TACC: Science Powerhouses Aid Search for Gravitational Waves

[bystander]

Science Powerhouses Unite to Help Search for Gravitational Waves
Texas Advanced Computing Center | University of Texas | 2014 Dec 03

Texas Advanced Computing Center (TACC) and the Laser Interferometer Gravitational-Wave Observatory (LIGO) collaborate to develop data workflow for next-generation experiment

Scientists since Albert Einstein have believed that when major galactic events like supernova explosions or black hole mergers occur in the universe, they leave a trace. That trace, it is believed, takes the form of gravitational waves, ripples in the curvature of space-time that propagate as a wave, travelling outward from the source.

For over a decade, scientists and engineers have engaged in one of the most ambitious research efforts ever undertaken: to design, build and operate the Laser Interferometer Gravitation Observatory (LIGO) to identify signs of gravitational waves. ...

To date, no waves have been detected. Yet most astronomers believe they're still out there, waiting to be discovered if only we use the right tools. For that reason, the NSF, along with the UK Science and Technology Facilities Council, the German Max Planck Society, and the Australian Research Council, have supported the creation of a follow-up to LIGO called Advanced LIGO (ALIGO), which replaces the original detectors with ones more than 10 times more sensitive. ALIGO is expected to go online in 2015. ...

In addition to all of the astronomical considerations that must be attended to in a project like this – the placement of the observatories, the sensitivity of the detectors, the modeling of the expected signals – Advanced LIGO is also a "Big Data" problem. ...

Discussing the matter with program officers at the NSF, they decided to see if the Extreme Science and Engineering Discovery Environment (XSEDE) could help. XSEDE, another NSF-supported project, oversees the nation's network of supercomputers and digital resources. These resources allow scientists to solve otherwise impossible computing problems and pursue really big science.

Perhaps it could do the same for Advanced LIGO. ...

To achieve their goal, the team overlaid LIGO's computing environment on top of the Stampede supercomputer at TACC, one of the most powerful in the world. They then used a tool called Condor to break their large computing problems into smaller parts that could be distributed and solved on individual nodes on the supercomputer. ...

Not only were the researchers able to prove they could compute on a big national supercomputer, in the process they ended up making the Advanced LIGO software four times more efficient, ultimately saving money and time. ...

[neufer]

• Advanced LIGO gravitational wave hunt looks ready to begin its quest.

[b][color=#0000FF][size=110]Advanced LIGO detectors will be able to see inspiraling binaries made up of two 1.4 M neutron stars to a distance of 300 Mpc, some 15x further than the initial LIGO, and giving an event rate some 3000x greater. Neutron star - black hole (BH) binaries will be visible to 650 Mpc; and coalescing BH+BH systems will be visible to cosmological distance, to z=0.4.[/size][/color][/b]

---

<<The Advanced LIGO interferometers promise an improvement over initial LIGO (Laser Interferometer Gravitational-wave Observatories) in the limiting sensitivity by more than a factor of 10 over the entire initial LIGO frequency band. It also increases the bandwidth of the instrument to lower frequencies (from ~40 Hz to ~10 Hz) and allows high-frequency operation due to its tunability. These improvements will enable the next generation of interferometers to study sources not accessible to initial LIGO, and to extract detailed astrophysical information.

The gravitational wave "sky" is entirely unexplored. Since many prospective gravitational wave sources have no corresponding electromagnetic signature (e.g., black hole interactions), there are good reasons to believe that the gravitational-wave sky will be substantially different from the electromagnetic one. Mapping the gravitational-wave sky will provide an understanding of the universe in a way that electromagnetic observations cannot. As a new field of astrophysics it is quite likely that gravitational wave observations will uncover new classes of sources not anticipated in our current thinking.>>
.....................................................
<<The sensitivity goals for the Advanced LIGO detector systems are chosen to enable the advance from plausible detection to likely detection and rich observational studies of sources.

The basic optical configuration is a power-recycled and signal-recycled Michelson interferometer with Fabry-Perot "transducers" in the arms. Using the initial LIGO design as a point of departure, this requires the addition of a signal-recycling mirror at the output "dark" port, and changes in the interferometer readout and control systems. This additional mirror allows the gravitational wave induced sidebands to be stored or extracted (depending upon the state of "resonance" of the signal recycling cavity), and leads to a tailoring of the interferometer response according to the character of a source (or specific frequency in the case of a fixed-frequency source). The upgrade includes the three LIGO interferometers, allowing e.g., one interferometer at Hanford and the interferometer at Livingston to be tuned to be broadband, and the second interferometer at Hanford to be used as a higher-frequency narrowband detector.

To improve the quantum-limited sensitivity, the laser power is increased from the initial LIGO value of 10 W to ~200 W. The conditioning of the laser light follows initial LIGO closely, with a ring-cavity mode cleaner and reflective mode-matching telescope.

Whereas initial LIGO uses 25-cm, 11-kg, fused-silica test masses, the fused silica test mass optics for Advanced LIGO are larger in diameter (~34 cm) to reduce thermal noise contributions and more massive (~40 kg) to keep the radiation pressure noise to a level comparable to the suspension thermal noise. Compensation of the thermal lensing in the test mass optics (due to absorption in the substrate and coatings) is added to handle the much-increased power - of the order of 1 MW in the arm cavities. The test mass is suspended by fused silica fibers, in contrast to the steel wire sling suspensions used in initial LIGO. The resulting suspension thermal noise is anticipated to be less than the radiation pressure noise (in broad-band observation mode) and to be comparable to the Newtonian background ("gravity gradient" noise) at 10 Hz. The complete suspension has four pendulum stages, contributing to the seismic isolation and providing multiple points for actuation.

The seismic isolation system is built on the initial LIGO piers and support tubes but otherwise is a complete replacement, required to bring the seismic cutoff frequency from 40 Hz (for initial LIGO) to 10 Hz. RMS motions (frequencies less than 10 Hz) are reduced by active servo techniques. The result is to render the seismic noise negligible at all observing frequencies. Through the combination of the seismic isolation and suspension systems, the required control forces on the test masses will be reduced by many orders of magnitude in comparison with initial LIGO, reducing also the probability of non-Gaussian noise in the test mass.>>

[bystander]

• Advanced LIGO gravitational wave hunt looks ready to begin its quest.

A Large Step Closer to the Direct Detection of Gravitational Waves
Albert Einstein Institute | Leibniz University, Hannover
Max Planck Institute for Gravitational Physics | 2015 May 18

Dedication of Advanced LIGO
California Institute of Technology | 2015 May 19

Newly Dedicated Observatory to Search for Gravitational Waves
National Science Foundation | 2015 May 19