Monday, October 19, 2015 to Friday, October 23, 2015

TeachWeek Caltech

Wednesday, October 21, 2015
Keck Center

Engaging Students Beyond Their Field

Tuesday, October 21, 2014
Keck Center

Engaging Students Beyond Their Field

Thursday, October 22, 2015

Confessions of a Converted Lecturer: TeachWeek Keynote by Eric Mazur

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Advanced LIGO to Begin Operations

The Advanced LIGO begins operations this week, after 7 years of enhancement.

The Advanced LIGO Project, a major upgrade of the Laser Interferometer Gravitational-Wave Observatory, is completing its final preparations before the initiation of scientific observations, scheduled to begin in mid-September. Designed to observe gravitational waves—ripples in the fabric of space and time—LIGO, which was designed and is operated by Caltech and MIT with funding from the National Science Foundation (NSF), consists of identical detectors in Livingston, Louisiana, and Hanford, Washington.

"The LIGO scientific and engineering team at Caltech and MIT has been leading the effort over the past seven years to build Advanced LIGO, the world's most sensitive gravitational-wave detector," says David Reitze, the executive director of the LIGO program at Caltech. Groups from the international LIGO Scientific Collaboration also contributed to the design and construction of the Advanced LIGO detector.

Gravitational waves were predicted by Albert Einstein in 1916 as a consequence of his general theory of relativity, and are emitted by violent events in the universe such as exploding stars and colliding black holes. These waves carry information not only about the objects that produce them, but also about the nature of gravity in extreme conditions that cannot be obtained by other astronomical tools.

"Experimental attempts to find gravitational waves have been on going for over 50 years, and they haven't yet been found. They're both very rare and possess signal amplitudes that are exquisitely tiny," Reitze says.

Although earlier LIGO runs revealed no detections, Advanced LIGO, also funded by the NSF, increases the sensitivity of the observatories by a factor of 10, resulting in a thousandfold increase in observable candidate objects. "The first Advanced LIGO science run will take place with interferometers that can 'see' events more than three times further than the initial LIGO detector," adds David Shoemaker, the MIT Advanced LIGO project leader, "so we'll be probing a much larger volume of space."

Each of the 4-kilometer-long L-shaped LIGO interferometers uses a laser beam split into two beams that travel back and forth through the long arms, within tubes from which the air has been evacuated. The beams are used to monitor the distance between precisely configured mirrors. According to Einstein's theory, the relative distance between the mirrors will change very slightly when a gravitational wave passes by.

The original configuration of LIGO was sensitive enough to detect a change in the lengths of the 4-kilometer arms by a distance one-thousandth the diameter of a proton; this is like accurately measuring the distance from Earth to the nearest star—over four light-years—to within the width of a human hair. Advanced LIGO, which will utilize the infrastructure of LIGO, is much more powerful.

While earlier LIGO observing runs did not confirm the existence of gravitational waves, the influence of such waves has been measured indirectly via observations of a binary system called PSR B1913+6. The system consists of two objects, both neutron stars—the compact cores of dead stars—that orbit a common center of mass. The orbits of these two stellar bodies have been observed to be slowly contracting due to the energy that is lost to gravitational radiation. Binary star systems such as these that are in the very last stages of evolution—just before and during the inevitable collision of the two objects—are key targets of the planned observing schedule for Advanced LIGO.

"Ultimately, Advanced LIGO will be able to see 10 times as far as initial LIGO and, based on theoretical predictions, should detect many binary neutron star mergers per year," Reitze says.

The improved instruments will be able to look at the last minutes of the life of pairs of massive black holes as they spiral closer together, coalesce into one larger black hole, and then vibrate much like two soap bubbles becoming one. Advanced LIGO also will be able to pinpoint periodic signals from the many known pulsars that radiate in the range of 10 to 1,000 Hertz (frequencies that roughly correspond to low and high notes on an organ). In addition, Advanced LIGO will be used to search for the gravitational cosmic background, allowing tests of theories about the development of the universe only 10-35 seconds after the Big Bang.

"We expect it will take five years to fully optimize the detector performance and achieve our design sensitivity," Reitze says. "It has been a long road, and we're very excited to resume the hunt for gravitational waves."

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Farthest Galaxy Detected

Caltech astronomers detect the farthest galaxy yet with Keck telescope.

A team of Caltech researchers that has spent years searching for the earliest objects in the universe now reports the detection of what may be the most distant galaxy ever found. In an article published August 28, 2015 in Astrophysical Journal LettersAdi Zitrin, a NASA Hubble Postdoctoral Scholar in Astronomy, and Richard Ellis—who recently retired after 15 years on the Caltech faculty and is now a professor of astrophysics at University College, London—describe evidence for a galaxy called EGS8p7 that is more than 13.2 billion years old. The universe itself is about 13.8 billion years old.

