Laser Interferometer Gravitational-Wave Observatory (LIGO)! A Brief Overview!

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1 Laser Interferometer Gravitational-Wave Observatory (LIGO) A Brief Overview Sharon Brunett California Institute of Technology Pacific Research Platform Workshop October 15, 2015 Credit: AEI, CCT, LSU LIGO G v2 1

2 What is LIGO? LIGO is the world s leading facility for conducting gravitational-wave science LIGO Livingston Observatory LIGO Hanford Observatory LIGO is discovery science. It will open the field of gravitationalwave astronomy through the direct detection of gravitational waves from compact sources and conduct a long term astrophysical observing program. 2

3 LIGO Organization LIGO = LIGO Laboratory + LIGO Scientific Collaboration (LSC) LIGO Laboratory, jointly managed by Caltech and MIT, is responsible for operating LIGO Hanford and Livingston Observatories under a cooperative agreement from the NSF Caltech LIGO Laboratory MIT» ~200 staff members LIGO science conducted through the LIGO Scientific Collaboration» International collaboration of ~1000 members at 80+ institutions located in 16 countries» The LSC is the LIGO User Community and includes LIGO Laboratory staff (scientists, engineers, and technicians) The LSC collaborates with other large gravitational-wave collaborations as part of a global network essential for multimessenger gravitational-wave astronomy» The LSC has a full data sharing agreement with the Virgo Collaboration» The LSC and Virgo signed an intent to share data with KAGRA LIGO Hanford 2015 Advanced Ground-based GW Network LIGO Livingston 2015 Virgo 2016 LIGO India 2022 KAGRA

4 Measuring Gravitational-waves Gravitational waves are propagating dynamic fluctuations in the curvature of space-time» Physically manifested as strains» Emitted from accelerating mass distributions, unimpeded by matter; need astrophysical sources to generate detectable strains» Travel at the speed of light (according to general relativity) GW interferometers use enhanced Michelson interferometry to detect the strains Passing GWs dynamically modulate ( stretch and compress ) the distance between the end test mass and the beam splitter The interferometer acts as a transducer, turning GWs into photocurrent» A coherent detector à signal is proportional to amplitude of GW h( f ) = ΔL( f ) L Vacuum 4

5 LIGO Instruments LIGO recently completed an upgrade to Advanced LIGO detectors that are designed to be a factor of 10x more sensitive than Initial LIGO Transient events that would have been seen once per decade with Initial LIGO will, therefore, be detected once every few days. Initial LIGO Image courtesy of Beverly Berger Cluster map by Richard Powell 5 5

6 Fundamental Questions that LIGO Observations can Answer Is general relativity the correct theory of gravity? What is the nature of one of the four fundamental forces? What happens when two black holes collide? Do black holes really have no hair? What are the progenitors of short gamma ray bursts? What is the engine that powers them? 6 6

7 Fundamental Questions that LIGO Observations can Answer How does core collapse power a supernova? Is there a mass gap between neutron stars and black holes? What is the maximum mass of a neutron star? What is the nuclear equation of state at very high densities? Do neutron star mergers power kilonovae? What is the origin of r-process elements (gold, platinum,...)? 7 7

8 Observational Targets for LIGO: Energetic and Violent Compact Astrophysical Events Gravitational Wave Bursts Coalescing Compact Binary Systems: Neutron Star-NS, Black Hole-NS, BH-BH - Strong emitters, well-modeled, template-based searches Credit: Chandra X-ray Observatory - transient - not well-modeled, excess power searches - Galactic core collapse supernovae, cosmic strings, soft gamma repeaters, pulsar - transient Credit: AEI, CCT, LSU Spinning neutron stars and pulsars Stochastic Gravitationalwave Background - (effectively) monotonic waveform - stochastic background from incoherent ensemble of point emitters, (& primordial universe) - Long duration - Long duration NASA/WMAP Science Team Casey Reed, Penn State 8

