Lopsided Star Explosion Holds the Key to Other Supernova Mysteries

New observations of a recently exploded star are confirming supercomputer model predictions made at Caltech that the deaths of stellar giants are lopsided affairs in which debris and the stars' cores hurtle off in opposite directions.

While observing the remnant of supernova (SN) 1987A, NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, recently detected the unique energy signature of titanium-44, a radioactive version of titanium that is produced during the early stages of a particular type of star explosion, called a Type II, or core-collapse supernova.

"Titanium-44 is unstable. When it decays and turns into calcium, it emits gamma rays at a specific energy, which NuSTAR can detect," says Fiona Harrison, the Benjamin M. Rosen Professor of Physics at Caltech, and NuSTAR's principal investigator.

By analyzing direction-dependent frequency changes—or Doppler shifts—of energy from titanium-44, Harrison and her team discovered that most of the material is moving away from NuSTAR. The finding, detailed in the May 8 issue of the journal Science, is the best proof yet that the mechanism that triggers Type II supernovae is inherently lopsided.

NuSTAR recently created detailed titanium-44 maps of another supernova remnant, called Cassiopeia A, and there too it found signs of an asymmetrical explosion, although the evidence in this case is not as definitive as with 1987A.

Supernova 1987A was first detected in 1987, when light from the explosion of a blue supergiant star located 168,000 light-years away reached Earth. SN 1987A was an important event for astronomers. Not only was it the closest supernova to be detected in hundreds of years, it marked the first time that neutrinos had been detected from an astronomical source other than our sun.

These nearly massless subatomic particles had been predicted to be produced in large quantities during Type II explosions, so their detection during 1987A supported some of the fundamental theories about the inner workings of supernovae.

With the latest NuSTAR observations, 1987A is once again proving to be a useful natural laboratory for studying the mysteries of stellar death. For many years, supercomputer simulations performed at Caltech and elsewhere predicted that the cores of pending Type II supernovae change shape just before exploding, transforming from a perfectly symmetric sphere into a wobbly mass made up of turbulent plumes of extremely hot gas. In fact, models that assumed a perfectly spherical core just fizzled out.

"If you make everything just spherical, the core doesn't explode. It turns out you need asymmetries to make the star explode," Harrison says.

According to the simulations, the shape change is driven by turbulence generated by neutrinos that are absorbed within the core. "This turbulence helps push out a powerful shock wave and launch the explosion," says Christian Ott, a professor of theoretical physics at Caltech who was not involved in the NuSTAR observations.

Ott's team uses supercomputers to run three-dimensional simulations of core-collapse supernovae. Each simulation generates hundreds of terabytes of results—for comparison, the entire print collection of the U.S. Library of Congress is equal to about 10 terabytes—but represents only a few tenths of a second during a supernova explosion.

A better understanding of the asymmetrical nature of Type II supernovae, Ott says, could help solve one of the biggest mysteries surrounding stellar deaths: why some supernovae collapse into neutron stars and others into a black hole to form a space-time singularity. It could be that the high degree of asymmetry in some supernovae produces a dual effect: the star explodes in one direction, while the remainder of the star continues to collapse in all other directions.

"In this way, an explosion could happen, but eventually leave behind a black hole and not a neutron star," Ott says.

The NuSTAR findings also increase the chances that Advanced LIGO—the upgraded version of the Laser Interferometer Gravitational-wave Observatory, which will begin to take data later this year—will be successful in detecting gravitational waves from supernovae. Gravitational waves are ripples that propagate through the fabric of space-time. According to theory, Type II supernovae should emit gravitational waves, but only if the explosions are asymmetrical.

Harrison and Ott have plans to combine the observational and theoretical studies of supernova that until now have been occurring along parallel tracks at Caltech, using the NuSTAR observations to refine supercomputer simulations of supernova explosions.

"The two of us are going to work together to try to get the models to more accurately predict what we're seeing in 1987A and Cassiopeia A," Harrison says.

Additional Caltech coauthors of the paper, entitled "44Ti gamma-ray emission lines from SN1987A reveal an asymmetric explosion," are Hiromasa Miyasaka, Brian Grefenstette, Kristin Madsen, Peter Mao, and Vikram Rana. The research was supported by funding from NASA, the French National Center for Space Studies (CNES), the Japan Society for the Promotion of Science, and the Technical University of Denmark.

