Gravitational Waves Detected 100 Years After Einstein’s Prediction

For the first time, scientists have observed ripples in the fabric of spacetime called gravitational waves, arriving at the earth from a cataclysmic event in the distant universe. This confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window onto the cosmos.

Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot otherwise be obtained. Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. This collision of two black holes had been predicted but never observed.

The gravitational waves were detected on September 14, 2015 at 5:51 a.m. Eastern Daylight Time (9:51 UTC) by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA. The LIGO Observatories are funded by the National Science Foundation (NSF), and were conceived, built, and are operated by Caltech and MIT. The discovery, accepted for publication in the journal Physical Review Letters, was made by the LIGO Scientific Collaboration (which includes the GEO Collaboration and the Australian Consortium for Interferometric Gravitational Astronomy) and the Virgo Collaboration using data from the two LIGO detectors.

University of Maryland Physics Professor Joseph Weber (1919-2000) with one of the world's first gravitational wave detectors. Credit: Special Collections and University Archives, University of Maryland LibrariesUniversity of Maryland Physics Professor Joseph Weber (1919-2000) with one of the world's first gravitational wave detectors. Credit: Special Collections and University Archives, University of Maryland Libraries

Researchers in the University of Maryland Department of Physics contributed to the international effort that led to the discovery of these gravitational waves, building on the university’s long history in this field. In the early 1960s, the late UMD Physics Professor Joseph Weber built the world’s first gravitational wave detectors on the university’s College Park, Md. campus, inspiring a new field of research.

“Sharing the detection of this binary black hole merger event is a sheer joy for all of us who have been working in this field,” said Peter Shawhan, an associate professor of physics at UMD and a LIGO Scientific Collaboration (LSC) principal investigator. “It’s a dream finally realized, but it is just the beginning of the science that we can do with LIGO and other gravitational wave detectors.” 

Shawhan helped to validate the analysis software that identified the black-hole merger signal a few minutes after the LIGO detectors recorded it. He also acted as a liaison with astronomers before and during the LIGO observing run. UMD physics graduate student Min-A Cho developed software to communicate the properties of promising signals to astronomers for follow-up observations with their telescopes and other instruments.

Cregg Yancey, also a UMD physics graduate student, helped to check that the detectors operated properly when the signal was detected. The black-hole merger signal stood up to all scrutiny during months of painstaking analysis and cross checks and was ultimately named GW150914, indicating the date of its arrival at Earth.

Alessandra Buonanno, a UMD Research Professor of Physics who also has an appointment as Director at the Max Planck Institute for Gravitational Physics in Potsdam, Germany, together with many students and postdoctoral researchers at both institutions, have developed highly accurate models of gravitational waves that black holes would generate in the final process of orbiting and colliding with each other.

UMD alumnus Andrea Taracchini (Ph.D. '14, physics), who is now a postdoctoral researcher in Buonanno's division at the Max Planck Institute in Germany; Buonanno; Yi Pan, a former assistant research scientist in physics at UMD; and Enrico Barausse, a former postdoctoral researcher in physics at UMD, developed waveform models that were employed in the search that observed the black-hole merger with high-enough significance to be confident in its detection.

"We spent years modeling the gravitational-wave emission from one of the most extreme events in the universe: pairs of massive black holes orbiting each other and then merging. And that’s exactly the kind of signal we detected!” said Buonanno, who is also an LSC principal investigator.

Buonanno also co-led an effort to determine whether the signal detected by LIGO matches exactly the predictions of Einstein’s theory of general relativity. So far, all tests find the signal to be consistent with this theory.

“It is overwhelming to see how exactly Einstein’s theory of relativity describes reality,” said Buonanno. “GW150914 gives us a remarkable opportunity to see how gravity operates under some of the most extreme conditions possible.” 

