Free Astronomy Magazine July-August 2024 ARABIC VERSION

51 Cometary globules are a subclass of the dark nebulae known as Bok globules — isolated clouds of dense cosmic gas and dust surrounded by hot, ionized material. When these clouds exhibit stripping of material that results in an extended tail, they are referred to as cometary globules because of their vague resemblance to a comet, though they have noth- ing in common. The features that classify CG 4 as a cometary globule are hard to miss in this image cap- tured with the Department of En- ergy-fabricated Dark Energy Camera (DECam) mounted on the U.S. Na- tional Science Foundation Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), a Program of NSF NOIRLab. Its dusty head, which has a diameter of 1.5 light-years, and its long, faint tail, which is about eight light-years long, make CG 4 a comparatively small Bok globule, a general charac- teristic of cometary globules. First recognized in 1976 from pic- tures taken with the UK Schmidt Telescope in Australia, cometary globules went undetected by as- tronomers for a long time because they are so faint. Their tails, shrouded in dark stellar dust, block most light from passing through. But with its special Hydrogen-alpha filter, DE- Cam can pick up the faint red glow of ionized hydrogen present within CG 4’s head and around its outer rim. This light is produced when hy- drogen becomes excited after be- ing bombarded by radiation from nearby hot, massive stars. The intense radiation generated by these neighboring massive stars, however, is gradually destroying the head of the globule and sweeping away the tiny particles that scatter the starlight. Still, the dusty cloud of CG 4 con- tains enough gas