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/

Writer: 
Robert Tindol
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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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Robert Tindol
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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

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RT

Gamma-ray bursts are caused by explosive death of massive stars, new study reveals

In two papers appearing in an upcoming issue of the Astrophysical Journal, an international team of astrophysicists led by Shri Kulkarni of the California Institute of Technology reveals that new data show that supernovae are the source of gamma-ray bursts.

The new information was obtained from a gamma-ray burst that was detected in November and studied by the Hubble Space Telescope, the Australia Telescope Compact Array, the Anglo-Australian Telescope, and optical telescopes in Chile.

For the last few years astronomers have been chasing clues linking the mysterious gamma-ray bursts to their favored suspect: massive stars. Previous observations hinted at debris from an exploding star, but the observations were inconclusive.

Careful observations of gamma-ray burst GRB 011121 have uncovered remnants of the exploded star, whose signature was buried in the bright, fading embers. Now, for the first time, two compelling tell-tale signatures of the massive star were observed.

As explained by Kulkarni, who is the McArthur Professor of Astronomy and Planetary Sciences at Caltech and the head of the international team that made this discovery, "With these observations we have tied this gamma-ray burst to an exploding star. I am absolutely delighted that nature provided us with such a clean answer."

At the core of the observations, the data show that a supernova accompanied the burst. Supernovae are a natural consequence of exploding stars and difficult to make by other means. Joshua Bloom, Caltech graduate student and lead author on the supernova paper, said. "It is not often that a graduate student gets the chance to make a major discovery. I am very fortunate to be involved in this one."

The astronomers were also able to deduce that the explosion took place in a cocoon of gas fed by a "wind" of matter emanating from the progenitor star. Paul Price, graduate student at the Australian National University and a lead author on the second paper, was "intensely excited. Once it became clear that we had not only seen the supernova but also the cocoon I was very happy; I couldn't sleep for days."

The gamma-ray burst in question was detected on November 21, 2001, by the Italian-Dutch Satellite BeppoSAX in the southern-sky constellation of Chamaeleon. The position was quickly refined by a network of satellites. Astronomers from Poland and Chile, as well as another U.S. team from Harvard, used optical telescopes in Chile to rapidly identify the ``afterglow,'' or glowing embers, of the gamma-ray burst and determined that the galaxy in which the burst was located was quite near - a paltry five billion light-years from Earth.

The sensitive optical and infrared observations were in part possible because of the relatively small distance to the burst. Given the proximity, the Caltech team decided to dedicate a large portion of their allocated Hubble Space Telescope time toward observing any possible supernova component. Kulkarni says of the decision, "We simply went for broke because of the potential payoff."

Kulkarni believes that this is just the beginning of a new era in our understanding of the death of massive stars. The stars die by collapsing, and the collapse both fuels the explosion and leaves a stellar residue of neutron stars and black holes. Indeed, theorists have long speculated that gamma-ray bursts are the birth cry of spinning black holes. New facilities such as the Chandra X-Ray Observatory, and future facilities such as gravitational-wave observatories and neutrino telescopes, will allow astronomers to investigate the dramatic collapse process.

Kulkarni cautions, however, that all is still not known about gamma-ray bursts. It may be that other exotic phenomena, such as two colliding neutron stars, or a neutron star colliding with a black hole, produce some of the events that we see. "Despite extensive efforts, until now we have not seen clear signatures for a cocoon in dozens of other gamma-ray bursts, and there have been only hints of a supernova in a few other bursts," Bloom says.

Price adds, "It means there will be lots more to do in the future. I have a secure thesis now!"

In addition to Kulkarni, Bloom, and Price, members of the team reporting the results are Caltech professors S. George Djorgovski and Fiona Harrison and postdoctoral fellows and scholars Daniel Reichart, Derek Fox, Titus Galama, and Re'em Sari. Edo Berger and Sara Yost are Caltech graduate students also on the team, as are Dale Frail from the National Radio Astronomy Observatory, and many other international collaborators. Separately, P. M. Garnavich of the University of Notre Dame and his collaborators have reached similar conclusions with data taken from the Magellan telescope in Chile.

