IEEE BYTE VOLUME-3 ISSUE-1 | Page 22

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The​ ​working​ ​of​ ​LIGO:
LIGO, ​ ​the​ ​largest​ ​and​ ​most​ ​ambitious​ ​project​ ​ever​ ​funded​ ​by​ ​NSF, ​ ​consists​ ​of​ ​two massive​ ​L-shaped​ ​tubes​ ​called​ ​interferometers, ​ ​one​ ​in​ ​Louisiana​ ​and​ ​the​ ​other​ ​in​ ​Washington State. ​ ​Each​ ​arm​ ​of​ ​an​ ​L-tube​ ​is​ ​4​ ​km​ ​in​ ​length. ​ ​Light​ ​beams​ ​are​ ​made​ ​to​ ​travel​ ​along​ ​the​ ​arms between​ ​pairs​ ​of​ ​mirrors. ​ ​A​ ​passing​ ​gravitational​ ​wave​ ​would​ ​stretch​ ​space​ ​in​ ​one​ ​direction​ ​and shrink​ ​it​ ​in​ ​the​ ​perpendicular​ ​direction. ​ ​This​ ​would​ ​increase​ ​the​ ​distance​ ​between​ ​one​ ​pair​ ​of mirrors​ ​and​ ​decrease​ ​the​ ​distance​ ​between​ ​the​ ​other​ ​pair. ​ ​By​ ​swinging​ ​thus, ​ ​the​ ​mirrors​ ​are responding​ ​to​ ​the​ ​stretching​ ​and​ ​compression​ ​of​ ​space-time. ​ ​The​ ​minute​ ​changes​ ​in​ ​distance can​ ​then​ ​be​ ​registered​ ​by​ ​a​ ​detector, ​ ​put​ ​in​ ​place​ ​to​ ​record​ ​the​ ​laser​ ​light​ ​returning​ ​from​ ​the​ ​two interferometer​ ​arms. ​ ​To​ ​ensure​ ​that​ ​the​ ​signal​ ​received​ ​was​ ​an​ ​authentic​ ​gravitational​ ​wave, both​ ​interferometers​ ​need​ ​to​ ​do​ ​the​ ​ " dancing​ ​mirrors " ​ ​thing​ ​together​ ​causing​ ​the​ ​signal​ ​to​ ​be picked​ ​up​ ​by​ ​both​ ​detectors. When​ ​did​ ​LIGO​ ​detect​ ​waves?
On​ ​11​ ​February​ ​2016, ​ ​the​ ​LIGO​ ​collaboration​ ​announced​ ​the​ ​detection​ ​of​ ​gravitational waves, ​ ​from​ ​a​ ​signal​ ​detected​ ​at​ ​09:50:45​ ​GMT​ ​on​ ​14​ ​September​ ​2015​ ​of​ ​two​ ​black​ ​holes​ ​with masses​ ​of​ ​29​ ​and​ ​36​ ​solar​ ​masses​ ​merging​ ​about​ ​1.3​ ​billion​ ​light​ ​years​ ​away. On​ ​15​ ​June​ ​2016, ​ ​the​ ​LIGO​ ​group​ ​announced​ ​the​ ​detection​ ​of​ ​a​ ​second​ ​set​ ​of​ ​gravitational waves, ​ ​which​ ​was​ ​observed​ ​at​ ​03:38:53​ ​GMT​ ​on​ ​26​ ​December​ ​2015.
The​ ​singularities​ ​about​ ​LIGO:
● Unlike​ ​optical​ ​or​ ​radio​ ​telescopes, ​ ​LIGO​ ​cannot​ ​see​ ​electromagnetic​ ​radiation​ ​because gravitational​ ​waves​ ​are​ ​not​ ​part​ ​of​ ​the​ ​electromagnetic​ ​spectrum.
● As​ ​there​ ​is​ ​no​ ​need​ ​to​ ​collect​ ​light​ ​from​ ​stars​ ​or​ ​other​ ​objects​ ​in​ ​the​ ​Universe, ​ ​LIGO doesn ' t​ ​need​ ​to​ ​be​ ​dish-shaped. ​ ​LIGO​ ​has​ ​two​ ​long​ ​steel​ ​vacuum​ ​tubes​ ​arranged​ ​in​ ​the shape​ ​of​ ​an​ ​“ L”.
● Gravitational​ ​wave​ ​observatories​ ​like​ ​LIGO​ ​cannot​ ​operate​ ​solo. ​ ​The​ ​only​ ​way​ ​to definitively​ ​detect​ ​a​ ​gravitational​ ​wave​ ​is​ ​by​ ​operating​ ​in​ ​unison​ ​with​ ​a​ ​distant​ ​twin.
What​ ​other​ ​pioneering​ ​work​ ​is​ ​being​ ​done? After​ ​decades​ ​of​ ​development​ ​and​ ​delays, ​ ​the​ ​European​ ​Space​ ​Agency​ ​( ESA) ​ ​has​ ​given​ ​the Laser​ ​Interferometer​ ​Space​ ​Antenna​ ​( LISA) ​ ​mission​ ​there​ ​green​ ​signal. ​ ​LISA​ ​will​ ​use​ ​three spacecraft​ ​to​ ​detect​ ​these​ ​minute​ ​ripples​ ​in​ ​the​ ​fabric​ ​of​ ​space-time. ​ ​The​ ​spacecrafts​ ​will​ ​be stationed​ ​millions​ ​of​ ​kilometres​ ​apart​ ​in​ ​space, ​ ​and​ ​linked​ ​via​ ​laser​ ​beams. ​ ​Each​ ​spacecraft carries​ ​test​ ​masses​ ​that​ ​are​ ​shielded​ ​in​ ​such​ ​a​ ​way​ ​that​ ​the​ ​only​ ​force​ ​they​ ​respond​ ​to​ ​is​ ​gravity. Lasers​ ​measure​ ​the​ ​distances​ ​to​ ​test​ ​masses​ ​in​ ​all​ ​three​ ​spacecraft. ​ ​Tiny​ ​changes​ ​in​ ​the lengths​ ​of​ ​each​ ​two-spacecraft​ ​arm​ ​signals​ ​the​ ​passage​ ​of​ ​gravitational​ ​waves​ ​through​ ​the formation.
Thus, ​ ​gravitational​ ​waves​ ​are​ ​the​ ​very​ ​foundation​ ​of​ ​“ new​ ​astronomy” ​ ​-​ ​astronomy​ ​in​ ​which information​ ​about​ ​new​ ​cosmic​ ​events​ ​will​ ​be​ ​given​ ​not​ ​through​ ​light​ ​but​ ​through​ ​ripples​ ​in​ ​the fabric​ ​of​ ​spacetime​ ​itself. ​ ​Only​ ​time​ ​can​ ​tell​ ​what​ ​new​ ​mysteries​ ​gravitational​ ​waves​ ​might​ ​solve.