First Fully Automatic Design of a Protein Achieved by Caltech Scientists

PASADENA—Caltech scientists have found the Holy Grail of protein design. In fact, they've snatched it out of a giant pile of 1.9 x 1027 other chalices.

In the October 3 issue of the journal Science, Stephen L. Mayo, an Assistant Professor of Biology and a Howard Hughes Medical Institute Assistant Investigator, and chemistry graduate student Bassil I. Dahiyat report on their success in constructing a protein of their choice from scratch.

Researchers for some time have been able to create proteins in the lab by stringing together amino acids, but this has been a very hit-and-miss process because of the vast number of ways that the 20 amino acids found in nature can go together.

The number 1.9 x 1027, in fact, is the number of slightly different chains that 28 amino acids can form. And because slight differences in the geometry of protein chains are responsible for biological functions, the total control of formation is necessary to create new biological materials of choice.

By using a Silicon Graphics supercomputer to sort through all possible combinations for a selected protein, Mayo and Dahiyat have identified the target protein's best possible amino acid sequence. Then they have managed to take this knowledge and create the protein in the lab with existing technical processes.

This is a first, says Mayo. "Our goal has been to design brand-new proteins that do what we want them to do. This new result is the first major step in that direction. "Moreover, it shows that a computer program is the way to go in creating biological materials."

The technique they use, automated protein design, combines experimental synthesis of molecules with supercomputer-powered computational chemistry.

Proteins are the molecular building blocks of all living organisms. Composed of various combinations of the 20 amino acids, protein molecules can each comprise just a few hundred atoms, or literally millions of atoms. Most proteins involved in life processes have at least 100 amino acids, Mayo says.

Mayo and Dahiyat, who have been working on this research for five years, have developed a system that automatically determines the string of amino acids that will fold to most nearly duplicate the 3-D shape of a target structure. The system calculates a sequence's 3-D shape and evaluates how closely this matches the 3-D structure of the target protein.

One problem the researchers face is the sheer number of combinations needed to design a protein of choice. The protein that is the subject of this week's Science paper is a fragment of a fairly inconspicuous molecule involved in gene expression, and as such has only 28 amino acids. Even this small number takes a prodigious amount of computational power. A more desirable protein might involve 100 amino acids, which could make the staggering number of 10130 possible amino acid sequences.

Because this number is larger than the number of atoms in the universe, the researchers have had to find clever computational strategies to circumvent the impossible task of grinding out all the calculations.

In this case, the fastest way to the answer is by working backward. Starting with all the amino acid sequences possible for the protein, the computer program finds arrangements of amino acids that are a bad fit to the target structure. By repeatedly searching for, and eliminating, poorly matching amino acid combinations, the system rapidly converges on the best possible sequence for the target.

Subsequently, the simulation can be used to find other sequences that are nearly as good a fit as the best one.

This process has been honed by designing sequences for several different proteins, synthesizing them in the laboratory, and testing their actual properties.

With their innovative strategy, Mayo and Dahiyat are now reproducing proteins that are very similar to the target molecules. (The accompanying illustration shows how closely the protein they have formulated matches the target protein.)

But the goal is not just to create the proteins that already exist in nature. The researchers can actually improve on nature in certain circumstances. By making subtle changes in the amino acid sequence of a protein, for example, they are able to make a molecule more stable in harsh chemicals or hot environments (proteins tend to change irreversibly with a bit of heat, as anyone who has cooked an egg can attest).

"Our technology can actually change the proteins so that they behave a lot better," said Dahiyat, who recently finished his Caltech doctorate in chemistry and will now head Xencor, a start-up company established to commercialize the technology. The ability to create new proteins, and to adapt existing proteins to different environments and functions, could have profound implications for a number of emerging fields in biotechnology.

And, of course, it could help further the understanding of living processes.

"Paraphrasing Richard Feynman, if you can build it, you can understand it," says Mayo. "We think we can soon achieve a better understanding of proteins by going into a little dark room and building them to do exactly what we want them to do."

Robert Tindol

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.

Caltech Question of the Week: Will Future Mars Colonies Utilize Local Martian Rocks and Soil for Building Materials?

Question of the Month Submitted through e-mail by Dave Cooley, Costa Mesa, California, and answered by Albert Yen, Caltech grad student in planetary science; and Peter Goldreich, professor of astrophysics and planetary physics.

