Tuesday, October 20, 2015 to Wednesday, October 21, 2015
Center for Student Services 360 (Workshop Space) – Center for Student Services

Guest Consultations on Teaching, with Chris Duffy

Tuesday, October 20, 2015
Dabney Hall, Lounge – Dabney Hall

Bringing Joy into Your Teaching: A Workshop by Chris Duffy

Monday, October 19, 2015
Guggenheim 101 (Lees-Kubota Lecture Hall) – Guggenheim Aeronautical Laboratory

The Future of Teaching and Learning at Caltech: An Innovation Showcase

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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