to feed the active formation of several new, Sun-sized stars. While astronomers have ob- JULY-AUGUST 2024 اﻟﻜﺮات ا ﺬﻧﺒ ﺴ ﺔ ﻫﻲ ﻓﺌﺔ ﻓﺮﻋﻴﺔ ﻣﻦ اﻟﺴﺪم ا ﻈﻠ ﻤﺔ ا ﻌﺮوﻓﺔ ﺑﺎﺳﻢ ﻛـﺮات ﺑـﻮك وﻫـﻲ ﺳﺤﺐ ﻣﻌﺰوﻟﺔ ﻣﻦ اﻟﻐﺎز اﻟﻜـﻮﻧﻲ اﻟﻜﺜﻴـﻒ وا ﻟﻐﺒﺎر ﻣﺤﺎﻃـﺔ ﺑﻤـﻮاد ﺳـﺎﺧﻨﺔ وﻣﺘﺄﻳﻨـﺔ ﻋﻨﺪﻣﺎ ﺗﻈﻬﺮ ﻫﺬه اﻟﺴـﺤﺐ ﺗﻌﺮﻳـﺔ ﻟ ﻠﻤـﻮاد ﺗﻜـﻮن اﻟﻨﺘﻴﺠـﺔ ذﻳـﻞ ﻣﻤﺘـﺪ ﻳُﺸـﺎر إﻟﻴﻬـﺎ ﺑﺎﻟﻜﺮ ات ا ﺬﻧﺒ ﻴ ﺔ ﺑﺴﺒﺐ ﺗﺸﺎﺑﻬﻬﺎ اﻟﻐـﺎﻣﺾ ﺎتﺒ ﻣﻊ ا ﺬﻧ ﻋﲆ اﻟﺮﻏﻢ ﻣﻦ أﻧﻪ ﻻ ﻳﻮﺟﺪ ﳾء ﻣﺸـﱰك ﺑﻴﻨﻬﻤـﺎ . ﻣـﻦ اﻟﺼـﻌﺐ أن ﺗﻔـﻮت ا ﻴﺰات اﻟﺘﻲ ﺗﺼـﻨﻒ CG4 ﻋـﲆ أﻧﻬـﺎ ﻛـﺮة ﻴ ﻣﺬﻧﺒ ﺔ ﰲ ﻫﺬه اﻟﺼﻮرة ا ﻠﺘﻘﻄـﺔ ﺑﻮاﺳـﻄﺔ ﻛﺎﻣ ا اﻟﻄﺎﻗﺔ ا ﻈﻠﻤﺔ ) دي ﻛﺎم ( ا ﺼـﻨﻌﺔ ﻣﻦ ﻗﺒﻞ وزارة اﻟﻄﺎﻗﺔ اﻷ ﻣﺮﻳﻜﻴـﺔ وا ﺜﺒﺘـﺔ ﻋﲆ ﺗﻠﺴـﻜﻮب ﻓﻴﻜﺘـﻮر إم ﺑﻼﻧﻜـﻮ ﺑﻘﻄـﺮ أرﺑﻌﺔ أﻣﺘﺎ ر ﰲ ﻣﺮﺻﺪ ﺳـ و ﺗﻮﻟﻮﻟـﻮ وﻫـﻮ ﺑﺮﻧﺎﻣﺞ ﺨﺘـﱪ ﻧـﻮﻳﺮﻻب اﻟﺘـﺎﺑﻊ ﺆﺳﺴـﺔ اﻟﻌﻠﻮم اﻟﻮﻃﻨﻴﺔ اﻻﻣﺮﻳﻜﻴﺔ . إن رأﺳﻬ ﺎ ا ﻐـﱪ اﻟﺬي ﻳﺒﻠﻎ ﻗﻄﺮه 1.5 ﺳﻨﺔ ﺿـﻮﺋﻴﺔ ﺎ وذﻳﻠﻬـ اﻟﻄﻮﻳ ﻞ اﻟﺨﺎﻓﺖ اﻟـﺬي ﻳﺒﻠـﻎ ﻃﻮﻟـﻪ ﺣـﻮاﱄ ﺛﻤﺎﻧﻲ ﺳﻨﻮات ﺿﻮﺋﻴﺔ ﻳﺠﻌـﻼن ﻣـﻦ CG4 ﻛﺮة ﺑﻮك ﺻﻐ ة ﻧﺴﺒﻴﺎً وﻫﻲ ﺳـﻤﺔ ﻋﺎﻣـﺔ ا ﻟﻠﻜﺮ .ﺔﻴ ت ا ﺬﻧﺒ ﺗﻢ اﻟﺘﻌﺮف ﻋﲆ اﻟﻜﺮ ا ﻴ ت ا ﺬﻧﺒ ﺔ ﻷول ﻣﺮة ﰲ ﻋ ـﺎم 1976 ﻣ ـﻦ ﺧ ـﻼل ﺻـﻮ ر اﻟﺘﻘﻄ ـﺖ ﺑﺎﺳ ـﺘﺨﺪام ﺗﻠﺴــﻜﻮب ﺷ ـﻤﻴﺪت ا ﻤﻠﻜــﺔ ا ﺘﺤﺪة ﰲ أﺳﱰاﻟﻴﺎ وﻟﻢ ﻳﺘﻤﻜﻦ اﻟﻔﻠﻜﻴﻮن ﻣﻦ اﻛﺘﺸﺎﻓﻬﺎ ﻟﻔﱰة ﻃﻮﻳﻠﺔ ﻷﻧﻬﺎ ﺧﺎﻓﺘﺔ ﻟﻠﻐﺎﻳﺔ . ذﻳﻮ ﻟﻬﺎ ﻣﻐﻄﺎة ﺑﺎﻟﻐﺒﺎر اﻟﻨﺠﻤﻲ اﻟـﺪاﻛﻦ ﻣـﺎ ﻳ ﻤﻨﻊ ﻣﻌﻈﻢ اﻟﻀﻮء ﻣﻦ ا ﺮور ﻋﱪﻫﺎ ﻦ ﻟﻜو ﺑﻔﻀـﻞ ﻣﺮﺷـﺢ ﻫﻴـﺪروﺟ أﻟﻔـﺎ ﻳﻤﻜـﻦ ﻟ ) ﻜﺎﻣ ا دي ﻛﺎم ( اﻟﺘﻘﺎط اﻟﺘـﻮﻫﺞ اﻷﺣﻤـﺮ اﻟﺨﺎﻓﺖ ﻟﻠﻬﻴﺪروﺟ ا ﺘﺄﻳﻦ ا ﻮﺟﻮد داﺧـﻞ رأس CG4 وﺣﻮل ﺣﺎﻓﺘﻬ ﺎ اﻟﺨﺎرﺟﻴﺔ وﻳﻨﺘﺞ ﻫﺬا اﻟﻀﻮء ﻋﻨﺪﻣﺎ ﻳﺜـﺎر اﻟﻬﻴـﺪروﺟ ﺑﻌـﺪ ﺗﻌﺮﺿﻪ ﻟﻘﺼﻒ ﻣﻦ اﻟﻨﺠﻮم اﻟﺤﺎرة اﻟﻀﺨﻤﺔ اﻟﻘﺮﻳﺒﺔ وﻣﻊ ذﻟـﻚ ﻓـﺈن اﻹﺷـﻌﺎع ا ﻜﺜـﻒ اﻟﻨﺎﺗ ﺞ ﻋﻦ ﻫﺬه اﻟﻨﺠﻮم اﻟﻀﺨﻤﺔ ا ﺠـﺎورة ﻳﺪﻣﺮ رأس اﻟﻜﺮة ﺗﺪرﻳﺠﻴﺎً وﻳﺠﺮف اﻟﺠﺰﻳﺌﺎت اﻟﺼﻐ ة اﻟﺘﻲ ﺗﺒﻌﺜﺮ ﺿﻮء اﻟﻨﺠﻢ . ﻣـﻊ ذﻟـﻚ ﻓـﺈن اﻟﺴـﺤﺎﺑﺔ اﻟﻐﺒﺎرﻳ ـﺔ CG4 ﺗﺤﺘﻮي ﻋﲆ ﻣﺎ ﻳﻜﻔـﻲ ﻣـﻦ اﻟﻐـﺎز ﻟﺘﻐﺬﻳـﺔ اﻟﺘﻜﻮﻳﻦ اﻟﻨﺸﻂ ﻟﻌﺪة ﻧﺠﻮم ﺟﺪﻳﺪة ﺣﺠﻤﻬﺎ ﻣﺜﻞ ﺣﺠﻢ اﻟﺸﻤﺲ . ﻣﺠﻠﺔ FreeAstronomy ﺎﻟﻌﺮ ﺔ 51 - ﻳﻮﻟﻴﻮ ﺃﻏﺴﻄﺲ 2 0 2 4