Astronomija

Ali lahko gravitacijski valovi prehajajo skozi črno luknjo?

Ali lahko gravitacijski valovi prehajajo skozi črno luknjo?


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Kot pravi naslov, kaj se zgodi, ko se gravitacijski val približa črni luknji? Predvidevam, da se zgodi kaj zanimivega zaradi načina delovanja vesolja v bližini črnih lukenj, vendar nimam znanja, ki bi to podprl.


Ne, gravitacijski valovi ne morejo skozi črno luknjo.

Gravitacijski val sledi poti skozi vesolje-čas, ki se imenuje ničelna geodezija. To je ista pot, ki bi ji sledil svetlobni žarek, ki potuje v isti smeri, na gravitacijske valove pa črne luknje vplivajo enako kot svetlobni žarki. Tako lahko na primer gravitacijske leče lomijo gravitacijske valove tako kot svetlobni valovi. In tako kot svetlobni valovi, če gravitacijski val prečka obzorje dogodkov, ki obkroža črno luknjo, je potem obsojen potovati navznoter do singularnosti in nikoli ne more uiti.

To je eno opozorilo. Ko govorimo o gravitacijskem valu, običajno mislimo na valovanje v vesolju in času, ki je razmeroma majhno. Natančneje je dovolj majhen, da energija gravitacijskega vala ne vpliva bistveno na ukrivljenost prostora-časa. Torej, ko izračunamo pot gravitacijskega vala blizu črne luknje, vzamemo geometrijo črne luknje, kot je fiksna, tj. Ne vpliva na val, in izračunamo pot vala v tem fiksnem ozadju.

To je popolnoma enak pristop, kot ga uporabljamo za izračun poti svetlobnih žarkov. Ker svetlobni žarki nosijo energijo in zagon, imajo vsaj načeloma lastna gravitacijska polja. Toda za svetlobne žarke in gravitacijske valove, ki bi lahko obstajali v vesolju, je prenesena energija premajhna, da bi lahko bistveno prispevala k ukrivljenosti vesolja in časa.

Ko v svojem vprašanju rečete:

Predvidevam, da se zgodi kaj zanimivega zaradi načina delovanja vesolja v bližini črnih lukenj

Predvidevam, da mislite, da bi gravitacijski val lahko spremenil geometrijo v bližini črne luknje, toda kot je opisano zgoraj, tipični gravitacijski valovi nimajo dovolj energije za to. Smiselno bi bilo vprašati se, kaj se zgodi, če damo valu dovolj energije, vendar se izkaže, da se ta ne vede več kot preprost val.

Gravitacijski valovi obstajajo v režimu, ki se imenuje linearizirana gravitacija, kjer upoštevajo valovno enačbo, ki je v osnovi podobna svetlobni valovni enačbi. Če energijo toliko povečamo, da gravitacija postane nelinearna (kot v primeru črnih lukenj), potem nihanja v ukrivljenosti prostora-čas niso več podrejena valovni enačbi in jih je treba opisati s celotno Einsteinovo enačbo. Na primer, bilo je predlagano, vendar ni dokazano, da bi resnično visokoenergijski gravitacijski (ali svetlobni) valovi lahko medsebojno vplivali in tvorili vezano stanje, imenovano geon. Priznam, da nisem prepričan, koliko dela je bilo opravljenega s preučevanjem nihanj v tem režimu.


Gravitacijske valove bi morali masivni predmeti lečiti na zelo podoben način kot svetloba.

Svetlobni žarki (in s tem tudi gravitacijski valovi) oddaljenega predmeta, ki preidejo v 1,5-kratnem polmeru Schwarzschilda (za nevrtljivo črno luknjo), imajo usmeritve, ki se nato usmerjajo proti obzorju dogodkov. Valovi na takšnih poteh ne morejo uiti iz črne luknje, zato je osnovni odgovor ne, gravitacijski valovi ne morejo "skozi črno luknjo".

Vendar pa bi vmesna črna luknja daleč od tega, da bi "skrila" vir gravitacijskih valov, povzročila prisotnost leče in povečanih slik. Za popolno poravnavo vira, črne luknje in opazovalca bi obstajal močan "Einsteinov obroč" s kotnim polmerom, ki je odvisen od relativne razdalje vira in črne luknje.

Seveda gravitacijskih valov trenutno ni mogoče zaznati, zato bi lahko zaznali nenormalno ojačan signal gravitacijskega vala.

Vse zgoraj je v geometrijska optika omejitev, da je valovna dolžina majhna v primerjavi z lečo. Če je črna luknja dovolj majhna (kar je odvisno od njene mase) ali je valovna dolžina gravitacijskega vala dovolj velika, bi moralo biti obnašanje analogno ravninskemu valu, ki naleti na majhen neprosojen disk (Takahashi & Nakamura 2003).

V tem primeru bi dobili a difrakcijski vzorec in morda "svetlo" Aragovo točko v središču, čeprav takšnih izračunov v literaturi ne poznam.

To ni malo verjeten scenarij. Na primer, gravitacijski valovi, ki jih zazna LIGO, imajo sorazmerno visoke frekvence 10-1000 Hz in zato valovne dolžine 30.000-300 km, ki so velike kot Schwarzschildovi polmeri 10.000 - 100 črnih lukenj sončne mase in zagotovo večje od ostankov črne luknje zvezdnega razvoja.


Vprašajte Ethana: Kako gravitacijski valovi pobegnejo iz črne luknje?

Dve združeni črni luknji, zlasti v zadnji fazi združitve, oddajata ogromno. [+] gravitacijski valovi. Zasluga za sliko: SXS, projekt Simulacija eXtreme Spacetimes (SXS) (http://www.black-holes.org).

Morda največje odkritje od vseh napovedanih v letu 2016 je bilo neposredno zaznavanje gravitacijskih valov. Čeprav jih je predvidevala Einsteinova splošna teorija relativnosti pred 101 leti, je bil potreben razvoj laserskega interferometra, občutljivega na valovanje v vesolju, ki bi premaknil dve ogledali, ločeni z več kilometri, za manj kot 10 ^ -19 metrov ali 1 / 10.000-ta širina protona. To se je končno zgodilo med izvajanjem podatkov LIGO za leto 2015 in iz podatkov sta nedvoumno izstopila dva dobroverna dogodka združitve črne luknje in črne luknje. Kako pa fizika to dejansko dopušča? Mārtiņš Kalvāns želi vedeti:

To vprašanje me že dolgo zmede. Članki o odkritju LIGO navajajo, da je bil določen odstotek mase združitve črne luknje izžarevan, tako da je nastala črna luknja manjša od [vsote] prvotnih združitev. Vendar je sprejeto, da črnim luknjam nič ne uide [. ] Moje vprašanje je torej: kako je bila energija izžarevana iz združitev črnih lukenj?

To je res globoko vprašanje in gre naravnost v osrčje fizike črne luknje in splošne relativnosti.

Prikaz črne luknje in njenega okoliškega, pospeševalnega in padajočega akrecijskega diska. The. [+] singularnost se skriva za obzorjem dogodkov. Kreditna slika: NASA.

Po eni strani imamo črno luknjo. Vsa njegova masa / energija je koncentrirana v singularnosti v središču in je zunanjemu opazovalcu za vedno nevidna zaradi prisotnosti obzorja dogodkov. Znotraj določenega območja vesolja (opredeljenega s horizontom dogodkov) ga bo katera koli pot, ne glede na hitrost ali energijo, masivna ali brezmasna, neizogibno pripeljala v osrednjo singularnost črne luknje. To pomeni, da kateri koli delci, ki vstopijo v horizont dogodkov, prestopijo v obzorje dogodkov ali se drugače kdaj znajdejo znotraj obzorja dogodkov, nikoli ne bodo mogli ven, zato je njegova energija za vedno ujeta znotraj. Ko ste v črni luknji, preprosto postanete del lastnosti singularnosti: masa, naboj (vseh vrst) in vrtenje. To je to.

Valovi v vesolju in času se pojavljajo na frekvenci medsebojne orbite črnih lukenj in so več. [+] intenzivne po velikosti, čim bližje so. Zasluga za sliko: R. Hurt - Caltech / JPL.

Po drugi strani pa nam Einsteinova splošna relativnost pravi, da ko dve množici (katere koli vrste) krožita ena okoli druge, ustvari valovanje v tkivu vesolja, ko same orbite propadajo. Te valove, znane kot gravitacijski valovi, se premikajo s svetlobno hitrostjo, povzročajo, da se prostor širi in krči, kadar koli prehajajo skozi njega, in nosijo energijo. Zaradi najbolj znane Einsteinove enačbe, E = mc 2 (ali, kot je napisal prvotno, m = E / c 2 ), vemo, da je en vir energije masa, en vir mase pa energija. Lahko se pretvorijo druga v drugo. Masa je le ena posebna oblika, ki jo lahko prevzame energija.