 

Writer: 
Robert Tindol
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Researchers find evidence for mechanismthat creates near-Earth binary asteroids

About one in six of all near-Earth asteroids are binaries – in other words, two bodies that travel in close companionship as they orbit the sun. A new study reveals that binaries most likely form when a single asteroid swings close to Earth, is ripped apart by the planet's tidal attraction, and eventually reforms into separate bodies.

In a refereed article to be released Thursday, April 11 on the Science Express Web site of the journal Science, California Institute of Technology astronomer Jean-Luc Margot and his co-authors report detailed information on the near-Earth asteroid currently assigned the rather unpoetic name 2000 DP107, and also on four other binary asteroids. 2000 DP107 comprises two bodies that are about three kilometers apart, the larger of the two being about 800 meters in diameter and the other about 300 meters. Using particularly detailed radar data, the study is a description of the system and explains how both these particular bodies and near-Earth binaries in general can be formed.

Near-Earth asteroids were formed between Mars and Jupiter, like all other asteroids, but are kicked into elliptical orbits by the gravitational influence of Jupiter and occasionally pass near Earth. An Earth-crossing orbit is one in which the asteroid actually crosses the path that Earth follows around the sun, which means the two bodies could eventually collide.

Margot, a postdoctoral researcher in the Division of Geology and Planetary Science at Caltech, led the observations in October 2000 that uncovered 2000 DP107's binary nature, just months after the asteroid was first discovered by MIT researchers. The current study, of which Margot is lead author, employs data obtained from the 70-meter Goldstone NASA tracking telescope and the Arecibo Observatory's radio telescope in Puerto Rico, which is funded by the National Science Foundation with additional support from NASA and operated by Cornell University, to yield a much more detailed picture of the two orbiting bodies and their dynamics.

Other details from the radar data show that the two bodies are probably in a tidal lock, which means that a person standing on the larger body would always see the same face of the smaller body, but a person on the smaller body would see the larger body spinning. This is exactly like the tidal lock of the Earth-moon system.

Further, the research suggests that the tidal force applied to an asteroid by a larger planet can be the cause of its breaking apart. The process, known as "spin and fission," means that a body approaching Earth is made to change its spin rate. Specifically, the tidal force tends to make an asteroid passing nearby spin at the orbital rate, which can increase rather substantially in a close approach to a planet. This increase in spin rate, coupled with the tidal pull itself, can cause a loosely-bound, gravel-like accumulation such as the near-Earth asteroids, to sling off material. Later, the weak gravitational attraction of the particles allows the material to reform in a second body.

But the most important issue raised by the paper is that near-Earth binaries are so common, says Jet Propulsion Laboratory researcher Steve Ostro, one of the authors. "The discovery of the existence and substantial abundance of binary asteroids in Earth-crossing orbits is a major one," says Ostro, an expert on the radar characterization of asteroids. "Presumably, binary asteroids have hit Earth in the past, and will do so in the future."

"Of course, the most important thing to know about any (potentially hazardous asteroid) is whether it is two objects or one, and this is why we want to observe these binaries with radar whenever possible."

"The use of radar allows precise measurements of asteroid densities, a very important indicator of their composition and internal structure," says Margot.

"Getting (near-Earth asteroid) densities from radar is dirt-cheap compared with getting a density with a spacecraft," Ostro explains.

In addition to Margot and Ostro, the other authors are Michael Nolan of the Arecibo Observatory; Lance Benner, Raymond Jurgens, Jon Giorgini, and Martin Slade, all of JPL; and Donald Campbell of Cornell University.

The article will be available Thursday on the Science Express Web site at http://www.scienceexpress.org.

