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  • richardmitnick 4:33 pm on August 20, 2018 Permalink | Reply
    Tags: , Anomalies, Bosons and fermions, Branes, Caltech, , , , Murray Gell-Mann, Parity violation, , , , , , , The second superstring revolution, Theorist John Schwarz   

    From Caltech: “Long and Winding Road: A Conversation with String Theory Pioneer” John Schwarz 

    Caltech Logo

    From Caltech

    08/20/2018

    Whitney Clavin
    (626) 395-1856
    wclavin@caltech.edu

    John Schwarz discusses the history and evolution of superstring theory.

    1
    John Schwarz. Credit: Seth Hansen for Caltech

    The decades-long quest for a theory that would unify all the known forces—from the microscopic quantum realm to the macroscopic world where gravity dominates—has had many twists and turns. The current leading theory, known as superstring theory and more informally as string theory, grew out of an approach to theoretical particle physics, called S-matrix theory, which was popular in the 1960s. Caltech’s John H. Schwarz, the Harold Brown Professor of Theoretical Physics, Emeritus, began working on the problem in 1971, while a junior faculty member at Princeton University. He moved to Caltech in 1972, where he continued his research with various collaborators from other universities. Their studies in the 1970s and 1980s would dramatically shift the evolution of the theory and, in 1984, usher in what’s known as the first superstring revolution.

    Essentially, string theory postulates that our universe is made up, at its most fundamental level, of infinitesimal tiny vibrating strings and contains 10 dimensions—three for space, one for time, and six other spatial dimensions curled up in such a way that we don’t perceive them in everyday life or even with the most sensitive experimental searches to date. One of the many states of a string is thought to correspond to the particle that carries the gravitational force, the graviton, thereby linking the two pillars of fundamental physics—quantum mechanics and the general theory of relativity, which includes gravity.

    We sat down with Schwarz to discuss the history and evolution of string theory and how the theory itself might have moved past strings.

    What are the earliest origins of string theory?

    The first study often regarded as the beginning of string theory came from an Italian physicist named Gabriele Veneziano in 1968. He discovered a mathematical formula that had many of the properties that people were trying to incorporate in a fundamental theory of the strong nuclear force [a fundamental force that holds nuclei together]. This formula was kind of pulled out of the blue, and ultimately Veneziano and others realized, within a couple years, that it was actually describing a quantum theory of a string—a one-dimensional extended object.

    How did the field grow after this paper?

    In the early ’70s, there were several hundred people worldwide working on string theory. But then everything changed when quantum chromodynamics, or QCD—which was developed by Caltech’s Murray Gell-Mann [Nobel Laureate, 1969] and others—became the favored theory of the strong nuclear force. Almost everyone was convinced QCD was the right way to go and stopped working on string theory. The field shrank down to just a handful of people in the course of a year or two. I was one of the ones who remained.

    How did Gell-Mann become interested in your work?

    Gell-Mann is the one who brought me to Caltech and was very supportive of my work. He took an interest in studies I had done with a French physicist, André Neveu, when we were at Princeton. Neveu and I introduced a second string theory. The initial Veneziano version had many problems. There are two kinds of fundamental particles called bosons and fermions, and the Veneziano theory only described bosons. The one I developed with Neveu included fermions. And not only did it include fermions but it led to the discovery of a new kind of symmetry that relates bosons and fermions, which is called supersymmetry. Because of that discovery, this version of string theory is called superstring theory.

    When did the field take off again?

    A pivotal change happened after work I did with another French physicist, Joël Scherk, whom Gell-Mann and I had brought to Caltech as a visitor in 1974. During that period, we realized that many of the problems we were having with string theory could be turned into advantages if we changed the purpose. Instead of insisting on constructing a theory of the strong nuclear force, we took this beautiful theory and asked what it was good for. And it turned out it was good for gravity. Neither of us had worked on gravity. It wasn’t something we were especially interested in but we realized that this theory, which was having trouble describing the strong nuclear force, gives rise to gravity. Once we realized this, I knew what I would be doing for the rest of my career. And I believe Joël felt the same way. Unfortunately, he died six years later. He made several important discoveries during those six years, including a supergravity theory in 11 dimensions.

    Surprisingly, the community didn’t respond very much to our papers and lectures. We were generally respected and never had a problem getting our papers published, but there wasn’t much interest in the idea. We were proposing a quantum theory of gravity, but in that era physicists who worked on quantum theory weren’t interested in gravity, and physicists who worked on gravity weren’t interested in quantum theory.

    That changed after I met Michael Green [a theoretical physicist then at the University of London and now at the University of Cambridge], at the CERN cafeteria in Switzerland in the summer of 1979. Our collaboration was very successful, and Michael visited Caltech for several extended visits over the next few years. We published a number of papers during that period, which are much cited, but our most famous work was something we did in 1984, which had to do with a problem known as anomalies.

    What are anomalies in string theory?

    One of the facts of nature is that there is what’s called parity violation, which means that the fundamental laws are not invariant under mirror reflection. For example, a neutrino always spins clockwise and not counterclockwise, so it would look wrong viewed in a mirror. When you try to write down a fundamental theory with parity violation, mathematical inconsistencies often arise when you take account of quantum effects. This is referred to as the anomaly problem. It appeared that one couldn’t make a theory based on strings without encountering these anomalies, which, if that were the case, would mean strings couldn’t give a realistic theory. Green and I discovered that these anomalies cancel one another in very special situations.

    When we released our results in 1984, the field exploded. That’s when Edward Witten [a theoretical physicist at the Institute for Advanced Study in Princeton], probably the most influential theoretical physicist in the world, got interested. Witten and three collaborators wrote a paper early in 1985 making a particular proposal for what to do with the six extra dimensions, the ones other than the four for space and time. That proposal looked, at the time, as if it could give a theory that is quite realistic. These developments, together with the discovery of another version of superstring theory, constituted the first superstring revolution.

    Richard Feynman was here at Caltech during that time, before he passed away in 1988. What did he think about string theory?

    After the 1984 to 1985 breakthroughs in our understanding of superstring theory, the subject no longer could be ignored. At that time it acquired some prominent critics, including Richard Feynman and Stephen Hawking. Feynman’s skepticism of superstring theory was based mostly on the concern that it could not be tested experimentally. This was a valid concern, which my collaborators and I shared. However, Feynman did want to learn more, so I spent several hours explaining the essential ideas to him. Thirty years later, it is still true that there is no smoking-gun experimental confirmation of superstring theory, though it has proved its value in other ways. The most likely possibility for experimental support in the foreseeable future would be the discovery of supersymmetry particles. So far, they have not shown up.

    What was the second superstring revolution about?

    The second superstring revolution occurred 10 years later in the mid ’90s. What happened then is that string theorists discovered what happens when particle interactions become strong. Before, we had been studying weakly interacting systems. But as you crank up the strength of the interaction, a 10th dimension of space can emerge. New objects called branes also emerge. Strings are one dimensional; branes have all sorts of dimensions ranging from zero to nine. An important class of these branes, called D-branes, was discovered by the late Joseph Polchinski [BS ’75]. Strings do have a special role, but when the system is strongly interacting, then the strings become less fundamental. It’s possible that in the future the subject will get a new name but until we understand better what the theory is, which we’re still struggling with, it’s premature to invent a new name.

    What can we say now about the future of string theory?

    It’s now over 30 years since a large community of scientists began pooling their talents, and there’s been enormous progress in those 30 years. But the more big problems we solve, the more new questions arise. So, you don’t even know the right questions to ask until you solve the previous questions. Interestingly, some of the biggest spin-offs of our efforts to find the most fundamental theory of nature are in pure mathematics.

    Do you think string theory will ultimately unify the forces of nature?

    Yes, but I don’t think we’ll have a final answer in my lifetime. The journey has been worth it, even if it did take some unusual twists and turns. I’m convinced that, in other intelligent civilizations throughout the galaxy, similar discoveries will occur, or already have occurred, in a different sequence than ours. We’ll find the same result and reach the same conclusions as other civilizations, but we’ll get there by a very different route.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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  • richardmitnick 7:50 am on August 18, 2018 Permalink | Reply
    Tags: AAReST (Autonomous Assembly of a Reconfigurable Space Telescope), , , , Caltech,   

    From Caltech: “Student-Built Satellite Telescope Prepares for Space” 

    Caltech Logo

    From Caltech

    1
    Artist’s concept of AAReST
    Credit: Sergio Pellegrino/Caltech

    After nearly a decade of work, a modular reconfigurable space telescope designed by students is nearly ready to launch.