Signal iz LIGO o prvem robustnem zaznavanju gravitacijskih valov. Prispevek slike: Opazovanje. [+] Gravitacijskih valov iz binarne združitve črne luknje B. P. Abbott et al., (LIGO Scientific Collaboration and Virgo Collaboration), Physical Review Letters 116, 061102 (2016).

Ko je LIGO januarja letos objavil rezultate dogodka, ki se je zgodil 14. septembra 2015, je bilo le rahlo presenetljivo, da so našli dve črni luknji - 36 in 29 sončnih mas -, ki sta se združili in ustvarili novo črno luknja 62 sončnih mas. Kam so izginile ostale 3 sončne mase (približno 5% celotne mase sistema)? V energiji gravitacijskih valov. Z nadaljnjimi dogodki, ki so bili zaznani, se pojavi približno enak trend: dve črni luknji primerljivih mas se inspirirata in združita skupaj, do približno 5% njunih skupnih začetnih mas pa seva v obliki gravitacijskih valov.

Toda vsaka črna luknja ima obzorje dogodkov. Vsak od parov ima enega pred združitvijo, končna črna luknja po združitvi ga ima in nobena točka med združitvijo niti ne postane singla "gola" ali kdajkoli izstopi iz obzorja dogodkov. Torej, kako pride masa ven?

Vsak predmet ali oblika, fizična ali nefizična, bi bila popačena, ko bi gravitacijski valovi prehajali. [+] skozi to. Upoštevajte, kako iz obzorja dogodkov črne luknje nikoli ne oddajajo valovi. Prispevek slike: NASA / Ames Research Center / C. Henze.

To ni samo zapleteno vprašanje, to je tudi trik vprašanje! Kot bi vprašali, kam gre masa, ko se protoni na Soncu zlijejo v devterij, helij-3 in nato helij-4. Zakaj je helij-4 manj masiven od štirih protonov, ki so ga tvorili? Zaradi jedrsko vezavne energije. Vezano stanje je bolj stabilno in ima manj energije (in s tem tudi manjšo maso) kot nevezano stanje. Ko se dve črni luknji inspiralno združita, združita in združita, ti dve črni luknji postajata bolj povezani - bolj gravitacijsko vezani - kot prej. Energija, ki jo izgubljajo, je posledica gravitacijske vezne energije, ne zato, ker bi katera od množic izstopila iz obzorja dogodkov.

Newtonov zakon o univerzalni gravitaciji je nadomestil Einsteinova splošna relativnost, vendar ga je. [+] je še vedno ilustrativno orodje za preučevanje količin, kot sta sila in energija. Zasluga za sliko: uporabnik Wikimedia commons Dennis Nilsson.

To lahko vidite samo iz Newtonove gravitacije. Predstavljajte si, da imate dve masi po 1 kg, vsako v mirovanju in medsebojno ločeni z neskončno razdaljo. V tem sistemu imajo določeno količino energije: 1,8 × 10 ^ 17 Joulov, ki jih lahko dobite iz Einsteinove enačbe, E = mc 2 . Zdaj jih pripeljite drug k drugemu in razdaljo zmanjšajte.

  • Če jih zdaj loči le en kilometer, je celoten sistem izgubil 6,67 × 10 ^ -14 džulov energije.
  • Če to ločitev zmanjšate na en centimeter, sistem izgubi 6,67 × 10 ^ -9 Joulov.
  • Če to ločitev zmanjšate na velikost protona, pri 10 ^ -15 metrih, sistem zdaj izgubi neverjetnih 6,67 × 10 ^ 4 Joula ali 66.700 Joulov. (Zdaj smo nekam!)
  • Torej, če želite izgubiti resnično veliko energije, si lahko predstavljate, da ločite vse do 10 ^ -27 metrov, kjer boste izgubili 6,67 × 10 ^ 16 Joulov ali približno 35% prvotnega energija!

Svetloba in valovi v vesolju, ko svetloba prehaja skozi neravni prostor, spremeni način opazovanja. [+] na katerem koli drugem mestu zaznava čas svetlobe. Zasluga za podobo: Evropski gravitacijski observatorij, Lionel BRET / EUROLIOS.

Seveda naše vesolje upošteva splošno relativnost na teh lestvicah, ne Newtonove gravitacije, vendar je slika enaka. Ne gre za to, da črne luknje izgubljajo maso, ampak zato, da se celotna količina energije v vesolju-času preoblikuje iz ene oblike - v dve dobro ločeni, nevezani masi - v drugo obliko: ena sama, tesno vezana masa plus gravitacijsko sevanje . Orbitalne lastnosti in mase prvotnih črnih lukenj določajo, kolikšen odstotek celotne prvotne mase postane vezavna energija, vendar je v vseh primerih vedno res, da je končna masa večja od katere koli prvotne mase, vendar manjša od kombinirane surove mase. 5% je količina, ki se oddaja v največjem primeru, kjer sta masi približno enaki. Če so imeli v svojih vrtljajih neverjetno veliko energije in so bili njihovi vrtljaji poravnani, se lahko ta odstotek poveča na približno 11%. Če pa je ena od množic veliko večja od druge, odstotek pade na črno luknjo z 1 sončno maso, ki se združi s 1.000.000 sončno maso in lahko odda le 0,0001% svoje energije.

Umetnikov vtis, da dve zvezdi krožita med seboj in napredujeta (od leve proti desni) do. [+] združitev z nastajajočimi gravitacijskimi valovi. To je sum kratkoročnega izbruha gama žarkov in tudi vir gravitacijskih valov. Zasluga za sliko: NASA / CXC / GSFC / T.Strohmayer.

Inspirala in združitev nimata za posledico ničesar, kar bi prišlo iz črne luknje ven, temveč v deformacijo vesolja in časa, da bi se upoštevala gravitacijska potencialna energija, ko se obe masi združita in združita. Faza zvonjenja - ki se zgodi na koncu združitve - predstavlja obzorje dogodkov, ki se vrne v svojo maksimalno učinkovito obliko: kroglo ali sferoid. To je zadnji del sekunde združitve, kjer se sprosti največ energije, vendar noben delček iz črne luknje ne izstopi. Einsteinove napovedi so zelo jasne in zato smo sploh lahko zaznali: ker smo izračunali, kateri signal naj iščemo. Naša intuicija nam lahko povzroča težave, toda zato imamo enačbe. Tudi če naši instinkti niso dobri, nam bodo izračuni dali znanstveno resnico.


Ali lahko gravitacijski valovi prehajajo skozi črno luknjo? - astronomija

465 kliki, objavljeni v STEM & raquo on 18. junij 2021 ob 8:54 (Pred 6 dnevi) | Priljubljeni | deliti:

Spekter: Ethan Siegel je končno skočil morskega psa.

Ja, toda ta morski pes je imel črno luknjo.

Dr. DJ Duckhunt: Spekter: Ethan Siegel je končno skočil morskega psa.

Ja, toda ta morski pes je imel črno luknjo.

Merltech: Še pomembneje je, ali pretvori 2d svet v 3d?

Ko bodo zadeli površino te črne luknje, si bodo želeli, da njihovi očetje nikoli ne bi srečali svojih mater. To je gotovo.

Kaj se zgodi, ko val preide čez odtok?

Mislim, da se zgodi zelo podobno. Črna luknja je značilnost ukrivljenosti prostora in časa. Takšen je tudi gravitacijski val. Zdi se, kot da sprašujete, kaj se zgodi, ko funkcije medija v interakciji, kar se mi ne zdi tako roman ali zanimivo. Mogoče pa se zgodi kakšen čuden šiat, ko izračunaš matematiko. Kdo ve.

Ugibate, da bi radi to raziskali, da bi poskusili modelirati Hawking Points v MBR?

Spekter: Ethan Siegel je končno skočil morskega psa.

Ne vem o tem, vendar je uporabil veliko besed, da bi le rekel: ja, črne luknje vplivajo na gravitacijske valove enako kot vplivajo na vsa druga znana brezmasna sevanja.

Čebelji oreški: Kaj se zgodi, ko val preide čez odtok?

Mislim, da se zgodi zelo podobno. Črna luknja je značilnost ukrivljenosti prostora in časa. Takšen je tudi gravitacijski val. Zdi se, kot da sprašujete, kaj se zgodi, ko funkcije medija v interakciji, kar se mi ne zdi tako roman ali zanimivo. Mogoče pa se zgodi kakšen čuden šiat, ko izračunaš matematiko. Kdo ve.

