TAURARON DA AKA KWAƁE, ABOKIN TAFIYA A ƁOYE, DA KEWAYA TA AWA 4.2

Wani ƙaramin tauraro mai zafi sosai a cikin Ƙaramin Gajimaren Magellan (Small Magellanic Cloud), a wajen damin taurarinmu na Milky Way, yana kammala zagaye ɗaya duk bayan awa 4 da minti 10 a kewayen wani abokin tafiya da ba ya fitar da wani haske. Sunansa DGL-3, kuma abokin tafiyarsa da ke ɓoye mai yiwuwa ne tauraron neutron, cibiya mai matuƙar matsewa da ta rushe, wadda ke ragewa idan babban tauraro ya fashe.

Tauraro da aka kwaɓe ɓawonsa na waje

DGL-3 tauraro ne da aka kwaɓe (stripped star): ya rasa ɓawonsa na waje mai yawan hydrogen sakamakon mu’amala da wani abokin tafiya. Abin da ya rage matsatse ne, mai zafi, mai ƙarancin hydrogen, kuma yana ƙona helium a cibiyarsa.

• Nauyi: kusan ninki 3.4 na na Rana, an ƙiyasta daga haskensa, da iyakar kuskure mara daidaito sosai (nauyin Rana 2.96 zuwa 7.72).
• Radius: kusan ninki 0.77 na na Rana; zafin saman jikinsa: kusan kelvin 71,000; hydrogen: 10% kawai na samansa.

Taurari masu wannan nauyi na “tsaka-tsaki” (intermediate) suna da isasshen nauyi da cibiyarsu za ta rushe ta zama tauraron neutron, amma ba su da isasshen nauyin da za su samar da baƙin rami (black hole). A samfuran yanzu, ma’auratan taurarin neutron da ke kusa da juna sosai har za su haɗe, suna murɗawa zuwa juna yayin da suke fitar da raƙuman nauyi (gravitational waves), suna fara wucewa ta daidai wannan mataki: tauraron neutron da ke kewaya tauraron da aka kwaɓe. Ba a taɓa ganin wannan mataki kai tsaye ba, kuma ƙiyasin yawan irin waɗannan haɗuwa ya bambanta da matakai da dama na girma (orders of magnitude).

Auna nauyin abokin tafiya da ba ya haskakawa

Ƙungiyar ta tattara bakan haske 38 (spectra) da na’urar hangen nesa ta Magellan mai faɗin mita 6.5 a ƙasar Chile tsakanin 2019 da 2022. Layukan bakan tauraron — layuka masu duhu a launuka takamaimai cikin haskensa — suna matsawa zuwa shuɗi idan yana zuwa wajenmu, zuwa ja kuma idan yana nesantawa (tasirin Doppler, Doppler effect); suna nuna shi yana kai-da-kawowa zuwa gare mu da nesa da mu da gudun da ya kai 151.4 km/s, a kan kewaya mai zagaye da yake kammalawa duk bayan awa 4.1693.

Lokacin zagaye da gudu suna ba da aikin nauyi (mass function), wanda ke haɗa nauyin abokin tafiyar da nauyin tauraron kansa da kuma karkatar kewayar kamar yadda ake ganinta daga Duniya (karkatarta, inclination). Kewaya da ake gani daidai ta gefe tana ba da abokin tafiya mafi sauƙin nauyi da kewayar ta yarda da shi; idan aka yi la’akari da rashin tabbas a nauyin tauraron, ƙimar da aka saba samu ta wannan mafi ƙanƙanci ita ce nauyin Rana 1.38 ± 0.25, ƙasa kaɗan da 1.4 da farin dodo zai iya kaiwa (duba ƙasa). Saboda haka kewayar kaɗai ba za ta iya kawar da yiwuwar farin dodo ba.

• Ba tauraro na al’ada ba: tauraro mai nauyi haka zai yi girma da yawa ya shiga cikin kewaya mai matsewa haka.
• Ba tauraro na biyu da aka kwaɓe ba: an saka abokan tafiya na bogi da aka kwaɓe cikin ainihin bakan haske, kuma an gano su a kowane lokaci, amma ainihin bayanan ba su nuna wata alama ba.

Abin da ya rage shi ne abu matsatse (compact object): farin dodo (cibiyar da ta rage mai matsewa ta tauraro mafi sauƙin nauyi), tauraron neutron ko baƙin rami.

