice for fluid analysis

Researchers at the California Institute of Technology announced today a new paradigm for large-scale integration of microfluidic devices. Using new techniques, they built chips with as many as 6,000 microvalves and up to 1,000 tiny individual chambers.

The technology is being commercialized by Fluidigm in San Francisco, which is using multi-layer soft lithography (MSL) techniques to create microfluidic chips to run the smallest-volume polymerase chain reactions documented—20,000 parallel reactions at volumes of 100 picoliters.

In a paper to appear in the journal Science, Caltech associate professor of applied physics and physics Stephen Quake and his colleagues describe the research on picoliter-scale chambers. Quake's team describes the 1,000 individually addressable chambers, and also demonstrates on a separate device with more than 2,000 microvalves, that two different reagents can be separately loaded to perform distinct assays in two subnanoliter chambers and then recover the contents of a single chamber.

According to Quake, who cofounded Fluidigm, the devices should have many new scientific, commercial, and biomedical applications. "We now have the tools in hand to design complex microfluidic systems and, through switchable isolation, recover contents from a single chamber for further investigation."

"Together, these advancements speak to the power of MSL technology to achieve large-scale integration and the ability to make a commercial impact in microfluidics," said Gajus Worthington, President and CEO of Fluidigm. "PCR is the cornerstone of genomics applications. Fluidigm's microprocessor, coupled with the ability to recover results from the chip, offers the greatest level of miniaturization and integration of any platform," added Worthington.

Fluidigm hopes to leverage these advancements as it pursues genomics and proteomics applications. Fluidigm has already shipped a prototype product for protein crystallization that transforms decades-old methodologies to a chip-based format, vastly reducing sample input requirements and improving cost and labor by orders of magnitude.

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MacArthur Foundation certifies two Caltech professors as geniuses

Two members of the California Institute of Technology faculty have been named MacArthur Fellows, a prestigious honor bestowed each year on innovators in a variety of fields and commonly known as the "genius grants."

Charles Steidel, an astronomer, and Paul Wennberg, an atmospheric scientist, are two of the 24 MacArthur Fellows announced today by the John D. and Catherine T. MacArthur Foundation of Chicago. Each of the 24 recipients will receive a $500,000 "no strings attached" grant over the next five years.

Steidel's expertise is cosmology, a field to which he has made numerous contributions in the ongoing attempt to understand the formation and evolution of galaxies and the development of large-scale structure in the universe. In particular, Steidel is known for the development of a technique that effectively locates early galaxies at prescribed cosmic epochs, allowing for the study of large samples of galaxies in the early universe.

Access to these large samples, which are observed primarily using the Keck telescopes on Mauna Kea on the Big Island of Hawaii, allows for the mapping of the distribution of the galaxies in space and for detailed observations of many individual galaxies. These are providing insights into the process of galaxy formation when the universe was only 10 to 20 percent of its current age.

Steidel says he hasn't yet decided what to do with the grant money. "I'm giving it some thought, but I'm still in the disbelief phase—it took me completely by surprise!" he said.

"The unique nature of the fellowship makes me feel like I should put a great deal of thought into coming up with a creative use for the money. It does feel a bit odd to be recognized for work that is by its nature collaborative and dependent on the hard work of many people, but at the same time I am very excited by the possibilities!"

A graduate of Princeton University and the California Institute of Technology, Steidel was a faculty member at MIT before returning to Caltech, where he is now a professor of astronomy. He is also a past recipient of fellowships from the Sloan and Packard foundations, and received a Young Investigator Award from the National Science Foundation in 1994. In 1997 he was presented the Helen B. Warner Prize by the American Astronomical Society for his significant early-career contributions to astronomy.

Wennberg holds joint appointments as a professor of atmospheric chemistry and a professor of environmental science and engineering. A specialist in how both natural and human processes affect the atmosphere, Wennberg is particularly interested in measuring a class of substances known as radicals and how they enter into atmospheric chemical reactions. These radicals are implicated in processes that govern the health of the ozone layer as well as the presence of greenhouse gases.