Contact: Robert Tindol (626) 395-3631

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RT

Caltech scientists demonstratecompact silica laser

A team of applied physicists at the California Institute of Technology have demonstrated an ultrasmall Raman laser that is 1,000 times more efficient than previous devices. The device could have significant applications for telecommunications and other areas where compact, highly efficient, and tunable lasers are desirable.

Reporting in the February 7 issue of the journal Nature, Caltech applied physics professor Kerry Vahala and graduate students Sean Spillane and Tobias Kippenberg describe their progress in making the tiny device, which incorporates a small spherical glass bead and a stretched fiber-optic wire. The laser is especially efficient because of the way it stores light inside the microsphere, or resonator, as well as the manner in which the stretched optical wire permits efficient coupling of light into the sphere.

According to Vahala, the light wraps around the sphere in a ring orbit and subsequently intensifies over hundreds of thousands of orbits, resulting in extreme concentration of optical power within the sphere. In this way, very weak signals applied to the sphere from the fiber-optic wire can build to enormous intensities within the sphere itself.

At these higher power levels, the physics within the sphere enters a nonlinear regime wherein conventional rules for light propagation break down. In the Caltech work, the molecules of the glass bead itself are distorted, resulting in a process called Raman emission and lasing. Because Raman lasers require enormous intensities to function, they are usually power-hungry devices. The Caltech team uses the physics of the sphere to reduce both power and size. Normal Raman lasers turn on "with a shout"—these new devices require "only a whisper."

Central to this breakthrough was the ability to couple directly to the ring orbits, or whispering gallery modes, of the sphere while preserving the exquisite perfection of the sphere in terms of its ability to store and concentrate light. The Caltech team uses stretched optical fiber in the form of a taper to achieve coupling efficiencies, in which loss is negligible, both to and from the sphere.

Because Raman lasers and amplifiers can operate over a very broad range of wavelengths, they are important devices that extend other lasers into new or previously inaccessible wavelength bands. For example, Raman amplifiers are now used widely in commercial long-distance fiber communications systems because of this wavelength flexibility.

Also, through a process called cascading, it is possible to cover even greater wavelength bands by using one Raman laser as the pump for another. In this way, a whole series of wavelengths can be generated in a kind of domino effect. More generally, it can be used to extend the wavelength range of other laser sources into difficult-to-access wavelength bands for sensing or other purposes.

The article is titled "Ultralow-threshold Raman laser using a spherical dielectric microcavity," and is available at www.nature.com.

In the photo, the sphere has been doped, which enables observation of the ring orbit as green luminescence. The photo is by M. Cai of Vahala group.

Further discussion of this and related work can be found at the Vahala Caltech group website: www.its.caltech.edu/~vahalagr.

CONTACT: Robert Tindol (626) 395-3631

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RT

First gamma burst detected by new NASA satellite is pinpointed at Palomar Observatory

Astrophysicists have combined the Palomar Mountain 200-inch Hale Telescope with the abilities of a new NASA satellite to detect and characterize a gamma-ray burst lying at a distance of only 5 billion light-years from Earth. This is the closest gamma-ray burst ever studied by optical telescopes.

The origin of cosmic gamma-ray bursts, spectacular flashes of high-energy radiation followed by slowly decaying optical and radio emission that can be seen from great distances, is still a puzzle to astronomers. Many scientists believe that the bursts result from explosions that signal the birth of black holes; however, all agree that more data are needed before we can really know black holes' origins and nature.

NASA's new High-Energy Transient Explorer (HETE) detected a gamma-ray burst on September 21. Data indicated that the event was located in the Lacerta constellation, and refined information from the Interplanetary Network (IPN), a series of satellites with gamma-ray detectors scattered about the solar system, reduced the region astronomers needed to search to find the fading embers of the explosion. Scientists at the California Institute of Technology's Palomar Observatory, using the historic Hale 200-inch reflector, were able to locate the visual afterglow the following day. This was the first burst from the HETE satellite to be pinpointed with an accuracy sufficient to study the remains.