Ugibate, da bi radi to raziskali, da bi poskusili modelirati Hawking Points v MBR?

Odločiti se morate, ali mislite, da je gravitacija temeljna sila ali ne. Prostor-čas je tudi konstrukt, pri katerem se moramo odločiti, ali obstaja ali ne. Ko se poglobimo v to, kako stvari delujejo, če to ni vesolje, ki ga vodijo dogodki, te stvari postanejo simptomi in ne vzroki in prožnost se nenadoma prikrade.

Osebno mislim, da je kvant rezultat ekstremnih situacij, ko se razkrije skrita fleksibilnost verjetnosti, ki je vpeta v tkanino vesolja. Veliko časa in truda smo porabili za gradnjo konstrukcij, da bi vse razložili, vendar mislim, da smo postaja smešno. Mislim, da smo šli predaleč in moramo narediti velik korak nazaj. Bilo je zabavno biti del D & Oslash-a in ICECUBE-ja in všeč mi je enostavnost standardnega modela. Toda kar se v resnici dogaja, mislim, da je to bolj priročno za znanstvenike, da razpravljajo o procesih in načrtih eksperimentov ali rezultatih, kot pa so dobro okno za to, kar je resnično.

sxacho: Predvidevam, da bi se vsi gravitacijski valovi, ki bi dosegli obzorje dogodkov, izgubili v črni luknji, medtem ko bi se vsi, ki ne bi dosegli obzorja dogodkov, upognili sorazmerno z oddaljenostjo.

Ja, če govorimo o stvareh, če je vaša prostorsko-časovna depresija dovolj globoka, da povzroči topografski krog glede na 3x10 ^ 8 m / s, mislim, da ste končali.

Aungen: BeesNuts: Kaj se zgodi, ko val preide čez odtok?

Mislim, da se zgodi zelo podobno. Črna luknja je značilnost ukrivljenosti prostora in časa. Takšen je tudi gravitacijski val. Zdi se, kot da sprašujete, kaj se zgodi, ko funkcije medija v interakciji, kar se mi ne zdi tako roman ali zanimivo. Mogoče pa se zgodi kakšen čuden šiat, ko izračunaš matematiko. Kdo ve.

Ugibate, da bi radi to raziskali, da bi poskusili modelirati Hawking Points v MBR?

Odločiti se morate, ali mislite, da je gravitacija temeljna sila ali ne. Prostor-čas je tudi konstrukt, pri katerem se moramo odločiti, ali obstaja ali ne. Ko se poglobimo v to, kako stvari delujejo, če to ni vesolje, ki ga vodijo dogodki, te stvari postanejo simptomi in ne vzroki in prožnost se nenadoma prikrade.

Osebno mislim, da je kvant rezultat ekstremnih situacij, ko se razkrije skrita fleksibilnost verjetnosti, ki je vpeta v tkanino vesolja. Veliko časa in truda smo porabili za gradnjo konstrukcij, da bi vse razložili, vendar mislim, da smo postaja smešno. Mislim, da smo šli predaleč in moramo narediti velik korak nazaj. Bilo je zabavno biti del D & Oslash-a in ICECUBE-ja in všeč mi je enostavnost standardnega modela. Toda kar se v resnici dogaja, mislim, da je to bolj priročno za znanstvenike, da razpravljajo o procesih in načrtih eksperimentov ali rezultatih, kot pa so dobro okno za to, kar je resnično.

Čeprav je agnosticizem glede nečesa na krvavem robu fizike razumen, mislim, da Splošna relativnost ni primerna za pohvale. Napovedoval je črne luknje in gravitacijske valove. In ni nič kvantnega, če bi v celoti delali v tem okviru.

RES NORO je, ali je ta dogodek nekako kodiran brez črne luknje. Ali se na nek način "spomni" dogodka? Takrat smo * globoko * v plevelu, kot pa vprašati, kako dve gravitacijski motnji medsebojno vplivata.

Z lahkoto bom priznal, da dejanska matematika, ki obkroža tak dogodek, verjetno zahteva nekaj čudne sinteze navier-stok-ov in splošne relativnosti ali kaj podobnega, in nisem fizik, ki bi to poskušal izpeljati.

sxacho: Predvidevam, da bi se vsi gravitacijski valovi, ki bi dosegli obzorje dogodkov, izgubili v črni luknji, medtem ko bi se vsi, ki ne bi dosegli obzorja dogodkov, upognili sorazmerno z oddaljenostjo.

To predpostavlja, da gravitacija vpliva na gravitacijo. Toda strinjam se, da bi izkrivljal val, ko je šel skozi. Vendar se lahko gravitacijski valovi tehnično širijo hitreje kot svetloba, zato je * možno *, da celoten val zapusti črno luknjo, pri čemer se najbolj prizadeti del gravitacijskega vala raztegne s faktorjem svoje hitrosti glede na črno luknjo deljeno s svetlobno hitrostjo. Če se širi počasneje od svetlobne hitrosti, si lahko nekako predstavljam, da lokalno diskombulira val in prekine vzročno zvezo med dvema "odrezanima polovicama" tega kozmičnega odmeva.

Čebelji oreški: aungen: BeesNuts: Kaj se zgodi, ko val preide čez odtok?

Mislim, da se zgodi zelo podobno. Črna luknja je značilnost ukrivljenosti prostora in časa. Takšen je tudi gravitacijski val. Zdi se, kot da sprašujete, kaj se zgodi, ko funkcije medija v interakciji, kar se mi ne zdi tako roman ali zanimivo. Mogoče pa se zgodi kakšen čuden šiat, ko izračunaš matematiko. Kdo ve.

Ugibate, da bi radi to raziskali, da bi poskusili modelirati Hawking Points v MBR?

Odločiti se morate, ali mislite, da je gravitacija temeljna sila ali ne. Prostor-čas je tudi konstrukt, pri katerem se moramo odločiti, ali obstaja ali ne. Ko se poglobimo v to, kako stvari delujejo, če to ni vesolje, ki ga vodijo dogodki, te stvari postanejo simptomi in ne vzroki in prožnost se nenadoma prikrade.

Osebno mislim, da je kvant rezultat ekstremnih situacij, ko se razkrije skrita fleksibilnost verjetnosti, ki je vpeta v tkanino vesolja. Veliko časa in truda smo porabili za gradnjo konstrukcij, da bi vse razložili, vendar mislim, da smo postaja smešno. Mislim, da smo šli predaleč in moramo narediti velik korak nazaj. Bilo je zabavno biti del D & Oslash-a in ICECUBE-ja in všeč mi je enostavnost standardnega modela. Toda kar se v resnici dogaja, mislim, da je to bolj priročno za znanstvenike, da razpravljajo o procesih in načrtih eksperimentov ali rezultatih, kot pa so dobro okno za to, kar je resnično.

Čeprav je agnosticizem glede nečesa na krvavem robu fizike razumen, mislim, da Splošna relativnost ni primerna za pohvale. Napovedoval je črne luknje in gravitacijske valove. In ni nič kvantnega, če bi v celoti delali v tem okviru.

RES NORO je, ali je ta dogodek nekako kodiran brez črne luknje. Ali se na nek način "spomni" dogodka? Takrat smo * globoko * v plevelu, kot pa vprašati, kako dve gravitacijski motnji medsebojno vplivata.

Z lahkoto bom priznal, da delam dejansko.

Uh. Seveda sta kvantna in splošna relativnost za seboj. Rivalstvo je dobesedno najvišje sadje na drevesu. Če zapečatiš to kršitev, si gos in zlato jajce, dobiš Nobela in se spustiš v zgodovinske knjige. Leta 2020 smo izvedli nekaj zanimivih študij o meritvah belih pritlikavcev, ki so morda omogočile prvo pravo povezavo med njimi. To je stvar, na kateri se dela.

Splošna relativnost je popolnoma urejena, če vas podrobnosti ne skrbijo. Če pa ste, raje bodite previdni. V njem so luknje. Velike, črne luknje.

Čebelji oreški: sxacho: Predvidevam, da bi se vsi gravitacijski valovi, ki bi dosegli obzorje dogodkov, izgubili v črni luknji, medtem ko bi se vsi, ki ne bi dosegli obzorja dogodkov, upognili sorazmerno z oddaljenostjo.

