Physics student wins acclaim for new theory of neutron-star spin

PASADENA--When you're beginning a career in cosmology, it's only fitting to start with a bang.

That's what Ben Owen will do now that he has his doctorate in physics from the California Institute of Technology. Not only did Owen win the annual Clauser Prize for the best Caltech dissertation at the June 12 commencement, but his work has also been the subject of an international symposium. In September, he'll fly to Germany for a new job at the Albert Einstein Institute (where the symposium was held) as a postdoctoral researcher.

The reason Owen's dissertation has stirred so much interest is that it solves a nagging, decades-old question in astrophysics and opens up vistas of new questions.

In particular, chapter 5 of his "Gravitational Waves from Compact Objects" shows why young neutron stars have such slow spins. The research of chapter 5, which was done with Lee Lindblom and Sharon Morsink, predicts that rapidly spinning, newborn neutron stars will pulsate wildly, throwing off their spin energy as gravitational waves. The work appears in the June 1 issue of the journal Physical Review Letters.

The new theory of Owen and his colleagues will be tested experimentally in a few years, after the Laser Interferometer Gravitational-Wave Observatory (LIGO) comes on-line.

Neutron stars are extremely compact bodies about the mass of the sun, packed into a sphere about 15 miles in diameter. They are typically formed in the supernova explosions of massive stars.

Because the fusion of lighter elements in the star has ceased, the material remaining after the explosion scrunches together so closely that the electrons and protons of most of its atoms actually fuse together to form neutrons—and thus the name.

Neutron stars are not so compact as black holes, which are regions so dense that not even light can escape. But neutron stars are still compact enough to generate some bizarre effects. If an astronaut landed on a neutron star, for example, both he and his spaceship would be smeared by gravity into an even layer of just a few atoms over the entire surface of the star.

Also, neutron stars are noteworthy for their tendency to spin like crazy. Astronomers on Earth infer this spin from a telltale "blinking" in radio signals or sometimes even in a strobelike blinking in visible light. Based on the rate of blinking, observers know that these particular neutron stars—known as pulsars—can spin as rapidly as 600 times per second.

But this is where the controversy comes in and where Owen's dissertation is stirring up so much interest. Based on the laws of Newtonian physics, there's no compelling reason why a slowly rotating normal star shouldn't speed up to the fastest rotation rate possible once it goes supernova and then collapses into a neutron star.

The same effect can be seen in an ice skater who pulls in her arms to rotate faster while spinning.

But all of the young neutron stars observed by astronomers spin at 120 revolutions per second or less—a factor of five slower than the fastest known pulsar, which is very old and is thought to have been spun up long after the supernova by other mechanisms.

Owen's theory is that a type of fluid circulation occurs on the neutron stars that creates a sort of drag in space-time. Called "r-modes" because they owe their existence to rotation, these motions look much like the ocean eddies that move currents in circular motions on Earth.

What Owen's dissertation has shown is that the r-modes of a rapidly rotating neutron star strongly emit gravitational waves. The drag effect, caused by the gravitational waves leaving the star, in turn causes the r-modes to grow when they would normally die away due to the internal friction found in young neutron stars. In the process, this forces the spinning neutron star to slow down.

Thus, newly created neutron stars can indeed start their lives spinning quite rapidly, but are quickly slowed down by the growing r-modes. Old neutron stars have much stronger friction and can be spun up again by other processes.

"The standard methods known right now say that these currents could grow very large," says Owen.

The size of the r-modes is the key, he explains. His work shows that, if an r-mode were to be so large that it sloshed material virtually from pole to pole, the neutron star should slow down to one-tenth its original rate of rotation within a year. This, in fact, conforms to the rates of rotation seen in existing pulsars.

But the effect is a self-defeating one, Owen says. The r-modes are kept going by gravitational waves, which are stronger when emitted by rapidly rotating stars. But the gravitational waves leaving the star cause it to spin down, which makes the waves weaker, which in turn means there is less power to keep the r-modes going. So the neutron star eventually reaches an equilibrium.

"If the r-modes get very large, they'll start radiating a lot of energy as gravitational waves," Owen says. "But they can't do that forever, because the rotational energy they're radiating is what keeps them alive in the first place."

So in the course of a year, Owen shows, just about any pulsar should be spun down to a rotation rate much less than the Newtonian maximum.

Owen's work is purely theoretical at this point, but could be tested when LIGO is operational. LIGO, a collaborative project between Caltech and MIT with twin detectors in southern Louisiana and central Washington, is designed expressly for the detection and detailed study of gravitational waves.

