Free Astronomy Magazine January-February 2025 ARABIC VERSION

temperature,bymeasuringcloserto the inner edge of the accretion disk thaneverbefore,” saidLynneHillen- brand of Caltech in Pasadena, Cali- fornia,andaco-authorofthepaper. “I think there was some hope that we would see something extra, like the interface between the star and its disk, but we were certainly not expectingit.Thefactwesawso muchextra—itwasmuchbrighter intheultravioletthanwepredicted — that was the big surprise.” Originally deemed to be a unique caseamongstars,FUOriexemplifies aclassofyoung,eruptivestarsthatund ergodramaticchangesinbright- ness.Theseobjectsareasubsetof classicalTTauristars,whichare newly forming stars that are build- ing up by accreting material from theirdiskandthesurroundingneb- ula.InclassicalTTauristars,thediskdoe snottouchthestardirectlybe- causeitisrestrictedbytheoutwardpre ssureofthestar’smagneticfield.The accretion disks around FU Ori objects, however, are susceptible to instabilities due to their enormous mass relative to the central star, in- teractionswithabinarycompan- ﻣﺠﻠﺔ FreeAstronomy ﺎﻟﻌﺮ ﺔ 45 ﰲ اﻟﺘﺤﻘﻖ ﻣﻦ ﺻﺤﺔ اﻟﺠﺰء اﻷ ﻛﺜﺮ ﺳـﺨﻮﻧﺔ ﻣﻦ ﻧﻤﻮذج ﻗﺮص اﻟﱰاﻛﻢ ﻟﺘﺤﺪﻳـﺪ أﻗﺼـ ﻰ ـ درﺟﺔ ﺣﺮارة ﻟﻪ ﻣﻦ ﺧﻼل اﻟﻘﻴﺎس ﺑـﺎﻟﻘﺮب ﻣﻦ اﻟﺤﺎﻓﺔ اﻟﺪاﺧﻠﻴﺔ ﻟﻘﺮص اﻟﱰاﻛﻢ أ ﻛﺜﺮ ﻣﻦ أي وﻗﺖ ﻣﴣ . أﻋﺘﻘﺪ أﻧﻪ ﻛﺎن