This article also references the paper "Magnetorotational Core-collapse Supernovae in Three Dimensions," which appeared in the April 20, 2014, issue of Astrophysical Journal Letters.

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Searching for Vibrations from the Big Bang

Watson Lecture Preview

For a brief instant after the Big Bang, the universe went through a period of rapid expansion during which space itself was flung apart faster than the speed of light. This "inflationary epoch" sowed the gravitational seeds that formed galaxies and clusters of galaxies. Its echoes linger as fluctuations imprinted on the so-called cosmic microwave background radiation—the Big Bang's glow, which pervades the universe today.

For the last 15 years, James J. (Jamie) Bock, a professor of physics at Caltech and a senior research scientist at JPL, has been searching for a distinctive polarization pattern in the background that gravitational waves from the epoch of inflation may have produced. At 8 p.m. on Wednesday, May 6, 2015, in Caltech's Beckman Auditorium, Bock will discuss how this hunt has led to instruments at the South Pole, on stratospheric balloons, and in outer space. Admission is free.

 

Q: What do you do?

A: I study the early universe empirically, which is often a good approach in a field where we continue to make discoveries driven by new data. My lab builds experiments that address a particular problem is cosmology. Starting out, we think, "What would be the perfect instrument to go after this question?" and that often leads to a new approach. We've been working on the search for B-mode polarization in the microwave background since the year 2000, shortly after theorists came up with the idea that such a polarization signal might be the best way to look for gravitational waves from the era of inflation.

Einstein's equations say that gravitational waves—they stretch and squeeze space and propagate at the speed of light—also have a "handedness." It is similar to how light waves can have a left-handed or a right-handed state. If you look at the cosmic microwave background's polarization across the sky, you can ask yourself, "Which parts of that pattern will look the same in a mirror? Which parts will look different?" The B-mode pattern is the part of the pattern that looks different in a mirror. You can see similar handedness in the brushstrokes of Vincent van Gogh's The Starry Night. A B-mode pattern has to originate from a source that has a handedness, such as gravitational waves. So we're mapping the microwave background to find such a pattern, which in turn will tell us more about how inflation occurred.

 

Q: How do you map polarization?

A: We use detectors called superconducting polarimeters, which are focal plane array detectors developed at JPL. Sometimes, when you figure out the instrument you need, there is a key technology yet to be invented. We dreamed up the basic concept for these detectors in 1999, and JPL has taken them from this initial idea to a fully mature technology.

We previously developed detectors that looked like a spider's web to map temperature variations in the background. These devices were quite successful and flew on the BOOMERanG experiment on a high-altitude balloon and on the Planck satellite in space. However we could see that we needed a completely new approach to map polarization, which led us to superconducting polarimeters. This development is a bit like going from analog film to digital photography. Except here we are literally printing out miniature cameras—the lens, filter, film and a polarizer—on a chip. The detector uses a superconducting thermometer to detect the energy from the background.

The cosmic microwave background means we have to carry out our measurements where microwaves are not strongly affected by the earth's atmosphere. Water vapor copiously absorbs microwave energy. The ideal site from the ground for us is the Antarctic Plateau, where the air is cold and very, very dry. Our observing season at the South Pole begins when the sun goes down for the six-month Antarctic winter, when the air is the driest.

 

Q: How did you get into this line of work?

A: I was a fan of Carl Sagan when I was growing up, and I also really liked a BBC show called Connections, hosted by James Burke. Connections explored the unexpected twists and turns that led to revolutions in technology and science. These often started with a desire to make money or build a new weapon, but that impetus then spawned new technologies, and new ways to use them, that would go off in directions you would never have expected. There's an element of that here—we're using the principles of superconductivity as the best way to explore the very early universe!

As a graduate student at Berkeley I discovered a certain satisfaction in designing instruments developed for a particular purpose, building and testing them, and seeing them actually work. This is hard to explain unless you have actually done it, but maybe the closest analogy is finishing an advanced project in high school shop class. The process definitely requires some patience and determination due to all the steps involved, but once you've built something new, and it works, you want to do it again.