Wennberg has earned recognition in the field for developing airborne sensors to study radicals and their chemistry. One of the early scientific results from these measurements demonstrated that conventional thinking was incorrect about how ozone is destroyed in the lower stratosphere, affecting assessments of the environmental impacts of chlorofluorocarbons and stratospheric aircraft.

Wennberg said he was "blown over by the award" when he received notification. "It is a wonderful recognition of the work that I have done in association with the atmospheric scientists working on NASA's U-2 aircraft chemistry program."

"I have been pondering how I might use the funds, but have no concrete plans at the moment. It will certainly enable me to do things I wouldn't have thought possible—perhaps even take up the bassoon again! "

A graduate of Oberlin College and Harvard University, Wennberg was a research associate at Harvard before joining the Caltech faculty. In 1999 he was named recipient of a Presidential Early Career Award in Science and Engineering.

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Five Caltech Faculty Members Elected to Membership in the American Academy of Arts and Sciences

PASADENA, Calif. — The American Academy of Arts and Sciences has announced that five members of the Caltech faculty have been elected to membership in the academy for contributions to their respective scientific fields.

The Caltech faculty members who have been elected are Richard Andersen, Boswell Professor of Neuroscience; David Anderson, professor of biology and investigator with the Howard Hughes Medical Institute (HHMI); Ronald Drever, professor of physics, emeritus; Mary Kennedy, Davis Professor of Biology; and Mark Wise, McCone Professor of High Energy Physics.

Richard Andersen is receiving recognition for his work in the fields of neuroscience, cognitive science, and behavioral biology. With the assistance of his postdoctoral and graduate students, he has examined the functions of the brain in relation to seeing, hearing, orientation, balance, and movement planning.

The author of more than 130 scholarly articles on the functions of the brain, Andersen has been honored with the Spencer Award from Columbia University, the McKnight Foundation Scholars Award, a Sloan Foundation Fellowship, a Regent's Fellowship, and an Abraham Rosenberg Fellowship, and is a Fellow of the American Association for the Advancement of Science.

David Anderson is being honored for his work in the fields of neurobiology, developmental biology, and genetics, where he has been able to make advances in stem-cell research that he hopes will eventually help fight brain diseases and spinal-cord injuries. Anderson has also made important discoveries in the field of angiogenesis, the study of blood vessel formation.

Anderson, who has authored more than 140 scholarly publications in the field of genetics and neuroscience, has also been honored with the Searle Scholars Award, the Charles Judson Herrick Award in Comparative Neurology, and the W. Alden Spencer Award in Developmental Neurobiology from Columbia University. His current affiliations include the American Association for the Advancement of Science, the Society for Neuroscience, and the Neuron editorial board.

Ronald Drever is being recognized for his work relating to gravitational physics and for his pioneering research on gravitational radiation detection. His group carried out early searches for gravitational waves, and he was cofounder of the Laser Interferometer Gravitational-Wave Observatory, a project shared by Caltech and MIT. Drever invented many of the techniques in gravitational-wave detection, including a high-precision method for controlling laser frequency now widely used in many science and technology applications.

Drever is a Fellow of the American Physical Society and is a former vice president of the Royal Astronomical Society.

Mary Kennedy is being honored for her contributions to the field of brain biochemistry and the mechanisms of learning and memory. Her research group is studying the effects of proteins in the brain and their relation to how memories are stored.

Kennedy holds numerous memberships and has been the recipient of several grants, as well as publishing a number of scientific works. Her honors include a McKnight Neuroscience Development Award, and she is an elected councilor of the Society for Neuroscience. Kennedy has also received a Faculty Award for Women Scientists and Engineers, and she is a member of the scientific advisory board of the Hereditary Disease Foundation, and the Scientific Advisory Board of the French Foundation for Alzheimer Research.