99.4% daga kai-da-kawowar 2.5%

A ranar 18 ga Disamba 2022, wata kyamara mai sauri a kan na’urar hangen nesa mai faɗin mita 3.5 a La Silla ta ɗauki hoton DGL-3 duk bayan daƙiƙa 20 na tsawon kusan awa 3.4. Haskensa yana hawa da sauka da kusan 2.5%, sau biyu a kowane zagaye: ƙarfin janyewar abokin tafiyar yana ɗan miƙa tauraron ya zama siffar ƙwai, wanda muke ganin dogon gefensa sau biyu a kowane zagaye, gwargwadon da ya dogara da nauyin abokin tafiyar da kuma karkatar kewayar.

Ƙungiyar ta gudanar da samfura 500,000 na wannan layin haske (light curve) kuma ta auna kowanne gwargwadon yadda ya dace da bayanan. Game da nauyin abokin tafiyar:

• ƙimar da ta fi yiwuwa ita ce nauyin Rana 1.58;
• 0.6% kawai na yiwuwar ne ke ƙasa da nauyin Rana 1.4, iyakar Chandrasekhar (Chandrasekhar limit) da ke kawar da farin dodo: don haka akwai yiwuwar 99.4% cewa abokin tafiyar ya yi nauyi da yawa ya zama farin dodo;
• 3.4% kawai ne ke cikin kewayon baƙaƙen ramukan da aka tabbatar; sauran dogon wutsiyar manyan nauyi ta faɗa cikin giɓin da ke tsakanin taurarin neutron da baƙaƙen ramuka.

Saboda haka tauraron neutron shi ne abokin tafiya mafi yiwuwa: yiwuwa ce, ba hujja ba. Na’urorin hangen nesa na X-ray ba su gano komai ba; tauraron neutron da ke haɗiye iskar gas daga abokin tafiyarsa zai haskaka a hasken X-ray, amma marubutan sun ga cewa wannan shiru ya dace da tauraron neutron da wata raunanniyar iskar tauraro (stellar wind) ke ciyarwa.

Makoma da samfurin kwamfuta ya rubuta

Daga nan ƙungiyar ta bunƙasa tsarin da manhajar juyin halittar taurari MESA: tauraron da aka kwaɓe mai nauyin Rana 3.6, tauraron neutron mai nauyin 1.4, da kewaya ta awa 4.2. Abin da ke biye hasashe ne, ba abin da aka lura ba.

1. Tauraron yana ci gaba da ƙona helium a cibiyarsa na ƙarin shekaru miliyan 1.4, sannan ya kumbura. A cikin kewaya mai matsewa haka, ƙaruwa da rabin radius na Rana kawai yana sa ya cika ya zubar da iskar gas kan abokin tafiyarsa.
2. A cikin shekaru 26,000, nauyin Rana 1.2 suna tserewa zuwa sararin samaniya. Tauraron neutron yana haɗiye nauyin Rana 0.00072 kawai, wanda ya isa ya ƙara saurin juyawarsa zuwa juyi ɗaya duk bayan milisakan 79. Kewayar tana raguwa zuwa awa 1.9.
3. Bayan an kwaɓe masa dukkan hydrogen ɗinsa, tauraron yana fashewa a matsayin supernova kuma ya bar tauraron neutron na biyu. Da gudun kewaya na kusan 800 km/s, sai dai wani bugu (kick) mai girma ba kamar yadda aka saba ba — koma-baya da fashewar za ta iya ba sabon tauraron neutron — ne zai iya raba ma’auratan.
4. Fashewar tana hura kusan nauyin Rana ɗaya na iskar gas. Taurarin neutron biyu suna ragewa, a kan kewaya mai faɗi kuma mai tsawo ta awa 4.4, kuma suna haɗewa bayan shekaru miliyan 220.

Inda hasashen zai iya kasawa

Mafi raunin wuri, a cewar marubutan, shi ne yawan ƙarfin juyawa (angular momentum), wato “adadin juyawar” kewayar, da iskar gas mai tserewa ke tafiya da shi. A cikin ɗaya daga cikin nau’o’in samfuri bakwai, iskar gas da aka rasa tana samar da faifai a kewayen taurarin biyu, kuma ma’auratan suna haɗewa kafin supernova ta biyu. A cikin sauran shidan, taurarin neutron biyu suna samuwa kuma daga baya su haɗe, tsakanin shekaru miliyan 175 da biliyan 7.9 bayan haka.

DGL-3 yana da nisan kusan parsec 60,600 — kimanin shekarun haske 200,000 (parsec ɗaya kusan shekarun haske 3.26 ne). Da a ce yana kusa ninki 60 zuwa 600, cikin parsec 100 zuwa 1,000, cibiyoyin lura da raƙuman nauyi masu ƙarancin mita (low-frequency) kamar LISA za su gano shi, in ji marubutan.