To predpostavlja, da gravitacija vpliva na gravitacijo. Toda strinjam se, da bi izkrivljal val, ko je šel skozi. Vendar se lahko gravitacijski valovi tehnično širijo hitreje kot svetloba, zato je * možno *, da celoten val zapusti črno luknjo, pri čemer se najbolj prizadeti del gravitacijskega vala raztegne s faktorjem svoje hitrosti glede na črno luknjo deljeno s svetlobno hitrostjo. Če se širi počasneje od svetlobne hitrosti, si lahko nekako predstavljam, da lokalno diskombulira val in prekine vzročno zvezo med dvema "odrezanima polovicama" tega kozmičnega odmeva.

V kakšnih okoliščinah lahko gravitacijski valovi potujejo hitreje (ali počasneje) kot svetlobna hitrost? Brez napak, samo resnično radoveden.

hawcian: BeesNuts: sxacho: Predvidevam, da bi se vsi gravitacijski valovi, ki bi dosegli obzorje dogodkov, izgubili v črni luknji, medtem ko bi se vsi, ki ne bi dosegli obzorja dogodkov, upognili sorazmerno z oddaljenostjo.

To predpostavlja, da gravitacija vpliva na gravitacijo. Toda strinjam se, da bi izkrivljal val, ko je šel skozi. Vendar se lahko gravitacijski valovi tehnično širijo hitreje kot svetloba, zato je * možno *, da celoten val zapusti črno luknjo, pri čemer se najbolj prizadeti del gravitacijskega vala raztegne s faktorjem svoje hitrosti glede na črno luknjo deljeno s svetlobno hitrostjo. Če se širi počasneje od svetlobne hitrosti, si lahko nekako predstavljam, da lokalno diskombulira val in prekine vzročno zvezo med dvema "odrezanima polovicama" tega kozmičnega odmeva.

V kakšnih okoliščinah lahko gravitacijski valovi potujejo hitreje (ali počasneje) kot svetlobna hitrost? Brez napak, samo resnično radoveden.

Gravitacijski valovi potujejo s hitrostjo širjenja. Svetloba se upočasni, ko prehaja skozi medij.

Aungen: hawcian: BeesNuts: sxacho: Predvidevam, da bi se vsi gravitacijski valovi, ki bi dosegli horizont dogodkov, izgubili v črni luknji, medtem ko bi se vsi, ki ne bi dosegli obzorja dogodkov, upognili sorazmerno z oddaljenostjo.

To predpostavlja, da gravitacija vpliva na gravitacijo. Toda strinjam se, da bi izkrivljal val, ko je šel skozi. Vendar se lahko gravitacijski valovi tehnično širijo hitreje kot svetloba, zato je * možno *, da celoten val zapusti črno luknjo, pri čemer se najbolj prizadeti del gravitacijskega vala raztegne s faktorjem svoje hitrosti glede na črno luknjo deljeno s svetlobno hitrostjo. Če se širi počasneje od svetlobne hitrosti, si lahko nekako predstavljam, da lokalno diskombulira val in prekine vzročno zvezo med dvema "odrezanima polovicama" tega kozmičnega odmeva.

V kakšnih okoliščinah lahko gravitacijski valovi potujejo hitreje (ali počasneje) kot svetlobna hitrost? Brez napak, samo resnično radoveden.

Gravitacijski valovi potujejo s hitrostjo širjenja. Svetloba se upočasni, ko prehaja skozi medij.

Svetloba se skozi medij ne upočasni, pot se podaljša z odbijanjem znotraj medija, preden izstopi z enako konstantno hitrostjo, kot jo je ohranila.

Gravitacija je artefakt samega vesoljsko-časovnega kontinuuma in pravila GenRev "nič ni hitrejše od svetlobe" veljajo samo za fizične predmete, ki potujejo skozi omenjeni kontinuum. Razlika je v tem, zakaj se je lahko zgodila kozmična inflacija.

mcmnky: Spekter: Ethan Siegel je končno skočil morskega psa.

Ne vem o tem, vendar je uporabil veliko besed, da bi le rekel: ja, črne luknje vplivajo na gravitacijske valove enako kot vplivajo na vsa druga znana brezmasna sevanja.

Ja, to je povsem na znamki.

Če predpostavimo, da sferični morski pes enakomerne gostote potuje z relativno hitrostjo v ergosferi supermasivne galaktične črne luknje, jo je vedno preskakoval.

AdrienVeidt: aungen: hawcian: BeesNuts: sxacho: Predvidevam, da bi se vsi gravitacijski valovi, ki bi dosegli horizont dogodkov, izgubili v črni luknji, medtem ko bi se vsi, ki ne bi dosegli obzorja dogodkov, upognili sorazmerno z oddaljenostjo.

To predpostavlja, da gravitacija vpliva na gravitacijo. Toda strinjam se, da bi izkrivljal val, ko je šel skozi. Vendar se lahko gravitacijski valovi tehnično širijo hitreje kot svetloba, zato je * možno *, da celoten val zapusti črno luknjo, pri čemer se najbolj prizadeti del gravitacijskega vala raztegne s faktorjem svoje hitrosti glede na črno luknjo deljeno s svetlobno hitrostjo. Če se širi počasneje od svetlobne hitrosti, si lahko nekako predstavljam, da lokalno diskombulira val in prekine vzročno zvezo med dvema "odrezanima polovicama" tega kozmičnega odmeva.

V kakšnih okoliščinah lahko gravitacijski valovi potujejo hitreje (ali počasneje) kot svetlobna hitrost? Brez napak, samo resnično radoveden.

Gravitacijski valovi potujejo s hitrostjo širjenja. Svetloba se upočasni, ko prehaja skozi medij.

Svetloba se skozi medij ne upočasni, pot se podaljša z odbijanjem znotraj medija, preden izstopi z enako konstantno hitrostjo, kot jo je ohranila.

Gravitacija je artefakt samega vesoljsko-časovnega kontinuuma in pravila GenRev "nič ni hitrejše od svetlobe" veljajo samo za fizične predmete, ki potujejo skozi omenjeni kontinuum. Razlika je v tem, zakaj se je lahko zgodila kozmična inflacija.

c je največja hitrost svetlobe, ki lahko potuje skozi vesolje-čas. Pravzaprav ni omejitve hitrosti vesolja-časa.

porfromchichis: AdrienVeidt: aungen: hawcian: BeesNuts: sxacho: Predvidevam, da bi se vsi gravitacijski valovi, ki bi dosegli horizont dogodkov, izgubili v črni luknji, medtem ko bi se vsi, ki ne bi dosegli obzorja dogodkov, upognili sorazmerno z oddaljenostjo.

To predpostavlja, da gravitacija vpliva na gravitacijo. Toda strinjam se, da bi izkrivljal val, ko je šel skozi. Vendar se lahko gravitacijski valovi tehnično širijo hitreje kot svetloba, zato je * možno *, da celoten val zapusti črno luknjo, pri čemer se najbolj prizadeti del gravitacijskega vala raztegne s faktorjem svoje hitrosti glede na črno luknjo deljeno s svetlobno hitrostjo. Če se širi počasneje od svetlobne hitrosti, si lahko nekako predstavljam, da lokalno diskombulira val in prekine vzročno zvezo med dvema "odrezanima polovicama" tega kozmičnega odmeva.

V kakšnih okoliščinah lahko gravitacijski valovi potujejo hitreje (ali počasneje) kot svetlobna hitrost? Brez napak, samo resnično radoveden.

Gravitacijski valovi potujejo s hitrostjo širjenja. Svetloba se upočasni, ko prehaja skozi medij.

Svetloba se skozi medij ne upočasni, pot se podaljša z odbijanjem znotraj medija, preden izstopi z enako konstantno hitrostjo, kot jo je ohranila.

Gravitacija je artefakt samega vesoljsko-časovnega kontinuuma in pravila GenRev "nič ni hitrejše od svetlobe" veljajo samo za fizične predmete, ki potujejo skozi omenjeni kontinuum. Razlika je v tem, zakaj se je lahko zgodila kozmična inflacija.

c je največja hitrost svetlobe, ki lahko potuje skozi vesolje-čas. Pravzaprav ni omejitve hitrosti vesolja-časa.

Delci, ki potujejo hitreje kot svetloba skozi medij, oddajajo tako imenovano Čerenkovovo sevanje, ki ga lahko vidimo kot modri udarni val svetlobe za seboj. Muoni to počnejo na primer. In nevtrini lahko prispejo pred svetlobo supernove. Obe postavki se posebej uporabljata v večnacionalnih eksperimentih.

Noben od teh delcev ne potuje hitreje od hitrosti širjenja (c). Bozoni imajo radi potovanje svetlobe s hitrostjo širjenja in jih upočasnijo interakcije in zapleti. Delci, kot so nevtrini, gredo nekoliko počasneje, vendar ignorirajo snov.