If a supernova goes off in our cosmic neighborhood-say, within 60 million light-years-LIGO should be able to detect the gravitational waves thrown toward Earth. And if the waves change at the predicted rate over the course of a year, Owen's theoretical work will be borne out by observation.

"Several supernovae should go off every year at a distance close enough for LIGO to detect the waves," he says. "So when a supernova occurs, we should first see the waves start very abruptly at up to 1,000 cycles per second, and then chirp down to about 100 to 200 cycles per second over the course of a year."

The work of Owen, Lindblom and Morsink raises a vista of new questions, with which cosmologists and gravity-wave experimenters world-wide are now struggling. Just how large does the sloshing in a young neutron star get, and what limits its growth? Can LIGO experimenters redesign their computer programs to find Owen's predicted waves in LIGO's plethora of data? What other kinds of stars will slosh wildly, like Owen's newborn neutron stars, and what will that sloshing do to them, and can LIGO be tuned to find their gravitational waves?

Owen's thesis supervisor at Caltech was Kip Thorne, a renowned theoretical physicist who is author of the popular book Black Holes and Time Warps: Einstein's Outrageous Legacy.

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Gamma-ray Burst Found To Be Most Energetic Event in Universe

PASADENA—A team of astronomers from the California Institute of Technology announced today that a recently detected cosmic gamma-ray burst was as bright as the rest of the universe, releasing a hundred times more energy than previously theorized.

The team has measured the distance to a faint galaxy from which the burst, designated GRB 971214, originated. It is about 12 billion light-years from Earth (one light-year is approximately 5.9 trillion miles.) Combined with the observed brightness of the burst, this large distance implies an enormous energy release. The team's findings appear in the May 7 issue of the scientific journal Nature.

"The energy released by this burst in its first few seconds staggers the imagination," said Caltech professor Shrinivas Kulkarni, one of the two principal investigators on the team. The burst appears to have released several hundred times more energy than an exploding star, called a supernova, until now the most energetic known phenomenon in the universe.

"For about one or two seconds, this burst was as luminous as all the rest of the entire universe," said Caltech professor George Djorgovski, the other principal investigator on the team.

Finding such a large energy release over such a brief period of time is unprecedented in astronomy, except for the Big Bang itself.

"In a region about a hundred miles across, the burst created conditions like those in the early universe, about one millisecond [1/1,000 of a second] direction in the sky: unlike visible light, gamma-rays are exceedingly difficult to observe with a telescope, and the bursts' short duration exacerbates the problem. The Italian/Dutch satellite BeppoSAX, launched in 1996, had the ability to localize the bursts on the celestial sphere with a sufficient precision to permit follow-up observations with the world's most powerful ground-based telescopes.

The image shows the same field as seen about two months later, after the burst afterglow has faded away, revealing a faint galaxy at its position (also marked with an arrow).

This breakthrough led to the discovery of long-lived "afterglows" of bursts in X-rays, visible and infrared light, and radio waves. While gamma-ray bursts last only a few seconds, their afterglows can be studied for several months. This, in turn, led to the discovery that the bursts do not originate within our own galaxy, the Milky Way, but rather are associated with high-redshift, extremely distant galaxies in the universe.

The gamma-ray burst was detected on December 14, 1997, by the BeppoSAX and CGRO satellites. BeppoSAX and NASA's Rossi X-ray Timing Explorer spacecraft detected an X-ray afterglow. BeppoSAX precision led to the detection of a visible light afterglow, found by a team from Columbia University and Dartmouth College, including Professors Jules Halpern, David Helfand, John Torstensen, and their collaborators, using a 2.4-meter telescope at Kitt Peak, Az., but no distance could be measured from these observations.

As the visible light from the burst afterglow faded, the Caltech team detected an extremely faint galaxy at its location, using one of the world's largest telescopes, Caltech's W. M. Keck Observatory's 10-meter Keck II telescope, on Mauna Kea, Hawaii. The galaxy is about as faint as an ordinary 100-watt light bulb would be as seen from a distance of a million miles.

Subsequent images taken with the Hubble Space Telescope confirmed the association of the burst afterglow with this faint galaxy.

The Caltech team succeeded in measuring the distance to this galaxy, using the light-gathering power of the Keck II telescope. The galaxy is at a redshift of z=3.4, or about 12 billion light-years distant (assuming the universe to be about 14 billion years old).