    08/16/2018

    Robert Perkins
    (626) 395-1862
    rperkins@caltech.edu

    After nine years, a student-designed-and-built satellite is being readied for launch into orbit, where it will be a test bed for a new type of space telescope that assembles itself in flight from multiple components.

    With telescopes, bigger is better: the larger their primary mirror, the more light they can capture and the better the images they can create. Currently, however, space telescopes are limited in size and must be folded up to fit inside the rockets that launch them into space. Hubble is 2.4 meters in diameter, for instance, and the James Webb Space Telescope will be 6.5 meters in diameter when it launches in 2021. To build a telescope that exceeds 10 meters, scientists and engineers will need to develop new, modular designs that can be sent to space in multiple pieces—even on multiple rockets.

    In 2008, a series of workshops at the Keck Institute of Space Studies (KISS) at Caltech inspired a low-cost mission to demonstrate the feasibility of sending a telescope to space in pieces and having it assemble itself once in orbit.

    That telescope, which came to be known as AAReST (Autonomous Assembly of a Reconfigurable Space Telescope), was designed and built in large part by students in Caltech’s Ae 105 Aerospace Engineering class, working in collaboration with the Surrey Space Centre in England and the Indian Institute of Space Science and Technology. Over the years, these students planned the mission and designed the telescope. With the spacecraft nearly complete, 2018 marks the conclusion of the AAReST project for the Ae 105 students. The AAReST satellite is scheduled to be launched on an Indian Space Research Organization (ISRO) rocket in 2019.

    Ae 105 is a yearlong class taught by JPL instructors Oscar Alvarez-Salazar, Andy Klesh, Scott Ploen, and Dan Scharf. At Caltech, aerospace engineer Sergio Pellegrino is AAReST’s campus coordinator and JPL’s John Baker is its project manager. Over the past near decade, the Ae 105 students have dealt with countless design and technical issues regarding the project. But by far the biggest challenge the class faced, Pellegrino says, was an informational one: how to pass on information from one generation of students to the next.

    “Continuity is a challenge in every project. You always have to cope with the fact that people leave because they retire or get different jobs. But in our case, the entire workforce was replaced every year,” says Pellegrino, the Joyce and Kent Kresa Professor of Aerospace and Civil Engineering and a JPL senior research scientist. “In a normal project, outgoing team members produce detailed write-ups. For us, that just wasn’t enough.”

    To cope with the turnover, Pellegrino invited many former students to stay on as mentors to the incoming Ae 105 classes. This ultimately spawned a second class, Ae 205, Advanced Space Project, to formalize the student-mentorship role. That student mentorship, coupled with the fact that the mission was actually going to space, translated into a uniquely valuable experience according to those who went through the program.

    “Having a form of practical experience to point to is very useful after university when looking for a job,” says Lee Wilson (PhD ’17), who now works on spacecraft design at Deep Space Industries in San Jose. “This project helped expose me to vibration testing and spacecraft design, assembly, and integration, and actually let me get my hands dirty.”

    Thibaud Talon, who took Ae 105 during the 2013–14 school year and remains involved in the project to this day as a graduate student, echoes Wilson’s sentiments.

    “Since the class is taught by JPL engineers, I started to make a network at JPL. I still meet, talk, and sometimes work with the professors who taught me Ae 105,” says Talon. “Also, working on an actual space mission is a great addition to my resume. As many people working in the space industry told me, such an experience is very valuable and looked at when applying for a job. Participating in such a project teaches you many concepts of designing a space mission that are hard to learn otherwise.”

    The final design that the students came up with for the AAReST spacecraft features a central core unit that contains the attitude and control system, the radio and the antennas, and two rigid mirrors. Surrounding that central unit are two smaller spacecraft containing deformable mirrors that will be co-focused with the rigid mirrors on the main spacecraft. The whole package is small, measuring just 46 x 34 x 30 centimeters. Once in orbit, the two smaller spacecraft will detach from the main one via splitting bolts and then float about 30 centimeters away from the spacecraft before reconnecting to the main body in a wider configuration via electromagnets.

    The final project for this year’s Ae 105 class was focused on testing the main spacecraft, with particular attention paid to ensuring that the recoil from the splitting bolts will not throw the side segments too far away from the main spacecraft.

    Ae 105 will no longer focus on AAReST, but there are still several details to be worked out before the spacecraft is launched, so Pellegrino will be taking a sabbatical during the 2018–19 academic year to work with the senior students on the project. Soon-Jo Chung, associate professor of aerospace and Bren Scholar and JPL research scientist, will take over Ae 105 and pick a new project for its students to tackle.

    Pellegrino says that the Caltech students working on AAReST have learned how to collaborate across continents and gained skills that will continue to serve them for years to come. In addition, he says, he’s proud to have given several generations of aerospace students the opportunity to work on a real space mission. When the mission launches in 2019, dozens of past and present Caltech students—along with their collaborators nearby and abroad—will be watching and holding their breath to see whether their hard work pays off.

    Manan Arya (PhD ’16), an Ae 105 student from 2011 who now works on large deployable spacecraft structures at JPL, says he’s looking forward to watching the launch. “Overall it’s a feeling of excitement and great joy that something that I’ve worked on will end up in space, mixed with the nervousness that all engineers must experience when they press the ‘on’ button and hope, wish, and pray that it actually turns on.”

    The AAReST mission is a collaborative effort between Caltech, the University of Surrey in England, and the Indian Institute of Space Science and Technology. The AAReST project has received funding from KISS; Caltech’s Division of Engineering and Applied Science; and the Innovation in Education Fund, which was made possible in part by the Caltech Associates.

    See the full article here .


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    Please help promote STEM in your local schools.


    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

    Caltech campus

     
  • richardmitnick 12:14 pm on June 2, 2018 Permalink | Reply
    Tags: , , , , Caltech, , Harry Atwater   

    From Caltech: “Building the Starshot Sail: A Q&A with Harry Atwater” 

    Caltech Logo

    From Caltech

    06/01/2018

    Robert Perkins
    (626) 395-1862
    rperkins@caltech.edu

    Breakthrough Starshot image. Credit: Breakthrough Starshot

    When manmade probes finally reach other stars, they will not be powered by rockets. Instead, they may be riding on a gossamer-thin sail that is being blasted by a giant laser beam. Harry Atwater, Howard Hughes Professor of Applied Physics and Materials Science, is a project leader of the Breakthrough Starshot Program,which seeks to make these probes a reality. In a new paper published on May 7 in Nature Materials, Atwater explores some of the major challenges the project will face in its bid to make humanity an interstellar species. We recently sat down with him to talk about the program.

    What exactly is the Breakthrough Starshot Program?

    It is a multi-disciplinary $100-million project that was announced in 2016, aimed at designing a spacecraft that can be launched to planets surrounding other stars and reach them within our lifetime. The idea is to develop spacecraft that are capable of traveling at nearly 20 percent of the speed of light.
    Why can’t that be done with conventional rockets?

    The issue with traditional rocket propulsion is that the final velocity of the rocket is limited by the final velocity of the fuel ejected from the rocket. For chemical propellants, the upper limit of the final velocity is way too low. The fastest spacecraft that has ever been launched would take tens of thousands of years to reach the nearest star, Alpha Centauri C. That is clearly impractical for any interstellar mission.

    To overcome that, we’re planning to use light itself as the fuel. In other words, we are taking advantage of the principle of conservation of momentum between light and materials. If I have a reflective object and I shine light on it, the recoiling or reflecting photons impart momentum to the object. If the object is light enough, that momentum can act as a propulsive force, and then the final velocity of that probe is limited only by the velocity of light itself.

    What is your role in the project?

    I’m an advisor to the Breakthrough Starshot Program. The program has three big technical challenges: The first is to build the so-called photon engine, the laser that’s capable of propelling the sail; the second is to design the sail itself; and the third is to design the payload, which will be a tiny spacecraft capable of taking images and spectral data and then beaming them back to the earth. My role is to help the program define pathways to making a viable lightsail that’s compatible with the other objectives of the whole program. It isn’t going to be easy: we have to make an ultra-lightweight large-scale object that is firmly and dynamically stable under propulsion.