On October 17 the Caltech team used the Hale Telescope to obtain a redshift for the burst. This allowed a distance to be inferred, implying that the burst happened some 5 billion years ago. This makes the burst one of the closest ever found, and thus easier to study in detail. Also on October 17 the team members, led by Dale Frail from the National Radio Astronomy Observatory, detected a twinkling radio counterpart of the burst using the Very Large Array in New Mexico.

According to Shri Kulkarni, who is the MacArthur Professor of Astronomy and Planetary Science at Caltech, the team was able to find the rare optical afterglow because of the quick detection and localization abilities of the HETE satellite and the rapid follow-up with the Palomar Mountain Hale Telescope.

HETE, the first satellite dedicated to the study of gamma-ray bursts, is on an extended mission until 2004. Launched on October 9, 2000, HETE was built by MIT as a mission of opportunity under the NASA Explorer Program. The HETE program is a collaboration between MIT; NASA; Los Alamos National Laboratory, New Mexico; France's Centre National d'Etudes Spatiales, Centre d'Etude Spatiale des Rayonnements, and Ecole Nationale Superieure del'Aeronautique et de l'Espace; and Japan's Institute of Physical and Chemical Research. The science team includes members from the University of California (Berkeley and Santa Cruz) and the University of Chicago, as well as from Brazil, India, and Italy.

"I'm very excited. I could not sleep for two nights after making the discovery," said Paul Price, the Caltech graduate student who first identified the optical afterglow from Palomar.

"With this first confirmed observation of a gamma-ray burst and its afterglow, we've really turned the corner," said George Ricker of the Massachusetts Institute of Technology, principal investigator for HETE. "As HETE locates more of these bursts and reports them quickly, we will begin to understand what causes them.

"The unique power of HETE is that it not only detects a large sample of these bursts, but it also relays the accurate location of each burst in real time to ground-based optical and radio observatories," Ricker said.

Because the enigmatic bursts disappear so quickly, scientists can best study the events by way of their afterglow. HETE detects these bursts as gamma rays or high-energy X rays, and then instantly relays the coordinates to a network of ground-based and orbiting telescopes for follow-up searches for such afterglows.

Additional observations of this event, made with the Italian BeppoSAX satellite and the Ulysses space probe, were coordinated by HETE team member Kevin Hurley at the University of California. The combination of the localization by the Interplanetary Network with the original HETE localization provided the refined information needed by ground-based observers to point their optical telescopes.

The opportunity to see the afterglow in optical light provides crucial information about what is triggering these mysterious bursts, which scientists speculate to be the explosion of massive stars, the merging of neutron stars and black holes, or possibly both. Follow-up observations of GRB 010921 using the Hubble Space Telescope and the telescopes on the ground should move us a few steps closer to the answer of this cosmic puzzle.

The team that identified the counterpart to GRB010921 includes—in addition to Caltech Professors Shri Kulkarni, Fiona Harrison, and S. George Djorgovski—postdoctoral fellows and scholars Re'em Sari, Titus Galama, Daniel Reichart, Derek Fox, and Ashish Mahabal, graduate students Joshua Bloom, Paul Price, Edo Berger, and Sara Yost, Dale Frail from the National Radio Astronomy Observatory, and many other collaborators.

More information on HETE can be found at: http://space.mit.edu/HETE Palomar Observatory: http://www.astro.caltech.edu/palomar/ Caltech Media Relations: http://pr.caltech.edu/media/.

Writer: 
Robert Tindol
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Physicist Awarded Prize for Development of Superstring Theory

PASADENA, Calif.—A theoretical physicist's research lab consists of little more than a chalkboard and chalk, a world of knotty mathematical equations that seek to explain why our physical world is the way it is.