Earlier this year, EGS8p7 had been identified as a candidate for further investigation based on data gathered by NASA's Hubble Space Telescope and the Spitzer Space Telescope. Using the multi-object spectrometer for infrared exploration (MOSFIRE) at the W.M. Keck Observatory in Hawaii, the researchers performed a spectrographic analysis of the galaxy to determine its redshift. Redshift results from the Doppler effect, the same phenomenon that causes the siren on a fire truck to drop in pitch as the truck passes. With celestial objects, however, it is light that is being "stretched" rather than sound; instead of an audible drop in tone, there is a shift from the actual color to redder wavelengths.

Redshift is traditionally used to measure distance to galaxies, but is difficult to determine when looking at the universe's most distant—and thus earliest—objects. Immediately after the Big Bang, the universe was a soup of charged particles—electrons and protons—and light (photons). Because these photons were scattered by free electrons, the early universe could not transmit light. By 380,000 years after the Big Bang, the universe had cooled enough for free electrons and protons to combine into neutral hydrogen atoms that filled the universe, allowing light to travel through the cosmos. Then, when the universe was just a half-billion to a billion years old, the first galaxies turned on and reionized the neutral gas. The universe remains ionized today.

Prior to reionization, however, clouds of neutral hydrogen atoms would have absorbed certain radiation emitted by young, newly forming galaxies—including the so-called Lyman-alpha line, the spectral signature of hot hydrogen gas that has been heated by ultraviolet emission from new stars, and a commonly used indicator of star formation.

Because of this absorption, it should not, in theory, have been possible to observe a Lyman-alpha line from EGS8p7.

"If you look at the galaxies in the early universe, there is a lot of neutral hydrogen that is not transparent to this emission," says Zitrin. "We expect that most of the radiation from this galaxy would be absorbed by the hydrogen in the intervening space. Yet still we see Lyman-alpha from this galaxy."

They detected it using the MOSFIRE spectrometer, which captures the chemical signatures of everything from stars to the distant galaxies at near-infrared wavelengths (0.97-2.45 microns, or millionths of a meter).

"The surprising aspect about the present discovery is that we have detected this Lyman-alpha line in an apparently faint galaxy at a redshift of 8.68, corresponding to a time when the universe should be full of absorbing hydrogen clouds," Ellis says. Prior to their discovery, the farthest detected galaxy had a redshift of 7.73.

One possible reason the object may be visible despite the hydrogen-absorbing clouds, the researchers say, is that hydrogen reionization did not occur in a uniform manner. "Evidence from several observations indicate that the reionization process probably is patchy," Zitrin says. "Some objects are so bright that they form a bubble of ionized hydrogen. But the process is not coherent in all directions."

"The galaxy we have observed, EGS8p7, which is unusually luminous, may be powered by a population of unusually hot stars, and it may have special properties that enabled it to create a large bubble of ionized hydrogen much earlier than is possible for more typical galaxies at these times," says Sirio Belli, a Caltech graduate student who worked on the project.

"We are currently calculating more thoroughly the exact chances of finding this galaxy and seeing this emission from it, and to understand whether we need to revise the timeline of the reionization, which is one of the major key questions to answer in our understanding of the evolution of the universe," Zitrin says.

The paper "Lyman α Emission from a Luminous z = 8.68 Galaxy: Implications for Galaxies as Tracers of Cosmic Reionization" was co-authored by Ivo Labbe, Rychard Bouwens, Guido Roberts-Borsani, Daniel P. Stark, Pascal A. Oesch, and Renske Smit. The research was sponsored by NASA through a Hubble Fellowship, the Institute of Astronomy at the University of Edinburgh, and the National Science Foundation. MOSFIRE was made possible by funding provided by the National Science Foundation and astronomy benefactors Gordon and Betty Moore. Cooperating institutions include Yale University, the University of Arizona, University College London, Leiden University (Netherlands), and the University of Durham (UK).

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After a Half Century, the Exotic Pentaquark Particle is Found

In July, scientists at the Large Hadron Collider (LHC) reported the discovery of the pentaquark, a long-sought particle first predicted to exist in the 1960s as a consequence of the theory of elementary particles and their interactions proposed by Murray Gell-Mann, Caltech's Robert Andrews Millikan Professor of Theoretical Physics, Emeritus.

In work for which he won the Nobel Prize in Physics in 1969, Gell-Mann introduced the concept of the quark—a fundamental building block of matter. Quarks come in six types, known as "flavors": up, down, top, bottom, strange, and charm. As described in his model, groups of quarks combine into composite particles called hadrons. Combining a quark and an antiquark (a quark's antimatter equivalent) creates a type of hadron called a meson, while baryons are hadrons composed of three quarks. Protons, for example, have two up quarks and one down quark, while neutrons have one up and two down quarks. Gell-Mann's scheme also allowed for more exotic forms of composite particles, including tetraquarks, made of four quarks, and the pentaquark, consisting of four quarks and an antiquark.