    What other challenges are there?

    The challenges that we address in our latest paper are developing the design and materials requirements for this really extreme set of engineering conditions. We require something that has a mass of no more than a gram, but which covers an area of about 10 square meters. That means that the average thickness will be on the order of tens to hundreds of nanometers; much thinner than a human hair.

    This wafer-thin material will be subject to intense laser radiation during the propulsion phase, with an intensity of megawatts per square meter. That’s not the highest intensity that has ever been generated in a laboratory, but it’s a very high intensity to interact with an ultra-thin, gossamer-like membrane structure of the kind that we’re talking about here. So the biggest requirement is that it has to be ultra-reflective so we can impart momentum and propel the lightsail.

    Are there any materials, or families of materials, that look promising for this?

    Yes. The best materials are the ones that are dielectric, or insulating, rather than metallic materials, which transmit electrical charges. A good example of a dielectric that everyone is familiar with is glass, which is highly non-absorbing. Unfortunately, glass is a little too low in its reflectivity to be an efficient candidate for lightsail material, but nonetheless it points the way. The best materials to think about are ones that have higher reflectivity but similarly low absorption coefficients.

    How does this work fit in with your broader research goals?

    My research team is very interested in how light interacts with nanoscale materials, or materials that are sculpted or shaped at the scale of the wavelength itself. One of the things that’s fascinating is that nanostructured materials may be able to generate really optimal trade-offs between mass and reflectivity, and also help give stability to the sail. We need the sail to be passably stable, meaning that it doesn’t fall off the laser beam, so to speak.

    [My totally uneducated surmise: Don’t hold your breath.]

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.


    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

    Caltech campus

     
  • richardmitnick 9:52 am on April 13, 2018 Permalink | Reply
    Tags: , , , Caltech, , , New WM Keck Observatory Remote Viewing Facility opens at Swinburne,   

    From Swinburne: “New WM Keck Observatory Remote Viewing Facility opens at Swinburne” 

    Swinburne U bloc

    Swinburne University of Technology

    12 April 2018

    Lea Kivivali
    +61 3 9214 5428
    lkivivali@swin.edu.au


    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft), above sea level, showing also NASA’s IRTF and NAOJ Subaru

    World-class facility enables researchers to remotely control the twin Keck Observatory telescopes in Hawaii from Hawthorn.
    Swinburne researchers have access to the observatory for up to 10 nights a year.
    The facility is partially funded through a donation from the Eric Ormond Baker Charitable fund.

    Pioneering astrophysics research in Australia has received a boost with the launch of the WM Keck Observatory Remote Viewing Facility at Swinburne University of Technology’s Luton Lane offices in Hawthorn.

    This world-class facility enables researchers and astronomy students to remotely control the twin Keck Observatory telescopes – the world’s most scientifically productive optical and infrared telescopes – based in Hawaii.

    More than 9000 kilometres from the observatory, Swinburne astronomers have been able to control the Keck telescopes with a direct video link to the telescopes since 2009 from a small on-campus control room.

    Deputy Vice-Chancellor (Research and Development), Professor Aleksandar Subic, says the Caltech partnership and access to Keck remote viewing and observation has allowed Swinburne researchers to conduct world leading research that is leading to new discoveries and transforming knowledge.

    A strategic research agreement with the California Institute for Technology (Caltech) for a further five years gives Swinburne access to the W M Keck Observatory for up to 10 nights a year until 2023.

    “The potential discoveries have the ability to answer some of life’s biggest questions and lead to breakthrough technologies that could benefit many fields and industries. We are already seeing a huge impact that the recent discovery of gravitational waves is having,” Professor Subic says.

    2
    No image caption or credit.

    The new facility can accommodate larger research teams and provides a new base for the Deeper, Wider Faster astrophysics program that has been searching for Fast Radio Bursts, the fastest explosions in the Universe.

    “The ability to remotely operate the Keck telescopes from Melbourne has placed the Swinburne campus in the frontline of international astrophysics,” says Director of Swinburne’s Centre for Astrophysics and Supercomputing, Professor Karl Glazebrook.

    “It is really exciting to be in the remote observing room and see, in real time, the newest and faintest signals from the most distant objects coming in live. It allows Swinburne astronomers to make decisions on the spot that lead to major discoveries about the Universe and facilitates wide engagement of our staff and students in these moments.”

    Using the W M Keck Observatory’s cutting-edge instrumentation, Swinburne astronomers have produced landmark discoveries about the Universe such as:

    The monster galaxy that grew up too fast.
    New method solves 40 year-old mystery on the size of shadowy galaxies.
    New spin on star forming galaxies.
    The detection of superluminous supernovae.

    Astronomers from other research centres will also have access to the new facility.

    Researchers will also be able to remotely control the Anglo-Australian Telescope in New South Wales.

    The new facility was unveiled at a special event held for Swinburne alumni and donors. It has been partially funded through a generous donation from the Eric Ormond Baker Charitable fund, represented by trustee and Swinburne Online staff member Graeme Baker, and managed by Equity Trustees.

    See the full article here .

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    Swinburne U Campus

    Swinburne is a large and culturally diverse organisation. A desire to innovate and bring about positive change motivates our students and staff. The result is in an institution that grows and evolves each year.

     
  • richardmitnick 1:18 pm on March 5, 2018 Permalink | Reply
    Tags: , , , Caltech, , , Schrödinger Equation   

    From Caltech: “Massive Astrophysical Objects Governed by Subatomic Equation” 

    Caltech Logo

    Caltech

    03/05/2018
    Lori Dajose

    1
    Schrödinger in Space: An artist’s impression of research presented in Batygin (2018), MNRAS 475, 4. Propagation of waves through an astrophysical disk can be understood using Schrödinger’s equation – a cornerstone of quantum mechanics.
    Credit: James Tuttle Keane, California Institute of Technology

    The Schrödinger Equation makes an unlikely appearance at the astronomical scale.

    Quantum mechanics is the branch of physics governing the sometimes-strange behavior of the tiny particles that make up our universe. Equations describing the quantum world are generally confined to the subatomic realm—the mathematics relevant at very small scales is not relevant at larger scales, and vice versa. However, a surprising new discovery from a Caltech researcher suggests that the Schrödinger Equation—the fundamental equation of quantum mechanics—is remarkably useful in describing the long-term evolution of certain astronomical structures.

    The work, done by Konstantin Batygin (MS ’10, PhD ’12), a Caltech assistant professor of planetary science and Van Nuys Page Scholar, is described in a paper appearing in the March 5 issue of Monthly Notices of the Royal Astronomical Society.

    Massive astronomical objects are frequently encircled by groups of smaller objects that revolve around them, like the planets around the sun. For example, supermassive black holes are orbited by swarms of stars, which are themselves orbited by enormous amounts of rock, ice, and other space debris. Due to gravitational forces, these huge volumes of material form into flat, round disks. These disks, made up of countless individual particles orbiting en masse, can range from the size of the solar system to many light-years across.

    Astrophysical disks of material generally do not retain simple circular shapes throughout their lifetimes. Instead, over millions of years, these disks slowly evolve to exhibit large-scale distortions, bending and warping like ripples on a pond. Exactly how these warps emerge and propagate has long puzzled astronomers, and even computer simulations have not offered a definitive answer, as the process is both complex and prohibitively expensive to model directly.

    While teaching a Caltech course on planetary physics, Batygin (the theorist behind the proposed existence of Planet Nine) turned to an approximation scheme called perturbation theory to formulate a simple mathematical representation of disk evolution. This approximation, often used by astronomers, is based upon equations developed by the 18th-century mathematicians Joseph-Louis Lagrange and Pierre-Simon Laplace. Within the framework of these equations, the individual particles and pebbles on each particular orbital trajectory are mathematically smeared together. In this way, a disk can be modeled as a series of concentric wires that slowly exchange orbital angular momentum among one another.