Future colonies on Mars will maximize the use of in situ resources in order to minimize the supplies that need to be transported from Earth. Fuel, oxygen, and building materials can all be obtained from the Martian atmosphere and regolith (or loose bedrock). In fact, a lander will be launched to Mars in 2001 which will demonstrate the ability to produce propellant from the gases in the atmosphere.

Building materials for a sustained human presence on Mars will be derived from the rocks and soil. One of the basic uses of the regolith would be to cover the habitat to provide a radiation shield against high-energy solar particles. In more advanced stages of settlement, bricks could be made from soil by heating under pressure. Mortar and cement produced on Mars could be based on the sulfur that is found at the surface (about 3% by weight).

Iron and other metals are on Mars, but steel might not be necessary for construction purposes. Our best evidence is that there is little seismic activity or plate tectonics on Mars today, so it might be possible to dispense with the steel structural materials and build entirely with stone. We know that the latter material is in abundance, of course, because we have been seeing the graphic evidence every day since Pathfinder landed on July 4.

Building with stone might simplify things even more than we know: though Mars has iron, it might be hard to mine it for some reason or other. And since a major reason you would want to use metal in building is for protection against seismic activity, future Mars colonists might be able to build as most of the residents of Earth do now — with commonly available stone reasonably near the building site.

Caltech Named Recipient of Federal Computational Science and Simulation Contract

WASHINGTON—The California Institute of Technology has been awarded a multimillion-dollar contract as part of a major new Department of Energy (DOE) effort to advance computational modeling.

The five-year contract to Caltech is one of five announced at a press conference in Washington today by DOE Secretary Federico Peña as part of the new 10-year, $250 million Academic Strategic Alliances Program (ASAP) of the Accelerated Strategic Computing Initiative (ASCI). The goal of the ASCI research program is to ensure the safety and reliability of America's nuclear stockpile without actual nuclear testing.

Academic institutions chosen to participate in the ASAP program will not be involved in research related to nuclear weapons. Rather, each university will pursue the simulation of an overarching application and will collaborate with the national laboratories in developing the computational science and infrastructure required for "virtual testing." In the process, scientists say, the program will also pave the way for significant advances in a host of peacetime applications requiring high-performance computing.

"President Clinton has challenged us to find a way to keep our nuclear stockpile safe, reliable and secure without nuclear testing," said Secretary Peña. "We're going to meet his challenge through computer simulations that verify the safety, reliability and performance of our nuclear weapons stockpile. I believe these Alliances will produce a flood of new technologies and ideas that will improve the quality of our lives and boost our economy. In fact — with the Academic Strategic Alliance Program in place — Americans will begin to see the results, as the acronym suggests, ASAP."

Caltech's role in the ASCI-ASAP initiative will be to model the response of materials to intense shock waves caused by explosions or impact at high velocity. According to faculty participants, the research will be of great benefit to a number of civilian applications where the behavior of materials exposed to shock waves is important.

Professor Steven Koonin, Caltech's vice president and provost and a professor of theoretical physics, commented that "this grant will enable Caltech researchers to advance the frontiers of large-scale computer simulation, to develop the algorithms and software that can exploit the extraordinarily capable hardware available.

"It is also important that our ASCI effort will educate students in broadly applicable simulation technology," Koonin added. "And by strengthening Caltech's ties with the national laboratories, the Institute will be contributing to the major national goal of science-based stockpile stewardship."

Dan Meiron, professor of applied mathematics at Caltech and principal investigator of the project, said that "the ASAP research program is unique in that by posing the challenge of developing the large-scale modeling and simulation capability required to address our particular overarching application, ASCI pushes multidisciplinary research to a new level."

Dr. Paul Messina, Caltech's assistant vice president for scientific computing and director of the Center for Advanced Computing Research (CACR), said that the ASCI initiative is an important step toward computational fidelity. "The exciting thing for me is the tremendous progress we'll make in computational science and engineering.

"This major project is unique in that it requires the integration of software components developed by researchers from a number of disciplines." Messina added that the ASCI initiative will lead quickly to advances in both computer hardware and software.

"The proposed research will involve all three of the state-of-the-art ASCI-class machines," Messina said, adding that these three computers are located at the Livermore, Sandia, and Los Alamos national labs. The first of the machines that was completed, which is located at Sandia, recently became the first computer to complete a trillion numerical computations in a second.