From the distance and the observed brightness of the burst, astronomers derived the amount of energy released in the flash. Although the burst only lasted a few seconds, the energy released was hundreds of times larger than the energy given out in supernova explosions, and it is about equal to the amount of energy radiated by our entire galaxy over a period of a couple of centuries.

This is only the energy seen in the gamma rays. It is possible that other forms of radiation, such as neutrinos or gravity waves, which are extremely difficult to detect, carried a hundred times more energy than that.

While the origin of the bursts remains a mystery, what happens to the burst's glowing remnant appears to be reasonably well understood, within the so-called cosmic-fireball model. The observations of the burst afterglow by the Caltech team helped determine in some detail its physical parameters.

"It is gratifying to see that we do have some theoretical understanding of this remarkable phenomenon," said Kulkarni.

In addition to Professors Kulkarni and Djorgovski, the team includes Dr. Dale Frail from the National Radio Astronomy Observatory in Socorro, New Mexico; Drs. A. N. Ramaprakash, Tom Kundic, Stephen Odewahn, and Lori Lubin from Caltech; Dr. Mark Dickinson from the Johns Hopkins University, in Baltimore, Maryland; Dr. Robert Goodrich from the W. M. Keck Observatory in Hawaii; graduate students Joshua Bloom and Kurt Adelberger from Caltech; and many others.

Full scale images of the GRB 971214 field are available.

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Robert Tindol
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Physicists create first nanometer-scale mechanical charge detector

PASADENA—Wristwatch cellular phones and space probes the size of baseballs would certainly have some eager customers, but both are still the stuff of science fiction.

Nonetheless, physicists are making strides these days in the sort of miniaturization that could someday make tiny electromechanical devices a reality. One such milestone, the first nanometer-scale mechanical charge detector, is reported in the current issue of Nature.

According to Michael Roukes, professor of physics at Caltech and coinventor of the device, the new electrometer is among the most sensitive charge detectors in existence, and definitely the first based upon nanomechanical principles.

"One compelling reason for doing this sort of thing is to explore entirely new avenues for making small, ultralow power electronic devices," says Roukes.

"Making new types of electronic devices that involve moving elements, which we call nanoelectromechanical systems, will open up a huge variety of new technological applications in areas such as telecommunications, computation, magnetic resonance imaging, and space exploration. And the physics is exciting, besides."

The device fabricated at Caltech by Roukes and his former postdoctoral collaborator, Andrew Cleland (now an assistant professor at UC Santa Barbara), is a good example of the type of advances in solid-state devices that currently are loosely gathered these days under the rubric "nanotechnology." Roukes says he generally avoids using the term. "Rather, this is the kind of science that is building the foundation for real nanotechnology, not the stuff of fiction. Right now Mother Nature is really the only true nanotechnologist."

A nanometer is one-billionth of a meter, which is about a hundred-thousandth the width of a human hair. A few atoms stacked side-by-side span about a nanometer.

To give an idea of the scale, Roukes points out that the devices are far smaller than cellular organisms; a clear picture of the device's inner workings can only be taken with an electron microscope.

The scale is especially noteworthy when one considers that the electrometer is actually a mechanical device, in the same manner as an old-fashioned clock. In other words, there are moving parts at its heart. In the Caltech devices, movement is induced by tiny wires that exert forces on the nanomechanical elements when a minute external electrical current is applied to them.

"The simplest kinds of mechanical structures are resonators, for example, cantilevers—in other words, a structure like a diving board—or thin clamped beams, something like a thick guitar string attached at both ends," Roukes explains. "They really are mechanical structures—you 'pluck' them to get them to vibrate."

"What's fascinating is that, if you can get these things small enough, they'll vibrate billions of times per second—which gives them the same frequency as the microwaves used in telecommunications," he says. "That's because their mass is very small, which means there's less inertia for internal forces to overcome.

There is a second important aspect to nanomechanical systems, Roukes adds. "Because the distances involved are very small, the amplitudes of their vibrations are very small. For this reason, the amount of energy you would have to put into such devices to get them going is extremely minute.

"This means that for certain critical applications—like small communicators and miniaturized satellites—you would not have to carry along nearly as much energy to run the device."

The latter would be fortuitous in any circumstances where carrying along power is difficult. Transistors in the best receiving devices today can run on a few thousandths of a watt, but with nanotechnology, they could run on a few billionths of a watt, or less. Thus, planetary space probes (which employ such devices in spades) could be much smaller, since they could get by with a much smaller energy source.

At the center of the Caltech nanoelectromechanical charge detection device are small rods that vibrate something like a nanoscale tuning fork. In their ultimate incarnation, which Roukes believes his lab can achieve in the next few years, these rods will be about 100 nanometers long, 10 nanometers wide, and 10 nanometers thick.