ﻫﻨﺎك ﺑﻌـﺾ اﻷﻣﻞ ﰲ أن ﻧﺮى ﺷﻴﺌًﺎ إﺿﺎﻓﻴ ﺎً ﻣﺜﻞ ا ﻟﻮاﺟﻬـﺔ ﺑ اﻟﻨﺠﻢ وﻗﺮﺻﻪ ﻟﻜﻨﻨﺎ ﺑﺎﻟﺘﺄﻛﻴﺪ ﻟﻢ ﻧﺘﻮﻗـﻊ اﻟﺤ. ذﻟﻚ ﻘﻴﻘﺔ أﻧﻨﺎ رأﻳﻨﺎ اﻟﻜﺜـ ﻓﻘـﺪ ﻛـﺎن اﻟﻨﺠﻢ اﻟ ـﻨﺠﻢ أﻛﺜ ـﺮ ﺳ ـﻄﻮﻋ ﰲ ا ﺎً ﻷﺷ ـﻌﺔ ﻓ ـﻮق اﻟﺒﻨﻔﺴﺠﻴﺔ ﻣﻤﺎ ﺗﻮﻗﻌﻨﺎ ﻛﺎﻧﺖ ﻫﺬه ا ﻔﺎﺟﺄة اﻟﻜﱪى ." أﺳﺎﺳﺎ اﻋﺘُﱪ اﻟﻨﺠﻢ ﻓﻮ اورﻳﻮﻧﻴﺲ ﺣﺎﻟﺔ ﻓﺮﻳﺪة ﺑ اﻟﻨﺠﻮم، وﻫﻮ ﻳﻤﺜﻞ ﻓﺌﺔ ﻣﻦ اﻟﻨﺠﻮم اﻟﺸﺎﺑﺔ اﻟﺜﻮرﻳﺔ اﻟﺘﻲ ﺗﺨﻀﻊ ﻟﺘﻐ ات دراﻣﺎﺗﻴﻜﻴﺔ ﰲ اﻟﺴﻄﻮع . ﻫﺬه اﻷﺟﺴﺎم ﻫﻲ ﻣﺠﻤﻮﻋــﺔ ﻓﺮﻋﻴــﺔ ﻣــﻦ ﻧﺠــﻮم أورﻳــﺲ اﻟﻜﻼﺳﻴﻜﻴﺔ وﻫﻲ ﻧﺠـﻮم ﺣﺪﻳﺜـﺔ اﻟﺘﻜـﻮﻳﻦ ﺗﺘﻜﻮن ﻋﻦ ﻃﺮﻳﻖ ﺗﺮاﻛﻢ ا ﻮاد ﻣﻦ ﻗﺮﺻـﻬﺎ واﻟﺴـﺪﻳﻢ ا ﺤـﻴ . ﻂ ﺑﻬـﺎ ﰲ ﻧﺠـﻮم أورﻳـﺲ اﻟﻜﻼﺳﻴﻜﻴﺔ ﻻ ﻳﻠﻤﺲ اﻟﻘﺮص اﻟﻨﺠﻢ ﺑﺸﻜﻞ ﻣﺒـﺎﴍﻷﻧـﻪ ﻣﻘﻴـﺪ ﺑﺎﻟﻀـﻐﻂ اﻟ ﺨـﺎرﺟﻲ ﻟﻠﻤﺠﺎل ا ﻐﻨﺎﻃﻴﴘ ﻟﻠﻨﺠﻢ وﻣﻊ ذﻟـﻚ ﻓـﺈن أﻗﺮاص اﻟﱰاﻛﻢ ﺣﻮل أﺟﺴﺎ م ﻓﻮ اورﻳﻮﻧﻴﺲ ﻋﺮﺿـﺔ ﻟﻌـﺪم اﻻﺳـﺘﻘﺮار ﺑﺴـﺒﺐ ﻛﺘﻠﺘﻬـ ﺎ اﻟﻬﺎﺋﻠﺔ ﺑﺎﻟﻨﺴﺒﺔ ﻟﻠﻨﺠﻢ ا ﺮﻛﺰي واﻟﺘﻔﺎﻋﻼت ﻣﻊ رﻓﻴﻖ ﺛﻨﺎﺋﻲ أو ا ﻮاد اﻟﺴﺎﻗﻄﺔ . ﻟﻘﺪ ﺘﻤﺘ اﺳﺘﺨﺪم ﻋﻠﻤﺎء اﻟﻔﻠﻚ ﻓﻲوﻗﺖﺳﺎﺑﻖ ﻗﺪرات اﻷﺷﻌﺔ ﻓﻮق اﻟ ﻨﻔﺴﺠ ﺔ اﻟ ﻊ ﺑﻬﺎ ﺗﻠﺴ ﻮب ﺳـﻄﺢ ﻫﺎﺑﻞ اﻟﻔﻀﺎﺋﻲ ﻟﻤﻌﺮﻓـﺔ اﻟﻤﺰ ـﺪ ﻋـﻦ اﻟﺘﻔﺎﻋـﻞ ﺑـ اﻟـ ـﺎن ﻨ ﻢ ﻓـﻮ اور ـﻮﻧ ﺲوﻗـﺮص اﻟـ ا ﻢ اﻟـﺬ ﻔـــﺮغ اﻟﻐـــﺎزﻋﻠـــﻰ اﻟـــﻨ ﻢ اﻟﻨـــﺎﻣﻲﻣﻨـــﺬ ﻣـــﺎ ﻘـــﺮ ﻣـــﻦ 90 . ﺎً ﻋﺎﻣـــ ﻟﻘـــﺪ وﺟـــﺪوا أن اﻟﻘـــﺮص اﻟـــﺪاﺧﻠﻲ اﻟـــﺬ ﻼﻣــﺲ اﻟــﻨ ــﺎن ﻣﺘﻮﻗﻌــ ﻢ أﻛــ ﺳــﺨﻮﻧﺔ ﻣﻤـــﺎ - ﺎً 16000 ﻠﻔــﻦ - أي ﻣــﺎ ﻘـــﺮ ﻣــﻦ ﺛﻼﺛــ ﺔ أﺿــﻌﺎف درﺟـــﺔ ﺣﺮارة ﺳﻄﺢ اﻟﺸﻤﺲ . ﻫﺬﻩ درﺟﺔ اﻟ ـ ـ ﺤﺮارة اﻟ ﺤﺎرﻗﺔ ﻫﻲﺿﻌﻒﻣﺎ ﺎن ُﻌﺘﻘﺪﺳﺎ ﻘ . ﺎً ] NASA-JPL, Caltech [ - ﻳﻨﺎﻳﺮ ﻓﺒﺮﺍﻳﺮ 2 0 2 5