ƘANANAN TAURARI SUN ƘARYATA TSALLEN NAUYI

Sararin samaniya yana faɗaɗa, kuma saurin faɗaɗarsa na yanzu ana auna shi da wata lamba da ake kira madaidaicin Hubble (Hubble constant). Matsalar ita ce rukunonin ma’aunai biyu suna ba da amsoshi daban-daban. Ma’aunan da suka dogara kan taurari na kusa da supernova — “tsanin nisa” (distance ladder) — ba su jitu da ƙimar da aka samu daga hasken microwave na bayan sararin samaniya (cosmic microwave background), haske mafi tsufa a sararin samaniya, a matakin kusan sigma 5 ya danganta da bayanan. Hasken microwave na bayan sararin samaniya ne ke ba da ƙimar da ta fi ƙasa. Wannan shi ne rikicin Hubble (Hubble tension), ɗaya daga cikin matsalolin da suka fi gaggawa a ilimin sararin samaniya.

Wasu bayanai suna ɗora laifi kan kurakurai da ke ɓoye. Wasu kuma suna kira da a nemi sabuwar kimiyyar lissafi. Ɗaya daga cikin shawarwari mafi ƙarfin hali shi ne samfurin “G-step”: madaidaicin nauyi na Newton, G, wanda ke ƙayyade ƙarfin nauyi, ya canza farat ɗaya a lokacin baya-bayan nan na tarihin sararin samaniya.

Canji kwatsam, shekaru miliyan 73 zuwa 130 da suka wuce

Ra’ayin shi ne cewa supernova, waɗanda ake amfani da su a matsayin sandunan auna sararin samaniya, suna haskakawa da haske da ya dogara da G. Idan G ya bambanta kafin wani lokaci, supernova masu nisa (da ake ganinsu yadda suke kafin canjin) da na kusa (bayan canjin) ba za su zama sanda ɗaya ba, kuma za a yi kuskure wajen tantance saurin faɗaɗa. An gwada nau’i biyu a nan:

• samfurin asali: nauyi ya fi ƙarfi da kashi 11 kafin wani tsalle shekaru miliyan 130 da suka wuce;
• samfurin da aka faɗaɗa: ya fi ƙarfi da kashi 4 kafin wani tsalle shekaru miliyan 73 da suka wuce.

Taurari masu dogon tunawa

Jeremy Sakstein, na Jami’ar Hawai’i, da Harry Desmond, na Jami’ar Portsmouth, sun samo wani shaida da ba a zata ba: jajayen ƙananan taurari (red dwarfs), taurari mafi ƙanƙanta, waɗanda nauyinsu bai kai kusan kashi ɗaya bisa uku na nauyin Rana ba. Ana gauraya waɗannan taurari daga cibiyarsu zuwa samansu kuma suna mayar da martani ga kowane tashin hankali da matuƙar jinkiri. Lokacin da suke ɗauka kafin su natsu bayan canji a girmansu ya kai kusan shekaru miliyan 100 — kusan daidai da lokacin da ya wuce tun bayan tsallen da ake zato.

Sakamakon, wanda aka fitar da alƙalami da takarda sannan da wata manhajar ci gaban taurari (stellar-evolution code): jajayen ƙanana da ya rayu ƙarƙashin nauyi mai ƙarfi, sannan ya ga G ya sauko zuwa ƙimarsa ta yau, yana kumbura da sauri, sannan ya sake raguwa a hankali kawai. A yau, zai kasance har yanzu ya ɗan fi girma idan aka kwatanta da nauyinsa.

Taurari takwas a kan sikeli

Don tabbatarwa, masanan biyu sun yi amfani da jajayen ƙanana takwas a cikin taurari biyu-biyu masu kusufi (eclipsing binaries) — taurari biyu da ke wucewa a gaban juna idan aka duba daga Duniya, abin da ke ba da wasu daga cikin nauyi da radius mafi daidai da aka sani na kowane tauraro. Sun zaɓi taurari masu nauyin Rana 0.1 zuwa 0.31, cikin biyu-biyu da ke nesa da juna sosai don rage tasirin jan hankali na igiyoyin ruwa (tidal effects).

Akwai wata matsala: tabon taurari (starspots) su ma suna kumbura tauraro. Marubutan sun bar yawan tabon kowane tauraro ya canza yadda ya ga dama, daga babu zuwa cikakke, ta yadda tabon za su iya ɗaukar kowane kumburi idan hakan zai yiwu.

Babu alamar tsalle

Ga lokutan biyu, mafi dacewa shi ne nauyin da bai taɓa canzawa ba. An fitar da tsalle biyun da aka gabatar:

• kashi 4, shekaru miliyan 73 da suka wuce: an fitar da shi a kusan sigma 3.1;
• kashi 11, shekaru miliyan 130 da suka wuce: an fitar da shi a kusan sigma 4.0.

Tabon taurari ba za su iya ceto samfurin ba: ga waɗannan tsalle, huɗu daga cikin taurari takwas tuni suna buƙatar tabo sifili, kuma tauraro ba zai iya samun ƙasa da babu ba.

Shaida mai nauyi

Marubutan sun gwada yadda sakamakon ke da rauni. Idan samfuran taurari sun riƙa ƙara radius da kashi 1 a kowane lokaci, fitarwar za ta yi rauni amma za ta ci gaba da kasancewa. Sun kuma nuna cewa tauraro ɗaya, J2343+29, shi ke ɗauke da yawancin nauyin: idan babu shi, fitarwar ta sauka zuwa sigma 2.45 da 1.90 — har yanzu babu fifiko ga kowane canji a nauyi.

Binciken bai warware rikicin Hubble ba. Yana takaita fagen: waɗannan nau’o’i biyu na tsallen nauyi na baya-bayan nan yanzu suna cin karo da taurarin Damin Taurarinmu (Galaxy).