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

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Sharon Brunett!California Institute of Technology!

Pacific Research Platform Workshop!October 15, 2015 !

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LIGO G1101200-v2

Credit: AEI, CCT, LSU

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What is LIGO?

LIGO is the world’s leading facility for conducting gravitational-wave science !

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LIGO is discovery science. It will open the field of gravitational-wave astronomy through the direct detection of gravitational

waves from compact sources and conduct a long term astrophysical observing program. !

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LIGO Livingston Observatory

LIGO Hanford Observatory

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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!

»  ~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 multi-messenger 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 !

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Caltech

MIT

LIGO Laboratory

LIGO Hanford 2015

LIGO Livingston 2015

LIGO India 2022

Virgo 2016

KAGRA 2018

Advanced Ground-based GW Network

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!

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h( f ) = ΔL( f )L

Vacuum

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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.!!!!! Image courtesy of Beverly Berger

Cluster map by Richard Powell

Initial LIGO

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?

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Fundamental Questions that LIGO Observations can Answer

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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, ...)?

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Observational Targets for LIGO: Energetic and Violent Compact Astrophysical Events

Casey Reed, Penn State

Credit: AEI, CCT, LSU

Coalescing Compact Binary Systems: Neutron Star-NS, Black Hole-NS, BH-BH

- Strong emitters, well-modeled, template-based searches

- transient Credit: Chandra X-ray Observatory

Gravitational Wave ‘Bursts’

-  not well-modeled, excess power searches

-  Galactic core collapse supernovae, cosmic strings, soft gamma repeaters, pulsar

-  transient

NASA/WMAP Science Team

Stochastic Gravitational-wave Background -  stochastic background

from incoherent ensemble of point emitters, (& primordial universe)

-  Long duration

Spinning neutron stars and pulsars - (effectively) monotonic waveform - Long duration

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!

●  Einstein@Home 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 !

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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.!

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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 2015-2016 compute needs. !

●  Totals for all compute classes in years 2015/2016/2017 – 61/194/390 MSUs!

»  1 SU = 1 core hr of execution time on reference Intel Xeon E5-2670 !

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LIGO Computing Latencies

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 !!.!!!

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LIGO Computing Model

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Triggers

Triggers

Triggers

Triggers

CDS:

DAQ

Calibration!Pipeline

Data Quality!Pipelines

Deep Search Pipelines

Strain V1

PE/Validation Pipelines

Alerts!Out

Data

Buf

fers

RDS!Pipeline RDS

Raw

SFT!Pipeline SFT

Data Quality!Databases

Trend

Data Quality!Pipelines

Alerts!In

Low-latency!Pipelines

Candidate!Database

PE/Validation Pipelines

Calibration!Pipeline Strain V2+

Mai

n Da

ta A

rchi

ve: A

ll Da

ta

LIGO Open Science Center

Data

Buf

fer

CW Search!Pipelines

Tier-1-Observatories Tier-1-Caltech XSEDE, Tier-2 LDG &!Einstein@Home

Other Catalogs

Stream Data

GW Catalog

Minutes

Hours

Days

Weeks

GW Catalog

Candidate!Database

Scientists: Key Science Projects,!

Publications & Data Releases

Months

Ope

rato

r/Sci

entis

ts: O

pera

tions

and

Eng

inee

ring

Seconds

Data

Buf

fer

Site

Ar

chiv

e

Stor

age:

Stra

in, R

DS, S

FT, T

rigge

rs

PE/Validation Pipelines

Control & Diagnostic System

Legend

Processing Pipelines

Data Files (Stream, Trigger, etc)

Databases

Public Facing Data & Services

Data PathwayData Transfer Service From Virgo and/or

other detectors

Tim

e-cr

itica

l Joi

nt G

W-E

M O

bser

ving

Deep

Sea

rch

that

relie

s pr

imar

ily o

n G

W d

ata

From Virgo and/or other detectors

LIGO Laboratory Facilities Other Facilities

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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!!

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