Mark Wise is receiving membership for his involvement in the field of high-energy physics, where he has developed information on the essential characteristics of particles and how they interact with each other to create the physical world.

Wise has been the recipient of a Sloan Foundation research grant and the Sakurai Prize, which reflects the admiration of his peers for his work and accomplishments in his field. Wise is also a member of the American Physical Society.

Founded in 1780 in Cambridge, Massachusetts, the American Academy of Arts and Sciences serves as a hub for complex study and discussion of multidisciplinary problems. This year, the academy elected 177 fellows and 30 foreign honorary members.

CONTACT: Ken Watson, Media Relations (626) 395-3227 Visit the Caltech Media Relations Web site: http://pr.caltech.edu/media

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Researchers make progress in understanding the basics of high-temperature superconductivity

High-temperature superconductors have long been the darlings of materials science because they can transfer electrical current with no resistance or heat loss. Already demonstrated in technologies such as magnetic sensors, magnetic resonance imaging (MRI), and microwave filters in cellular-phone base stations, superconductors are potentially one of the greatest technological triumphs of the modern world if they could just be made to operate more reliably at higher temperatures. But getting there will probably require a much better understanding of the basic principles of superconductivity at the microscopic level.

Now, physicists at the California Institute of Technology have made progress in understanding at a microscopic level how and why high-temperature superconductivity can occur. In a new study appearing in the June 3 issue of Physical Review Letters, Caltech physics professor Nai-Chang Yeh and her colleagues report on the results of an atomic-scale microprobe revealing that the only common features among many families of high-temperature superconductors are paired electrons moving in tandem in a background of alternately aligned quantum magnets. The paper eliminates many other possibilities that have been suggested for explaining the phenomenon.

Yeh and her collaborators from Caltech, the Jet Propulsion Laboratory, and Pohang University of Science and Technology in Korea report on their findings on "strongly correlated s-wave superconductivity" in the simplest form of ceramic superconductors, which are based on copper oxides, or cuprates. The paper differentiates the behavior of the two basic types of high-temperature superconductors that have been studied since the mid-1980s—the "electron doped" type that contains added electrons in its lattice-work, and the "hole-doped" type that has open slots for electrons.

The cuprate materials were discovered to be superconductors in the 1980s, thereby instantaneously raising the temperature at which superconductivity could be demonstrated in the lab. This allowed researchers to produce devices that could be cooled to superconductivity with commonly available liquid nitrogen, which is used in a huge variety of industrial processes throughout the world. Before the high-temperature superconducting materials were discovered, experts could achieve superconductivity only by cooling the materials with liquid helium, which is much more expensive and difficult to make.

The arrival of high-temperature superconductivity heralded speculation on novel applications and machines, including virtually frictionless high-speed magnetically levitated trains, as well as power transmission at a fraction of the current cost. Indeed the progress of the 1980s led to demonstrations of technologies such as magnetic sensors, microwave filters, and small-scale electronic circuits that could potentially increase the speed of computers by many thousands of times.

A certain amount of progress has been made since the high-temperature superconductors were discovered, and researchers remain optimistic that even the current generation may be adequate for such futuristic devices as extremely high-speed computers, provided that other technological hurdles can be overcome. But a primary roadblock to rapid progress has been and continues to be a limited understanding of precisely how high-temperature superconductivity works at the microscopic level.

A better fundamental understanding would allow researchers better to determine which materials to use in applications, which manufacturing procedures to employ, and possibly how to design new cuprates with higher superconducting transition temperatures. This is important because researchers would have a better idea of the molecular architecture most essential to the desired properties.

In this sense, Yeh and her colleagues' new paper is a step toward a more fundamental understanding of the phenomenon. "The bottom line is that we can eliminate a lot of things people thought were essential for high-temperature superconductivity," she says. "I feel that we have narrowed down the possibilities for the mechanism."