For his pioneering work in the development of one such possible explanation, known as superstring theory, John Schwarz, the Harold Brown Professor of Theoretical Physics at the California Institute of Technology, has been awarded the 2002 Dannie Heineman Prize for Mathematical Physics. The prize is awarded annually by the American Physical Society and the American Institute of Physics for, "valuable published contributions made in the field of mathematical physics." Schwarz is sharing the award with Dr. Michael B. Green of the University of Cambridge.

String theory evolved in the 1970s in an attempt to provide one all-encompassing framework that would explain the nature of nature—everything from the macro level of the cosmos to the micro level of subatomic particles (particles hundreds of times smaller than the nucleus of an atom). Further, it incorporated all the forces of nature (such as gravity) that affect the basic structure of the world.

With string theory, physicists take a different view of the fundamental units of matter. When combined, these smallest building blocks create all the physical things we see. Instead of viewing them as infinitesimally tiny points in space, though, string theorists view them as tiny, one-dimensional, stringlike bits of matter that vibrate. They are not ordinary strings, but they behave in ways that can be described mathematically, by equations that also account for two other physical laws of nature, relativity and quantum mechanics. (In a similar vein, mathematicians can write equations to describe the patterns of vibration that produce different notes from the string of a guitar; thus the term "string theory.") Each pattern of vibration of the string corresponds to a different particle of matter.

But by the late 1970s interest in string theory had faded after a number of predictions it made conflicted with the results of experiments. Most physicists therefore abandoned the theory.

But not Schwarz, Green, and a handful of others. Schwarz, for one, stuck to his guns, saying at the time that "the mathematical structure of string theory was so beautiful and had so many miraculous properties that it had to be pointing toward something deep."

In 1984, Schwarz and Green published a landmark paper that was based on more than 12 years of research. In it, they found a way to resolve these conflicts, by suggesting, among other things, that more dimensions may exist in our world then the three—height, width, and depth—we are familiar with.

Instead, they suggested a mathematical theory that included 10 dimensions. It's a world we can't experience, but that mathematically makes sense. How can we think of our world as having extra dimensions? As one physicist explained it, imagine that you can move only in two dimensions, length and width, in a big room. But the third dimension, height, isn't large like the other two but instead is curled up at each point of matter in a tiny circle, so that you don't experience it. Presumably, the additional dimensions suggested by Schwarz and Green are so small, existing at the subatomic level, that we can't experience them. However, the properties of these extra dimensions are expected to have other consequences that can be observed.

Schwarz termed this new theory superstring theory, because it incorporates a special kind of symmetry called supersymmetry. Symmetry, which is very common and important in physics, concerns the fact that equations (and sometimes nature) look the same when observed in different ways. For example, a sphere looks the same after it is rotated. Supersymmetry, which is one of the spin-offs of string theory, is a less intuitive and more quantum mechanical kind of symmetry. Their research reignited string theory, which today remains one of the hottest areas in theoretical physics. It is also the leading candidate for the elusive "theory of everything" that physicists seek. It is for this work that Schwarz and Green have been awarded the Heineman Prize.

Schwarz has worked on superstring theory for most of his professional career. In 1986 he became a Fellow of the American Physical Society. In 1987 he received a prestigious MacArthur Fellowship, and in 1997 he was elected to the National Academy of Sciences. The Dannie Heineman prize was established in 1959 to encourage further research in the field of mathematical physics. As a recipient, Schwarz joins a number of esteemed physicists, including Caltech's Murray Gell-Mann (1959) and the likes of Freeman Dyson (1965), Roger Penrose (1971), and Stephen Hawking (1977). The prize was established by the Heineman Foundation for Research, Educational, Charitable, and Scientific Purposes, Inc., and is administered jointly by the American Physical Society (APS) and the American Institute of Physics.

The prize will be awarded at the April 2002 APS meeting to be held in Albuquerque, New Mexico.