Torej prejmete nevtrinski utrip prej kot svetlobni utrip umirajoče zvezde, skoraj vsakič. Nevtrinski val lahko opozori teleskope, da se obrnejo v določeno smer in poiščejo razcvet.

Aungen: por pora: AdrienVeidt: aungen: hawcian: BeesNuts: sxacho: [odreži po dolžini]

Delci, ki potujejo hitreje kot svetloba skozi medij, oddajajo tako imenovano Čerenkovovo sevanje, ki ga lahko vidimo kot modri udarni val svetlobe za seboj. Muoni to počnejo na primer. In nevtrini lahko prispejo pred svetlobo supernove. Obe postavki se posebej uporabljata v večnacionalnih eksperimentih.

Noben od teh delcev ne potuje hitreje od hitrosti širjenja (c). Bozoni imajo radi potovanje svetlobe s hitrostjo širjenja in jih upočasnijo interakcije in zapleti. Delci, kot so nevtrini, gredo nekoliko počasneje, vendar ignorirajo snov.

Torej prejmete nevtrinski utrip prej kot svetlobni utrip umirajoče zvezde, skoraj vsakič. A neutrino wave can alert telescopes to turn in a certain direction to look for a boom.

Sure, light can arrive later than neutrinos or gravity waves, because light interacts with the medium it travels through, but BeesNuts was talking about gravitational waves escaping black holes. The implication is that gravitational waves can travel faster than the propagation speed of light (they even specifically said "propagate faster than light").

Gravitational waves, which do not interact the same as light waves, should travel at propagation speed (c), and not slow down like light does.

The ONLY thing I wonder about, is whether a gravity wave can ripple that first topographical circle around a black hole relative to propagation speed. I think it can.

So are black holes bigger on the inside, like a tardis?

They're constantly warping space and that curved space ends up inside the event horizon.

hawcian: BeesNuts: sxacho: I would guess that any gravity waves that would reach the event horizon would be lost to the black hole while any that don't reach the event horizon will be bent in proportion to the distance away.

This presupposes that gravity is affected by gravity. But I tend to agree that it would distort the wave as it passed through. However, gravity waves can technically propagate faster than light, so it's *possible* for the entire wave to exit a black hole, with the most extremely affected portion of the gravitational wave getting stretched out by a factor of its velocity relative to the black hole divided by the speed of light. If it's propagating slower than light speed, I can kind of imagine it locally discombobulating the wave, breaking the causal relationship between two "severed halves" of this cosmic echo.

Under what circumstances can gravity waves travel faster (or slower) than the speed of light? No snark, just genuinely curious.

They are distortions in the fabric of spacetime, so they aren't really "moving", since they are kind of the medium through which they are moving. More like they are propagating through the medium. Nothing in special or general relativity gets in the way of that propagation speed exceeding the speed of light. In fact, the *reason* light can't escape a black hole is because spacetime itself is falling into the hole faster than light speed.

/super simplified, words only explanation.
//Leonard Susskind has a couple excellent lectures on wtf we believe to be happening on the other side of the event horizon that gives excellent background on how cosmologists think about these things.

SoundOfOneHandWanking: So are black holes bigger on the inside, like a tardis?

They're constantly warping space and that curved space ends up inside the event horizon.

If you really wanna cook your noodle, current theory is that space and time switch dimensional roles the moment you cross the event horizon. Meaning you can move freely in any direction on the time axis, but that you are inexorably dragged towards the spatial singularity.

aungen: Gravitational waves, which do not interact the same as light waves, should travel at propagation speed (c), and not slow down like light does.

The ONLY thing I wonder about, is whether a gravity wave can ripple that first topographical circle around a black hole relative to propagation speed. I think it can.

I'm not so sure. there's still a question about whether the event horizon is a physical . thing. It's external topology might be causally disconnected from the rest of spacetime, and more connected to its internal geometry, whatever the fark that might end up actually being. The *real* Holographic Principle says that the topology of the event horizon is actually a full informatic description of infalling and radiating matter and energy. If that's true, then the only way to impact that topology would be to leave something behind in the black hole.

If that's *not* true, then holy hell would that be a life affirming observation to hear about. It might actually imply that there is no true singularity inside black holes, which would have *huge* implications about deep time. It'd definitely throw a monkey wrench into Sir Penrose's Conformal Cyclic Cosmology.

I suspect there is no singularity, but someone else will have to figure out how to prove that. I think you're spot on with the assessment.


Ask Ethan: How do gravitational waves escape from a black hole?

“I think there are a number of experiments that are thinking about how you could look in different frequency bands, and get a glimpse of the primordial gravitational wave background. I think that would be really revolutionary, because that would be your first glimpse at the very first instant of our Universe.” -Dave Reitze, LIGO’s executive director

Perhaps the greatest discovery of all announced in 2016 was the direct detection of gravitational waves. Even though they had been predicted by Einstein’s general theory of relativity 101 years prior, it took the development of a laser interferometer sensitive to ripples in space that would displace two mirrors separated by multiple kilometers by less than 10^-19 meters, or 1/10,000th the width of a proton. This finally came to pass during LIGO’s 2015 data run, and two bona fide black hole-black hole merger events unambiguously popped out of the data. But how does physics actually allow this? Mārtiņš Kalvāns wants to know:

This question has puzzled me for a long time. Articles about LIGO discovery state that some percentage of black hole merger mass was radiated away, leaving [a] resulting black hole smaller than [the] sum of [the] original mergers. Yet it is accepted that nothing escapes black holes […] So my question is: how was energy radiated from black hole mergers?

This is a really deep question, and goes straight to the heart of black hole physics and general relativity.

On the one hand, we have a black hole. All of its mass/energy is concentrated together at a singularity at the center, and it’s forever invisible to the outside observer thanks to the presence of an event horizon. Inside a certain region of space (defined by the event horizon), any path that any particle can take, whether massive or massless, regardless of speed or energy, will inevitably take it into the black hole’s central singularity. This means that any particle that enters the event horizon, crosses into the event horizon or otherwise ever finds itself inside the event horizon will never be able to get out, and thus its energy is trapped inside forever. Once you’re inside a black hole, you simply become part of the singularity’s properties: mass, charge (of all different types), and spin. That’s it.

On the other hand, Einstein’s general relativity tells us that when two masses (of any type) orbit one another, it creates ripples in the fabric of space itself as the orbits themselves decay. These ripples, known as gravitational waves, move at the speed of light, cause space to expands-and-contract whenever they pass through it, and carry energy. Because of Einstein’s most famous equation, E = mc2 (or, as he wrote it originally, m = E/c2), we know that one source of energy is mass and one source of mass is energy. They can be converted into one another mass is only one particular form that energy can take on.

So when LIGO released the results of the event that occurred on September 14, 2015 in January of this year, it was only mildly surprising that they found two black holes — of 36 and 29 solar masses — merging together to create a new black hole of 62 solar masses. Where did the other 3 solar masses (about 5% of the total system’s mass) go? In the energy of gravitational waves. With subsequent events that have been detected, roughly the same trend emerges: two black holes of comparable masses inspiral and merge together, and up to around 5% of their total initial masses gets radiated away in the form of gravitational waves.

But each black hole has an event horizon. Each of the pairs has one before the merger, the final post-merger black hole has one, and at no point during the merger does either singularity become “naked” or ever emerge from an event horizon. So, how does the mass get out?

It’s not just a tricky question it’s a trick question! It’s like asking where the mass goes when protons fuse into deuterium, helium-3 and then helium-4 in the Sun. Why is helium-4 less massive than the four protons that made it up? Because of nuclear binding energy. A bound state is more stable and has less energy (and hence, less mass) than the unbound state. When two black holes inspiral, coalesce and merge, these two black holes are becoming more bound — more gravitationally bound — than they were before. The energy they’re losing is due to gravitational binding energy, not because either of the masses is exiting the event horizon.

You can see this just from Newtonian gravity. Imagine you have two masses of 1 kg each, each at rest and mutually separated by an infinite distance. They have a certain amount of energy inherent to them in this system: 1.8 × 10¹⁷ Joules, which you can get from Einstein’s equation, E = mc2. Now bring them in to one another, and bring the distance down.

  • If they’re now separated by only one kilometer, the whole system has lost 6.67 × 10^-14 Joules of energy.
  • If you reduce that separation to one centimeter, the system loses 6.67 × 10^-9 Joules.
  • If you bring that separation down to the size of a proton, at 10^-15 meters, the system now loses an incredible 6.67 × 10⁴ Joules, or 66,700 Joules. (Now we’re getting somewhere!)
  • And so if you want to lose a really significant amount of energy, you can imagine taking the separation all the way down to 10^-27 meters, where you’ll lose 6.67 × 10¹⁶ Joules, or about 35% of the original energy!