More specifically, the type of cuprates investigated by the Caltech team has the simplest form among all cuprate superconductors, with a structure consisting of periodic stacks of one copper oxide layer followed by one layer of metal atoms. This structure differs from all other cuprates in that multiple layers of complex components between consecutive copper oxide layers are absent, and the latter are known to be the building blocks of high-temperature superconductivity.

This unique structure appears to have a profound effect on the superconducting properties of the cuprate, resulting in a more three-dimensional "s-wave pairing symmetry" for the tandem motion of electrons in the simplest cuprate, in contrast to the more two-dimensional "d-wave pairing symmetry" in most other cuprates. This finding eliminates the commonly accepted notion that d-wave pairing may be essential to the occurrence of high-temperature superconductivity.

Another new finding is the absence of the "pseudogap phenomenon," the existence of which would imply that electrons or holes could begin to form pairs at relatively high temperatures, although these pairs could not move in tandem until the temperature fell below the superconducting transition temperature. The pseudogap phenomenon is quite common in many cuprates, and physicists have long speculated that its existence may be of fundamental importance. The absence of pseudogap, as found in the simplest form of cuprates, can now effectively rule out theories for high-temperature superconductivity based on the pseudogap phenomenon.

Contact: Robert Tindol (626) 395-3631

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Researchers make plasma jets in the labthat closely resemble astrophysical jets

Astrophysical jets are one of the truly exotic sights in the universe. They are usually associated with accretion disks, which are disks of matter spiraling into a central massive object such as a star or a black hole. The jets are very narrow and shoot out along the disk axis for huge distances at incredibly high speeds.

Jets and accretion disks have been observed to accompany widely varying types of astrophysical objects, ranging from proto-star systems to binary stars to galactic nuclei. While the mechanism for jet formation is the subject of much debate, many of the proposed theoretical models predict that jets form as the result of magnetic forces.

Now, a team of applied physicists at the California Institute of Technology have brought this seemingly remote phenomenon into the lab. By using technology originally developed for creating a magnetic fusion configuration called a spheromak, they have produced plasmas that incorporate the essential physics of astrophysical jets. (Plasmas are ionized gases and are excellent electrical conductors; everyday examples of plasmas are lightning, the northern lights, and the glowing gas in neon signs.)

Reporting in an upcoming issue of the Monthly Notices of the Royal Astronomical Society, Caltech professor of applied physics Paul Bellan and postdoctoral scholar Scott Hsu describe how their work helps explain the magnetic dynamics of these jets. By placing two concentric copper electrodes and a coaxial coil in a large vacuum vessel and driving huge electric currents through hydrogen plasma, these scientists have succeeded in producing jet-like structures that not only resemble those in astronomical images, but also develop remarkable helical instabilities that could help explain the "wiggled" structure observed in some astrophysical jets.

"Photographs clearly show that the jet-like structures in the experiment form spontaneously," says Bellan, who studies laboratory plasma physics but chanced upon the astrophysical application when he was looking at how plasmas with large internal currents can self-organize. "We originally built this experiment to study spheromak formation, but it also dawned on us that the combination of electrode structure, applied magnetic field, and applied voltage is similar to theoretical descriptions of accretion disks, and so might produce jet-like plasmas."

The theory Bellan refers to states that jets can be formed when magnetic fields are twisted up by the rotation of accretion disks. Magnetic field lines in plasma are like elastic bands frozen into jello. The electric currents flowing in the plasma (jello) can change the shape of the magnetic field lines (elastic bands) and thus change the shape of the plasma as well. Magnetic forces associated with these currents squeeze both the plasma and its embedded magnetic field into a narrow jet that shoots out along the axis of the disk.

By applying a voltage differential across the gap between the two concentric electrodes, Bellan and Hsu effectively simulate an accretion disk spinning in the presence of a magnetic field. The coil produces magnetic field lines linking the two concentric electrodes in a manner similar to the magnetic field linking the central object and the accretion disk.