Roukes indicates that a silicon beam of such small dimensions would vibrate at about 7 gigahertz (or 7 billion times per second) if it is clamped down at both ends. When one considers that a top-of-the-line personal computer these days has a clock speed about twenty times slower, the advantages become apparent.

But it's not necessarily the replacement of conventional computer components that Roukes is after. It turns out that the small resonators his group is currently able to manufacture on campus—if cooled to temperatures a few tenths of a degree above absolute zero—sit right at the border where the quantum effects governing individual atoms and particles take over.

Working with these quantum effects is a daunting technological challenge, but success could lead to devices such as quantum computers.

"There is a natural dividing line that depends on the temperature and the frequency. Basically, if you can get the temperature low enough and the frequency is high enough, then you can operate at the quantum level.

"We could do this today," Roukes says. "In my laboratories we can get to temperatures a few thousandths of a degree above absolute zero. We also have the sizes small enough to give us sufficiently high frequencies.

"But what we don't yet know how to do is to probe these structures optimally."

In fact, one of the main themes of work in Roukes's group on nanoscale electromechanical devices is pretty much "how to talk to the devices and how to listen to them," he says. To measure a system is to probe it somehow, and to probe it is to interact with it.

The problem is that interacting with the system is, in essence, to alter its properties. In the worst case, which is easy to do, one could actually heat it sufficiently to raise its energy above the point at which it would cease functioning as a quantum-limited mechanical device.

"But there are lots of different physical processes on which we can base signal transducers. We are looking for the right approach that will allow us to listen to and hear from these devices at the scale of the quantum limit," he says.

"There's lots of interesting physics, and practical applications that we are learning about in the process."

As far as the device reported in Nature is concerned, Roukes says that the scales involved set a milestone—that of submicron mechanical structures—that is encouraging for scientists and technologists in the field. In addition to possibilities for telecommunications, techniques on which the experimental prototype is based should also lead to significant improvements in magnetic resonance detection.

These, in turn, could lead to imaging with a thousand times better resolution than that currently available.

Roukes's group, in close collaboration with P. Chris Hammel's group at Los Alamos National Laboratory, is already hard at work on these possibilities.

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Robert Tindol
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ACE Satellite Now In Place Between Earth and Sun; Will Seek To Determine What Sun Is Made Of

PASADENA—Tanning aficionados, beach bums, surfers, and other solar enthusiasts may not realize it yet, but there is a new satellite making a huge looping halo around the sun. And it's a satellite that's going to be a benefit to weather forecasters in predicting solar flares as well as to astrophysicists in understanding the nature of the universe.

The satellite is called the Advanced Composition Explorer, or ACE for short. Launched August 25, the satellite has reached its destination about a million miles from Earth toward the sun at a position known as L1. That's the point at which the gravitational pull from Earth and sun, plus centrifugal effects, exactly balance each other.

"So, a spacecraft can orbit this invisible point, maintaining a fixed distance from Earth as Earth orbits the sun," says Ed Stone, Morrisroe Professor of Physics at Caltech and principal investigator of the ACE science mission.

Stone and Caltech physicist Dick Mewaldt are leading the satellite's science mission at the ACE Science Center at Caltech. There, they obtain spacecraft telemetry from the flight operations team at the Goddard Space Flight Center, and process the data for the astrophysics community.

The satellite is designed to collect a wide range of information on the matter it encounters. Its mission can broadly be classified in two phases:

® The satellite incorporates a real-time solar wind system that will provide around-the-clock coverage of interplanetary conditions that affect Earth. This is especially of benefit to those living at high northern and southern latitudes, because Earth's magnetic field is such that a coronal mass ejection can more easily disrupt power systems close to the poles.

While the ACE can do nothing to prevent this phenomenon from occurring, the satellite can at least provide an hour of warning that a coronal mass ejection may create a magnetic storm. The warning could help minimize and perhaps even eliminate some of the outages.

The National Oceanic and Atmospheric Administration (NOAA) will analyze the data and issue forecasts and warnings of solar storms. According to NOAA, it will be possible to issue geomagnetic storm alerts with virtually 100 percent accuracy.

® The ACE science mission is designed to measure and compare the composition of three samples of matter that can be found in interplanetary space. These are the solar material in the form of the solar wind and energetic particles accelerated by violent eruptions of the sun, the gas from the nearby space between the stars, and high-energy cosmic rays that come from more distant regions in the Milky Way.