    As an analogy, in our own solar system one can imagine breaking each planet into pieces and spreading those pieces around the orbit the planet takes around the sun, such that the sun is encircled by a collection of massive rings that interact gravitationally. The vibrations of these rings mirror the actual planetary orbital evolution that unfolds over millions of years, making the approximation quite accurate.

    Using this approximation to model disk evolution, however, had unexpected results.

    “When we do this with all the material in a disk, we can get more and more meticulous, representing the disk as an ever-larger number of ever-thinner wires,” Batygin says. “Eventually, you can approximate the number of wires in the disk to be infinite, which allows you to mathematically blur them together into a continuum. When I did this, astonishingly, the Schrödinger Equation emerged in my calculations.”

    The Schrödinger Equation is the foundation of quantum mechanics: It describes the non-intuitive behavior of systems at atomic and subatomic scales. One of these non-intuitive behaviors is that subatomic particles actually behave more like waves than like discrete particles—a phenomenon called wave-particle duality. Batygin’s work suggests that large-scale warps in astrophysical disks behave similarly to particles, and the propagation of warps within the disk material can be described by the same mathematics used to describe the behavior of a single quantum particle if it were bouncing back and forth between the inner and outer edges of the disk.

    The Schrödinger Equation is well studied, and finding that such a quintessential equation is able to describe the long-term evolution of astrophysical disks should be useful for scientists who model such large-scale phenomena. Additionally, adds Batygin, it is intriguing that two seemingly unrelated branches of physics—those that represent the largest and the smallest of scales in nature—can be governed by similar mathematics.

    “This discovery is surprising because the Schrödinger Equation is an unlikely formula to arise when looking at distances on the order of light-years,” says Batygin. “The equations that are relevant to subatomic physics are generally not relevant to massive, astronomical phenomena. Thus, I was fascinated to find a situation in which an equation that is typically used only for very small systems also works in describing very large systems.”

    “Fundamentally, the Schrödinger Equation governs the evolution of wave-like disturbances.” says Batygin. “In a sense, the waves that represent the warps and lopsidedness of astrophysical disks are not too different from the waves on a vibrating string, which are themselves not too different from the motion of a quantum particle in a box. In retrospect, it seems like an obvious connection, but it’s exciting to begin to uncover the mathematical backbone behind this reciprocity.”

    The paper is titled “Schrödinger Evolution of Self-Gravitating Disks.” Funding was provided by the David and Lucile Packard Foundation.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

    Caltech campus

     
  • richardmitnick 8:08 am on March 2, 2018 Permalink | Reply
    Tags: , , , , Caltech, , ,   

    From Caltech: “A Better Way to Model Stellar Explosions” 

    Caltech Logo

    Caltech

    03/01/2018

    Whitney Clavin
    (626) 395-1856
    wclavin@caltech.edu

    1
    Artist’s concept of two neutron stars colliding. Credit: NSF/LIGO/Sonoma State University/A. Simonnet

    Caltech scientists create new computer code for calculating neutron stars’ “equation of state”.

    Neutron stars consist of the densest form of matter known: a neutron star the size of Los Angeles can weigh twice as much as our sun.

    Astrophysicists don’t fully understand how matter behaves under these crushing densities, let alone what happens when two neutron stars smash into each other or when a massive star explodes, creating a neutron star.

    One tool scientists use to model these powerful phenomena is the “equation of state.” Loosely, the equation of state describes how matter behaves under different densities and temperatures. The temperatures and densities that occur during these extreme events can vary greatly, and strange behaviors can emerge; for example, protons and neutrons can arrange themselves into complex shapes known as nuclear “pasta.”

    But, until now, there were only about 20 equations of state readily available for simulations of astrophysical phenomena. Caltech postdoctoral scholar in theoretical astrophysics Andre da Silva Schneider decided to tackle this problem using computer codes. Over the past three years, he has been developing open-source software that allows astrophysicists to generate their own equations of state. In a new paper in the journal Physical Review C, he and his colleagues describe the code and demonstrate how it works by simulating supernovas of stars 15 and 40 times the mass of the sun.

    The research has immediate applications for researchers studying neutron stars, including those analyzing data from the National Science Foundation’s Laser Interferometer Gravitational-wave Observatory, or LIGO, which made the first detection of ripples in space and time, known as gravitational waves, from a neutron star collision, in 2017. That event was also witnessed by a cadre of telescopes around the world, which captured light waves from the same event.

    UC Santa Cruz

    UC Santa Cruz

    14

    A UC Santa Cruz special report

    Tim Stephens

    Astronomer Ryan Foley says “observing the explosion of two colliding neutron stars” [see https://sciencesprings.wordpress.com/2017/10/17/from-ucsc-first-observations-of-merging-neutron-stars-mark-a-new-era-in-astronomy ]–the first visible event ever linked to gravitational waves–is probably the biggest discovery he’ll make in his lifetime. That’s saying a lot for a young assistant professor who presumably has a long career still ahead of him.

    2
    The first optical image of a gravitational wave source was taken by a team led by Ryan Foley of UC Santa Cruz using the Swope Telescope at the Carnegie Institution’s Las Campanas Observatory in Chile. This image of Swope Supernova Survey 2017a (SSS17a, indicated by arrow) shows the light emitted from the cataclysmic merger of two neutron stars. (Image credit: 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

    Carnegie Institution Swope telescope at Las Campanas, Chile, 100 kilometres (62 mi) northeast of the city of La Serena. near the north end of a 7 km (4.3 mi) long mountain ridge. Cerro Las Campanas, near the southern end and over 2,500 m (8,200 ft) high, at Las Campanas, Chile

    A neutron star forms when a massive star runs out of fuel and explodes as a supernova, throwing off its outer layers and leaving behind a collapsed core composed almost entirely of neutrons. Neutrons are the uncharged particles in the nucleus of an atom, where they are bound together with positively charged protons. In a neutron star, they are packed together just as densely as in the nucleus of an atom, resulting in an object with one to three times the mass of our sun but only about 12 miles wide.

    “Basically, a neutron star is a gigantic atom with the mass of the sun and the size of a city like San Francisco or Manhattan,” said Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz.

    These objects are so dense, a cup of neutron star material would weigh as much as Mount Everest, and a teaspoon would weigh a billion tons. It’s as dense as matter can get without collapsing into a black hole.

    THE MERGER

    Like other stars, neutron stars sometimes occur in pairs, orbiting each other and gradually spiraling inward. Eventually, they come together in a catastrophic merger that distorts space and time (creating gravitational waves) and emits a brilliant flare of electromagnetic radiation, including visible, infrared, and ultraviolet light, x-rays, gamma rays, and radio waves. Merging black holes also create gravitational waves, but there’s nothing to be seen because no light can escape from a black hole.

    Foley’s team was the first to observe the light from a neutron star merger that took place on August 17, 2017, and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Now, for the first time, scientists can study both the gravitational waves (ripples in the fabric of space-time), and the radiation emitted from the violent merger of the densest objects in the universe.

    3
    The UC Santa Cruz team found SSS17a by comparing a new image of the galaxy N4993 (right) with images taken four months earlier by the Hubble Space Telescope (left). The arrows indicate where SSS17a was absent from the Hubble image and visible in the new image from the Swope Telescope. (Image credits: Left, Hubble/STScI; Right, 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

    It’s that combination of data, and all that can be learned from it, that has astronomers and physicists so excited. The observations of this one event are keeping hundreds of scientists busy exploring its implications for everything from fundamental physics and cosmology to the origins of gold and other heavy elements.


    A small team of UC Santa Cruz astronomers were the first team to observe light from two neutron stars merging in August. The implications are huge.

    ALL THE GOLD IN THE UNIVERSE

    It turns out that the origins of the heaviest elements, such as gold, platinum, uranium—pretty much everything heavier than iron—has been an enduring conundrum. All the lighter elements have well-explained origins in the nuclear fusion reactions that make stars shine or in the explosions of stars (supernovae). Initially, astrophysicists thought supernovae could account for the heavy elements, too, but there have always been problems with that theory, says Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz.

    4
    The violent merger of two neutron stars is thought to involve three main energy-transfer processes, shown in this diagram, that give rise to the different types of radiation seen by astronomers, including a gamma-ray burst and a kilonova explosion seen in visible light. (Image credit: Murguia-Berthier et al., Science)

    A theoretical astrophysicist, Ramirez-Ruiz has been a leading proponent of the idea that neutron star mergers are the source of the heavy elements. Building a heavy atomic nucleus means adding a lot of neutrons to it. This process is called rapid neutron capture, or the r-process, and it requires some of the most extreme conditions in the universe: extreme temperatures, extreme densities, and a massive flow of neutrons. A neutron star merger fits the bill.