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International team uses powerful cosmic lensto find galactic building block in early universe

Exploiting a phenomenon known as gravitational lensing, an international team of astrophysicists has detected a very small, faint stellar system in the process of its formation during the first half billion years or so of the universe's existence.

The discovery is being reported in the October 20 issue of the Astrophysical Journal. According to lead author Richard Ellis, a professor of astronomy at the California Institute of Technology, the faint object is an excellent candidate for the long sought after "building blocks" thought to be abundant at early times and which later assembled to make present-day galaxies.

The discovery was made possible by examining small areas of sky viewed through a massive intervening cluster of galaxies, Abell 2218, 2 billion light-years away. The cluster acts as a powerful gravitational lens, magnifying distant objects and allowing the scientists to probe how distant galaxies assembled at very early times.

Gravitational lensing, a dramatic feature of Einstein's theory of general relativity, means that a massive object in the foreground bends the light rays radiating from one in the background because mass curves space. As a result, an object behind a massive foreground galaxy cluster like Abell 2218 can look much brighter because the foreground object has bent additional photons toward Earth, in much the same way that glass lenses in binoculars will bend more photons toward the eyes.

In the case of the system detected by Ellis and coworkers, the effect makes the image at least 30 times brighter than would be the case if the Abell 2218 cluster were not in the foreground. Without this boost, neither the Keck 10-meter Telescopes nor the Hubble Space Telescope would have detected the object.

Ellis explains, "Without the benefit of the powerful cosmic lens, the intriguing source would not even have been detected in the Hubble Deep Fields, historic deep exposures taken in 1995 and 1998."

Using the 10-meter Keck Telescopes at Mauna Kea, the collaboration found a faint signal corresponding to a pair of feeble images later recognized in a deep Hubble Space Telescope picture.

Spectroscopic studies made possible with the superior light-gathering power of the Keck confirmed that the images arise via the magnification of a single source diagnosed to be extremely distant and in the process of formation.

"The system contains about a million or so stars at a distance of 13.4 billion light-years, assuming that the universe is 14 billion years old," claims Ellis. "While more distant galaxies and quasars have been detected with the Keck Telescopes, by virtue of the magnification afforded by the foreground cosmic lens, we are witnessing a source much smaller than a normal galaxy forming its first generation of stars." " Our work is a little like studying early American history," says team member Mike Santos, a Caltech graduate student in astronomy. "But instead of focusing on prominent individuals like George Washington, we want to know how everyday men and women lived.

"To really understand what was going on in the early universe, we need to learn about the typical, commonplace building blocks, which hold important clues to the later assembly of normal galaxies. Our study represents a beginning to that understanding."

The precise location of the pair of images in relation to the lensing cluster allowed the researchers to confirm the magnification. This work was the contribution of team member Jean-Paul Kneib of the Observatoire Midi-Pyrénées near Toulouse, France, an expert in the rapidly developing field of gravitational lensing.

The team concludes that the star system is remarkably young (by cosmic standards) and thus may represent the birth of a subcomponent of a galaxy or "building block." Such systems are expected to have been abundant in the early universe and to have later assembled to form mature large galaxies like our own Milky Way.

Santos explains, "The narrow distribution of intensity observed with the Keck demonstrates we are seeing hydrogen gas heated by newly formed stars. But, crucially, there is not yet convincing evidence for a well-established mixture of stars of different ages. This suggests we are seeing the source at a time close to its formation."

In their article, the researchers infer that the stars had been forming at a rate of one solar mass per year for not much longer than a million years. Such a structure could represent the birth of a globular cluster, stellar systems recognized today to be the oldest components of the Milky Way galaxy. The work represents part of an ongoing survey to determine the abundance of such distant star-forming sources as well as to fix the period in cosmic history when the bulk of these important objects formed.