Understanding the nature of this matter can help researchers provide answers to fundamental questions about the origin of matter. Additional information on the precise mix of elements in the solar wind, for example, will also serve as a benchmark for understanding the composition of other bodies in the solar system.

The ACE satellite is carrying nine scientific instruments that were developed by a team of scientists representing 10 institutions in the United States and Europe. These instruments are an array of mass spectrometers that measure the mass of individual ions. The satellite is already collecting data, and is expected to do so for at least five years.

"Our first look at the data tells us that the performance of the instruments is excellent," says Stone. "We should be learning what the sun is made of in the months ahead."

[Note to editors: See http://www.srl.caltech.edu/ACE/ for more on the ACE science mission. Also, NOAA on Jan. 23 issued a press release on the ACE satellite's space weather forecasting capabilities.]

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Black Hole That Periodically Ejects Its Inner Disk As Jets Discovered

WASHINGTON—Astronomers observing a disk of matter spiralling into a black hole in our galaxy have discovered that the black hole periodically hurls the inner portion of the disk into space as jets travelling at near the speed of light.

According to Stephen Eikenberry, an astrophysicist at the California Institute of Technology, the superhot gas in the inner disk shines brightly in X-rays, and dramatic dips in the X-ray emission suggest that the inner disk vanishes every 20 to 40 minutes. Infrared and radio observations at the same time show huge flares which indicate that matter is being thrown out of the system.

Eikenberry and colleagues from the Massachusetts Institute of Technology and NASA's Goddard Space Flight Center will discuss their findings at a 9:30 a.m. press conference on Wednesday, January 7, during the winter meeting of the American Astronomical Society.

The scientists observed the disappearance of the inner portion of the disk, known as an accretion disk, at the same time that glowing plasma is ejected from the black hole system. In August, Eikenberry and his collaborators at Caltech observed infrared flares from the black hole system, known as GRS 1915+105, using the Mt. Palomar 200-inch telescope.

At the same time, Ronald Remillard and his collaborators at MIT monitored X-ray dips from the same black hole using NASA's Rossi X-ray Timing Explorer (RXTE) satellite. Jean Swank and her collaborators at NASA/GSFC observed similar dips, antion between the disappearance of the inner disk and the jet ejection has never been seen until now."

"This work is also exciting because it may help us understand many other types of systems with jets," notes Robert Nelson, who works with Eikenberry at Caltech. "Astronomers have found jets in a wide range of objects, from quasars—incredibly powerful objects seen out to the edge of the observable universe—to young protostars."

The half-hour spacing between the ejections may be telling researchers that what they had thought were smooth, continuous outflows may in fact be intermittent explosions.

"There are many fine details in the X-ray dips that we may now seriously investigate to better understand the ejection mechanism," adds Edward R. Morgan, who works with Remillard at MIT. "In particular, there is a very unusual X-ray flash at the bottom of these dips in which the X-ray spectrum changes significantly. This may be the trigger for the rapid acceleration of the disk material."

The black hole in GRS 1915+105 became known to astronomers in 1992 as an X-ray nova, which is believed to signify the sudden flow of hot gases into a black hole from a companion star in a binary system. The black hole in GRS 1915+105 is thought to have a mass equal to ten Suns or more, all crushed by its own gravity into a tiny sphere contained within an "event horizon," which itself has a radius of about 20 km.

When a black hole pulls gas from the atmosphere of a companion star, the matter spirals in toward the event horizon like water going down a drain, and the swirling disk created by the flow is known to astronomers as an "accretion disk." The gas in the disk heats up dramatically due to the large acceleration and friction. Just before entering the event horizon, the gas reaches temperatures of millions of degrees, causing it to glow in X-rays.

In 1994, Mirabel and Luis Rodriguez observed radio emission from jets in GRS 1915+105, and they determined that the speed of the jets was greater than 90 percent of the speed of light, or roughly 600 million miles per hour. Since RXTE began observing the X-ray sky in early 1996, the exceptionally chaotic behavior of GRS 1915+105 in X-rays has been chronicled on many occasions.

The new results gained by Eikenberry's team brings together these phenomena by showing that modest jet ejections and the pattern of X-ray variations are synchronized in an organized way.

"The repeated ejections are really amazing," says Craig Markwardt, a member of the NASA/GSFC team. "The system behaves like a celestial version of Old Faithful. At fairly regular intervals, the accretion disk is disrupted and a fast-moving jet is produced."