In the experiment an electric current of about 100 kiloamperes is driven through the tenuous plasma, resulting in two-foot-long jet-like structures traveling at approximately 90 thousand miles per hour. More intense currents cause a jet to become unstable so that it deforms into a theoretically predicted helical shape known as a kink. Even greater currents cause the kinked jets to break off and form a spheromak. The jets last about 5 to 10 millionths of a second, and are photographed with a special high-speed camera.

"These things are very scalable, which is why we're arguing that the work applies to astrophysics," Bellan explains. "If you made the experiment the size of Pasadena, for example, the jets might last one second; or if it were the size of the earth, they would last about 10 minutes. But obviously, that's impractical."

The importance of the study, Bellan and Hsu say, is that it provides compelling evidence in support of the idea that astrophysical jets are formed by magnetic forces associated with rotating accretion disks, and it also provides quantitative information on the stability properties of these jets.

The work was supported by a grant from the U.S. Department of Energy.

Contact: Robert Tindol (626) 395-3631

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Astronomers discover the strongest known magnet in the universe

Astrophysicists at the California Institute of Technology, using the Palomar 200-inch telescope, have uncovered evidence that a special type of pulsar has the strongest magnetic field in the universe.

Reporting in the May 30 issue of the journal Nature, Caltech graduate student Brian Kern and his advisor Chris Martin report on the nature of pulses emanating from a faint object in the constellation Cassiopeia. Using a specially designed camera and the Palomar 200-inch telescope, the team discovered that a quarter of the visible light from the pulsar known as 4U0142+61 is pulsed, while only 3 percent of the X rays emanating from the object are pulsed, meaning that the pulsar must be an object known as a magnetar.

"We were amazed to see how strongly the object pulsed in optical light compared with X rays," said Martin, who is a professor of physics at Caltech. "The light had to be coming from a strong, rotating magnetic field rather than a disk of infalling gas."

To explain the precise chain of reasoning that led the team to their conclusion, a certain amount of explanation of the nature of stars and pulsars is in order. Normal stars are powered by nuclear fusion in their hot cores. When a massive star exhausts its nuclear fuel, its core collapses, causing a titanic "supernova" explosion.

The collapsing core forms a "neutron star" which is as dense as an atomic nucleus and the size of Los Angeles. The very weak magnetism of the original star is greatly amplified (a billion- to a trillion-fold) during the collapse. The slow rotation of the original star grows as well, just as an ice skater spins much faster when her arms are drawn in.

The combination of a strong magnetic field and rapid spin often produces a "pulsar," an object that rotates its beam of light just like a lighthouse, but usually in the radio band of the electromagnetic spectrum. Pulsars have been discovered that rotate almost one thousand times every second. In conventional pulsars that have been studied since their discovery in the 1960s, the source of the energy that produces this pulsing light is the rotation itself.

In the last decade, a new type of pulsar has been discovered that is very different from the conventional radio pulsar. This type of object, dubbed an "anomalous X-ray pulsar," has a very lazy rotation (one every 6 to 12 seconds) and pulses in the X- ray frequencies but is invisible in radio waves. However, the X-ray power is hundreds of times the power provided by their slow rotation. Their source of energy is unknown, and therefore "anomalous." One of the brightest of these pulsars is 4U0142+61, named for its sky coordinates and detection by the Uhuru X-ray mission in the 1970s.

Two sources of energy for the X rays are possible. In the first model, bits of gas blown off in the supernova explosion fall back onto the resulting neutron star, whose magnetic field is no stronger than an ordinary pulsar's. As the gas slowly falls (accretes) onto the surface, it becomes hot and emits X rays.

A second model, proposed by Robert Duncan (University of Texas) and Christopher Thompson (Canadian Institute for Theoretical Astrophysics), holds that anomalous X-ray pulsars are magnetars, or neutron stars with ultra-strong magnetic fields. The magnetic field is so strong that it can power the neutron star by itself, generating X rays and optical light. Magnetic fields power solar flares in our own sun, but with only a tiny fraction of the power of nuclear fusion. Magnetars would be the only objects in the universe powered mainly by magnetism.