Finally, I am constantly amazed that we can learn so much about something so deeply fundamental as the beginnings of the universe with a small team of scientists. We hunt for imprints from inflation with a team of highly motivated graduate students and postdocs. Our program is exploring the universe some 10–32 seconds after the Big Bang, and the fact that that era is accessible right now, today, if you can just develop the means to do it—well, that is pretty amazing. The early universe is not only knowable, it's within grasp. We live in a special time in history in which we are learning the answers, and some of those answers recently have been deeply surprising. I can't think of anything more exciting than that!

 

Named for the late Caltech professor Earnest C. Watson, who founded the series in 1922, the Watson Lectures present Caltech and JPL researchers describing their work to the public. Many past Watson Lectures are available online at Caltech's iTunes U site.

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Simon Wins International Mathematics Prize

Barry Simon, the IBM Professor of Mathematics and Theoretical Physics at Caltech, has been awarded the International János Bolyai Prize of Mathematics for 2015 by the Hungarian Academy of Sciences. The prize is given every five years and honors internationally outstanding works in mathematics. As the award was discontinued for almost a century following World War I, Simon, whose work focuses on mathematical physics, is its sixth recipient.

In particular, Simon is being recognized for his book titled Orthogonal Polynomials on the Unit Circle, in which he connects two important fields of mathematics: the theory of orthogonal polynomials and operator theory. Orthogonal polynomials are important in solving, expanding, and interpreting solutions to many kinds of differential equations. Operator theory has fundamental applications in the study of solutions to the Schrödinger equation, which is crucial to an understanding of quantum mechanics. Simon's connection between the fields has led to diverse applications, from probability theory to theoretical physics.

Simon first arrived at Caltech as a Sherman Fairchild Distinguished Visiting Scholar in 1980, joining the faculty permanently in 1981. He is a fellow of the American Academy of Arts and Sciences. He also received the Poincaré Prize in 2012, named for mathematician Henri Poincaré. Poincaré was, incidentally, the first recipient of the Bolyai Prize in 1905.

Hungarian Academy of Sciences President László Lovász will award Simon with the prize at a public session of the academy's Section of Mathematics conference in the second half of 2015.

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JPL News: NuSTAR Captures Possible Beacons from Dead Stars

Peering into the heart of the Milky Way galaxy, NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) has spotted a mysterious glow of high-energy X-rays that, according to scientists, could be the "howls" of dead stars as they feed on stellar companions.

"We may be witnessing the beacons of a hitherto hidden population of pulsars in the galactic center," said co-author Fiona Harrison of Caltech, principal investigator of NuSTAR. "This would mean there is something special about the environment in the very center of our galaxy."

Read the full story from JPL News

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Sean Carroll Awarded Guggenheim Fellowship

Sean Carroll, a research professor of physics, has been named a 2015 Fellow of the John Simon Guggenheim Memorial Foundation. Established in 1925, the Guggenheim Fellowship Program awards mid-career fellowships for those who have "demonstrated exceptional capacity for productive scholarship or exceptional creative ability in the arts." This year, the Guggenheim Foundation awarded 173 fellowships, two of which went to physicists.

Carroll came to Caltech in 2006. His research interests are broadly spread across theoretical physics, ranging from cosmology and general relativity to quantum mechanics and particle physics. His proposal to the Guggenheim Foundation, titled "Emergent Structures and the Laws of Physics," focuses on the concept of emergence: how the deepest levels of reality—quantum mechanics, field theory, and space-time—are connected to higher and more complex phenomena, like statistical mechanics and organized structures.

"Since the very notion of complexity does not have a universally-agreed-upon definition, any progress we can make in understanding its basic features is potentially very important," Carroll says in his Guggenheim application.

Carroll has also done research into the relationship between philosophy and physics, particularly within the developing field of philosophy of cosmology. Studies in the field take philosophical approaches to traditional physics problems, such as the arrow of time—the idea that there is a distinction between past and future throughout the observable universe, although the laws of physics would be the same if the direction of time were reversed.

"While science was my first love and remains my primary passion, the philosophical desire to dig deep and ask fundamental questions continues to resonate strongly with me," Carroll says in the "Career Narrative" portion of his application. "I'm convinced that familiarity with modern philosophy of science can be invaluable to physicists trying to tackle questions at the foundations of the discipline."