    Ramirez-Ruiz and other theoretical astrophysicists use supercomputers to simulate the physics of extreme events like supernovae and neutron star mergers. This work always goes hand in hand with observational astronomy. Theoretical predictions tell observers what signatures to look for to identify these events, and observations tell theorists if they got the physics right or if they need to tweak their models. The observations by Foley and others of the neutron star merger now known as SSS17a are giving theorists, for the first time, a full set of observational data to compare with their theoretical models.

    According to Ramirez-Ruiz, the observations support the theory that neutron star mergers can account for all the gold in the universe, as well as about half of all the other elements heavier than iron.

    RIPPLES IN THE FABRIC OF SPACE-TIME

    Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity, but until recently they were impossible to observe. LIGO’s extraordinarily sensitive detectors achieved the first direct detection of gravitational waves, from the collision of two black holes, in 2015. Gravitational waves are created by any massive accelerating object, but the strongest waves (and the only ones we have any chance of detecting) are produced by the most extreme phenomena.

    Two massive compact objects—such as black holes, neutron stars, or white dwarfs—orbiting around each other faster and faster as they draw closer together are just the kind of system that should radiate strong gravitational waves. Like ripples spreading in a pond, the waves get smaller as they spread outward from the source. By the time they reached Earth, the ripples detected by LIGO caused distortions of space-time thousands of times smaller than the nucleus of an atom.

    The rarefied signals recorded by LIGO’s detectors not only prove the existence of gravitational waves, they also provide crucial information about the events that produced them. Combined with the telescope observations of the neutron star merger, it’s an incredibly rich set of data.

    LIGO can tell scientists the masses of the merging objects and the mass of the new object created in the merger, which reveals whether the merger produced another neutron star or a more massive object that collapsed into a black hole. To calculate how much mass was ejected in the explosion, and how much mass was converted to energy, scientists also need the optical observations from telescopes. That’s especially important for quantifying the nucleosynthesis of heavy elements during the merger.

    LIGO can also provide a measure of the distance to the merging neutron stars, which can now be compared with the distance measurement based on the light from the merger. That’s important to cosmologists studying the expansion of the universe, because the two measurements are based on different fundamental forces (gravity and electromagnetism), giving completely independent results.

    “This is a huge step forward in astronomy,” Foley said. “Having done it once, we now know we can do it again, and it opens up a whole new world of what we call ‘multi-messenger’ astronomy, viewing the universe through different fundamental forces.”

    IN THIS REPORT

    Neutron stars
    A team from UC Santa Cruz was the first to observe the light from a neutron star merger that took place on August 17, 2017 and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO)

    5
    Graduate students and post-doctoral scholars at UC Santa Cruz played key roles in the dramatic discovery and analysis of colliding neutron stars.Astronomer Ryan Foley leads a team of young graduate students and postdoctoral scholars who have pulled off an extraordinary coup. Following up on the detection of gravitational waves from the violent merger of two neutron stars, Foley’s team was the first to find the source with a telescope and take images of the light from this cataclysmic event. In so doing, they beat much larger and more senior teams with much more powerful telescopes at their disposal.

    “We’re sort of the scrappy young upstarts who worked hard and got the job done,” said Foley, an untenured assistant professor of astronomy and astrophysics at UC Santa Cruz.

    7
    David Coulter, graduate student

    The discovery on August 17, 2017, has been a scientific bonanza, yielding over 100 scientific papers from numerous teams investigating the new observations. Foley’s team is publishing seven papers, each of which has a graduate student or postdoc as the first author.

    “I think it speaks to Ryan’s generosity and how seriously he takes his role as a mentor that he is not putting himself front and center, but has gone out of his way to highlight the roles played by his students and postdocs,” said Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz and the most senior member of Foley’s team.

    “Our team is by far the youngest and most diverse of all of the teams involved in the follow-up observations of this neutron star merger,” Ramirez-Ruiz added.

    8
    Charles Kilpatrick, postdoctoral scholar

    Charles Kilpatrick, a 29-year-old postdoctoral scholar, was the first person in the world to see an image of the light from colliding neutron stars. He was sitting in an office at UC Santa Cruz, working with first-year graduate student Cesar Rojas-Bravo to process image data as it came in from the Swope Telescope in Chile. To see if the Swope images showed anything new, he had also downloaded “template” images taken in the past of the same galaxies the team was searching.

    9
    Ariadna Murguia-Berthier, graduate student

    “In one image I saw something there that was not in the template image,” Kilpatrick said. “It took me a while to realize the ramifications of what I was seeing. This opens up so much new science, it really marks the beginning of something that will continue to be studied for years down the road.”

    At the time, Foley and most of the others in his team were at a meeting in Copenhagen. When they found out about the gravitational wave detection, they quickly got together to plan their search strategy. From Copenhagen, the team sent instructions to the telescope operators in Chile telling them where to point the telescope. Graduate student David Coulter played a key role in prioritizing the galaxies they would search to find the source, and he is the first author of the discovery paper published in Science.

    10
    Matthew Siebert, graduate student

    “It’s still a little unreal when I think about what we’ve accomplished,” Coulter said. “For me, despite the euphoria of recognizing what we were seeing at the moment, we were all incredibly focused on the task at hand. Only afterward did the significance really sink in.”

    Just as Coulter finished writing his paper about the discovery, his wife went into labor, giving birth to a baby girl on September 30. “I was doing revisions to the paper at the hospital,” he said.

    It’s been a wild ride for the whole team, first in the rush to find the source, and then under pressure to quickly analyze the data and write up their findings for publication. “It was really an all-hands-on-deck moment when we all had to pull together and work quickly to exploit this opportunity,” said Kilpatrick, who is first author of a paper comparing the observations with theoretical models.

    11
    César Rojas Bravo, graduate student

    Graduate student Matthew Siebert led a paper analyzing the unusual properties of the light emitted by the merger. Astronomers have observed thousands of supernovae (exploding stars) and other “transients” that appear suddenly in the sky and then fade away, but never before have they observed anything that looks like this neutron star merger. Siebert’s paper concluded that there is only a one in 100,000 chance that the transient they observed is not related to the gravitational waves.

    Ariadna Murguia-Berthier, a graduate student working with Ramirez-Ruiz, is first author of a paper synthesizing data from a range of sources to provide a coherent theoretical framework for understanding the observations.

    Another aspect of the discovery of great interest to astronomers is the nature of the galaxy and the galactic environment in which the merger occurred. Postdoctoral scholar Yen-Chen Pan led a paper analyzing the properties of the host galaxy. Enia Xhakaj, a new graduate student who had just joined the group in August, got the opportunity to help with the analysis and be a coauthor on the paper.

    12
    Yen-Chen Pan, postdoctoral scholar

    “There are so many interesting things to learn from this,” Foley said. “It’s a great experience for all of us to be part of such an important discovery.”

    13
    Enia Xhakaj, graduate student

    IN THIS REPORT

    Scientific Papers from the 1M2H Collaboration

    Coulter et al., Science, Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source

    Drout et al., Science, Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis

    Shappee et al., Science, Early Spectra of the Gravitational Wave Source GW170817: Evolution of a Neutron Star Merger

    Kilpatrick et al., Science, Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger

    Siebert et al., ApJL, The Unprecedented Properties of the First Electromagnetic Counterpart to a Gravitational-wave Source

    Pan et al., ApJL, The Old Host-galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational-wave Source

    Murguia-Berthier et al., ApJL, A Neutron Star Binary Merger Model for GW170817/GRB170817a/SSS17a

    Kasen et al., Nature, Origin of the heavy elements in binary neutron star mergers from a gravitational wave event

    Abbott et al., Nature, A gravitational-wave standard siren measurement of the Hubble constant (The LIGO Scientific Collaboration and The Virgo Collaboration, The 1M2H Collaboration, The Dark Energy Camera GW-EM Collaboration and the DES Collaboration, The DLT40 Collaboration, The Las Cumbres Observatory Collaboration, The VINROUGE Collaboration & The MASTER Collaboration)

    Abbott et al., ApJL, Multi-messenger Observations of a Binary Neutron Star Merger

    PRESS RELEASES AND MEDIA COVERAGE


    Watch Ryan Foley tell the story of how his team found the neutron star merger in the video below. 2.5 HOURS.