"Scientists would be thrilled to investigate these enormous magnetic fields, if they exist," says Kern. "Identifying 4U0142+61 as a magnetar is the essential first step in these studies."

The missing observational clue to distinguish between these very different power sources was provided by a novel camera designed to look at optical light coming from very faint pulsars. While most of the light appears in X-ray frequencies, anomalous X-ray pulsars emit a small amount of optical light. In pulsars powered by disks of gas, optical pulsations would be a diluted byproduct of X-ray pulsations, which are weak in this pulsar. A magnetar, on the other hand, would be expected to pulse as much or more in optical light as in X ray frequencies.

The problem is that the optical light from the object is extremely faint, about the brightness of a candle sitting on the moon. Astronomical cameras designed to look at very faint stars and galaxies must take very long exposures, as long as many hours, in order to detect the faint light, even with a 200-inch telescope. But in order to detect pulsations that repeat every eight seconds, the rotation period of 4U0142+61, exposure times must be very short, less than a second.

Martin and Kern invented a camera to solve this problem. The camera takes 10 separate pictures of the sky during a single rotation of the pulsar, each picture for less than one second. The camera then shuffles the pictures back to their starting point, and re-exposes the same 10 pictures for the next pulsar rotation. This exposure cycle is repeated hundreds of times before the camera data is recorded. The final image shows the pulsar at 10 different points in its repetitive cycle. During the cycle, part of the image is bright while part is dim. The large optical pulsations seen in 4U0142+61 show that it must be a magnetar.

How strong is the magnetic field of this magnetar? It is as much as a quadrillion times the strength of the earth's magnetic field, and ten billion times as strong as the strongest laboratory magnet ever made. A toy bar magnet placed near the pulsar would feel a force of a trillion pounds pulling its ends into alignment with the pulsar's magnetic poles.

A magnetar would be an unsafe place for humans to go. Because the pulsar acts as a colossal electromagnetic generator, a person in a spacecraft floating above the pulsar as it rotated would feel 100 trillion volts between his head and feet.

The magnetism is so strong that it has bizarre effects even on a perfect vacuum, polarizing the light traveling through it. Kern and Martin hope to measure this polarization with their camera in the near future in order to measure directly the effects of this ultra-strong magnetism, and to study the behavior of matter in extreme conditions that will never be reproduced in the laboratory.

Additional information available at http://www.astro.caltech.edu/palomar/

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Astrophysicists announce surprising discoveryof extremely rare molecule in interstellar space

A rare type of ammonia that includes three atoms of deuterium has been found in a molecular cloud about 1,000 light-years from Earth. The comparative ease of detecting the molecules means there are more of them than previously thought.

In a study appearing in the May 20 issue of the Astrophysical Journal Letters, an international team of astronomers reports on the contents of a molecular cloud in the direction of the constellation Perseus. The observations were done with the Caltech Submillimeter Observatory atop Mauna Kea in Hawaii.

The molecule in question is called "triply deuterated ammonia," meaning that each molecule is composed of a nitrogen atom and three deuterium atoms (heavy hydrogen), rather than the usual single nitrogen atom and three hydrogen atoms found in the typical bottle of household ammonia. While not unknown on Earth, the molecules, until recently, were thought by experts to be quite rare—so rare, in fact, that the substance was considered too sparse to even be detectable from Earth.

But now that scientists have detected triply deuterated ammonia in the interstellar medium, they're still wondering why they were able to do so at all, says Tom Phillips, a physics professor at the California Institute of Technology, director of the Caltech Submillimeter Observatory, and leader of the Caltech team. No other molecules containing three deuterium atoms have ever been detected in interstellar space.

"From simple statistics alone, the chances for all three hydrogen atoms in an ammonia molecule to be replaced by the very rare deuterium atoms are one in a million billion," Phillips explains. "This is like buying a $1 state lottery ticket two weeks in a row and winning a $30 million jackpot both weeks. Astronomical odds indeed!"

