Free Astronomy Magazine July-August 2024 ARABIC VERSION

T shows a his excerpt close-up of CG 4 seemingly about to devour the edge-on spiral galaxy ESO 257- 19 (PGC 21338). But in reality, this galaxy is more than a hundred million light-years be- yond CG 4 and only appears to be close because of a chance alignment. Near the head of the cometary glob- ule are two young stellar ob- jects (YSOs). YSOs are stars in their early stage of evolution, before they be- come main-se- quence stars, that often ex- hibit characteris- tics such as jets, bipolar out- flows, proto- planetary discs, and other indicators of a new star being born. [CTIO/NOIRLab/DOE/NSF/AURA. Image Processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), D. de Martin & M. Zamani (NSF’s NOIRLab)] served these structures throughout the Milky Way, the overwhelming majority of them, including CG 4, are found within a huge patch of glowing gas called the Gum Nebula. Believed to be the expanding re- mains of a supernova that took place about a million years ago, the Gum Nebula is currently known to contain at least 31 cometary glob- ules in addition to CG 4. The mechanism by which these comet-like objects get their distinct shape is not entirely known, but as- tronomers have developed two main ideas about their origins. The first idea is that they could have originally been spherical nebulae — like the well-known Ring Nebula — which were then disrupted by a nearby supernova explosion, possi- bly the original explosion that cre- ated the Gum Nebula. The second idea is that cometary globules are shaped