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Understanding the Earth at Caltech

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Credit: Courtesy J. Andrade/Caltech

The ground beneath our feet may seem unexceptional, but it has a profound impact on the mechanics of landslides, earthquakes, and even Mars rovers. That is why civil and mechanical engineer Jose Andrade studies soils as well as other granular materials. Andrade creates computational models that capture the behavior of these materials—simulating a landslide or the interaction of a rover wheel and Martian soil, for instance. Though modeling a few grains of sand may be simple, predicting their action as a bulk material is very complex. "This dichotomy…leads to some really cool work," says Andrade. "The challenge is to capture the essence of the physics without the complexity of applying it to each grain in order to devise models that work at the landslide level."

Credit: Kelly Lance ©2013 MBARI

Geobiologist Victoria Orphan looks deep into the ocean to learn how microbes influence carbon, nitrogen, and sulfur cycling. For more than 20 years, her lab has been studying methane-breathing marine microorganisms that inhabit rocky mounds on the ocean floor. "Methane is a much more powerful greenhouse gas than carbon dioxide, so tracing its flow through the environment is really a priority for climate models and for understanding the carbon cycle," says Orphan. Her team recently discovered a significantly wider habitat for these microbes than was previously known. The microbes, she thinks, could be preventing large volumes of the potent greenhouse gas from entering the oceans and reaching the atmosphere.

Credit: NASA/JPL-Caltech

Researchers know that aerosols—tiny particles in the atmosphere—scatter and absorb incoming sunlight, affecting the formation and properties of clouds. But it is not well understood how these effects might influence climate change. Enter chemical engineer John Seinfeld. His team conducted a global survey of the impact of changing aerosol levels on low-level marine clouds—clouds with the largest impact on the amount of incoming sunlight Earth reflects back into space—and found that varying aerosol levels altered both the quantity of atmospheric clouds and the clouds' internal properties. These results offer climatologists "unique guidance on how warm cloud processes should be incorporated in climate models with changing aerosol levels," Seinfeld says.

Credit: Yan Hu/Aroian Lab/UC San Diego

Tiny parasitic worms infect nearly half a billion people worldwide, causing gastrointestinal issues, cognitive impairment, and other health problems. Biologist Paul Sternberg is on the case. His lab recently analyzed the entire 313-million-nucleotide genome of the hookworm Ancylostoma ceylanicum to determine which genes turn on when the worm infects its host. A new family of proteins unique to parasitic worms and related to the early infection process was identified; the discovery could lead to new treatments targeting those genes. "A parasitic infection is a balance between the parasites trying to suppress the immune system and the host trying to attack the parasite," Sternberg observes, "and by analyzing the genome, we can uncover clues that might help us alter that balance in favor of the host."

Credit: K.Batygin/Caltech

Earth is special, not least because our solar system has a unique (as far as we know) orbital architecture: its rocky planets have relatively low masses compared to those around other sun-like stars. Planetary scientist Konstantin Batygin has an explanation. Using computer simulations to describe the solar system's early evolution, he and his colleagues showed that Jupiter's primordial wandering initiated a collisional cascade that ultimately destroyed the first generation population of more massive planets once residing in Earth's current orbital neighborhood. This process wiped the inner solar system's slate clean and set the stage for the formation of the planets that exist today. "Ultimately, what this means," says Batygin, "is that planets truly like Earth are intrinsically not very common."

Credit: Nicolás Wey-Gόmez/Caltech

Human understanding of the world has evolved over centuries, anchored to scientific and technological advancements and our ability to map uncharted territories. Historian Nicolás Wey-Gόmez traces this evolution and how the age of discovery helped shape culture and politics in the modern era. Using primary sources such as letters and diaries, he examines the assumptions behind Europe's encounter with the Americas, focusing on early portrayals of native peoples by Europeans. "The science and technology that early modern Europeans recovered from antiquity by way of the Arab world enabled them to imagine lands far beyond their own," says Wey-Gómez. "This knowledge provided them with an essential framework to begin to comprehend the peoples they encountered around the globe."

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At Caltech, researchers study the Earth from many angles—from investigating its origins and evolution to exploring its geology and inner workings to examining its biological systems. Taken together, their findings enable a more nuanced understanding of our planet in all its complexity, helping to ensure that it—and we—endure. This slideshow highlights just a few of the Earth-centered projects happening right now at Caltech.