The pentaquark was detected at the LHC—the most powerful particle accelerator on Earth—by scientists carrying out the "beauty" experiment, or LHCb. The LHC accelerates protons around a ring almost five miles wide to nearly the speed of light, producing two proton beams that careen toward each other. A small fraction of the protons collide, creating other particles in the process. During investigations of the behavior of one such particle, an unstable three-quark object known as the bottom lambda baryon that decays quickly once formed, LHCb researchers observed unusually heavy objects, each with about 4.5 times the mass of a proton. After further analysis, the researchers concluded that the objects were pentaquarks composed of two up quarks, one down quark, one charm quark, and one anticharm quark. A paper describing the discovery has been published in the journal Physical Review Letters.

It is thought that pentaquarks and other exotic particles may form naturally in violent environments such as exploding stars and would have been created during the Big Bang. A better understanding of these complex arrangements of quarks could offer insight into the forces that hold together all matter as well as the earliest moments of the universe.

"This is part of a long process of discovery of particle states," said Gell-Mann in a statement released by the Santa Fe Institute, where he currently is a Distinguished Fellow. "[In the future] they may find more and more of them, made of quarks and antiquarks and various combinations."

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Physicist Charles A. Barnes Dies

1921–2015

Charles A. Barnes, professor of physics, emeritus, at Caltech and an expert in the study of both the weak nuclear force—one of the fundamental forces of nature—and of the nuclear reactions that produce the majority of the elements in our universe, passed away on Friday, August 14, 2015. He was 93.

"Caltech was the place at which nuclear astrophysics was invented, and Charlie made many fundamental contributions in this field," says Fiona Harrison, the Kent and Joyce Kresa Leadership Chair of Caltech's Division of Physics, Mathematics and Astronomy and Benjamin Rosen Professor of Physics.

Born on December 12, 1921, in Toronto, Canada, Barnes received his bachelor of arts degree in physics and mathematics from McMaster University in 1943 and his master of arts degree in physics from the University of Toronto in 1944. He earned a doctorate in physics from the University of Cambridge in 1950. He came to Caltech as a research fellow in 1953 and became a senior research fellow in 1954, an associate professor in 1958, and a professor in 1962. Barnes retired in 1992.

Barnes was a fellow of the American Physical Society and the American Association for the Advancement of Science.

An experimental physicist who specialized in nuclear physics, Barnes performed pioneering research in two key areas. The first was in the study of the so-called nuclear weak force, which governs the radioactive decay of elements and is responsible for the fusion of protons to form deuterium. This fusion releases the energy that is the source of heat from our sun and other stars.

During the 1960s and 70s, in experiments using the particle accelerators in the basements of Caltech's Kellogg Radiation Laboratory and Alfred P. Sloan Laboratory of Mathematics and Physics, Barnes studied the breakdown of "mirror symmetry" in the weak force, the phenomenon that causes an experiment and its mirror experiment to give different results. "This is a surprising and novel feature of the weak nuclear force," says Caltech professor of physics Bradley W. Filippone.

Barnes was also an expert in nucleosynthesis, the formation of new atomic nuclei from simpler ones, a process that occurs on a cosmic scale in the cores of stars.  

"He is probably best known for his nucleosynthesis studies of the nuclear reaction that produces oxygen from carbon and helium," says Filippone. In 1974, Barnes and his student Peggy Dyer (PhD '73) performed the first careful measurement of this reaction. Over the next two decades, in collaboration with Filippone and others, Barnes improved upon the measurement; their work culminated in a precision measurement at TRIUMF, Canada's national laboratory for particle and nuclear physics, in 1993. This reaction rate was called "a problem of paramount importance" by Caltech's William A. Fowler, co-winner of the 1983 Nobel Prize in Physics for his research into the creation of chemical elements inside stars, in his Nobel address. Through his work, Barnes provided critical input in determining the final distribution of the chemical elements produced in stars—and whether the final fate of a star is to become a black hole or some other celestial object, such as a neutron star.

In addition to his scientific achievements, Barnes will be remembered fondly for his support of young scientists. "He was a superb mentor to young scientists—including me—providing encouragement, enthusiasm, and great ideas to a generation of nuclear physicists studying both the weak nuclear force as well as nuclear reactions that occur in stars," says Filippone.

"Charlie was still active when I came to Caltech, and I remember conversations with him about signatures we could look for to identify how rare chemical elements are manufactured in the universe," Harrison says.