"This jet is staggeringly more powerful than a geyser," adds Swank. "Every half hour, the black hole GRS 1915+105 throws off the mass of an asteroid at near the speed of light. This process clearly requires a lot of energy; each cycle is equivalent to 6 trillion times the annual energy consumption of the entire United States."

"Since the disk-jet interaction is so poorly understood, we're hoping that further analysis of these observations will show us more details of what is happening so close to the black hole," Eikenberry says. "We're planning more detailed studies for the coming year which should give us even more clues as to the nature of these incredibly powerful events.

"Right now, we still aren't even sure why these dips and ejections occur every half hour or so—why not every week or every 30 seconds, for instance?

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Caltech Astrophysicist Charles Steidel Receives $500,000 Packard Foundation Fellowship

PASADENA—A Caltech astrophysicist who searches for the oldest and most distant structures in the universe has been named a recipient of a $500,000 grant from the David and Lucile Packard Foundation.

Charles Steidel, an associate professor of astronomy, is the newest Caltech recipient of the Packard award. He plans to use the money largely for instruments to be fitted onto the 200-inch Hale Telescope at Palomar. These instruments will allow more efficient searches for extremely distant objects in deep space.

"My principal research interests are in the areas of the formation and evolution of galaxies, from the experimental perspective," Steidel says. "The central theme is the history of 'normal' galaxies like our Milky Way."

Nearby galaxies, as well as the stars in the Milky Way, are seen as they appeared when light left them. Thus, a galaxy one million light-years away is observed from Earth as it appeared one million years ago. But since the universe is probably 15 billion years old, astrophysicists must look at galaxies much farther away to learn about the early stages of galactic development. This is Steidel's specialty.

"Our goal for the next five years is to study galaxies, and their distribution in space, as they appeared when the universe was less than about 15 percent of its current age," Steidel says. "The hope is that this will tell us a lot about how and when the galaxies and large clusters of galaxies we see in the nearby universe came to be."

The success of the searches for these extremely distant galaxies depends on a vital combination of the Hale Telescope and the 10-meter W.M. Keck Telescopes on the island of Hawaii. The Hale can identify candidates based upon very deep images of relatively large areas of sky, and the W.M. Keck 10–meter telescopes can obtain the spectra of the very faint candidates, to allow more precise distances to be measured.

"It should be quite feasible, within the next few years, to trace the galaxies back to the point where they have not yet coalesced, and where the large-scale structures of galaxies we see today were just beginning to come together," he says.

The Fellowships in Science and Engineering were first awarded by The David and Lucile Packard Foundation of Los Altos, California, in 1988. The goals of the fellowship program are to support outstanding faculty as they build productive research programs and to help attract and retain faculty of the highest quality for our universities. With the announcement of the 20 awards for 1997, the foundation has awarded a total of 200 fellowships.

Founded in 1891, Caltech has an enrollment of some 2,000 students, and a faculty of about 280 professorial members and 284 research members. The Institute has more than 19,000 alumni. Caltech employs a staff of more than 1,700 on campus and 5,300 at JPL.

Over the years, 26 Nobel Prizes have been awarded to faculty members and alumni; and two faculty members and one alumnus have been awarded the Crafoord Prize. Forty-three Caltech faculty members and alumni have received the National Medal of Science; and eight alumni (two of whom are also trustees), two additional trustees, and one faculty member have won the National Medal of Technology.

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Astronomers Detect Relativistically Expanding Clouds Around the May 8 Gamma-Ray Burst

PASADENA—Astrophysicists still don't know what caused the gamma-ray burst of May 8, but they now have a size and rate of expansion for its remnant "fireball" to add to the location and distance.

New measurements by researchers at the California Institute of Technology and the National Radio Astronomy Observatory (NRAO) indicate that the fireball is now 85 times larger in diameter than our own solar system.

Further, the researchers have determined that the fireball is expanding at an extremely high rate of speed—perhaps as fast as 99.99 percent of the speed of light when the explosion first occured, and currently about 85 percent of light speed.

"This has all helped us to understand the mechanics of gamma-ray bursts once they take place," said Shrinivas Kulkarni, a Caltech astrophysicist who is coprincipal investigator of the work, which is reported in the September 18 issue of the journal Nature.

A few months ago the Caltech team, using the Palomar and the Keck telescopes, decisively showed that this gamma-ray burst occurred in a distant galaxy, settling one of the major controversies about the origin of these enigmatic objects.

Coprincipal investigator Dale Frail of NRAO added, "If you ask me what caused the burst, I'd still have to say it's pure speculation. It could have been a black hole smothering a neutron star, or maybe two neutron stars colliding, or perhaps even two black holes colliding.