9 LIGO Computing Model Analysis methods and search algorithms are specifically tailored and tuned to each source class. All can be efficiently decomposed into embarrassingly parallel tasks, using three basic classes of computing matched to science goals: Dedicated LIGO Laboratory resources for detector characterization and astrophysical searches that need low-latency results to meet their science goals Dedicated LIGO Scientific Collaboration and national/international shared resources, e.g., XSEDE, for production offline (high latency) searches and search development community computing for offline searches with low data-to-processing ratios that might otherwise be prohibitively expensive and for which very high latency of scientific results is acceptable 9

10 LIGO Computing Model Maintain sufficient flexibility gravitational-wave physics is still in a discovery phase and the first gravitational-wave signals detected may be different than expected Different astrophysical and detector characterization analyses rely on different methods and algorithms versatility comes from running on heterogeneous compute platforms. Increase the portability of existing data analysis pipelines so that they can take advantage of shared resources in addition to dedicated LIGO Data Grid resources. 10

11 LIGO Modes of Operation Production: analysis during science observing runs Simulation: simulations needed to measure the sensitivity to detections GW follow-up: resources needed to measure significance of strong gravitational wave signals Development: development of improved and optimized codes Some analyses require large amounts of data, others only small slices from reduced data sets. Low latency compute demands are mainly from two source classes: compact binary coalesences (CBC) and continuous waves (CW) ~30 Million Service Units (MSU) for compute needs. Totals for all compute classes in years 2015/2016/ /194/390 MSUs» 1 SU = 1 core hr of execution time on reference Intel Xeon E

12 LIGO Computing Latencies 12 12

13 LIGO Computing Model Follow the Flow of aligo data Calibrate aligo data (LIGO Lab) Aggregate data from multiple geographic locations (LIGO Lab) Run and interpret data-quality pipelines to generate summary information (LIGO Scientific Collaboration LSC) Run Detection and parameter estimation pipelines (LSC) Run large-scale simulations required by the scientific interpretation of the data (LSC) Deliver validated alerts of transient GW candidates within minutes of data acquisition (LSC) Archive data and results (LIGO Lab) Deliver validated catalogs of GW sources, data quality, and artifacts in the GW data stream (LSC) Distribute data to the broader research community (LIGO Lab) Improve efficiency and performance of scientific analysis (LIGO Lab and LSC) Workflow and job management via HT Condor 13

14 LIGO Computing Model LIGO Laboratory Facilities Tier-1-Observatories Tier-1-Caltech XSEDE, Tier-2 LDG & Calibration Pipeline From Virgo and/or other detectors Alerts In Alerts Out GW Catalog Other Facilities Seconds Minutes Hours Days Weeks Months 14 Operator/Scientists: Operations and Engineering CDS: DAQ Trend Raw RDS Pipeline Data Quality Legend RDS Data Buffers Control & Diagnostic System Strain V1 Data Files (Stream, Trigger, etc) Processing Databases Public Facing Data & Services Data Pathway Data Transfer Service Triggers Data Buffer Data Quality Site Archive Data Buffer Main Data Archive: All Data From Virgo and/or other detectors Low-latency Triggers Data Quality Databases SFT Pipeline Calibration Pipeline Candidate Database PE/Validation SFT Strain V2+ LIGO Open Science Center Stream Data Other Catalogs GW Catalog Candidate Database Storage: Strain, RDS, SFT, Triggers Deep Search Triggers CW Search Triggers PE/Validation PE/Validation Scientists: Key Science Projects, Publications & Data Releases 14 Time-critical Joint GW-EM Observing Deep Search that relies primarily on GW data

15 Responses To Misc Questions Data generated by interferometers (quantity 2): 1.6M files/yr, 800 TB/yr (after compression) Data generated by search groups (in TB/year):» Burst 254» Compact Binary Coalescences 1167» Continuous Wave - 493» Stochastic GW background 25» Detector Characterization 223 Archive storage via SAM-QFS (tape plus in-demand files on disk) A subset of the tools used to manipulate data:» Custom LIGO Data Replicator used by offline codes - detects files, publishes metadata, transfers files, tracks progress, etc.» Gridftp 15