"Charlie was a wonderful person, scientist, and collaborator," says George L. Argyros Professor of Chemistry Nate Lewis (BS '77, MS '77), who worked with Barnes during the late 1980s. "He was thorough, scholarly, and curious, and a shining example of the best qualities in a long tradition of truly world-class experimental nuclear physicists at Caltech."

Barnes was predeceased by his wife of six decades, Phyllis, who passed away on August 12, 2013. He is survived by his son, Steven Barnes, and his daughter, Nancy Wetherow; by four grandchildren; and by two great-grandchildren.

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Caltech Theoretical Physicist Receives the 2015 Dirac Medal and Prize

Alexei Kitaev, the Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics, has been awarded the 2015 Dirac Medal and Prize from the Abdus Salam International Centre for Theoretical Physics (ICTP). The prize, named after the esteemed theoretical physicist and Nobel Laureate Paul Dirac, is one of the most prestigious honors in theoretical physics. This year it was awarded jointly to Kitaev, Gregory W. Moore of Rutgers University, and Nicholas Read of Yale University for their work on condensed matter research.

The work of Kitaev, Moore, and Read has "played a fundamental role in recent advances in our understanding of the quantum states of matter and quantum entanglement theory," according to the ICTP's press release.

Kitaev is cited for proposing an innovative method of computation, called topological quantum computation, which builds upon Moore and Read's theory of non-Abelian anyons. Anyons are special quasiparticles that exist under the conditions of the fractional quantum Hall effect (FQHE). The FQHE is observed in semiconductor structures that contain a thin layer of mobile electrons. When such systems are cooled to very low temperatures and immersed in a strong magnetic field, the electrons form a collective state analogous to a liquid.

"Anyons are like bubbles and lumps in that liquid, which can move around, fuse, or annihilate," Kitaev explains. "However, these quasiparticles have very strange properties: they carry a fractional electron charge and defy the textbook classification into bosons and fermions. For bosons, such as photons, switching the places of two identical particles has no effect, while for fermions like electrons or protons, the particle exchange introduces a minus sign into the calculation. Switching the places of two identical anyons results in an extra factor other than 1 or -1."

"Non-Abelian anyons are even weirder because their state is not determined by where they are spatially; there is also some hidden state in the liquid between them. Exchanging two particles or moving one around the other alters that state."

As part of his proposed method of topological quantum computation, Kitaev suggested that using this hidden state as a quantum computer memory could make such computation more stable and error proof.

"Kitaev's work on fault-tolerant quantum computation using topological quantum phases with non-Abelian quasiparticles has had profound implications in quantum information theory," the award citation notes.

Caltech faculty who have previously been awarded the Dirac Medal are John H. Schwarz, the Harold Brown Professor of Theoretical Physics, Emeritus, in 1989; and John Hopfield, the Roscoe G. Dickinson Professor of Chemistry and Biology, Emeritus, in 2001.

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High School Students Visit for Women in STEM Preview Day

On Friday, August 7, 104 female high school seniors and their families visited Caltech for the fourth annual Women in STEM (WiSTEM) Preview Day, hosted by the undergraduate admissions office. The event was designed to explore the accomplishments and continued contributions of Caltech women in the disciplines of science, technology, engineering, and mathematics (STEM).

The day opened with a keynote address by Marianne Bronner, the Albert Billings Ruddock Professor of Biology and executive officer for neurobiology. Bronner, who studies the development of the central nervous system, spoke about her experiences in science and at Caltech.

"Caltech is an exciting place to be. It's a place where you can be creative and think outside the box," she said. "My advice to you would be to try different things, play around, and do what makes you happy." Bronner ended her address by noting the pleasure she takes in mentoring young scientists, and especially young women. "I was just like you," she said.

Over the course of the day, students and their families attended panels on undergraduate research opportunities and participated in social events where current students shared their experiences of Caltech life. They also listened to presentations from female scientists and engineers of the Jet Propulsion Laboratory.

"I really love science, and it's so exciting to be around all of these other people who share that," says Sydney Feldman, a senior from Maryland. "I switched around my whole summer visit schedule to come to this event and I'm having such a great time."

The annual event began four years ago with the goal of encouraging interest in STEM in high school women and ultimately increasing applications to Caltech by female candidates. In 2009, a U.S. Department of Commerce study showed that women make up 24 percent of the STEM workforce and hold a disproportionately low share of undergraduate degrees in STEM fields.

"Women are seriously underrepresented in these fields," says Caltech admissions counselor and WiSTEM coordinator Abeni Tinubu. "Our event really puts emphasis on how Caltech supports women on campus, and we want to show prospective students that."

This year, the incoming freshman class is a record 47 percent female students. "This is hugely exciting," says Jarrid Whitney, the executive director of admissions and financial aid. "We've been working hard toward our goal of 50 percent women, and it is clearly paying off thanks to the support of President Rosenbaum and the overall Caltech community."

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