    Press releases:

    UC Santa Cruz Press Release

    UC Berkeley Press Release

    Carnegie Institution of Science Press Release

    LIGO Collaboration Press Release

    National Science Foundation Press Release

    Media coverage:

    The Atlantic – The Slack Chat That Changed Astronomy

    Washington Post – Scientists detect gravitational waves from a new kind of nova, sparking a new era in astronomy

    New York Times – LIGO Detects Fierce Collision of Neutron Stars for the First Time

    Science – Merging neutron stars generate gravitational waves and a celestial light show

    CBS News – Gravitational waves – and light – seen in neutron star collision

    CBC News – Astronomers see source of gravitational waves for 1st time

    San Jose Mercury News – A bright light seen across the universe, proving Einstein right

    Popular Science – Gravitational waves just showed us something even cooler than black holes

    Scientific American – Gravitational Wave Astronomers Hit Mother Lode

    Nature – Colliding stars spark rush to solve cosmic mysteries

    National Geographic – In a First, Gravitational Waves Linked to Neutron Star Crash

    Associated Press – Astronomers witness huge cosmic crash, find origins of gold

    Science News – Neutron star collision showers the universe with a wealth of discoveries

    UCSC press release
    First observations of merging neutron stars mark a new era in astronomy

    Credits

    Writing: Tim Stephens
    Video: Nick Gonzales
    Photos: Carolyn Lagattuta
    Header image: Illustration by Robin Dienel courtesy of the Carnegie Institution for Science
    Design and development: Rob Knight
    Project managers: Sherry Main, Scott Hernandez-Jason, Tim Stephens

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

    Noted in the vdeo but not in te article:

    NASA/Chandra Telescope

    NASA/SWIFT Telescope

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

    Prompt telescope CTIO Chile

    NASA NuSTAR X-ray telescope

    “The equations of state help astrophysicists study the outcome of neutron star mergers—they indicate whether a neutron star is ‘soft’ or ‘stiff,’ which in turn determines whether a more massive neutron star or a black hole forms out of the collision,” says da Silva Schneider. “The more observations we have from LIGO and other light-based telescopes, the more we can refine the equation of state—and update our software so that astrophysicists can generate new and more realistic equations for future studies.”

    See the full article here

    That event was also witnessed by a cadre of telescopes around the world, which captured light waves from the same event.

    See the full article here .

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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  • richardmitnick 7:49 am on February 27, 2018 Permalink | Reply
    Tags: , , , Caltech, , , Whirlpool galaxy   

    From Caltech: “Beaming with the Light of Millions of Suns” 

    Caltech Logo

    Caltech

    Whitney Clavin
    (626) 395-1856
    wclavin@caltech.edu

    A Caltech-led astronomy team is homing in on the nature of extreme objects known as ULXs.

    1
    Image of the Whirlpool galaxy, or M51. X-ray light seen by NASA’s Chandra X-ray Observatory is shown in purple, and optical light from NASA’s Hubble Space Telescope is red, green and blue. The ultraluminous X-ray source, or ULX, in the new Caltech-led study is indicated. Credit: NASA/CXC/Caltech/M.Brightman et al.; Optical: NASA/STScI

    NASA/Chandra Telescope

    NASA/ESA Hubble Telescope

    In the 1980s, researchers began discovering extremely bright sources of X-rays in the outer portions of galaxies, away from the supermassive black holes that dominate their centers. At first, the researchers thought these cosmic objects—called ultraluminous X-ray sources, or ULXs—were hefty black holes with more than 10 times the mass of the sun. But observations beginning in 2014 from NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) and other space telescopes are showing that some ULXs, which glow with X-ray light equal in energy to millions of suns, are actually neutron stars—the burnt-out cores of massive stars that exploded. Three such ULXs have been identified as neutron stars so far.

    NASA NuSTAR X-ray telescope

    Now, a Caltech-led team using data from NASA’s Chandra X-ray Observatory has identified a fourth ULX as being a neutron star—and found new clues about how these objects can shine so brightly.

    Neutron stars are extremely dense objects—a teaspoonful of neutron star would weigh about a billion tons, or as much as a mountain. Their gravity pulls surrounding material from companion stars onto them; when this material is tugged on, it heats up and glows with X-rays. But as the neutron stars “feed” on the matter, there comes a time when the resulting X-ray light pushes the matter away. Astronomers call this point—the point at which the objects cannot accumulate matter any faster and cannot give off any more X-rays—the Eddington limit.

    “In the same way that we can only eat so much food at a time, there are limits to how fast neutron stars can accrete matter,” says Murray Brightman, a postdoctoral scholar at Caltech and lead author of a new report on the findings in Nature Astronomy. “But ULXs are somehow breaking this limit to give off such incredibly bright X-rays, and we don’t know why.”

    In the new study, the researchers looked at a ULX in the Whirlpool galaxy, also known as M51, which lies about 28 million light-years away. They analyzed archival X-ray data taken by Chandra and discovered an unusual dip in the ULX’s light spectrum. After ruling out all other possibilities, they figured out that the dip was from a phenomenon called cyclotron resonance scattering, which occurs when charged particles—either positively charged protons or negatively charged electrons—circle around in a magnetic field. Black holes don’t have magnetic fields, but neutron stars do, so the finding revealed that this particular ULX in M51 had to be a neutron star.

    Cyclotron resonance scattering creates telltale signatures in a star’s spectrum of light, and the presence of these patterns, called cyclotron lines, can provide information about the strength of the star’s magnetic field—but only if the cause of the lines, whether it be protons or electrons, is known. With regards to this ULX, the researchers don’t have a detailed-enough spectrum to say for certain.

    “If the cyclotron line is from protons, then we would know that these magnetic fields around the neutron star are extremely strong and may in fact be helping to breaking the Eddington limit,” says Brightman. Such strong magnetic fields could reduce the pressure from a ULX’s X-rays—the pressure that normally pushes away matter—allowing the neutron star to consume more matter than is typical and shine with the extremely bright X-rays.

    If the cyclotron line is from circling electrons, in contrast, then the magnetic field strength around the neutron star would not be exceptionally strong, and thus the field would probably not be the reason these stars break the Eddington limit.

    To further address the mystery of how neutron stars are breaking this limit, the researchers are planning to acquire more X-ray data on the ULX in M51 and look for more cyclotron lines in other ULXs.

    “The discovery that these very bright objects, long thought to be black holes with masses up to 1,000 times that of the sun, are powered by much less massive neutron stars, was a huge scientific surprise,” says Fiona Harrison, Caltech’s Benjamin M. Rosen Professor of Physics; the Kent and Joyce Kresa Leadership Chair of the Division of Physics, Mathematics and Astronomy; and the principal investigator of the NuSTAR mission. “Now we might actually be getting firm physical clues as to how these small objects can be so mighty.”

    The Nature Astronomy study, titled Magnetic field strength of a neutron-star-powered ultraluminous X-ray source, was funded by NASA and the Ernest Rutherford Fellowships. Other authors include Felix Fürst of the European Space Astronomy Centre; Matthew J. Middleton of the University of Southampton, United Kingdom; Dominic Walton and Andrew C. Fabian of the University of Cambridge, United Kingdom; Daniel Stern of the Jet Propulsion Laboratory; Marianne Heida of Caltech; Didier Barret of France’s Centre national de la recherche scientifique and the University of Toulouse; and Matteo Bachetti of Italy’s Istituto Nazionale di Astrofisica.

    See the full article here .