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Two Caltech Seniors Win Hertz Fellowships

Adam Jermyn and Charles Tschirhart join the 51st class of Hertz fellows

Caltech seniors Adam Jermyn and Charles Tschirhart have been named 2015 Hertz Fellowship winners. Selected from a pool of approximately 800 applicants, the awardees will receive up to five years of support for their graduate studies. According to the Hertz Foundation, fellows are chosen for their intellect, their ingenuity, and their potential to bring meaningful improvement to society. Jermyn and Tschirhart bring the number of Caltech undergraduate Hertz fellows to 60.

Adam Jermyn, a physics major from Longmeadow, Massachusetts, works with so-called "emergent phenomena," which "is a broad term referring to situations where we know all of the laws on a fundamental level but where there are so many pieces working together that the consequences aren't known," he says. For example, the basic laws governing fluid mechanics are simple equations that relate such easily measured quantities as density, velocity, and temperature to one another, but simulating the behavior of two gases as they mix in a turbulent flow can tax the capacity of a supercomputer.

Jermyn's senior thesis models how a pulsar—a type of celestial radio source that flashes as fast as a thousand times per second—disrupts the atmosphere of a companion star. Pulsars are neutron stars—supernova cinders that pack the mass of a couple of suns into a sphere roughly the size of Manhattan. The spin imparted by the supernova's explosion and equally violent collapse creates a beam of tightly focused radio waves. If a neutron star were "aimed" at Earth, the beam's fleeting illumination would register as a flash in our radio telescopes every time it swept across us. Meanwhile, the pulsar's intense gravity distorts the companion star, creating a bulge on its surface. Like Earth's moon, the star's rotation is tidally locked, always presenting the same side to its dominant neighbor. The companion star's atmosphere gets siphoned away, layer by layer, forming a turbulent tendril of gas that winds in an ever-tightening spiral around the pulsar as the stolen material accretes onto its surface.

Charles Tschirhart of Naperville, Illinois, is a double major in applied physics and chemistry. His interests lie at the opposite end of the scale—in the world of nanotechnology, where lengths are measured in nanometers, or billionths of a meter. In the summer of 2012, he was part of a team that built nanoelectrodes—tiny silicon needles that penetrate a cell wall without damaging the cell to monitor the electrical activity within.

Tschirhart and Jermyn share an interest in fluid mechanics. "I think the biggest difference between what Adam and I do is that he is a theorist, and I am an experimentalist," Tschirhart says. "Physicists pretend that a fluid is a continuum of infinitely divisible matter and thus doesn't have any 'graininess' to it." But because atoms and molecules do have finite sizes, "once you get down to small enough scales," he says, "even water becomes 'grainy.'" The fluid becomes more viscous, as it takes effort to force the grains past one another. For his senior thesis, Tschirhart determined the nanoviscosity of silicone oil by measuring the thickness of a thin film of oil, smearing it even thinner with a stream of air and measuring its thickness again. The thickness should decrease in a linear manner, but this doesn't happen when the layer gets thin enough. "These films aren't much thicker than the size of a molecule," he says. "This is where noncontinuum effects show up." These effects could affect how engineers approach tasks as diverse as lubricating hard drives and extracting crude oil from porous rocks.

Both students took Physics 11, a course taught by the late Professor Thomas Tombrello. Tombrello launched this class in 1989 to teach encourage freshman to think creatively, and taught it annually until his death in September 2014. This year, Jermyn and Tschirhart are helping teach it. "Physics 11 really shaped the way I ask questions, and I have Tom Tombrello to thank for that," says Jermyn. "He pushed us to think about things obliquely," Tschirhart concurs. "After I got over my initial nerves, I found myself enjoying [the two rounds of Hertz interviews], which made it much easier to answer the questions creatively."

Both plan to defer their Hertz doctoral fellowships while they take advanced degrees in England. Tschirhart will be attending the University of Nottingham as a Fulbright Scholar for one year, where he plans to develop new applications for atomic force microscopy, a powerful technique for "photographing" nanoscale objects. Jermyn will be at the University of Cambridge for two years as a Marshall Scholar investigating the processes by which planets form around binary star systems.

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Caltech Space Challenge: Mission to an Asteroid in Lunar Orbit

For one week at the end of March, 32 students from 20 universities and 14 countries came to Caltech for an intensive training experience in space mission design: the Caltech Space Challenge. Organizers hand-selected the undergraduate and graduate students from a pool of 220 applicants and created two "dream teams" of engineers, scientists, and designers to face off in a competition to see who could design the best mission.