Contact:Robert Tindol (626) 395-3631

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RT

Astronomers detect evidence of time when universe emerged from "Dark Ages"

Astronomers at the California Institute of Technology announced today the discovery of the long-sought "Cosmic Renaissance," the epoch when young galaxies and quasars in the early universe first broke out of the "Dark Ages" that followed the Big Bang.

"It is very exciting," said Caltech astronomy professor S. George Djorgovski, who led the team that made the discovery. "This was one of the key stages in the history of the universe."

According to a generally accepted picture of modern cosmology, the universe started with the Big Bang some 14 billion years ago, and was quickly filled with glowing plasma composed mainly of hydrogen and helium.

As the universe expanded and cooled over the next 300,000 years, the atomic nuclei and electrons combined to make atoms of neutral gas. The glow of this "recombination era" is now observed as the cosmic microwave background radiation, whose studies have led to the recent pathbreaking insights into the geometrical nature of the universe.

The universe then entered the Dark Ages, which lasted about half a billion years, until they were ended by the formation of the first galaxies and quasars. The light from these new objects turned the opaque gas filling the universe into a transparent state again, by splitting the atoms of hydrogen into free electrons and protons. This Cosmic Renaissance is also referred to by cosmologists as the "reionization era," and it signals the birth of the first galaxies in the early universe.

"It is as if the universe was filled by a dark, opaque fog up to that time," explains Sandra Castro, a postdoctoral scholar at Caltech and a member of the team. "Then the fires—the first galaxies—lit up and burned through the fog. They made both the light and the clarity."

The researchers saw the tell-tale signature of the cosmic reionization in the spectra of a very distant quasar, SDSS 1044-0125, discovered last year by the Sloan Digital Sky Survey (SDSS). Quasars are very luminous objects in the distant universe, believed to be powered by massive black holes.

The spectra of the quasar were obtained at the W. M. Keck Observatory's Keck II 10-meter telescope atop Mauna Kea, Hawaii. The spectra show extended dark regions, caused by opaque gas along the line of sight between Earth and the quasar. This effect was predicted in 1965 by James Gunn and Bruce Peterson, both then at Caltech. Gunn, now at Princeton University, is the leader of the Sloan Digital Sky Survey; Peterson is now at Mt. Stromlo and Siding Spring observatories, in Australia.

The process of converting the dark, opaque universe into a transparent, lit-up universe was not instantaneous: it may have lasted tens or even hundreds of millions of years, as the first bright galaxies and quasars were gradually appearing on the scene, the spheres of their illumination growing until they overlapped completely.

"Our data show the trailing end of the reionization era," says Daniel Stern, a staff scientist at the Jet Propulsion Laboratory and a member of the team. "There were opaque regions in the universe back then, interspersed with bubbles of light and transparent gas."

"This is exactly what modern theoretical models predict," Stern added. "But the very start of this process seems to be just outside the range of our data."

Indeed, the Sloan Digital Sky Survey team has recently discovered a couple of even more distant quasars, and has reported in the news media that they, too, see the signature of the reionization era in the spectra obtained at the Keck telescope.

"It is a wonderful confirmation of our result," says Djorgovski. "The SDSS deserves much credit for finding these quasars, which can now be used as probes of the distant universe—and for their independent discovery of the reionization era."

"It is a great example of a synergy of large digital sky surveys, which can discover interesting targets, and their follow-up studies with large telescopes such as the Keck," adds Ashish Mahabal, a postdoctoral scholar at Caltech and a member of the team. "This is the new way of doing observational astronomy: the quasars were found by SDSS, but the discovery of the reionization era was done with the Keck."

The Caltech team's results have been submitted for publication in the Astrophysical Journal Letters, and will appear this Tuesday on the public electronic archive, http://xxx.lanl.gov/list/astro-ph/new.

The W. M. Keck Observatory is a joint venture of Caltech, the University of California, and NASA, and is made possible by a generous gift from the W. M. Keck Foundation.

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Robert Tindol
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