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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  • richardmitnick 5:47 pm on February 15, 2018 Permalink | Reply
    Tags: , , Caltech, Cells Communicate in a Dynamic Code   

    From Caltech: “Cells Communicate in a Dynamic Code” 

    Caltech Logo

    Caltech

    02/15/2018

    Lori Dajose
    (626) 395-1217
    ldajose@caltech.edu

    1
    Artist’s concept of a cell expressing the Delta1 ligand (left) and a cell expressing the Delta4 ligand (right). While these two ligands activate cellular receptors in the same way, they do so in different patterns over time. In this way, a receiving cell can decode instructions.
    Credit: Caltech

    2
    Illustration of a message-receiving cell (bottom) expressing the Notch receptor, depicted as a satellite dish, to receive messages from cells expressing two different ligand “messages”, named Delta1 (left, blue) or Delta4 (right, red). The identity of the signaling molecule is encoded in pulsatile (left) or sustained (right) dynamics. These dynamics are in turn “decoded” by a module involving the genes HES1 and HEY1 (white box with dials) to control the cell’s decision to differentiate. Credit: Courtesy of the Elowitz laboratory

    A critically important intercellular communication system is found to encode and transmit more messages than previously thought.

    Multicellular organisms like ourselves depend on a constant flow of information between cells, coordinating their activities in order to proliferate and differentiate. Deciphering the language of intercellular communication has long been a central challenge in biology. Now, Caltech scientists have discovered that cells have evolved a way to transmit more messages through a single pathway, or communication channel, than previously thought, by encoding the messages rhythmically over time.

    The work, conducted in the laboratory of Michael Elowitz, professor of biology and bioengineering, Howard Hughes Medical Institute Investigator, and executive officer for Biological Engineering, is described in a paper in the February 8 issue of Cell.

    In particular, the scientists studied a key communication system called “Notch,” which is used in nearly every tissue in animals. Malfunctions in the Notch pathway contribute to a variety of cancers and developmental diseases, making it a desirable target to study for drug development.

    Cells carry out their conversations using specialized communication molecules called ligands, which interact with corresponding molecular antennae called receptors. When a cell uses the Notch pathway to communicate instructions to its neighbors—telling them to divide, for example, or to differentiate into a different kind of cell—the cell sending the message will produce certain Notch ligands on its surface. These ligands then bind to Notch receptors embedded in the surface of nearby cells, triggering the receptors to release gene-modifying molecules called transcription factors into the interior of their cell. The transcription factors travel to the cell’s nucleus, where the cell’s DNA is stored, and activate specific genes. The Notch system thus allows cells to receive signals from their neighbors and alter their gene expression accordingly.

    Ligands prompt the activation of transcription factors by modifying the structure of the receptors into which they dock. All ligands modify their receptors in a similar way and activate the same transcription factors in a receiving cell, and for that reason, scientists generally assumed that the receiving cell should not be able to reliably determine which ligand had activated it, and hence which message it had received.

    “At first glance, the only explanation for how cells distinguish between two ligands, if at all, seems to be that they must somehow accurately detect differences in how strongly the two ligands activate the receptor. However, all evidence so far suggests that, unlike mobile phones or radios, cells have much more trouble precisely analyzing incoming signals,” says lead author and former Elowitz lab graduate student Nagarajan (Sandy) Nandagopal (PhD ’18). “They are usually excellent at distinguishing between the presence or absence of signal, but not very much more. In this sense, cellular messaging is closer to sending smoke signals than texting. So, the question is, as a cell, how do you differentiate between two ligands, both of which look like similar puffs of smoke in the distance?”

    Nandagopal and his collaborators wondered whether the answer lay in the temporal pattern of Notch activation by different ligands—in other words, how the “smoke” is emitted over time. To test this, the team developed a new video-based system through which they could record signaling in real time in each individual cell. By tagging the receptors and ligands with fluorescent protein markers, the team could watch how the molecules interacted as signaling was occurring.

    The team studied two chemically similar Notch ligands, dubbed Delta1 and Delta4. They discovered that despite the ligands’ similarity the two activated the same receptor with strikingly different temporal patterns. Delta1 ligands activated clusters of receptors simultaneously, sending a sudden burst of transcription factors down to the nucleus all at once, like a smoke signal consisting of a few giant puffs. On the other hand, Delta4 ligands activated individual receptors in a sustained manner, sending a constant trickle of single transcription factors to the nucleus, like a steady stream of smoke.

    These two patterns are the key to encoding different instructions to the cell, the researchers say. In fact, this mechanism enabled the two ligands to communicate dramatically different messages. By analyzing chick embryos, the authors discovered that Delta1 activated abdominal muscle production, whereas Delta4 strongly inhibited this process in the same cells.

    “Cells speak only a handful of different molecular languages but they have to work together to carry out an incredible diversity of tasks,” says Elowitz. “We’ve generally assumed these languages are extremely simple, and cells can basically only grunt at each other. By watching cells in the process of communicating, we can see that these languages are more sophisticated and have a larger vocabulary than we ever thought. And this is probably just the tip of an iceberg for intercellular communication.”

    The paper is titled Dynamic Ligand Discrimination in the Notch Signaling Pathway. In addition to Nandagopal and Elowitz, other Caltech co-authors are Leah Santat, who is also a Howard Hughes Medical Institute Investigator, and Marianne Bronner, the Albert Billings Ruddock Professor of Biology. Additional co-authors are Lauren LeBon of Calico Life Sciences and David Sprinzak of Tel Aviv University. Funding was provided by the Defense Advanced Research Projects Agency, the National Institutes of Health, the National Science Foundation, and the Howard Hughes Medical Institute.

    See the full article here .

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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  • richardmitnick 4:04 pm on January 24, 2018 Permalink | Reply
    Tags: , , , Caltech, , Jim Fuller   

    From Caltech: “Taking the Pulse of Planets and Stars” Jim Fuller 

    Caltech Logo

    Caltech

    01/24/2018

    Whitney Clavin
    (626) 395-1856
    wclavin@caltech.edu

    HEY, J.L.T. IN L.A., YOU SHOULD READ THIS

    1
    Jim Fuller, assistant professor of theoretical astrophysics at Caltech. Credit: Caltech

    New faculty member Jim Fuller talks about the inner workings of cosmic spheres.

    New faculty member Jim Fuller, assistant professor of theoretical astrophysics, studies vibrating cosmic spheres, such as stars with “heartbeats,” and the gas giant Saturn, whose pulsations propagate through its rings. He is a theorist who uses math, physics, and numerical simulations to tackle astronomy problems, in particular those related to a planet’s or star’s internal structure and evolution. Fuller says he fell in love with astronomy when he was young and realized he could use his imagination.

    “In astronomy, you think about things you don’t encounter in your everyday life, like stars, where you really need to use your imagination because the scale is so large,” he says. “But at the same time, astronomy is concrete. There is really something happening out there, and we are applying math and physics to real situations to learn more about our universe.”

    Fuller received his bachelor’s degree from Whitman College in 2008, and his PhD in astronomy and space sciences in 2014 from Cornell University. He joined Caltech as a DuBridge Postdoctoral Fellow in 2013 and joined the Caltech faculty in 2017.

    Below Fuller describes, in his own words, some of the movies he has made to illustrate how to “take the pulse” of planets and stars.

    Heartbeat Stars
    “The pulsing orbs in this movie are known as “heartbeat” stars. These are binary star systems with very eccentric orbits. At closest approach, which occurs at around seven seconds into the movie, the stars come within a few stellar radii of each other. Their mutual gravitational forces distort the stars into elliptical shapes, changing their observed cross section and apparent brightness. This creates a heartbeat-like pulse in the light curve below the stars.

    The brightness changes caused by these so-called tidal distortions have been detected by NASA’s Kepler space telescope, leading to the discovery of hundreds of these heartbeat-star systems. Some heartbeat stars do not relax back to their original shape after their closest approach, and they continue to pulsate throughout their orbits as illustrated in this movie. These stellar oscillations cause the stars to dissipate orbital energy, which causes their orbits to circularize. You can also “hear” a heartbeat star below, where I have converted the light curve detected by Kepler into sound and sped things up by a factor of 5 million.

    I’m trying to better understand the evolution of heartbeat stars’ orbits through a combination of theory and observations.”


    Saturn’s Inner Pulse
    “Like stars, gaseous planets such as Jupiter and Saturn are continually distorted by their own minute pulsations. With Saturn, we cannot see these pulsations directly, but we have learned to use its rings as a giant seismograph. The small gravitational variations caused by pulsations of Saturn exert small torques on orbiting ring particles, generating spiral waves within the rings. These ring disturbances were detected using NASA’s Cassini satellite, which later plunged into Saturn in September 2017.

