TAURARIN MILKY WAY SUN YI LEBUR A MATAKI BIYU

Ana yawan bayyana faifan Damin Taurarinmu a matsayin faifai biyu a ɗaya: siririn faifai, mai “sanyi” ta fuskar motsi kuma mafi ƙuruciya, da faifai mai kauri, mai “zafi” kuma mafi tsufa. Taurari suna riƙe tunawa da inda da yadda aka haife su, wanda ke sa su zama burbushin haɗuwar Damin Taurarin — batun ilimin tarihin Damin Taurari (Galactic archaeology).

An san cewa tsofaffin taurari sun fi bazuwa sama da shimfiɗar. Amma me ya sa? Bayanai biyu suna fafatawa:

• Ɗumamawa a hankali: ana haifar taurari a cikin siririn layin gas mai sanyi, kuma tsawon biliyoyin shekaru manyan gizagizan ƙwayoyin sinadarai, hannayen karkace da sandar tsakiya suna buga zagayensu, suna sa su yi ta yawo sama-sama.
• Haihuwa ta juye (upside-down formation): faifan gas na Damin Taurarin a ƙuruciyarsa da kansa mai kauri ne kuma cikin hargitsi, saboda yawan tara abubuwa, haɗewa da ƙarfafan martani; kawai an haifi tsofaffin taurari da kauri, sannan gas ɗin ya huce ya kwanta.

Rarrabe su yana buƙatar ingantattun shekaru ga cikakkun samfuran taurari — musamman ga lokutan farko-farko, lokacin da abubuwa suka faru da sauri.

Ƙididdige shekarun taurari ta taron jama’a

David Mirabal, Carme Gallart da abokan aikinsu a Instituto de Astrofísica de Canarias, tare da abokan hulɗa a Granada, Teramo da Victoria (Kanada), suna aiki a kan aikin ChronoGal. Maimakon ƙididdige shekarun taurari ɗaya-ɗaya, suna daidaita dukkan zanen launi da haske (colour–magnitude diagram) na taurari kusa da Rana, wanda tauraron ɗan adam na Turai Gaia (fitowar bayanai ta 3) ya auna, da haɗe-haɗen rukunonin taurari na kwamfuta. Sakamakon taswira ce ta yawan taurarin da aka haifa a kowace shekara da kowane matakin ƙarfe (metallicity), da shekaru daidai fiye da kashi 5% — kusan rabin shekaru biliyan ga taurari mafi tsufa.

Sun yi nazarin taurari da ke cikin kiloparsec 1 na shimfiɗar Damin Taurarin, suka raba su zuwa samfuri mai “sanyi” ta fuskar motsi da wani mai “zafi”, suka yanka su zuwa layuka takwas a tsayi, kuma suka gyara don taurarin da zaɓin ya tsallake. Sannan wani algorithm na haɗa rukunoni ya tara taurari zuwa rukunoni masu kusan shekaru ɗaya da matakin ƙarfe ɗaya. Ga kowanne, ƙungiyar ta auna tsayin ma’auni (scale height) — yadda rukunin ke yawan kaiwa sama da shimfiɗar.

Sauyin gudu ba-zata

Kaurin rukunonin taurari idan aka kwatanta da shekarunsu: faɗuwa mai tsauri ga mafi tsufa, raguwa a hankali bayan sauyin a shekaru biliyan 10.85. Launuka suna nuna matakin ƙarfe. — Hoto na 2, Mirabal da abokan aiki (2026), arXiv:2610.03164.

Yayin da rukuni ya fi ƙuruciya, haka yake ƙara manne wa shimfiɗar. Amma dangantakar ba layi ɗaya ba ce. Daidaitawa da layuka madaidaita guda biyu ta gano sauyi shekaru biliyan 10.85 da suka wuce (ƙari ko ragi kusan shekaru biliyan 0.13):

• Kafin: kauri ya ragu da kusan kiloparsec 1.88 a kowace shekara biliyan. Rukunoni mafi tsufa sun kai kiloparsec 1.26 — mafi tsufa biyu ma fiye da haka, kusan 1.75 da 2.10 — kuma cikin kusan shekaru biliyan 2 kacal kaurin ya faɗi zuwa kusan kiloparsec 0.5.
• Bayan: siriranta ya yi jinkiri zuwa kiloparsec 0.038 a kowace shekara biliyan kawai. Rukunoni mafi ƙuruciya suna kusan kiloparsec 0.1, kuma taurarin da aka haifa yau za su kai kusan 0.12.

Rashin tabbas a kan saurin farko yana da yawa, amma matakan biyu sun bambanta a fili. Ko rukunonin da suka ɗan girmi sauyin, kimanin shekaru biliyan 11, sun fi faifai mai kauri gaba ɗaya kauri (kusan kiloparsec 0.9). Sauyin ya tsira daga gwaji da tsarin shekaru da matakan ƙarfe mai sauƙi kuma daidai-wa-daida maimakon rukunonin da aka ayyana kai tsaye.

An haife su da kauri

A wurin marubutan, ɗumamawa a hankali kaɗai ba za ta iya bayyana irin wannan saurin kwanciya ta farko ba: yawan haɗewa da ake yi zai riƙe faifan ƙuruciya da zafi har zuwa babbar haɗewa ta ƙarshe, wadda marubutan suka kira GSE, kimanin shekaru biliyan 10 da suka wuce. Maimakon haka, bayanan suna goyon bayan haihuwa ta juye a matakin farko. Gas ɗin da ke cikin hargitsi ya huce ya nutse zuwa tsakiyar shimfiɗar tsawon ’yan biliyoyin shekaru, ya samar da faifai mai kauri; faifai mai kauri da aka ayyana ta sinadarai ya kafu kimanin shekaru biliyan 11 da suka wuce.

Sannan, kusan bayan wannan haɗewa, Damin Taurarin ya shiga zamani mafi natsuwa, inda gas ɗin ya kwanta a hankali ya gina siririn faifan da muke gani a yau. Ga wannan lokaci na baya, bayanan kaɗai ba za su iya rarrabe ɗumamawa a hankali da kwanciya a hankali ba. Hoton ya yi daidai da kwaikwayon sararin samaniya na damin taurari masu kama da Milky Way, da wani ƙididdige lokacin da aka yi kwanan nan na “fara juyawa” (spin-up) na Damin Taurarin zuwa faifai mai juyawa.

A kalaman marubutan, babban tsayin taurari mafi tsufa “ba sakamakon ɗumamawar motsi ta dogon lokaci kaɗai ba ne, sai dai burbushin tsari ne na matakin haɗuwar Damin Taurarin na farko.”