UMD physicists are continuing a long tradition of gravitational wave research that began over 50 years ago. Weber’s early detectors used “resonant bars”, which were designed to ring when a gravitational wave passed through them. UMD Physics Professors Emeriti Ho Jung Paik and Jean-Paul Richard improved on Weber’s technique to develop more sensitive resonant detectors. Later technology improvements enabled the more-sensitive laser interferometer technique used by LIGO.

Over the years, the gravity theory research group at UMD has also made many key contributions to the theory of black hole dynamics, gravitational wave emission and possible alternative theories of gravity, through the work of UMD Physics Professors Emeriti Dieter Brill and Charles Misner and UMD Physics Professor Ted Jacobson.

“As we continue to improve our detectors and collect and analyze more data, we expect many more discoveries that will give us a fuller picture of the gravitational dynamics that have shaped our universe, with all its galaxies and stars, along with weird, wonderful things like neutron stars and black holes,” said Shawhan.

LIGO research is carried out by the LSC, a group of more than 1000 scientists from universities around the United States and in 14 other countries. More than 90 universities and research institutes in the LSC develop detector technology and analyze data; approximately 250 students are strong contributing members of the collaboration. The LSC detector network includes the LIGO interferometers and the GEO600 detector. The GEO team includes scientists at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI), Leibniz Universität Hannover, along with partners at the University of Glasgow, Cardiff University, the University of Birmingham, other universities in the United Kingdom, and the University of the Balearic Islands in Spain. 

LIGO was originally proposed as a means of detecting these gravitational waves in the 1980s by Rainer Weiss, professor of physics, emeritus, from MIT; Kip Thorne, Caltech’s Richard P. Feynman Professor of Theoretical Physics, emeritus; and Ronald Drever, professor of physics, emeritus, also from Caltech.

Virgo research is carried out by the Virgo Collaboration, consisting of more than 250 physicists and engineers belonging to 19 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in The Netherlands with Nikhef; the Wigner RCP in Hungary; the POLGRAW group in Poland and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy.

The discovery was made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared with the first-generation LIGO detectors, enabling a large increase in the volume of the universe probed—and the discovery of gravitational waves during its first observation run. The U.S. National Science Foundation leads in financial support for Advanced LIGO. Funding organizations in Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council, STFC) and Australia (Australian Research Council) also have made significant commitments to the project. Several of the key technologies that made Advanced LIGO so much more sensitive have been developed and tested by the German UK GEO collaboration. Significant computer resources have been contributed by the AEI Hannover Atlas Cluster, the LIGO Laboratory, Syracuse University and the University of Wisconsin-Milwaukee.  Several universities designed, built and tested key components for Advanced LIGO: The Australian National University, the University of Adelaide, the University of Florida, Stanford University, Columbia University of New York and Louisiana State University.

Press conference by the LIGO Observatories:

 

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The College of Computer, Mathematical, and Natural Sciences at the University of Maryland educates more than 7,000 future scientific leaders in its undergraduate and graduate programs each year. The college's 10 departments and more than a dozen interdisciplinary research centers foster scientific discovery with annual sponsored research funding exceeding $150 million.

 

New Material Becomes Invisible to Microwave Radiation with the Flip of a Switch

University of Maryland physicists have developed a new cloaking material that can become transparent to microwave radiation with the flip of a switch. Because many wireless communication devices rely on microwaves, the new material could be used to design more efficient communications networks. Additionally, the material has unique properties that could help bridge the gap between modern digital computers and next-generation “quantum” computers.

The new material can be selectively tuned to respond to a wide range of microwave wavelengths, making it more versatile than many previous attempts at cloaking technology. The achievement is described in a paper published on December 18, 2015 in the journal Physical Review X. The UMD researchers teamed with HYPRES, an advanced electronics company based in Elmsford, NY, on the project.

“Prior to this work, other cloaking materials were only effective at a single wavelength, which is not realistically useful,” said Daimeng Zhang, lead author of the study and a graduate student in electrical and computer engineering at UMD. “Our material is transparent across a broad range of microwave wavelengths. Also, we can turn the microwave transparency on and off. This hasn’t been explored before.”