This year, the teams—Team Explorer and Team Voyager—were tasked with designing a manned mission to an asteroid placed in orbit around the moon. Aside from determining details such as the best type of vehicle to use, the optimal launch date, and how to keep the astronauts safe, each team was asked to explain how its mission would explore and make use of the asteroid to enable future missions to more distant locales, such as Mars.

The Space Challenge takes place at Caltech every two years. For the inaugural challenge in 2011, participants designed a manned mission to a near-Earth asteroid. Two years later, the challenge involved planning a mission to one of Mars's moons.

This year, organizers based the challenge on NASA's Asteroid Redirect Mission (ARM), proposed for launch in 2020. The concept of that mission is to send a robotic spacecraft to a near-Earth asteroid, have it remove a large boulder from the asteroid's surface, and then move it into a lunar orbit. A version of a mission originally considered by the Keck Institute for Space Studies (KISS) at Caltech, NASA's ARM is part of a larger strategy to use asteroids as a stepping-stone to manned missions to Mars and beyond.

"KISS came up with this idea to redirect an asteroid and bring it here as a way to fulfill President Obama's vision of people going to an asteroid by 2025," explains Hayden Burgoyne, a graduate student in space engineering at Caltech and one of two student lead organizers for this year's challenge. "Basically, they said, 'It's hard to send people to an asteroid; it's easier to bring an asteroid to us.' But people are looking toward the end goal of Mars, and they want to know how the Asteroid Redirect Mission will help us get there. So we framed this challenge as a resource utilization challenge to show how this resource that they bring back—this asteroid—can be used to benefit future human exploration."

Throughout the week, the students attended lectures delivered by scientists and engineers from JPL and the aerospace industry on topics related to the challenge, such as mission formulation, human space exploration, asteroid mining, and chemical propulsion. They were also able to consult with mentors working in related fields who were available to help the teams troubleshoot.

"Basically, we brought together the best of the best," says Niccolo Cymbalist, a graduate student in aeronautics at Caltech and the event's other student lead organizer. "But one of the neat things is that the students had the opportunity to interact with sort of their future selves. The speakers and mentors who came in from JPL and from industry are also at the top of their fields, and many participants from previous years have gone on to work in space-related fields."

This year, the teams also had the opportunity to complete a half-day formalized study with a group in the Innovation Foundry at JPL, known as the A-Team. These JPL scientists and engineers help explore, develop, and evaluate early mission concepts and were able to advise the students on science, implementation, and programmatic elements of their respective missions.

At the end of the week, both teams turned in written reports and presented their mission concepts to an audience that included jurors from Caltech, JPL, the Planetary Society, Lockheed Martin, Northrop Grumman, SpaceX, and Millennium Space Systems.

In their mission plans, both groups opted to use two rockets—one to launch scientific cargo and another at a later date to deliver the crew. They also both decided that three astronauts would be optimal for this mission.

Beyond those similarities, though, the two teams had quite different approaches to the challenge. Team Explorer had the idea to use an autonomous swarm of robots to characterize the topology of the asteroid and to collect samples both at the surface and at depth, using a specially designed chamber to extract volatiles. They planned to purify water found on the asteroid, demonstrating that it could be used in a variety of ways, including to water a lettuce garden—something that might capture the attention of the general public. The mission would also determine whether the asteroid could be used as a resource depot for other missions, or as part of the Deep Space Network to help facilitate communication between Earth and operating spacecraft.

In contrast, Team Voyager planned to join their mission's cargo and crew vehicles with an inflatable habitat brought along as cargo once their astronauts reached the asteroid. The astronauts would then spend five days using a robotic arm to drill and to conduct seismic surveys as they determined whether it was safe to explore the asteroid further. They also would bring a suite of scientific instruments with them, including a device to extract oxygen, hydrogen, and methanol from the asteroid, and they would collect and return samples to Earth from the asteroid's subsurface core. Team Voyager's plan for engaging the public included social media and a live feed from a 3-D HD 360-degree camera mounted on an astronaut's helmet.

The organizers say both teams presented outstanding missions. "I was blown away by the quality of the work that the students produced," says Burgoyne.

The final results were presented at a closing reception and banquet at the Athenaeum on March 27. In the end, Team Voyager came out slightly ahead of Team Explorer. According to the jury, the deciding factor was Team Voyager's presentation and success in turning their technically detailed report into a compelling story for the audience.