"Such computational power is vital for success of the ASCI initiative, Messina said. "The data sets generated by these computations are very large. A big part of the program is how to manage those computational resources optimally when you have thousands of processors, and how to support one overarching application when you have a large variety of length and time scales."

Caltech's proposal to the DOE outlines the construction of "a virtual shock physics facility in which the full three-dimensional response of a variety of target materials can be computed from a wide range of compressive, tensional, and sheer loadings including those loadings produced by detonation of energetic materials." Goals of the research will include improving the ability to compute experiments employing shock and detonation waves, computing the dynamic response of materials to the waves, and validating the computations against real-world experimental data.

These shock waves will be simulated as they pass through various phases (i.e., gas, liquid, and solid). The work could have applications for the synthesis of new materials or the interactions of explosions with structures. The work will also provide lab scientists in the federal Science-Based Stockpile Stewardship (SBSS) program a tool to simulate high-explosive detonation and ignition.

The ASCI-ASAP program at Caltech will involve the research groups of 18 Caltech professors from across the campus, including Tom Ahrens, a geophysicist; Joe Shepherd, an aeronautics engineer; Oscar Bruno, an applied mathematician; William Goddard, a chemist; Tom Tombrello, a physicist; and Mani Chandy and Peter Schröder, computer scientists. James Pool, deputy director of the CACR, will serve as executive director for the project.

Caltech is the lead university of the ASCI-ASAP contract to simulate the dynamic response of materials. Also participating with Caltech in this project are the Carnegie Institute of Washington, Brown University, the University of Illinois, Indiana University, and the University of Tennessee.

The other schools to receive ASCI-ASAP contracts are the University of Chicago, the University of Utah, Stanford University, and the University of Illinois at Urbana-Champagne.

Caltech Question of the Week: How does molten lava in the center of Earth replenish itself?

Question of the Month Submitted by Greg McNeil, Monrovia, California.

Answered by Thomas Ahrens, professor of geophysics, Caltech.

The replenishment of lava—the molten rock which flows out on the surface from the rocky silicate mantle of the Earth, back into the Earth—is a key process that appears to be unique to our planet (relative to the other silicate mantle planets with iron cores: Mars, Venus, and Mercury).

Basalt is the most prevalent lava type found on Earth. This is true also for the other above-mentioned planets. Basalt rock, which has a specific gravity 2.7 to 3.1 times denser than that of water, consists of two key mineral groups: plagioclase, which contains mostly calcium, sodium, potassium, aluminum, silicon, and oxygen; and pyroxene, which contains mostly calcium, magnesium, iron, silicon, and oxygen. These essential minerals react at pressures in the range of 10 to 15 thousand atmospheres to form a denser garnet-bearing rock, called eclogite. Eclogite has a density in the range of 3.4 to 3.5.

Thus, as a large pile of basalt accumulates on the Earth's surface, a process called subduction, or sinking, occurs when the basalt-ecologite transition begins. This causes sections of the crust of Earth containing basalt, or rock of similar composition with thicknesses of 30 km or greater, to transform to eclogite. Because their density is greater than the underlying mantle (3.3), the materials sink, or subduct, into Earth. The basalt-eclogite reaction requires elevated temperatures and some moisture.

If the temperature becomes too high, however, greater than 1,300 degrees centigrade, the dense mineral garnet, the major dense constituent of eclogite, will not be stable and subduction does not occur. This seems to be the case for Venus, which both has a hotter interior and lacks even a fraction of the percentage of water required to assist the basalt-eclogite reaction. This is also true for the sun's nearest planet neighbor, Mercury.

Interestingly, Mars' interior appears to be too cold for eclogite formation. The subduction process is a key element in the process of recycling rock back into the Earth. Earth scientists began to understand this process in the early 1960s, and it is now recognized as a major feature of the theory of plate tectonics. Moreover, exploration of the properties of the other silicate mantle planets with iron cores suggests that only the Earth has active plate tectonics.