Of course, our Universe obeys general relativity on these scales, not Newtonian gravity, but the picture is the same. It isn’t that the black holes are losing mass it’s that the total amount of energy in spacetime is transforming from one form — in two well-separated, unbound masses — to another form: a single, tightly bound mass plus gravitational radiation. The orbital properties and the masses of the original black holes determine what percentage of the total original mass becomes binding energy, but in all cases it’s always true that the final mass is larger than either of the original masses but smaller than the combined raw masses. 5% is the amount that’s radiated away in the maximal case, where the two masses are roughly equal. If they had an incredible amount of energy in their spins and their spins were aligned, that percentage can be bumped up all the way to about 11%. But if one of the masses is much greater than the other, the percentage drops a 1 solar mass black hole merging with a 1,000,000 solar mass one can only radiate away 0.0001% of its energy.

The inspiral and merger doesn’t result in anything from inside the black hole getting out, but rather in spacetime deforming to account for the gravitational potential energy as the two masses coalesce and merge. The ringdown phase — which occurs at the end of the merger — represents the event horizon reverting to its maximally efficient shape: either a sphere or a spheroid. It’s the very last fraction-of-a-second of the merger where the most energy is released, but no particles from inside the black hole are getting out. Einstein’s predictions are very clear, and this is why we were able to make the detections in the first place: because we had calculated what signal to look for. Our intuition may give us trouble, but that’s why we have the equations. Even when our instincts are no good, the calculations will give us the scientific truth.


Astroquizzical: How Does Gravity Escape From A Black Hole?

If it only moves at the speed of light, and light can’t escape, how can gravity?

I’ve heard that gravity “moves” at the speed of light if it does, then how can a black hole’s influence extend outside of the event horizon? If the answer is that “it’s not light, it ‘moves’ in a different way that’s not subject to the same rules as light,” then why does it move at the same speed?

There’s a few things tangled up in here, but let’s see if we can untangle them.

The first is about how gravity affects space-time in general. Normally you see the gravitational distortion of, say, the Earth, represented like the following:

Or you might have run into the explanation that gravity acts like a bowling ball on a rubber sheet, with heavier objects causing deeper indentations in the sheet.

These are reasonable explanations, though simplified, since the indentations happen in all directions, so these ‘indentations’ are really three dimensional distortions, or condensations, of space itself. But these simplifications illustrate an important point — fundamentally, gravity is a distortion to space itself. Often we speak of this distortion in terms of a ‘well’, which goes back to this two dimensional sheet metaphor, since it’s easy to think of things rolling downhill into a divot, formed by the presence of a large amount of mass.

Mathematically, the influence of gravity is written out as directly proportionate to the mass of the object, and inversely proportional to the square of the distance between you and that object. This distance dependence is what creates the particular smooth curve away from the center of the object. If you’re very close to the object, the gravitational well is deep, and you feel a strong gravitational pull. If you’re further away, gravity can’t pull space that far out of shape, so you feel a much weaker gravitational force.

These distortions to space are always present — for instance, all the planets are in their own distortion of space, with moons that float in ellipses within this distortion. The Sun has its own, much deeper distortion that all the planets are circling. The Sun follows the distortion of the galaxy. And, critically, each distortion was present in a milder form before each of these objects collapsed into their current form, so these distortions didn’t spontaneously form at any stage — they simply contracted and deepened as density increased. A small gas cloud could have the same mass as a small planet, but the planet’s gravitational well will be steeper than the gas cloud’s. The steeper the gravitational well, the faster you need to go to escape it, but you need both extreme mass and extreme concentration of that mass before you make it to black hole territory.

The event horizon of a black hole, in this context, describes the location beyond which, the black hole’s gravitational well is so steep, that even light can’t escape it. If you take one of these rubber sheet diagrams, you could place down a circle to describe it’s location. But the event horizon itself doesn’t describe a physical boundary to the influences of gravity. The gravitational well itself exists continuously outside and inside of the event horizon — outside of the event horizon it’s just slightly less steep. You could place another circle outside the event horizon that describes the location at which you need to go half the speed of light to escape — there’s no change or boundary in the physical distortion at this circle, it’s just a descriptive line that might prove useful to understand or describe the object’s influence on space.

The stars which eventually turn into black holes are the most massive stars that form, which tend to burn bright blue, extremely hot, and burn out quickly. Typically the threshold for the mass of the star that can leave behind a black hole is given at around eight solar masses, though this is probably a slightly fuzzy boundary. These stars have had their own gravitational distortion since they were a cloud of dense gas, well before they were stars. The stars contract, and light up, and their gravitational twist of space gets more intense, but it’s not a sudden change. It’s more of a gradual shift towards a more and more dramatic gravitational well.

The ‘movement’ of gravity at the speed of light limit can be considered entirely separately while gravity has a broad extent across a wide swath of space, the speed of light imposes a limit on how quickly information about changes can travel across that space.

The common example is that if the Sun were to spontaneously vanish — not explode, but vanish completely — the Earth wouldn’t notice anything different until about 8 minutes later, when the sunshine would vanish. But the Earth would also continue to orbit around the physically nonexistent Sun for another 8 minutes, because the changes to the distortion of space due to the Sun’s presence also haven’t reached us yet. If you think of the speed of light more as an information speed limit than as a particle speed limit, this makes it slightly easier to think about.

Information doesn’t always travel at the speed of light, though — depending on the environment that the information is traveling through, and the form of that information (which is not always light), the speed of information can proceed at speeds that are much slower than the speed of light. The speed of light in a vacuum seems to be a hard upper limit that nothing can surpass, but if your information is in the form of a compression wave, like sound, then the information travels at the speed of sound in that medium.

Think of a lightning strike — unless you’re right underneath the strike, you hear the thunder several seconds after the lightning strike. Light travels faster through air than sound does, so even though they were created at the same time, it’s the light’s information that reaches you first, and this discrepancy grows the further away you are.
The speed of light in water is even slower than through air (1.3 times slower, in fact). Effectively, the more dense the material you’re working with, the slower information goes through it.

Going back to black holes, changes to the shape of the gravitational distortion are also information traveling through a medium, though the medium of space is generally almost a perfect vacuum, so we’re working close to our absolute speed limit. As far as we know, gravity doesn’t function in a way that would slow it down in a vacuum, so it should also pass along information at the speed of light.

Gravity is one of the least fundamentally understood forces of nature we have a very good descriptive understanding of when we expect it to be important, and a very accurate description of its strength, but we don’t know exactly how it functions. How does it interact with matter? Is there a particle mediating its interactions? We have to wait a bit longer to answer these questions, but hopefully we’ll have better answers as we build detectors able to observe tiny fluctuations in the gravitational field that surrounds us!

If you have your own questions you’d like Astroquizzical to cover, you can submit them at Astroquizzical’s ask page!


Hear the ‘chirp’ of gravitational waves passing through Earth

You are free to share this article under the Attribution 4.0 International license.

Researchers have announced the third detection of gravitational waves—ripples in the fabric of space and time.

Albert Einstein predicted gravitational waves as part of his theory of general relativity more than 100 years ago, but it has taken astrophysicists more than 50 years of trial and error to find the direct evidence to support his theory.

The Laser Interferometer Gravitational-wave Observatory (LIGO) made the detection January 4, 2017. Gravitational waves pass through Earth and the extremely sensitive LIGO detectors can “hear” them.

Hear the “chirps” of the gravitational waves in this podcast episode:

The long-awaited triumph in September 2015 of the first-ever direct observation of gravitational waves completed Einstein’s vision of a universe in which space and time are interwoven and dynamic.

“It is remarkable that humans can put together a story and test it, for such strange and extreme events that took place billions of years ago and billions of light-years distant from us.”

This third and latest detection points to merging black holes that are twice as far away from Earth as the two earlier pairs—about 3 billion light-years away. And this time the two black holes were unequal in size, one significantly lighter than the other. They merged into a black hole whose size is in the middle of the other two merged black hole pairs.

“Our handful of detections so far is revealing an intriguing black hole population we did not know existed until now,” says Vicky Kalogera, a senior astrophysicist with the LIGO Scientific Collaboration (LSC), which conducts research related to the twin LIGO detectors, located in the US. She is also director of Northwestern University’s astrophysics center, CIERA, and professor of physics and astronomy.

“Now we have three pairs of black holes, each pair ending their death spiral dance over millions or billions of years in some of the most powerful explosions in the universe. In astronomy, we say with three objects of the same type you have a class. We have a population, and we can do analysis.”