Alicia Lanz, a member of Team Voyager and a graduate student in physics at Caltech, says the best part of the experience was meeting and working with people from various parts of the world and with different scientific training. "It was so interesting to learn from people with different backgrounds and to see everyone work together to create a viable mission that was greater than anything a single individual could have contributed," she says. "The Caltech Space Challenge was an amazing opportunity."

The student technical lead for this year's Space Challenge was Jay Qi, a graduate student in mechanical engineering at Caltech. The faculty advisor was Beverley McKeon, professor of aeronautics at Caltech and associate director of the Graduate Aerospace Laboratories of the California Institute of Technology (GALCIT). Leon Alkalai of JPL was the program mentor. The Space Challenge is organized by GALCIT and supported by Caltech and its Division of Engineering and Applied Science, JPL, KISS, and corporate sponsors including Northrop Grumman, Lockheed Martin, SpaceX, Millennium Space Systems, and AGI.

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New NSF-Funded Physics Frontiers Center Expands Hunt for Gravitational Waves

The search for gravitational waves—elusive ripples in the fabric of space-time predicted to arise from extremely energetic and large-scale cosmic events such as the collisions of neutron stars and black holes—has expanded, thanks to a $14.5-million, five-year award from the National Science Foundation for the creation and operation of a multi-institution Physics Frontiers Center (PFC) called the North American Nanohertz Observatory for Gravitational Waves (NANOGrav).

The NANOGrav PFC will be directed by Xavier Siemens, a physicist at the University of Wisconsin–Milwaukee and the principal investigator for the project, and will fund the NANOGrav research activities of 55 scientists and students distributed across the 15-institution collaboration, including the work of four Caltech/JPL scientists—Senior Faculty Associate Curt Cutler; Visiting Associates Joseph Lazio and Michele Vallisneri; and Walid Majid, a visiting associate at Caltech and a JPL research scientist—as well as two new postdoctoral fellows at Caltech to be supported by the PFC funds. JPL is managed by Caltech for NASA.

"Caltech has a long tradition of leadership in both the theoretical prediction of sources of gravitational waves and experimental searches for them," says Sterl Phinney, professor of theoretical astrophysics and executive officer for astronomy in the Division of Physics, Mathematics and Astronomy. "This ranges from waves created during the inflation of the early universe, which have periods of billions of years; to waves from supermassive black hole binaries in the nuclei of galaxies, with periods of years; to a multitude of sources with periods of minutes to hours; to the final inspiraling of neutron stars and stellar mass black holes, which create gravitational waves with periods less than a tenth of a second."

The detection of the high-frequency gravitational waves created in this last set of events is a central goal of Advanced LIGO (the next-generation Laser Interferometry Gravitational-Wave Observatory), scheduled to begin operation later in 2015. LIGO and Advanced LIGO, funded by NSF, are comanaged by Caltech and MIT.

"This new Physics Frontier Center is a significant boost to what has long been the dark horse in the exploration of the spectrum of gravitational waves: low-frequency gravitational waves," Phinney says. These gravitational waves are predicted to have such a long wavelength—significantly larger than our solar system—that we cannot build a detector large enough to observe them. Fortunately, the universe itself has created its own detection tool, millisecond pulsars—the rapidly spinning, superdense remains of massive stars that have exploded as supernovas. These ultrastable stars appear to "tick" every time their beamed emissions sweep past Earth like a lighthouse beacon. Gravitational waves may be detected in the small but perceptible fluctuations—a few tens of nanoseconds over five or more years—they cause in the measured arrival times at Earth of radio pulses from these millisecond pulsars.

NANOGrav makes use of the Arecibo Observatory in Puerto Rico and the National Radio Astronomy Observatory's Green Bank Telescope (GBT), and will obtain other data from telescopes in Europe, Australia, and Canada. The team of researchers at Caltech will lead NANOGrav's efforts to develop the approaches and algorithms for extracting the weak gravitational-wave signals from the minute changes in the arrival times of pulses from radio pulsars that are observed regularly by these instruments.

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Friday, May 22, 2015
Dabney Hall, Garden of the Associates – The Garden of the Associates

Memorial Service for Gerry Neugebauer, Robert Andrews Millikan Professor of Physics, Emeritus

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