"What we do know is that this was a spectacular cosmic event—far more energetic than a supernova explosion."

Gamma-ray bursters were first discovered by military satellites almost 30 years ago. The field has advanced rapidly, thanks to the precise localization of the bursts offered by the Italian-Dutch satellite BeppoSAX. Astrophysicists have now found, rapidly in succession, that gamma-ray bursts occur at cosmological distances and are probably the most energetic events in the universe.

This particular burst was first reported by BeppoSAX on May 8, 1997. Before the advent of BeppoSAX, astrophysicists had no idea whether gamma bursts originated in our own galaxy or across the universe, and, in fact, had formulated competing theories accounting for either scenario.

The measurements were obtained at the Very Large Array, a radio telescope array operated by NRAO with funding from the National Science Foundation. Other authors of the paper include Greg Taylor of NRAO and two BeppoSAX team members, Luciano Nicastro and Marve event."

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Possible Planet-Forming Disk imaged by Caltech Radio Astronomers

PASADENA—A giant disk of gas and dust over 10 times the size of our own solar system has been detected rotating around a young star in the constellation of Auriga. The star is both more massive and brighter than our sun, and appears to be a young version of another star called Beta Pictoris, where astronomers have long suspected the presence of planets.

The new discovery was made by radio astronomers at the California Institute of Technology using the millimeter-wave array at Caltech's Owens Valley Radio Observatory in central California. The results appear in the current issue of the journal Nature, and concern a relatively massive star known as MWC480, which is about 450 light-years from Earth.

How prevalent is planet formation around young stars? Past work had shown that stars similar to our own sun possess protoplanetary disks in their youth, disks we believe will form planets, perhaps as our own solar system did. However, little was known about the propensity of disks to form planets around stars that are more massive than our sun.

According to Vince Mannings, the paper's first author, the new results provide unprecedentedly clear evidence for the presence of a rotating disk of gas surrounding MWC480, and support earlier indications of rotating disks encircling some less massive and young sunlike stars. Not only is the gas around MWC480 clearly discernible at radio wavelengths, he says, but the orbital rotation of the entire disklike cloud is also unambiguously observed.

The presence of rotation suggests that, as for the disks around the young sunlike stars, the disk structure around MWC480 is long-lived. Indeed, this massive reservoir of orbiting material could last long enough to form new planets. "Families of planets, perhaps resembling our own solar system, are thought to originate in such disks," says Mannings. "Our sun, when very young, possibly had a disk similar to that around MWC480."

The star in the middle of the MWC480 disk resembles a much older star called Beta Pictoris, which is surrounded by a comparatively lightweight "debris disk," probably composed in part of dust-grain remnants from processes connected with an earlier phase of planet building. The new results imply that, in its youth, Beta Pictoris may have possessed a massive disk comparable to that now identified around MWC480. Beta Pictoris might have been, effectively, a "planetary construction site," says Mannings.

Other members of the research team are David Koerner, an astronomer at the Caltech/NASA Jet Propulsion Lab, and Anneila Sargent, who is executive director of Caltech's Owens Valley Radio Observatory.

Mannings says, "We believe that the amount of material in this disk is sufficient to produce a system of planets. We detect enough gas and dust to build planets with the same total mass as that of the nine planets in our own solar system. But we emphasize that the possibility of planet building within this particular disk is speculation only."

The radio image is sufficiently detailed to show that the large disk of gas and dust is tilted about 30 degrees from face-on. A tantalizing aspect of the image is that the rotation of the disk can be detected by measuring the velocities of the gas, most of which is in the form of molecular hydrogen. About 1 percent of the disk is dust grains, and just a trace amount of the material is carbon monoxide. The hydrogen is not detected directly, but the gas velocities can be probed using spectral-line radio waves emitted by the carbon monoxide. The Caltech measurements demonstrate that gas south of the star travels approximately toward us, and away from us when north of the star. From our vantage point, the disk is inferred to be rotating roughly from south to north.

For the first time, astronomers have identified clearly a young massive disk that could gradually evolve into a debris disk such as that surrounding the older star Beta Pictoris, perhaps building planets along the way. By studying stars like MWC480, say Mannings, Koerner and Sargent, we can hope to learn not only about the origins of the Beta Pictoris debris disk, but perhaps about the beginnings of our own solar system too. Astronomers have targeted nearby sunlike stars for searches for new planets, but this discovery shows that brighter stars should also be included.

