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The LIGO Scientific Collaboration and the Virgo Collaboration identify a second gravitational wave event from another pair of black holes in the data from Advanced LIGO detectors

Gravitational waves detected from second pair of colliding black holes

The LIGO Scientific Collaboration and the Virgo Collaboration identify a second gravitational wave event in the data from Advanced LIGO detectors


PAPER: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.241103

IMAGES & AUDIO: https://caltech.app.box.com/v/LIGO-JuneAAS


On December 26, 2015 at 03:38:53 UTC, scientists observed gravitational waves–ripples in the fabric of spacetime–for the second time.

The gravitational waves were detected 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.

Gravitational waves carry information about their origins and about the nature of gravity that cannot otherwise be obtained, and physicists have concluded that these gravitational waves were produced during the final moments of the merger of two black holes–14 and 8 times the mass of the sun–to produce a single, more massive spinning black hole that is 21 times the mass of the sun.

“It is very significant that these black holes were much less massive than those observed in the first detection,” says Gabriela González, LIGO Scientific Collaboration (LSC) spokesperson and professor of physics and astronomy at Louisiana State University. “Because of their lighter masses compared to the first detection, they spent more time–about one second–in the sensitive band of the detectors. It is a promising start to mapping the populations of black holes in our universe.”

During the merger, which occurred approximately 1.4 billion years ago, a quantity of energy roughly equivalent to the mass of the sun was converted into gravitational waves. The detected signal comes from the last 27 orbits of the black holes before their merger. Based on the arrival time of the signals–with the Livingston detector measuring the waves 1.1 milliseconds before the Hanford detector–the position of the source in the sky can be roughly determined.

“In the near future, Virgo, the European interferometer, will join a growing network of gravitational wave detectors, which work together with ground-based telescopes that follow-up on the signals,” notes Fulvio Ricci, the Virgo Collaboration spokesperson, a physicist at Istituto Nazionale di Nucleare (INFN) and professor at Sapienza University of Rome. “The three interferometers together will permit a far better localization in the sky of the signals.”

The first detection of gravitational waves, announced on February 11, 2016, was a milestone in physics and astronomy; it confirmed a major prediction of Albert Einstein’s 1915 general theory of relativity, and marked the beginning of the new field of gravitational-wave astronomy.

The second discovery “has truly put the ‘O’ for Observatory in LIGO,” says Caltech’s Albert Lazzarini, deputy director of the LIGO Laboratory. “With detections of two strong events in the four months of our first observing run, we can begin to make predictions about how often we might be hearing gravitational waves in the future. LIGO is bringing us a new way to observe some of the darkest yet most energetic events in our universe.”

“We are starting to get a glimpse of the kind of new astrophysical information that can only come from gravitational wave detectors,” says MIT’s David Shoemaker, who led the Advanced LIGO detector construction program.

Both discoveries were made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared to the first generation LIGO detectors, enabling a large increase in the volume of the universe probed

“With the advent of Advanced LIGO, we anticipated researchers would eventually succeed at detecting unexpected phenomena, but these two detections thus far have surpassed our expectations,” says NSF Director France A. Córdova. “NSF’s 40-year investment in this foundational research is already yielding new information about the nature of the dark universe.”

Advanced LIGO’s next data-taking run will begin this fall. By then, further improvements in detector sensitivity are expected to allow LIGO to reach as much as 1.5 to 2 times more of the volume of the universe. The Virgo detector is expected to join in the latter half of the upcoming observing run.

LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of more than 1,000 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.

Virgo research is carried out by the Virgo Collaboration, consisting of more than 250 physicists and engineers belonging to 19 different European research groups: 6 from Centre National de la Recherche Scientifique (CNRS) in France; 8 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; 2 in The Netherlands with Nikhef; the MTA 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 NSF 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, the ARCCA cluster at Cardiff University, the University of Wisconsin-Milwaukee, and the Open Science Grid. Several universities designed, built, and tested key components and techniques for Advanced LIGO: The Australian National University, the University of Adelaide, the University of Western Australia, the University of Florida, Stanford University, Columbia University in the City of New York, and Louisiana State University. 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 Germany, and the University of the Balearic Islands in Spain.