by a combina- tion of stellar winds and radiation pressure from nearby hot, massive stars. In fact, all of the cometary globules found within the Gum Neb- ula appear to have tails pointing away from the center of the nebula, which is where the Vela Supernova Remnant and Vela Pulsar are lo- cated. The Vela Pulsar is a rapidly spinning neutron star that was formed when a massive star col- lapsed, and it’s possible that its stellar winds and radiation pressure are shaping the nearby globules. Also in this image it looks as if CG 4 is about to devour the edge-on spi- ral galaxy ESO 257-19 (PGC 21338), which appears to be placed so de- fenselessly in front of it. But in real- ity, this galaxy is more than a hundred million light-years beyond CG 4 and only appears to be close because of a chance alignment.      ﻣﺠﻠﺔ FreeAstronomy ﺎﻟﻌﺮ ﺔ 52 - ﻳﻮﻟﻴﻮ ﺃﻏﺴﻄﺲ 2 0 2 4 ﻈﻬــــــــــــــــــــــﺮ ﻫـــــــــــــــــــــــﺬا اﻟﻤﻘﺘ ﻄـــــــــــــــــﻒ ﻟﻘﻄـــــــــــــــــﺔ ﻣﻘﺮ ـــــﺔ ﻟــــــ CG4 واﻟـــــ ــــــﺪو ﻋﻠـــــــﻰ ﻋﻠــــــﻰ ﻣــــــﺎ ﻳ وﺷــﻚ اﻟﺘﻬــﺎم اﻟﻤﺠـــﺮة ـ اﻟـ ﺤﻠﺰوﻧ ﺔ ESO 257- 19 (PGC 21338 .( ﻟﻜــﻦ ﻓــﻲ اﻟﻮاﻗــﻊ ﺗﻘـــﻊ ﻫـــــــــﺬﻩ اﻟﻤﺠـــــــــﺮة ﻋﻠـــــــــﻰ ﻣﺴـﺎﻓﺔ أﻛـ ﻣـﻦ ﻣﺎﺋـﺔ ﻣﻠﻴـــــــﻮن ﺳـــــــﻨﺔ ﺿـــــــﻮﺋ ﺔ ﻣـﻦ CG 4 ـﺪو أﻧﻬــﺎ وﻳ ــــــــﺔ ﻓﻘــــــــﻂ ﺴــــــــ ﺐ ﻗﺮ اﻧﺘﻈﺎﻣﻬـــﺎ ﻋﻠـــﻰ ﻧﻔـــﺲ ـــــﺔ ﺧـــــﻂ اﻟﺮؤ ـــــﺎﻟﻘﺮ و ﻣـــﻦ رأسﻛـــﺮة اﻟﻤـــﺬﻧﺐ ﻳﻮﺟـﺪ ــﺎن ﺟﺴـﻤﺎن ﻧ ﻤ ) ﺷﺎ ﺎن YSOs .