BAƘAR LU'U-LU'U: ALAMAR ƘURA SHEKARU MILIYAN 500 BAYAN BIG BANG

Na’urar hangen nesa ta sararin samaniya ta James Webb tana ci gaba da gano cewa galaxy sun cika da ƙarafa (metals) da ƙura cikin sauri mai ban mamaki, a cikin shekaru biliyan na farko na tarihin sararin samaniya. Ƙura tana da wuyar nazari a irin wannan nisa: hasken zafinta yana da matuƙar wuyar ganowa. Amma ƙura kuma tana barin alamomi a kan hasken taurari da ke ratsa ta, kuma alama ɗaya tana da ma’ana musamman.

Rami a cikin ultraviolet

A cikin Milky Way, ƙura tana rage hasken ultraviolet tare da wani babban “ƙumburi” (bump) wanda cibiyarsa take kusa da ångström 2,175: rami a cikin bakan haske (spectrum), mafi ƙarfin siffa a cikin lanƙwasan rage haske (extinction curve) na Galaxy ɗinmu. Ana danganta shi sosai da ƙananan ƙwayoyi ko ƙwayoyin zarra masu yawan carbon, ko da yake waɗanne ne daidai har yanzu ana muhawara — ƙananan ƙwayoyin graphite, polycyclic aromatic hydrocarbons (PAHs) da carbon mara tsari suna cikin waɗanda ake zato. A kan hanyoyin gani daban-daban a cikin Milky Way, faɗi da ƙarfin ƙumburin suna bambanta, amma wurin cibiyarsa yana da kwanciyar hankali mai ban mamaki.

Webb ya tura binciken zuwa farkon sararin samaniya. Wani babban ganowa ya zo a cikin wani galaxy a redshift 6.71, kusan shekaru miliyan 800 bayan Big Bang, tare da ƙumburi wanda kololuwarsa take kusan 2,263 Å — ya fi ja fiye da na Milky Way. Wani kuma, a redshift 7.11, kololuwarsa tana 2,257 Å. A matsakaici, ƙumburin yana kamar yana raunana zuwa lokutan farko.

Galaxy a redshift 9.33

Giulia Rodighiero, ta Jami’ar Padua da INAF, da kusan abokan rubutu hamsin a Turai, Amurka (arewa da kudu) da Asiya sun bi bakan hasken NIRSpec na Webb daga shirye-shirye biyu masu haɗin gwiwa, ZENITH da EMBER. Sun duba tushe-tushe da suka wuce redshift 8, inda yankin 2,175 Å yake cikin abin da aka rufe, ba tare da zaɓar waɗanda suka riga suka nuna ƙumburi ba. Ɗaya ya fice. Suna kiransa Baƙar Lu’u-lu’u (the Black Pearl) — takardar ba ta faɗi dalili ba.

Layukan fitar haske na hydrogen da oxygen sun sanya shi a redshift 9.3335, ana ganinsa kamar yadda yake kusan shekaru miliyan 500 bayan Big Bang. Galaxy ne ƙarami kaɗan, tare da yawan taurari na kusan rana 10^8.35, yana samar da kusan taurari masu nauyin rana 2.4 a shekara, kuma ɗaya daga cikin galaxy mafi haske a ultraviolet da aka tabbatar ta bakan haske bayan redshift 9.

Hanyoyi biyu na ganin rami ɗaya

Bakan haskensa yana nuna wani faffaɗan kwari daidai inda ƙumburin ƙura zai kasance. Ƙungiyar ta auna shi ta hanyoyi biyu masu zaman kansu.

Na farko, kai tsaye: a daidaita ci gaban ultraviolet da lanƙwasa mai santsi sannan a auna ƙarin raguwar haske. An gano ramin a sigma 17.6, kuma ƙara siffa mai kama da ƙumburi yana inganta daidaitawar sosai (χ² na 474 ya faɗi zuwa 8.2). Kololuwar siffar tana a 2,132 ± 17 Å, tare da faɗin 413 ± 54 Å da raguwar haske mafi girma ta magnitude 0.21. Bincike-bincike sun kawar da wani layin fitar haske na carbon da ke kusa da kuma cakuɗen layuka da ba a raba su ba a matsayin sanadi.

Na biyu, tare da cikakken samfurin galaxy ɗin — taurari, iskar gas, ƙura da photometry — ta amfani da dokar ƙura mai sassauci wadda wurin ƙumburin da faɗinsa suke a buɗe. Duk tarihin samar da taurari biyu da aka gwada sun dawo da ƙumburi, a kusan 2,147 da 2,168 Å, sun yi daidai da ma’aunin kai tsaye ko da yake ba su kai shi daidaito ba.

Shin ramin baƙi (black hole) zai iya yin kwaikwayon sa? Cibiya mai aiki (active nucleus) za ta iya samar da gandun layukan iron da ke kwaikwayon rami. Layukan fitar haske suna nuna filin radiation mai tsanani kuma suna barin wuri ga wata gudummawa daga cibiya, amma ba ga wadda ta isa ƙarfin mamaye ultraviolet ba. Marubutan sun fi son ƙura, yayin da suke lura cewa ba za a iya kawar da cibiya, “wadda wataƙila ma babba ce”, gaba ɗaya ba.

Ya kauce zuwa ɓangaren da bai dace ba

Faɗin ya yi daidai da na Milky Way. Wurin bai yi ba: ya fi shuɗi da 43 Å fiye da matsakaicin Galaxy ɗinmu, a kusan sigma 2.5, kuma ya fi shuɗi da kusan 127 Å fiye da ƙumburi biyu da aka sani kusan redshift 7, waɗanda suka kauce zuwa ja. Ga marubutan, wannan bambancin yana jayayya da ƙumburi ɗaya na duniya baki ɗaya a farkon sararin samaniya: ƙwayoyin ƙurar da ke bayansa wataƙila sun bambanta daga galaxy zuwa galaxy.

Mene ne su? Lissafi na ƙananan ƙwayoyin graphite mafi ƙanƙanta sun kusanci siffar Baƙar Lu’u-lu’u, ba kamar na misalin redshift 6.71 na baya ba. Wasu ƙwayoyin zarra na PAH ɗaiɗai suma za su iya sake samar da shi — amma PAH ba su da yawa a cikin galaxy marasa ƙarafa a ƙananan redshift, kuma radiation mai tsanani da aka ƙiyasta a nan na iya lalata mafi ƙanƙantansu. Duka biyun suna da yiwuwa.

Ƙura cikin shekaru miliyan 200

Agogon da ya dace ba shekaru miliyan 500 tun Big Bang ba ne, amma lokacin da ya wuce tun da galaxy ɗin ya fara samar da taurari. Idan hakan ya fara kusan redshift 14, kusan shekaru miliyan 200 ne suka samu. Supernovae, girman ƙwayoyi tsakanin taurari kuma wataƙila taurarin AGB masu saurin canzawa za su iya ba da gudummawa; nawa kowanne ya yi har yanzu ba a sani ba.

Wannan galaxy ɗaya ne, kauce-kaucen ƙumburinsa yana da muhimmanci ne kawai a kusan sigma 2.5, kuma lanƙwasan rage haske ba sa nuna irin ƙwayoyi kai tsaye ɗaya-ɗaya. An aika takardar ga mujallar ApJ. Saƙonta shi ne cewa siffar ƙumburin, ba wanzuwarsa kaɗai ba, yanzu za ta iya bin diddigin yadda aka yi ƙurar farko.