 

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Trapping light with a twister

New understanding of how to halt photons could lead to miniature particle accelerators, improved data transmission.

By David L. Chandler


Researchers at MIT who succeeded last year in creating a material that could trap light and stop it in its tracks have now developed a more fundamental understanding of the process. The new work — which could help explain some basic physical mechanisms — reveals that this behavior is connected to a wide range of other seemingly unrelated phenomena.

The findings are reported in a paper in the journal Physical Review Letters, co-authored by MIT physics professor Marin Soljačić; postdocs Bo Zhen, Chia Wei Hsu, and Ling Lu; and Douglas Stone, a professor of applied physics at Yale University.

Light can usually be confined only with mirrors, or with specialized materials such as photonic crystals. Both of these approaches block light beams; last year’s finding demonstrated a new method in which the waves cancel out their own radiation fields. The new work shows that this light-trapping process, which involves twisting the polarization direction of the light, is based on a kind of vortex — the same phenomenon behind everything from tornadoes to water swirling down a drain.

Vortices of bound states in the continuum. The left panel shows five bound states in the continuum in a photonic crystal slab as bright spots. The right panel shows the polarization vector field in the same region as the left panel, revealing five vortices at the locations of the bound states in the continuum. These vortices are characterized with topological charges +1 or -1. Courtesy of the researchers Source: MIT
Vortices of bound states in the continuum. The left panel shows five bound states in the continuum in a photonic crystal slab as bright spots. The right panel shows the polarization vector field in the same region as the left panel, revealing five vortices at the locations of the bound states in the continuum. These vortices are characterized with topological charges +1 or -1.
Courtesy of the researchers
Source: MIT

In addition to revealing the mechanism responsible for trapping the light, the new analysis shows that this trapped state is much more stable than had been thought, making it easier to produce and harder to disturb.

“People think of this [trapped state] as very delicate,” Zhen says, “and almost impossible to realize. But it turns out it can exist in a robust way.”

In most natural light, the direction of polarization — which can be thought of as the direction in which the light waves vibrate — remains fixed. That’s the principle that allows polarizing sunglasses to work: Light reflected from a surface is selectively polarized in one direction; that reflected light can then be blocked by polarizing filters oriented at right angles to it.

But in the case of these light-trapping crystals, light that enters the material becomes polarized in a way that forms a vortex, Zhen says, with the direction of polarization changing depending on the beam’s direction.

Because the polarization is different at every point in this vortex, it produces a singularity — also called a topological defect, Zhen says — at its center, trapping the light at that point.

Hsu says the phenomenon makes it possible to produce something called a vector beam, a special kind of laser beam that could potentially create small-scale particle accelerators. Such devices could use these vector beams to accelerate particles and smash them into each other — perhaps allowing future tabletop devices to carry out the kinds of high-energy experiments that today require miles-wide circular tunnels.

The finding, Soljačić says, could also enable easy implementation of super-resolution imaging (using a method called stimulated emission depletion microscopy) and could allow the sending of far more channels of data through a single optical fiber.

“This work is a great example of how supposedly well-studied physical systems can contain rich and undiscovered phenomena, which can be unearthed if you dig in the right spot,” says Yidong Chong, an assistant professor of physics and applied physics at Nanyang Technological University in Singapore who was not involved in this research.

Chong says it is remarkable that such surprising findings have come from relatively well-studied materials. “It deals with photonic crystal slabs of the sort that have been extensively analyzed, both theoretically and experimentally, since the 1990s,” he says. “The fact that the system is so unexotic, together with the robustness associated with topological phenomena, should give us confidence that these modes will not simply

be theoretical curiosities, but can be exploited in technologies such as microlasers.”

The research was partly supported by the U.S. Army Research Office through MIT’s Institute for Soldier Nanotechnologies, and by the Department of Energy and the National Science Foundation.

Source: MIT News Office