Big Bear Observatory Telescopes and Dome To Be Named In Honor of Longtime Director Hal Zirin

PASADENA—Renowned solar astronomer Harold Zirin will be honored Wednesday when the solar telescopes and dome at Big Bear Solar Observatory are named for him.

The ceremony, set for 11 a.m. Wednesday, July 2, at the observatory near Big Bear City, Calif., also marks the official transfer of operations of the observatory management from the California Institute of Technology to the New Jersey Institute of Technology. Zirin, a longtime member of the astrophysics faculty at Caltech, has been the sole director of the facility since its founding in 1969.

"Hal Zirin's achievements in solar physics are recognized throughout the world," says Philip R. Goode, director of the Center for Solar Research at NJIT, in a special resolution. "It is fitting for his friends and associates to express deep admiration and respect for him as a scholar, a teacher, and a colleague."

Goode, the new director of Big Bear Solar Observatory, also said that, based on BBSO observations, Zirin had established BearAlerts, a service for forecasting solar activity and issuing flare warnings. Solar flares, if sufficiently powerful, can cause communication satellites to malfunction and can also cause electrical disturbances on Earth.

Zirin, a member of the Caltech faculty since 1963, is a leading authority on solar flares. He discovered the role of emerging flux regions in rearranging magnetic fields and triggering solar flares, as well as the role of delta sunspots in producing solar flares. He also established a chromosphere atmospheric reference model for the study of the solar atmosphere.

Speakers at the Wednesday ceremony, in addition to Zirin and Goode, will include Dr. Thomas E. Everhart, president of Caltech; and Saul K. Fenster, president of NJIT. The media are invited. For directions and to schedule tours of the facilities, please call in advance.

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Caltech Astronomers Crack the Puzzle of Cosmic Gamma-Ray Bursts

Additional Images can be obtained on the Caltech astronomy web site at http://astro.caltech.edu

PASADENA—A team of Caltech astronomers has pinpointed a gamma-ray burst several billion light-years away from the Milky Way. The team was following up on a discovery made by the Italian/Dutch satellite BeppoSAX.

The results demonstrate for the first time that at least some of the enigmatic gamma-ray bursts that have puzzled astronomers for decades are extragalactic in origin.

The team has announced the results in the International Astronomical Union Circular, which is the primary means by which astronomers alert their colleagues of transient phenomena. The results will be published in scientific journals at a later date.

Mark Metzger, a Caltech astronomy professor, said he was thrilled by the result. "When I finished analyzing the spectrum and saw features, I knew we had finally caught it. It was a stunning moment of revelation. Such events happen only a few times in the life of a scientist."

According to Dr. Shri Kulkarni, an astronomy professor at Caltech and another team member, gamma-ray bursts occur a couple of times a day. These brilliant flashes seem to appear from random directions in space and typically last a few seconds.

"After hunting clues to these bursts for so many years, we now know that the bursts are in fact incredibly energetic events," said Kulkarni.

For team member and astronomy professor George Djorgovski, "Gamma-ray bursts are one of the great mysteries of science. It is wonderful to contribute to its unraveling."

The bursts of high-energy radiation were first discovered by military satellites almost 30 years ago, but so far their origin has remained a mystery. New information came in recent years from NASA's Compton Gamma-Ray Observatory satellite, which has so far detected several thousand bursts. Nonetheless, the fundamental question of where the bursts came from remained unanswered.

Competing theories on gamma-ray bursts generally fall into two types: one, which supposes the bursts to originate from some as-yet unknown population of objects within our own Milky Way galaxy, and another, which proposes that the bursts originate in distant galaxies, several billion light-years away. If the latter (as was indirectly supported by the Compton Observatory's observations), then the bursts are among the most violent and brilliant events in the universe.

Progress in understanding the nature of ters had to make an extra effort to identify this counterpart quickly so that the Keck observations could be carried out when the object was bright. The discovery is a major step to help scientists understand the nature of the burst's origin. We now know that for a few seconds the burst was over a million times brighter than an entire galaxy. No other phenomena are known that produce this much energy in such a short time. Thus, while the observations have settled the question of whether the bursts come from cosmological distances, their physical mechanism remains shrouded in mystery.

The Caltech team, in addition to Metzger, Kulkarni, and Djorgovski, consists of professor Charles Steidel, postdoctoral scholars Steven Odewahn and Debra Shepherd, and graduate students Kurt Adelberger, Roy Gal, and Michael Pahre. The team also includes Dr. Dale Frail of the National Radio Astronomy Observatory in Socorro, New Mexico.

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Robert Tindol
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