    This movie shows an exaggerated example of a pulsation from Saturn propagating around the equator of the planet. The pulsation causes a spiral density wave in the rings that propagates at the same rate. The motion of these spiral patterns then tells us the frequency at which Saturn pulsates, and this can be used to measure properties of the interior of Saturn. My work suggests that Saturn’s interior is more complex than previously believed, with an “outer core” composed of a mix of the icy/rocky core material and the gaseous material found in the outer envelope.”


    Starquakes
    “Stars in a later stage of evolution, called red giants, exhibit minute pulsations caused by continual “starquakes.” Like terrestrial oscillations that occur after earthquakes, starquakes can be used to measure properties of the internal structures of stars because they result from sound waves that propagate through the stellar interior and carry information back to the surface. The movie illustrates a path that a wave would take on its journey between the core and surface of a star if it was able to travel unimpeded. By studying the theory of how waves travel through stars along with some observations of the phenomenon, I helped discover something new about red giants: magnetic fields disrupt the propagation of waves near the core of the star, causing the stellar pulsations to be suppressed. This suppression phenomenon has since been observed in thousands of red giants, suggesting strong internal magnetic fields are more common than we previously believed.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

    Caltech campus

     
  • richardmitnick 3:05 pm on January 12, 2018 Permalink | Reply
    Tags: , , , Caltech, Citizen Scientists Discover Five-Planet System, , Exoplanet Explorers   

    From Caltech: “Citizen Scientists Discover Five-Planet System” 

    Caltech Logo

    Caltech

    01/11/2018

    Whitney Clavin
    (626) 395-1856
    wclavin@caltech.edu

    Caltech staff scientist Jessie Christiansen is a founder of a citizen-scientist project called Exoplanet Explorers.

    1
    Artist’s visualization of the K2-138 system, the first multi-planet system discovered by citizen scientists. The central star is slightly smaller and cooler than our sun. The five known planets are all between the size of Earth and Neptune; planet b may potentially be rocky, but planets c, d, e, and f likely contain large amounts of ice and gas. All five planets have orbital periods shorter than 13 days and are all incredibly hot, ranging from 800 to 1800 degrees Fahrenheit. Credit: NASA/JPL-Caltech/R. Hurt (IPAC).

    2
    Artist’s concept of a top-down view of the K2-138 system discovered by citizen scientists, showing the orbits and relative sizes of the five known planets. Orbital periods of the five planets, shown to scale, fall close to a series of 3:2 mean motion resonances. This indicates that the planets orbiting K2-138, which likely formed much farther away from the star, migrated inward slowly and smoothly. Credit: NASA/JPL-Caltech/R. Hurt (IPAC).

    In its search for exoplanets—planets outside of our solar system—NASA’s Kepler telescope trails behind Earth, measuring the brightness of stars that may potentially host planets. The instrument identifies potential planets around other stars by looking for dips in the brightness of the stars that occur when planets cross in front of, or transit, them. Typically, computer programs flag the stars with these brightness dips, then astronomers look at each one and decide whether or not they truly could host a planet candidate.

    Over the three years of the K2 mission, 287,309 stars have been observed, and tens of thousands more roll in every few months. So how do astronomers sift through all that data?

    Enter the Exoplanet Explorers citizen scientist project, developed by UC Santa Cruz astronomer Ian Crossfield and Caltech staff scientist Jessie Christiansen. Exoplanet Explorers is hosted on Zooniverse, an online platform for crowdsourcing research.

    “People anywhere can log on and learn what real signals from exoplanets look like, and then look through actual data collected from the Kepler telescope to vote on whether or not to classify a given signal as a transit, or just noise,” says Christiansen. “We have each potential transit signal looked at by a minimum of 10 people, and each needs a minimum of 90 percent of ‘yes’ votes to be considered for further characterization.”

    In early April, just two weeks after the initial prototype of Exoplanet Explorers was set up on Zooniverse, it was featured in a three-day event on the ABC Australia television series Stargazing Live. In the first 48 hours after the project was introduced, Exoplanet Explorers received over 2 million classifications from more than 10,000 users. Included in that search was a brand-new dataset from the K2 mission—the reincarnation of the primary Kepler mission, ended three years ago. K2 has a whole new field of view and crop of stars around which to search for planets. No professional astronomer had yet looked through this dataset, called C12.

    Back in California, Crossfield and Christiansen joined NASA astronomer Geert Barentsen, who was in Australia, in examining results as they came in. Using the depth of the transit curve and the periodicity with which it appears, they made estimates for how large the potential planet is and how close it orbits to its star. On the second night of the show, the researchers discussed the demographics of the planet candidates found so far—44 Jupiter-sized planets, 72 Neptune-sized, 44 Earth-sized, and 53 so-called Super Earth’s, which are larger than Earth but smaller than Neptune.

    “We wanted to find a new classification that would be exciting to announce on the final night, so we were originally combing through the planet candidates to find a planet in the habitable zone—the region around a star where liquid water could exist,” says Christiansen. “But those can take a while to validate, to make sure that it really is a real planet and not a false alarm. So, we decided to look for a multi-planet system because it’s very hard to get an accidental false signal of several planets.”

    After this decision, Barentsen left to get a cup of tea. By the time he returned, Christiansen had sorted the crowdsourced data to find a star with multiple transits and discovered a star with four planets orbiting it. Three of the four planets had 100 percent “yes” votes from over 10 people, and the remaining one had 92 percent “yes” votes. This is the first multi-planet system of exoplanets discovered entirely by crowdsourcing.

    After the discovery was announced on Stargazing Live, Christiansen and her colleagues continued to study and characterize the system, dubbed K2-138. They statistically validated the set of planet signals as being “extremely likely,” according to Christiansen, to be signals from true planets. They also found that the planets are orbiting in an interesting mathematical relationship called a resonance, in which each planet takes almost exactly 50 percent longer to orbit the star than the next planet further in. The researchers also found a fifth planet on the same chain of resonances, and hints of a sixth planet as well. A paper describing the system has been accepted for publication in The Astronomical Journal.

    This is the only system with a chain of unbroken resonances in this configuration, and may provide clues to theorists looking to unlock the mysteries of planet formation and migration.

    “The clockwork-like orbital architecture of this planetary system is keenly reminiscent of the Galilean satellites of Jupiter,” says Konstantin Batygin, assistant professor of planetary science and Van Nuys Page Scholar, who was not involved with the study. “Orbital commensurabilities among planets are fundamentally fragile, so the present-day configuration of the K2-138 planets clearly points to a rather gentle and laminar formation environment of these distant worlds.”

    “Some current theories suggest that planets form by a chaotic scattering of rock and gas and other material in the early stages of the planetary system’s life. However, these theories are unlikely to result in such a closely packed, orderly system as K2-138,” says Christiansen. “What’s exciting is that we found this unusual system with the help of the general public.”

    The paper is titled “The K2-138 system: A Near-Resonant Chain of Five Sub-Neptune Planets Discovered by Citizen Scientists [The Astronomical Journal].” In addition to Christiansen, Crossfield, and Barentsen; other coauthors include Chris Lintott, Campbell Allen, Adam McMaster, Grant Miller, Martin Veldthuis of the University of Oxford; Thomas Barclay of NASA Goddard and the University of Maryland; Brooke Simmons of UC San Diego; Caltech postdoctoral scholar Erik Petigura; Joshua Schlieder of NASA Goddard; Courtney Dressing of UC Berkeley; Andrew Vanderburg of Harvard; Sarah Allen and Zach Wolfenbarger of the Adler Planetarium; Brian Cox of the University of Manchester; Julia Zemiro of the Australian Broadcasting Corporation; Caltech Professor of Astronomy Andrew Howard; John Livingston of the University of Tokyo; Evan Sinukoff of the Australian Broadcasting Corporation and the University of Hawai’i at Manoa; Timothy Catron of Arizona State University; Andrew Grey, Joshua Kusch, Ivan Terentev, and Martin Vales of Zooniverse as part of the University of Oxford; and Martti Kristiansen of the Technical University of Denmark. Funding was provided by the NASA Science Mission Directorate, Google, the Alfred P. Sloan Foundation, NASA, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

    Caltech campus

     
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