LIGOandVirgoResumeSearchforRipplesinSpaceandTimeTheNationalScienceFoundation'sLIGO(LaserInterferometerGravitational-WaveObservatory)issettoresumeitshuntforgravitationalwaves—ripplesinspaceandtime—onApril1,afterreceivingaseriesofupgradestoitslasers,mirrors,andothercomponents.LIGO—whichconsistsoftwindetectorslocatedinWashingtonandLouisiana—nowhasacombinedincreaseinsensitivityofabout40percentoveritslastrun,whichmeansthatitcansurveyanevenlargervolumeofspacethanbeforeforpowerful,wave-makingevents,suchasthecollisionsofblackholes.JoiningthesearchwillbeVirgo,theEuropean-basedgravitational-wavedetector,locatedattheEuropeanGravitationalObservatory(EGO)inItaly,whichhasalmostdoubleditssensitivitysinceitslastrunandisalsostartingupApril1."Forthisthirdobservationalrun,weachievedsignificantlygreaterimprovementstothedetectors'sensitivitythanwedidforthelastrun,"saysPeterFritschel,LIGO'schiefdetectorscientistatMIT."AndwithLIGOandVirgoobservingtogetherforthenextyear,wewillsurelydetectmanymoregravitationalwavesfromthetypesofsourceswe'veseensofar.We'reeagertoseeneweventstoo,suchasamergerofablackholeandaneutronstar."In2015,afterLIGObeganobservingforthefirsttimeinanupgradedprogramcalledAdvancedLIGO,itsoonmadehistorybymakingthefirstdirectdetectionofgravitationalwaves.TheripplestraveledtoEarthfromapairofcollidingblackholeslocated1.3billionlight-yearsaway.Forthisdiscovery,threeofLIGO'skeyplayers—Caltech'sBarryC.Barish,theRonaldandMaxineLindeProfessorofPhysics,Emeritus,andKipS.Thorne,theRichardP.FeynmanProfessorofTheoreticalPhysics,Emeritus,alongwithMIT'sRainerWeiss,professorofphysics,emeritus—wereawardedthe2017NobelPrizeinPhysics.Sincethen,theLIGO-Virgodetectornetworkhasuncoverednineadditionalblackholemergersandoneexplosivesmashupoftwoneutronstars.Thatevent,dubbedGW170817,generatednotjustgravitationalwavesbutlight,whichwasobservedbydozensoftelescopesinspaceandontheground."Withourthreedetectorsnowoperationalatasignificantlyimprovedsensitivity,theglobalLIGO-Virgodetectornetworkwillallowmoreprecisetriangulationofthesourcesofgravitationalwaves,"saysJovandenBrandofNikhef(theDutchNationalInstituteforSubatomicPhysics)andVUUniversityAmsterdam,whoisthespokespersonfortheVirgocollaboration."Thiswillbeanimportantsteptowardourquestformulti-messengerastronomy."Now,withthestartofthenextjointLIGO-Virgorun,theobservatoriesarepoisedtodetectanevengreaternumberofblackholemergersandotherextremeevents,suchasadditional
neutron-neutronstarmergersorayet-to-be-seenblackhole-neutronstarmerger.Oneofthemetricstheteamusesformeasuringincreasesinsensitivityistocalculatehowfarouttheycandetectneutron-neutronstarmergers.Inthenextrun,LIGOwillbeabletoseethoseeventsouttoanaverageof550millionlight-yearsaway,ormorethan190millionlight-yearsfartheroutthanbefore.Akeytoachievingthissensitivityinvolveslasers.EachLIGOinstallationconsistsoftwolongarmsthatformanLshapedinterferometer.Laserbeamsareshotfromthecornerofthe"L"andbouncedoffmirrorsbeforetravelingbackdownthearmsandrecombining.Whengravitationalwavespassby,theystretchandsqueezespaceitself,makingimperceptiblytinychangestothedistancethelaserbeamstravelandtherebyaffectinghowtheyrecombine.Forthisnextrun,thelaserpowerhasbeendoubledtomorepreciselymeasurethesedistancechanges,therebyincreasingthedetectors’sensitivitytogravitationalwaves.OtherupgradesweremadetoLIGO'smirrorsatbothlocations,withatotaloffiveofeightmirrorsbeingswappedoutforbetter-performingversions."Wehadtobreakthefibersholdingthemirrorsandverycarefullytakeouttheopticsandreplacethem,"saysCalumTorrie,LIGO'smechanical-opticalengineeringheadatCaltech."Itwasanenormousengineeringundertaking."Thisnextrunalsoincludesupgradesdesignedtoreducelevelsofquantumnoise.Quantumnoiseoccursduetorandomfluctuationsofphotons,whichcanleadtouncertaintyinthemeasurementsandcanmaskfaintgravitational-wavesignals.Byemployingatechniquecalled"squeezing,"initiallydevelopedforgravitational-wavedetectorsattheAustralianNationalUniversity,andmaturedandroutinelyusedsince2010attheGEO600detector,researcherscanshifttheuncertaintyinthephotonsaround,makingtheiramplitudeslesscertainandtheirphases,ortiming,morecertain.ThetimingofphotonsiswhatiscrucialforLIGO'sabilitytodetectgravitationalwaves.TorriesaysthattheLIGOteamhasspentmonthscommissioningallofthesenewsystems,makingsureeverythingisalignedandworkingcorrectly."OneofthethingsthatissatisfyingtousengineersisknowingthatallofourupgradesmeanthatLIGOcannowseefartherintospacetofindthemostextremeeventsinouruniverse."
MoreInformationabouttheLIGO-Virgocollaborations:LIGOisfundedbyNSFandoperatedbyCaltechandMIT,whichconceivedofLIGOandledtheInitialandAdvancedLIGOprojects.FinancialsupportfortheAdvancedLIGOprojectwasledbytheNSFwithGermany(MaxPlanckSociety),theU.K.(ScienceandTechnologyFacilitiesCouncil)andAustralia(AustralianResearchCouncil-OzGrav)makingsignificantcommitmentsandcontributionstotheproject.Nearly1,300scientistsfromaroundtheworldparticipateintheeffortthroughtheLIGOScientificCollaboration,whichincludestheGEOCollaboration.Alistofadditionalpartnersisavailableathttps://my.ligo.org/census.php.
TheVirgoCollaborationiscurrentlycomposedofapproximately350scientists,engineers,andtechniciansfromabout70institutesfromBelgium,France,Germany,Hungary,Italy,theNetherlands,Poland,andSpain.TheEuropeanGravitationalObservatory(EGO)hoststheVirgodetectornearPisainItaly,andisfundedbyCentreNationaldelaRechercheScientifique(CNRS)inFrance,theIstitutoNazionalediFisicaNucleare(INFN)inItaly,andNikhefintheNetherlands.AlistoftheVirgoCollaborationmemberscanbefoundathttp://public.virgo-gw.eu/the-virgo-collaboration/.MoreinformationisavailableontheVirgowebsiteathttp://www.virgo-gw.eu.
MediaContacts:
CaltechWhitneyClavinwclavin@caltech.edu626-390-9601MITAbigailAbazoriusabbya@[email protected][email protected]
Images:
DetectorengineersHughRadkins(foreground)andBetsyWeaver(background),arepicturedhereinsidethevacuumsystemofthedetectoratLIGOHanfordObservatory,beginningthehardwareupgradesnecessaryforAdvancedLIGO'sthirdobservingrun.[Imagecredit:LIGO/Caltech/MIT/JeffKissel]
LIGOteammembersinstallin-vacuumequipmentthatispartofthesqueezed-lightupgrade.[Imagecredit:LIGO/Caltech/MIT/MattHeintze]