As for the reasons the molecules would exist in the first place, says Dariusz Lis, a senior research associate in physics at Caltech and lead author of the paper, the frigid conditions of the dense interstellar medium allow the deuterium replacement of the hydrogen atoms to take place. At higher temperatures, there would be a back-and-forth exchange of the deuterium atoms between the ammonia molecules and the hydrogen molecules also present in the interstellar medium. But at the frosty 10-to-20 degrees above absolute zero that prevails in the clouds, the deuterium atoms prefer to settle into the ammonia molecules and stay there.

The study is important because it furthers the understanding of the chemistry of the cold, dense interstellar medium and the way molecules transfer from grains of dust to the gas phase, Phillips explains. The researchers think the triply deuterated ammonia was probably kicked off the dust grains by the energy of a young star forming nearby, thus returning to the gas state, where it could be detected by the Caltech Submillimeter Observatory.

The study was made possible because of the special capabilities of the Caltech Submillimeter Observatory, a 10.4-meter telescope constructed and operated by Caltech with funding from the National Science Foundation. The telescope is fitted with the world's most sensitive submillimeter detectors, making it ideal for seeking out the diffused gases and molecules crucial to understanding star formation.

In addition to the Caltech observers, the team also included international members from France led by Evelyne Roueff and Maryvonne Gerin from the Observatoire de Paris, funded by the French CNRS, and astronomers from the Max-Planck-Institut fuer Radioastronomie in Germany.

The main Web site for the Caltech Submillimeter Observatory is at http://www.submm.caltech.edu/cso.

 

 

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Cosmic Background Imager uncoversfine details of early universe

Cosmologists from the California Institute of Technology using a special instrument high in the Chilean Andes have uncovered the finest detail seen so far in the cosmic microwave background radiation (CMB), which originates from the era just 300,000 years after the Big Bang. The new images, in essence, are photographs of the cosmos before stars and galaxies existed, and they reveal, for the first time, the seeds from which clusters of galaxies grew.

The observations were made with the Cosmic Background Imager (CBI), which was designed especially to make fine-detailed high-precision pictures in order to measure the geometry of space-time and other fundamental cosmological quantities.

The cosmic microwave background (CMB) originated about 300,000 years after the Big Bang and it provides a crucial experimental laboratory for cosmologists to understand the origin and eventual fate of the universe because at that remote epoch matter had not yet formed galaxies and stars. Tiny density fluctuations at that time grew under the influence of gravity to produce all the structures we see in the universe today, from clusters of galaxies down to galaxies, stars and planets. These density fluctuations give rise to temperature fluctuations which are seen in the microwave background.

First predicted soon after World War II and first detected in 1965, the CMB arose when matter got cool enough for the electrons and protons to combine to form atoms, at which point the universe became transparent. Before this time the universe was an opaque fog because light couldn't travel very far before hitting an electron.

The CBI results released today provide independent confirmation that the universe is "flat." Also, the data yield a good measurement of the amount of the mysterious non-baryonic "dark matter" —which differs from the stuff everyday objects are made of—in the universe. The results also confirm that "dark energy" plays an important role in the evolution of the universe.

According to Anthony Readhead, the Rawn Professor of Astronomy at Caltech and principal investigator on the CBI project, "These unique high-resolution observations give a powerful confirmation of the standard cosmological model. Moreover this is the first direct detection of the seeds of clusters of galaxies in the early universe."

The flat universe and the existence of "dark energy" lend additional empirical credence to the theory of "inflation," which states that the universe grew from a tiny subatomic region during a period of violent expansion a split second after the Big Bang —a popular theory to account for troubling details about the Big Bang and its aftermath.

Because it sees finer details in the CMB sky, the CBI goes beyond the recent successes of the BOOMERANG and MAXIMA balloon-borne experiments and the DASI experiment at the South Pole.

The previous findings relied on a simple model which the higher resolution CBI observations have verified. If the interpretation were incorrect, it would require nature to be doubly mischievous to be giving the same wrong answers from observations on both large and small angular scales.