This schematic illustrates a new self-cloaking metamaterial developed by University of Maryland physicists in collaboration with HYPRES, Inc. An array of miniature devices (circular structures) called rf-SQUIDs can become transparent to microwave radiation with the flip of a switch. At left, the material is in transparent mode and allows microwaves to travel freely. At right, the material is in opaque mode and prevents microwaves from traversing the barrier. Image credit: Sean Kelley/JQI (Click image to download hi-res version.)

This schematic illustrates a new self-cloaking metamaterial developed by University of Maryland physicists in collaboration with HYPRES, Inc. An array of miniature devices (circular structures) called rf-SQUIDs can become transparent to microwave radiation with the flip of a switch. At left, the material is in transparent mode and allows microwaves to travel freely. At right, the material is in opaque mode and prevents microwaves from traversing the barrier. Image credit: Sean Kelley/JQI (Click image to download hi-res version.)

The cloaking material developed at UMD cannot make other objects (or people) disappear. Instead, by selectively becoming transparent to microwave radiation, it can either shield or expose a target to incoming microwaves. For this reason, the researchers use the terms “auto-cloaking” or “self-cloaking” to describe the material.

“In that sense, our material could be said to work in reverse. When the transparency is turned on, any object behind it is visible to microwave detection,” said Steven Anlage, senior author of the study and a professor of physics at UMD. “But when the transparency is turned off, the material becomes a barrier and conceals anything behind it. It’s a good hider.”

The cloaking material is considered a metamaterial, or a “smart” material engineered to have properties not found in nature. Metamaterials are made of an array of “meta-atoms,” which are not atoms in the true chemical sense, but rather the smallest component parts of a metamaterial. The meta-atoms used in the UMD cloaking material are tiny devices—not much wider than a human hair—called Radio Frequency Superconducting QUantum Interference Devices (rf-SQUIDs). Each rf-SQUID exhibits the same properties as the metamaterial, meaning that the technology theoretically can be scaled up to any size.

“Previous attempts at cloaking technology could only respond to one wavelength,” said Melissa Trepanier, a co-author of the study and a graduate student in physics at UMD. “Perhaps more importantly, the wavelength could not be changed after the material was created. This meant that engineers needed to decide on—and commit to—a target wavelength prior to the design and construction phase.”

The UMD researchers solved this problem by designing the rf-SQUIDs with properties that can be tuned by varying the magnetic field applied to the material and/or the temperature of the material.

Zhang, Trepanier and Anlage co-authored the study with Oleg Mukhanov, chief technology officer of HYPRES. The research was supported by the National Science Foundation’s Grant Opportunities for Academic Liaison with Industry (GOALI) program. The GOALI program is designed to fund high-risk/high-reward research projects and enhance collaborations between academic scientists and industry.

Beyond its use for cloaking, the rf-SQUID-based metamaterial might help solve other technological challenges, including the implementation of quantum computers.

“HYPRES is very interested in the interface between quantum computing and classical digital computing, so we are looking for new technology capable of connecting the two,” Mukhanov said. “This new metamaterial has properties that are sensitive to both quantum processes and superconducting digital logic, so it would most likely be cross-compatible.”

“We’re working on the edges of what anyone has done before,” Anlage added. “It’s wild stuff, but there is a lot of potential to help develop cool new technology.”

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This work was supported by the National Science Foundation through the Grant Opportunities for Academic Liaison with Industry (GOALI) program (Award No. ECCS-1158644). The content of this article does not necessarily reflect the views of this organization.

The research paper, “Tunable Broadband Transparency of Macroscopic Quantum Superconducting Metamaterials,” Daimeng Zhang, Melissa Trepanier, Oleg Mukhanov and Steven Anlage, was published on December 18, 2015 in the journal Physical Review X.

 

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