“Once again, the black holes are heavy,” says Shane L. Larson, researcher associate professor of physics and astronomy at Northwestern and an astronomer at the Adler Planetarium in Chicago.

“The first black holes LIGO detected were twice as heavy as we ever would have expected. Now we’ve all been churning our cranks trying to figure out all the interesting myriad ways we can imagine the universe making big and heavy black holes.”

The third detection is the subject of a new paper accepted for publication by the journal Fizična pregledna pisma.

So, why all the hubbub about gravitational waves?

“With the third confirmed detection of gravitational waves from the collision of two black holes, LIGO is establishing itself as a powerful observatory for revealing the dark side of the universe,” says David Reitze of Caltech, executive director of the LIGO Laboratory. “While LIGO is uniquely suited to observing these types of events, we hope to see other types of astrophysical events soon, such as the violent collision of two neutron stars.”

This three-dimensional projection of the Milky Way galaxy onto a transparent globe shows the probable locations of the three confirmed LIGO black-hole merger events—GW150914 (blue), GW151226 (orange), and the most recent detection GW170104 (magenta)—and a fourth possible detection, at lower significance (LVT151012, green). The outer contour for each represents the 90 percent confidence region the innermost contour signifies the 10 percent confidence region. (Credit: LIGO)

About 50X the mass of our sun

The latest finding solidifies the case for a new class of black hole pairs, or binary black holes, with masses that are larger than researchers believed possible before LIGO.

“As was the case with the first two detections, the waves detected in our new paper were generated when two black holes merged to form a larger black hole. In the latest merger, the final black hole was some 50 times the mass of our Sun,” explains coauthor Ling Sun, a PhD student at the University of Melbourne’s School of Physics and member of the Australian Research Council Centre of Excellence for Gravitational Wave (OzGrav).

This fills in a gap between the masses of the two merged black holes detected previously by LIGO, which had solar masses of 62 (first detection) and 21 (second detection).

“We have further confirmation of the existence of black holes that are heavier than 20 solar masses, objects we didn’t know existed before LIGO detected them,” says David Shoemaker of MIT, who is spokesperson for the LSC. “It is remarkable that humans can put together a story and test it, for such strange and extreme events that took place billions of years ago and billions of light-years distant from us.”

Powerful collisions

The new detection, called GW170104, occurred during LIGO’s current observing run, which began November 30, 2016, and will continue through the summer. Twin detectors, one in Hanford, Washington, and the other in Livingston, Louisiana, carry out LIGO’s observations.

Did gravitational wave detector find dark matter?

LIGO made the first detection of gravitational waves in September 2015 during its first observing run since undergoing major upgrades in a program called Advanced LIGO. The second detection took place in December 2015. (The LIGO detectors were offline for nearly a year, from January to November 2016.)

In all three cases, each of the twin detectors of LIGO detected gravitational waves from the tremendously energetic mergers of black hole pairs—collisions that produce more power during the instant before the black holes merge than is radiated as light by all the stars and galaxies in the universe at any given time.

The recent detection is the farthest yet, with the black holes located about 3 billion light-years away. (The black holes in the first and second detections are located 1.3 and 1.4 billion light-years away, respectively.)

Two theories

There are two primary models to explain how binary pairs of black holes can be formed.

In one model, the black holes come together later in life within crowded stellar clusters. The black holes pair up after they sink to the center of a star cluster. In this scenario, the black holes can spin in any direction relative to their orbital motion.

“This is the first time that we have evidence that the black holes may not be aligned, giving us just a tiny hint that binary black holes may form in dense stellar clusters,” comments B. P. Sathyaprakash, professor of physics and of astronomy and astrophysics at Penn State and co-leader of the paper.

The other model proposes that the black holes are born in the same binary system: they form when each star in a pair of stars explodes, and then, because the original stars were spinning in alignment, the black holes remain mostly aligned, even if not perfectly aligned.

GW170104 hints that at least one of the two black-hole spins might be misaligned with the binary orbit, mildly favoring the formation theory of dense stellar clusters.

The LIGO Laboratory receives funding from the National Science Foundation (NSF) and is operated by Caltech and MIT, which conceived and built the observatory. The NSF led in financial support for the Advanced LIGO project, with funding organizations in Germany (MPG), the UK (STFC), and Australia (ARC) making significant commitments to the project.

More than 1,000 scientists and engineers from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. LIGO partners with the Virgo Collaboration, which has the support of the Centre National de la Recherche Scientifique (CNRS), Istituto Nazionale di Fisica Nucleare (INFN), and Nikhef, as well as Virgo’s host institution, the European Gravitational Observatory, a consortium that includes 280 additional scientists throughout Europe. A list of additional partners is available here.


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Just Keep Spinning

One of the things mostly lost in the media fanfare over GW190814 is what the signal revealed about the objects’ spins. Scientists estimate merging black holes’ spins based on their analysis of the gravitational waves’ shape, and they visualize them in half-moon plots that look like this:

This diagram shows the range of possible spins that each black hole in the GW150914 merger event might have had in relation to their orbit around each other.
B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration) / Phys. Rev. X 2019, CC BY 4.0 International

The coordinates around the circumference indicate how tilted a black hole’s spin axis is with respect to the dance floor it circles with its partner. Zero degrees means the black hole was pointing straight up, 90° that it was rolling on its side, and 180° that it was upside-down compared with the black holes’ mutual orbit. The color shows which values are compatible with the data. As you can see, there are a lot of options.

But the spin plots for the two objects involved in GW190814 look like this:

Plot of the tilt-angle and spin magnitude for the 23-solar-mass black hole (left) and 2.6-solar-mass secondary object (right). The tilt angles are 0° for spins aligned, and 180° for spins anti-aligned, with the orbital angular momentum.
R. Abbott et al. / Astrophysical Journal Letters 2020, CC BY 3.0

See how tiny the purple region on the left is? When scrolling through the paper, I did a double take at this plot: We’ve seen nothing like it out of LIGO or Virgo before. The concentrated dot tells us that the larger black hole basically wasn’t spinning.

Calculations and previous gravitational-wave detections indicate that most merger-made black holes wind up with a spin about 70% of their maximum allowed rate. “Low spin means that that 23-solar-mass black hole came from a single star,” Kalogera says. “That’s a firm conclusion.”

The low spin has important implications for stellar evolution. As a star ages and swells, its rotation slows. Astronomers had predicted that both the star’s outer layers and its core will slow together, linked by magnetic fields. If the core spins slowly, then the black hole it becomes when the star dies should spin slowly, too. The large black hole in GW190814 supports that picture.

But X-ray measurements from a few black holes paired up with massive stars suggest those black holes are spinning fast. Not enough gas has poured onto them from the stars to have spun them up, either. Now the question becomes, are those measurements correct?

Scientists can’t tell how fast the 2.6-solar-mass object spun prior to the collision the right-hand spin plot is a uniform lavender cloud. That’s because the larger object dominates the signal, like a booming voice drowning out a whisper. It also largely dictated the spin of the black hole made by the merger, which is just above zero.

Black holes detected by gravitational-wave observations (blue) are almost all significantly more massive than those detected through electromagnetic observations (purple). Neutron stars measured with electromagnetic observations appear in yellow, and the neutron stars detected through gravitational waves are in orange. The new event, GW190814, is highlighted in the middle
LIGO-Virgo / Frank Elavsky & Aaron Geller (Northwestern)


New gravitational wave detector: can be used to find a black hole the size of a tennis ball

It is understood that the research team led by him has just developed an application of this type of detector to observe &ldquosmall&rdquo primitive black holes. Their research results have been published in &ldquoPhysical Review D&rdquo a few days ago. &ldquoUntil today, these primordial black holes are still hypothetical, because it is difficult to distinguish between the black holes produced by the implosion of the stellar core and the primordial black holes. If it is possible to observe a smaller black hole, that is, a black hole with a mass of a planet but only a few centimeters in size, the situation is It will be different,&rdquo the research team said. They continued: &ldquoWe are providing experimenters with a device that can detect them by capturing the gravitational waves emitted when they merge. The frequency of this gravitational wave is much higher than currently available.&rdquo

< p>But what is the technique? A gravitational wave &ldquoantenna&rdquo is composed of a specific metal cavity and is properly immersed in a strong external magnetic field. When gravitational waves pass through a magnetic field, electromagnetic waves are generated in the cavity. To a certain extent, gravitational waves make the cavity &ldquohiss&rdquo (resonance), not with sound but with microwaves.