Caltech Installs New High-Performance HP Exemplar System at Center for Advanced Computing Research

PASADENA—At a dedication ceremony to be held Monday, June 9, the California Institute of Technology will showcase the most powerful technical computing system developed by the Hewlett-Packard Company, a 256-CPU Exemplar technical server. The Exemplar system, which features peak performance of 184 gigaflops, 64 gigabytes of memory, and one terabyte of attached disk capacity, will serve as the premiere computing resource for Caltech's Center for Advanced Computing Research (CACR) and NASA's Jet Propulsion Laboratory. Computational scientists and engineers at Caltech and JPL will use the system for a number of "grand challenge" research applications in science and engineering, including chemistry, biology, astrophysics, computational fluid dynamics, nuclear physics, geophysics, environmental science, space science, and scientific visualization. For example, the Exemplar will be used to model the world's atmosphere and oceans to better understand climatic shifts, study the dynamics of pollutants in the atmosphere, simulate the evolution of the universe, study the collisions between electrons and molecules that drive the chemistry in plasma reactors used in microelectronics manufacturing, and provide interactive access to large multispectral astronomy databases, creating a "digital sky."

The installation of a 256-processor Exemplar is the first of a three-phase collaborative project between HP and Caltech. The collaboration will include work on a range of systems software areas, such as implementing efficient support of shared-memory programming on a large number of processors. The second phase of the collaboration includes installation of an Exemplar system based on the Intel IA-64 processor. (IA-64 is Intel architecture—64-bit, jointly defined by HP and Intel.) The final project phase provides for expansion of that Exemplar system to provide peak performance of as much as one teraflop (one trillion computations per second) and one terabyte (1,024 gigabytes) of physical memory. "The collaboration between Caltech and HP is a strategic scalable computing partnership that will provide a powerful research resource with a single programming model that can be applied to computational science and engineering applications using UNIX systems, even for programs so large that their execution requires the use of the entire system," said Paul Messina, CACR director and assistant vice president for scientific computing at Caltech. "The Exemplar server is a very powerful system with features that researchers tackling today's ever larger and more complex applications have been seeking for a long time." "NASA scientists at the Jet Propulsion Laboratory will employ the Exemplar system to tackle the most challenging issues in spacecraft design and space science data analysis," said Carl Kukkonen, manager of supercomputing at JPL. According to Kukkonen, the Exemplar will be used to analyze and visualize data from Mars, calculate the precise gravitational fields of Mars and the moon, model the solar wind, conduct high-fidelity modeling of Earth's oceans, process synthetic aperture radar (SAR) images in near real time, and design and simulate new generations of spacecraft. "We are very enthusiastic about collaborating with the innovative team at Caltech to develop the 'commodity teraflops' that the market is looking for," said Steve Wallach, chief technology officer at HP's Convex Division, part of the Enterprise Server Group. "Because of HP's long-term commitment to high-end technical computing, we understand the importance of providing the platforms that advanced researchers require. In technical computing, there is no doubt that the supercomputer performance of today will be the workstation performance of tomorrow and the desktop of the future."

Caltech's Center for Advanced Computing Research conducts multidisciplinary application-driven research in computational science and engineering and participates in a variety of high-performance computing and communications activities. To carry out its mission, the CACR focuses on providing a rich, creative intellectual environment that cultivates multidisciplinary collaborations and on harnessing new technologies to create innovative large-scale computing environments.

JPL's Supercomputing Project has partnered with Caltech for the last decade to provide state-of-the-art computing facilities to enable breakthrough science and engineering for JPL's NASA space missions.

Hewlett-Packard Company is a leading global provider of computing, Internet and Intranet solutions, services, communications products and measurement solutions, all of which are recognized for excellence in quality and support. It is the second-largest computer supplier in the United States, with computer-related revenue in excess of $31.4 billion in its 1996 fiscal year. HP has 114,600 employees and had revenue of $38.4 billion in its 1996 fiscal year.

Note to editors: Dedication ceremonies for the new computing system begin at 10 a.m. in Ramo Auditorium on the Caltech campus. Luncheon reception immediately following; tours of the CACR computing facilities 11:30 a.m. to 3:30 p.m. Information about HP and its products can be found on the World Wide Web at More information on Caltech CACR's research efforts and Caltech scientific and engineering applications can be found on the World Wide Web at

Caltech Question of the Week: What Would Be the Effect If All Plate Tectonics Movement Stopped Forever?

Submitted by Jack Collins, Duarte, California, and answered by Kerry Sieh, Professor of Geology, Caltech.

