SUPERNOVA ƊAYA, HOTUNA BIYAR, SAURIN FAƊAƊAR SARARIN SAMANIYA

Da wane sauri Sararin Samaniya ke faɗaɗa a yau? Lambar da ke amsa wannan ita ce Hubble constant, H0. Biyu daga cikin manyan hanyoyin auna ta — “tsani” na nisa zuwa taurari da galaxies na kusa, da kuma hasken saura mara ƙarfi na Sararin Samaniya matashi, wato cosmic microwave background — a yanzu suna ba da ƙimomi da suka bambanta sosai. Wannan giɓi, Hubble tension, ɗaya ne daga cikin manyan tambayoyin da ba a amsa ba a ilimin sararin samaniya (cosmology).

Akwai hanya ta uku, kuma ba ta dogara ga ɗayan biyun ba.

Ruwan tabarau na sararin samaniya mai agogo a ciki

Idan wani abu mai nauyi sosai — galaxy ko dukan gungun galaxies — yana gaban wani tushe mai nisa, nauyinsa (gravity) yana lanƙwasa haske kuma zai iya raba tushen zuwa hotuna da dama. Wannan shi ne strong gravitational lensing. Hasken yana bin hanyoyi masu tsayi daban-daban. Idan haskakawar tushen ta canza, hotunan suna canzawa ɗaya bayan ɗaya.

Waɗannan jinkirin lokaci sun dogara ne kan nauyin ruwan tabarau da kan nisan sararin samaniya — saboda haka kuma kan H0. Refsdal ne ya gabatar da ra’ayin a 1964, da supernovae da ake gani a hotuna da dama.

Supernova ta farko irin wannan, wadda yanzu ake kira SN Refsdal, an gano ta a 2014 a bayan gungun galaxies MACS J1149.5+2223. Da farko ta bayyana a matsayin hotuna huɗu a kewayen wani galaxy na gungun; ana sa ran hoto na biyar, wanda ƙira suka yi hasashe, kusan shekara ɗaya daga baya. Jinkirin da aka auna sun haɗa da ɗaya na kwanaki 376 tsakanin hotuna biyu.

Pixels 77,000 a maimakon ƙalilan ɗigo

Abu mai wuya shi ne sanin yadda nauyin gungun ya rarrabu daidai. Har zuwa yanzu, ƙira sun yi amfani da wuraren hotuna masu yawa na galaxies na baya kawai. Stefan Schuldt, na Jami’ar Turku da Jami’ar Milan, da abokan aikinsa a Italiya, Jamus, Spain da Finland, sun yi gaba fiye da haka.

Ƙirarsu ta riga ta ƙunshi galaxies 308 na gungun, halos na dark matter, da hotuna masu yawa fiye da 100 na tushe 17 na baya. A kan haka, sun ƙara dukan siffa da hasken galaxy da ke masaukin supernova: pixels 77,000 daga Hubble Space Telescope. Wannan shi ne karo na farko da aka auna parameter na sararin samaniya da irin wannan ƙira ga gungun galaxies.

Don tsaro, sun gwada hanyoyi huɗu na ba bayanan nauyi kuma suka ƙidaya bambance-bambancen da ke tsakaninsu a matsayin ƙarin rashin tabbas.

Ma’auni na kashi 3%

• H0 = 65.0 (+2.0 / −1.8) kilomita a kowace daƙiƙa a kowane megaparsec, tare da abin da Sararin Samaniya ya ƙunsa na kayan halitta (matter), Ωm = 0.30, da aka auna a lokaci guda.
• Rashin tabbas shi ne kashi 3.0%: ƙima mafi daidaito da aka taɓa samu daga ruwan tabarau mai ƙarfi ɗaya, gaba da sakamakon kashi 3.9% daga wani quasar da aka lanƙwasa haskensa.
• Ƙara pixels ya rage rashin tabbas da ninki 2.0 idan aka kwatanta da ƙira iri ɗaya da ke amfani da wuraren hotuna kawai.
• Dukan sigogin ƙirar sun yarda da juna da kuma nazarin baya na SN Refsdal.

Ƙimar ta yarda da wadda aka samu daga cosmic microwave background da aikin Planck ya auna, da kuma da wata supernova da aka lanƙwasa haskenta, SN Encore. Tana nesa da ƙimar tsanin nisa ta ƙungiyar SH0ES.

Rashin tabbas daga ƙirar nauyi yanzu ya yi daidai da rashin tabbas na jinkiri mafi tsawo. Ma’ana, agogon, ba taswira ba, ne ya zama abin da ke takurawa.

Abin da har yanzu zai iya canza lambar

Marubutan sun lissafa abin da kashi 3% ɗinsu bai haɗa ba. Sun riƙe girke-girken nauyin gungun a tsaye don kwatancen da tsofaffin ƙira ya zama adalci, don haka ba a ƙidaya bayanan wannan girke-girke a matsayin rashin tabbas ba. Wani sananne wurin makanta na lensing, wato “mass-sheet degeneracy”, an horar da shi ne wani ɓangare kawai. Kuma idan layukan gani ta cikin gungun galaxies sun fi matsakaici fanko, ruwan tabarau na gungu za su rage ƙiyasin H0.

Gwaji na gaba yana kusa: wata supernova da aka lanƙwasa haskenta, SN Requiem, ya kamata ta sake bayyana a 2026 ko 2027, kusan shekaru goma bayan an fara ganinta. Ya kamata a auna jinkirinta da daidaito sosai, kuma tare da ƙira kamar wannan za ta iya ba da H0 cikin ɗan kashi kaɗan. Ana sa ran Rubin Observatory za ta gano ƙarin irin waɗannan supernovae da yawa.