This device is only a few meters in size, but it is enough to detect the fusion of primitive small black holes millions of light-years away from Earth. It is much more compact than common detectors several kilometers long like LIGO, Virgo and KAGRA interferometers. This detection method makes it very sensitive to very high frequency gravitational waves (of the order of 100 MHz, while LIGO / Virgo / Kagra gravitational waves are only 10-1000 Hz), and these gravitational waves are not caused by fusion, neutron stars or stellar black holes. And other ordinary astrophysical sources.

On the other hand, it is an ideal tool for detecting small black holes. The mass and size of the planet has changed from a small ball to a tennis ball. &ldquoOur detector solution combines what we have mastered and the technologies we have in everyday life, such as the magnetron in the microwave oven, nuclear magnetic resonance magnets, and radio antennas. But don&rsquot take your home appliances apart and start taking risks: read us first. Article, and then order your equipment, figure out the equipment and the output signal,&rdquo the researcher said with a smile.

Although this patented technology is still in the advanced theoretical modeling stage, it has all the necessary elements to enter a more specific stage, namely the construction of a prototype. In any case, it paved the way for basic research on the origin of our universe. In addition to primitive black holes, this type of detector can also directly observe the gravitational waves emitted during the Big Bang to detect physics with higher energy than that achieved in particle accelerators.


Gravitational waves: a new era for astronomy

The first ever direct obser­va­tion of grav­i­ta­tion­al waves in 2015 by the LIGO Sci­en­tif­ic Col­lab­o­ra­tion in the US is undoubt­ed­ly one of the biggest sci­en­tif­ic dis­cov­er­ies of the last decade, or even this cen­tu­ry. Six years lat­er, what can we say about these waves, and why is it so impor­tant to study them?

Grav­i­ta­tion­al waves (GWs), first pre­dict­ed to exist by Albert Ein­stein in 1916, allow for a brand-new way of look­ing at the uni­verse. Before their detec­tion, astronomers could only observe the sky using vis­i­ble light, and oth­er types of elec­tro­mag­net­ic radi­a­tion (includ­ing infrared, ultra­vi­o­let and gam­ma rays).

While light is the prop­a­ga­tion of elec­tro­mag­net­ic fields vibrat­ing in space and time, GWs are com­plete­ly dif­fer­ent: they are rip­ples in the very fab­ric of space-time itself. They can thus be emit­ted by non-lumi­nous objects.

Study­ing black hole mergers

Cre­at­ing such rip­ples in the (rather rigid) fab­ric of space-time is not easy though. Indeed, GWs can only be pro­duced by accel­er­at­ing very small and extreme­ly mas­sive objects close to the speed of light. The best can­di­dates are there­fore black holes (which are the most com­pact objects in the uni­verse), and cer­tain very dense stars known as neu­tron stars (which are between 1.4 and 2.4 solar mass­es with a diam­e­ter of less than 20 km). To com­pare, the Sun has a diam­e­ter of 1.39 mil­lion kilometres.

In gen­er­al, an iso­lat­ed black hole does not pro­duce GWs. It needs a com­pan­ion to which it remains bound for a long time (much like Earth is bound to the Moon) to form what is called a bina­ry sys­tem. As they are extreme­ly dense, the black holes deform space-time in their vicin­i­ty as they orbit each oth­er, gen­er­at­ing GW rip­ples that prop­a­gate across the uni­verse at the speed of light.

As it emits these GWs, the bina­ry los­es some of the ener­gy that binds the black holes, which end up spi­ralling ever clos­er to each oth­er. This infer­nal waltz pro­duces more and more intense GWs (that can trav­el bil­lions of light-years across the uni­verse) until the black holes even­tu­al­ly merge. From time to time, one of these bina­ries pro­duces GWs with an ampli­tude that is just large enough to be detect­ed when it reach­es Earth, even though the sig­nal is extreme­ly weak.

The LIGO detection

The first sig­nal from such a bina­ry black-hole coa­les­cence, which occurred approx­i­mate­ly 1.3 bil­lion light-years from Earth, was detect­ed in Sep­tem­ber 2015 by an instru­ment called LIGO (for Laser Inter­fer­om­e­ter Grav­i­ta­tion­al-Wave Obser­va­to­ry) 1 2 . The coa­les­cence includes the “inspi­ral” (when the black holes become clos­er), the “merg­er” (when they touch) and the “ring­down” (when the new­ly formed, big­ger black hole relax­es into a steady state).

The two black holes in ques­tion, of about 36 and 29 solar mass­es, even­tu­al­ly merged to form a sin­gle black hole of 62 solar mass­es. The 3 solar mass dif­fer­ence was entire­ly con­vert­ed into grav­i­ta­tion­al ener­gy car­ried by the GWs.

LIGO is a col­lab­o­ra­tive project with over 1000 sci­en­tists and engi­neers from more than 20 coun­tries, and three of its mem­bers were award­ed the 2017 Nobel Prize in Physics 3 . It took near­ly 50 years of intense research to build the GW detec­tors, and in June 2016 the researchers announced that they had observed a sec­ondary bina­ry black hole coa­les­cence 4 . The obser­va­tion was made on 26 Decem­ber 2015, and this time, the black holes were about 1.4 bil­lion light-years away. Rough­ly 50 such merg­er events have been detect­ed since this time. All these dis­cov­er­ies great­ly advanced many research fields and kicked off the era of grav­i­ta­tion­al-wave astronomy.

Tiny length changes

Instru­ments like LIGO and oth­er ground-based GW detec­tors, such as Vir­go in Italy and Kagra in Japan, rely on an advanced sens­ing method called laser inter­fer­om­e­try. This tech­nique has long been used to detect dif­fer­ent sorts of sig­nals, but it had nev­er been pushed to the lim­it need­ed to detect the very weak sig­nals that GWs produce.

The LIGO facil­i­ty basi­cal­ly works by send­ing twin laser beams down two 4 km-long “arms” arranged in an L‑shape and kept under a near-per­fect vac­u­um. The beams are reflect­ed by mir­rors pre­cise­ly posi­tioned at the ends of each arm. As a GW pass­es through the obser­va­to­ry, it caus­es extreme­ly tiny dis­tor­tions in the dis­tance trav­elled by each laser beam. The instru­ment is thus able to mea­sure the local con­trac­tion and expan­sion of space-time caused by the GW.

The extreme sen­si­tiv­i­ty of the instru­ment means that it is prey to all sorts of exter­nal vibra­tions (such as those from planes fly­ing by and waves on a dis­tant shore). LIGO engi­neers there­fore had to design sev­er­al inge­nious noise-reduc­tion sys­tems that not only great­ly enhance the pre­ci­sion of the detec­tors, but also allow them to dif­fer­en­ti­ate between ter­res­tri­al arte­facts and the pre­cious GW signals.

By mea­sur­ing how long it takes for the laser beams to trav­el along an arm, researchers can extract infor­ma­tion such as the fre­quen­cy and ampli­tude of the GW from the sig­nal. These quan­ti­ties are of major impor­tance since they con­tain key phys­i­cal infor­ma­tion about the source of the wave, such as its dis­tance from Earth and its posi­tion in the sky, as well its mass and whether it is a black hole or a neu­tron star.

Future detec­tors

The char­ac­ter­is­tics of inter­fer­om­e­ters like LIGO makes them sen­si­tive only to grav­i­ta­tion­al waves with­in a cer­tain fre­quen­cy band, from about 10 Hz to 10 kHz, which cor­re­sponds to black holes of about 10 to 100 solar masses.

To extend this fre­quen­cy range, the most promis­ing future project is the Laser Inter­fer­om­e­ter Space Anten­na (LISA) 5 . This Euro­pean space-based obser­va­to­ry, due to come online in 2034, will tar­get fre­quen­cies in the low­er mil­li­hertz range to detect waves from the merg­er of much big­ger black holes. These “super­mas­sive” objects are found at the cen­tres of most galax­ies – includ­ing our Milky Way – and have mass­es that are mil­lions or even bil­lions of times that of the Sun.

LISA should also be able to observe “asym­met­ric” pairs, such as a neu­tron star orbit­ing a super­mas­sive black hole, and even the so-called “cos­mic grav­i­ta­tion­al-wave back­ground”, which is very impor­tant for cos­mol­o­gy since it con­tains infor­ma­tion about the pri­mor­dial GW cre­at­ed right after the Big-Bang 6 . Far more pre­cise than its ter­res­tri­al cousins, LISA will be a mil­lions-of-kilo­me­tre-long instru­ment con­sist­ing of three tiny robots posi­tioned in an equi­lat­er­al tri­an­gle pat­tern in solar orbit just behind Earth.


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