"We have been fortunate at CITA to work closely with Caltech as members of both the CBI and BOOMERANG teams to help analyze the cosmological implications of these exquisite high precision experiments," says Richard Bond, director of the Canadian Institute for Theoretical Astrophysics, " It is hard to imagine a more satisfying marriage of theory and experiment."

Given the radical nature of the results coming from cosmological observations, it is crucial that all aspects of cosmological theory be thoroughly tested. The fact that the CBI observations compared with others are at very different resolution, and that the various observations are made with widely differing techniques, at different frequencies, and cover different parts of the sky, and yet agree so well, gives great confidence to the findings.

The CBI hardware was designed primarily by Steven Padin, chief scientist on the project, while the software was designed and implemented by senior research associate Timothy Pearson and staff scientist Martin Shepherd. Postdoctoral Scholar Brian Mason and three graduate students, John Cartwright, Jonathan Sievers, and Patricia Udomprasert all played critical roles in the project.

The photons we see today with instruments like the CBI, the earlier COBE satellite, and the BOOMERANG, MAXIMA, and DASI experiments, have been traveling through the universe since first emitted from matter about 14 billion years ago.

The temperature differences observed in the CMB are so slight, only about one part in 100,000, that it has taken 37 years to get images with details as fine as these presented today. Though first detected with a ground-based antenna in 1965, the cosmic microwave background appeared to be quite smooth to earlier experimentalists due to the limitation of the instruments available to them. It was the COBE satellite in the early 1990s that first demonstrated slight variations in the cosmic microwave background. The celebrated COBE images were of the entire sky, but the details were many times larger than any known structures in the present universe.

The CBI and the DASI instrument of the University of Chicago, which is operating at the South Pole, are sister projects that share much commonality of design, both making interferometry measurements of extremely high precision.

The BOOMERANG experiment, led by Caltech's Goldberger Professor of Physics Andrew Lange, demonstrated the flatness of the universe two years ago. The BOOMERANG observations, together with observations from the MAXIMA and DASI experiments, not only indicated the geometry of the universe, but also bolstered the inflation theory via accurate measurements of many of the fundamental cosmological parameters. The combination of these previous results with those announced today covers a range of angular scales from about one-tenth of a moon diameter to about one hundred moon diameters, and this gives great confidence in the combined results.

The CBI is a microwave telescope array comprising 13 separate antennas, each about three feet in diameter, set up in concert so that the entire machine acts as an interferometer. The detector is located at Llano de Chajnantor, a high plateau in Chile at 16,700 feet, making it by far the most sophisticated scientific instrument ever used at such high altitudes. The telescope is so high, in fact, that members of the scientific team must each carry bottled oxygen to do the work.

In five separate papers submitted today to the Astrophysical Journal, Readhead and his colleagues at Caltech, together with collaborators from the Canadian Institute for Theoretical Astrophysics, the National Radio Astronomy Observatory, the University of Chicago, the Universidad de Chile, the University of Alberta, the University of California at Berkeley, and the Marshall Space Flight Center, report on observations of the cosmic microwave background they have obtained since the CBI began operation in January 2000. The images obtained cover three patches of sky, each about 70 times the size of the moon, but showing fine details down to only one percent the size of the moon.

The next step for Readhead and his CBI team is to look for polarization in the photons of the cosmic microwave background. This will be a two-pronged attack involving both the CBI and DASI instruments and teams in complementary observations, which will enable them to tie down the value of these fundamental parameters with significantly higher precision. Funds for the upgrade of the CBI to polarization capability have been generously provided by the Kavli Institute.

The CBI is supported by the National Science Foundation, the California Institute of Technology, and the Canadian Institute for Advanced Research, and has also received generous support from Maxine and Ronald Linde, Cecil and Sally Drinkward, Stanley and Barbara Rawn, Jr., and the Kavli Institute.

Contact: Robert Tindol (626) 395-3631

Writer: 
RT

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