If all plate motion stopped, Earth would be a very different place. The agent responsible for most mountains as well as volcanoes is plate tectonics, so much of the activity that pushes up new mountain ranges and creates new land from volcanic explosions would be no more. The volcanoes of the Pacific Ring of Fire, in South and North America, Japan, the Philippines, and New Zealand, for example, would shut off, and the steady southeastward migration of volcanic activity along the Hawaiian Islands would stop. Volcanism would just continue on the big island. There would also be far fewer earthquakes, since most are due to motion of the plates.

Erosion would continue to wear the mountains down, but with no tectonic activity to refresh them, over a few million years they would erode down to low rolling hills. So the whole planet would be flatter, and the topography would be a heck of a lot less exciting. You'd probably be less inclined to go trekking in Nepal.

One big problem with plate tectonics stopping is that plate motion is the mechanism by which Earth is cooling down and getting rid of its internal heat. If the plates stopped moving, the planet would have to find a new and efficient means to blow off this heat. It's not clear what that mechanism might be.

Caltech Question of the Week: Why Does There Need To Be Water On a Planet or Moon To Have Life?

Question of the Month Submitted by Traci Salazar, 13, Alhambra, California, and answered by Richard Terrile, scientist, Jet Propulsion Laboratory, Caltech.

Water is a tremendously important ingredient in that it's a very good solvent and a very good medium for chemical reactions. It's also very common.

Water is nearly everywhere in the solar system, it's easy to make from two ingredients (hydrogen and oxygen) that are both very common throughout the solar system and the universe, and it can exist in some truly harsh environments.

In fact, the harsh Earth environments in which liquid water is found give us good reason to think that water could be associated with extraterrestrial life. Anywhere you look on Earth, no matter how inhospitable the environment seems, liquid water apparently always harbors life of some sort. This is true for subterranean rocks as well as superheated ocean vents. So since you can find life in such Earth environments, it makes sense that life could also exist in harsh environments elsewhere.

Thus, water is a great substance for conducting chemistry. And life is very sophisticated chemical activity.

Caltech Question of the Week: How Can Different Kinds of Vegetables Contain Different Vitamins When Grown in the Same Soil?

Question of the Month Submitted by Doris Bower, Arcadia, Calif., and answered by Dr. Elliot Meyerowitz, Professor of Biology, Caltech.

Only some vitamins are found in plants—others we must obtain from other sources such as bacteria and yeast, or from animal products. Vitamin B12 is an example of one vitamin that is not found in higher plants. Some plants are good sources of certain vitamins, however, or to be precise, they are good sources either of vitamins (such as vitamin B1 in rice husks or vitamin C in citrus fruits) or of provitamins, which are converted to vitamins in our bodies. An example is beta-carotene, also known as provitamin A, which is converted in our livers to vitamin A. Beta-carotene is abundant in carrots.

There are two answers to your question. The first is that each species of plant has its own methods of regulating the biosynthetic pathways by which they make provitamins, vitamins, and other substances. The plants themselves don't get vitamins from the soil, but they do get the raw materials they need to manufacture these vitamins for their own needs. These raw materials are phosphorus, potassium, nitrates, and about a dozen other elements in lesser quantities, such as iron and magnesium.

Also, the plants take in carbon dioxide from the air, and energy from sunlight. Each species of plant synthesizes different amounts of vitamins and provitamins from the available nutrients, both because of species differences and because plants regulate their biosynthetic pathways in response to the environment. Thus, even in the same environment, different species or varieties of plants will make different amounts of vitamins, and the same variety of plant will make different amounts of vitamins in different environments.

The second answer is that we eat different parts of different plants, and different parts will have different vitamin concentrations. Depending on the vegetable in question, we may eat the leaves, roots, or fruits. So you may get a good dose of vitamin A if you eat the root of the carrot plant. But if you develop a taste for fruits such as squash, you probably won't get nearly as much.

In the case of carrots and provitamin A, there is more to the story—plants synthesize beta-carotene as an aid to photosynthesis, and also as a pigment. As an aid to photosynthesis it is required mainly in leaves, where it is usually found in high concentrations. But beta-carotene is also a pigment; it is the substance that gives most of the orange color to carrots. Since consumers prefer bright orange carrots, plant breeders have deliberately bred carrots that contain high levels of beta-carotene.

Robert Tindol

Caltech Astronomers Crack the Puzzle of Cosmic Gamma-Ray Bursts

Additional Images can be obtained on the Caltech astronomy web site at

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.

Robert Tindol


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