( إن اﻟﻨﺠــــﻮم YSO ﻫــــﻲ ﻧﺠــــــ ﻮم ﻓــــــﻲﻣﺮﺣﻠﺘﻬــــــﺎ اﻟﻤ ﻜــــــﺮة ﻣــــــﻦ اﻟﺘﻄـــــــﻮر ﻗﺒـــــــﻞ أن ﺗﺼـــــــﺒﺢ ﻧﺠـــــــﻮم ﺗﺴﻠﺴــــــــــــــــــــﻞ ر ﺴــــــــــــــــــــﻲ وﻫــﻲﻏ ـــﺎ ﻣــﺎ ﺗﻈﻬـــﺮ ﺎﻟ ﺧﺼﺎﺋﺺ ﻣﺜﻞ اﻟﻨﻔﺎﺛﺎت واﻟﺘـــــﺪﻓﻘﺎت اﻟـــــ ـ ﺨﺎرﺟ ﺔ ــــــــــــــــــــــــــﺔ اﻟﻘﻄـــــــــــــــــــــــــــﺐ ﺛﻨﺎﺋ ـــــــــــﺔ واﻟﺘـــــــــــﺪﻓﻘﺎت اﻷوﻟ و أﻗــــــــــــــﺮاص اﻟ ﻮاﻛــــــــــــــﺐ وﻏ ﻫــــــــــــــــــــــــــــــــﺎ ﻣـــــــــــــــــــــــــــــــــﻦ اﻟﻤﺆﺷــــــــــــــــــﺮات ﻋﻠـــــــــــــــــــﻰ وﻻدة ﻧ ﻢ ﺟﺪ ﺪ . [CTIO/NOIRLab/DOE/NSF/AURA. Image Processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), D. deMartin &M. Zamani (NSF’s NOIRLab)] ﺑﻴﻨﻤﺎ رﺻﺪ ﻋﻠﻤﺎء اﻟﻔﻠـﻚ ﻫـﺬه اﻟﻬﻴﺎﻛـﻞ ﰲ ﺟﻤﻴ ـﻊ أﻧﺤـﺎء ﻣﺠـﺮة درب اﻟﺘﺒﺎﻧـﺔ ﻓ ـﺈن اﻟﻐﺎﻟﺒﻴﺔ اﻟﻌﻈﻤﻰ ﻣﻨﻬﺎ ﺑﻤﺎ ﰲ ذﻟﻚ CG4 ﺗـﻢ اﻟﻌﺜﻮر ﻋﻠﻴﻬﺎ داﺧﻞ رﻗﻌﺔ ﺿﺨﻤﺔ ﻣﻦ اﻟﻐﺎز ا ﺘﻮﻫﺞ ﺗﺴﻤﻰ ﺳﺪﻳﻢ اﻟﺼﻤﻎ . ﻳُﻌﺘﻘــﺪ أن ﺳــﺪﻳﻢ اﻟﺼــﻤﻎ ﻫــﻮ اﻟﺒﻘﺎﻳــﺎ ا ﺘﻮﺳﻌﺔ ﺴﺘﻌ ﺮ أﻋﻈﻢ ﺣـﺪث ﻣﻨـﺬ ﺣـﻮاﱄ ﻣﻠﻴﻮن ﺳﻨﺔ وﻳﻌﺮف ﺎً ﺣﺎﻟﻴ أن ﺳﺪﻳﻢ اﻟﺼﻤﻎ ﻳﺤﺘﻮي ﻋﲆ ﻣﺎ ﻻ ﻳﻘﻞ ﻋﻦ 31 ﻛـﺮة ﻣﺬﻧﺒـﺔ ﺑﺎﻹﺿﺎﻓﺔ إﱃ .CG4 إن اﻵﻟﻴﺔ اﻟﺘﻲ ﺗﺤﺼﻞ ﺑﻬـﺎ ﻫـﺬه اﻷﺟﺴـﺎم اﻟﺸﺒﻴﻬﺔ ﺑﺎ ﺬﻧﺒﺎت ﻋﲆ ﺷﻜﻠﻬﺎ ا ﻤﻴﺰ ﻟﻴﺴﺖ ﻣﻌﺮوﻓﺔ ﺗﻤﺎﻣﺎً ﻟﻜﻦ ﻋﻠﻤـﺎء اﻟﻔﻠـﻚ ﻃـﻮروا ﻓﻜﺮﺗﻴﺖ اﻟﻔﻴﺰﻳﺎﺋﻴﺔ ﻟـ PDRs واﻟﺘﻄﻮر اﻟﺠﺰﻳﺌﻲ ﻓﻜﺮﺗ رﺋﻴﺴﻴﺘ ﺣـﻮل أﺻـﻮﻟﻬﺎ . اﻟﻔﻜـﺮة اﻷوﱃ ﻫﻲ أﻧﻪ ﻣﻦ ا ﻤﻜﻦ أن ﺗﻜﻮن ﰲ اﻷﺻﻞ ﺳﺪم - ﻛﺮوﻳﺔ ﻣﺜﻞ اﻟﺴﺪﻳﻢ اﻟﺪاﺋﺮي ا ﻌﺮوف واﻟﺬي اﺿﻄﺮب ﺑﻌـﺪ ذﻟـﻚ ﺑﺴـﺒﺐ اﻧﻔﺠـﺎر ﻣﺴﺘﻌﺮ أﻋﻈﻢ ﻗﺮﻳﺐ و رﺑﻤﺎ اﻻﻧﻔﺠﺎر اﻷﺻﲇ اﻟﺬ ي ﺗﺸﻜﻞ ﻋﻨﻪ ﺳﺪﻳﻢ اﻟﺼﻤﻎ . اﻟﻔﻜـﺮة اﻟﺜﺎﻧﻴـﺔ ﻫـﻲ أن اﻟﻜـ اتﺮ ا ﺬﻧﺒ ﺔ ﻴـ ﺗﺘﺸﻜﻞ ﻣﻦ ﺧﻼل ﻣﺰﻳﺞ ﻣﻦ اﻟﺮﻳﺎح اﻟﻨﺠﻤﻴﺔ وﺿـﻐﻂ اﻹﺷـﻌﺎع ﻣـ ﻦ اﻟﻨﺠـﻮم اﻟﺴـﺎﺧﻨﺔ اﻟﻀﺨﻤﺔ اﻟﻘﺮﻳﺒﺔ و ﰲ اﻟﻮاﻗﻊ ﻳﺒﺪو أن ﺟﻤﻴﻊ اﻟﻜـﺮ ا ﻴـ ت ا ﺬﻧﺒ ﺔ ا ﻮﺟـﻮدة داﺧـ ﻞ ﺳـﺪﻳﻢ اﻟﺼﻤﻎ ﻟﻬﺎ ذﻳﻮل ﻃﻮﻳﻠﺔ ﺗﺘﺠـﻪ اًﺪ ﺑﻌﻴـ ﻋـﻦ ﻣﺮﻛﺰ اﻟﺴﺪﻳﻢ ﺗﻮﺟـﺪ ﺣﻴﺚ ﺑﻘﺎﻳـﺎ ا ﺴـﺘﻌﺮ اﻷ ﻋﻈﻢ اﻟﺸـﺮاع ــ ﻈﻢﻋاﻷ اﻟﺸـﺮاع إﺿﺎﻓﺔ إﱃ ﻧﺠـﻢ اﻟـ ﴩاع ـ اﻟﻨﺎﺑﺾ . إن ﻧﺠﻢ اﻟـﴩاع اﻟﻨﺎﺑﺾ ﻫﻮ ﻧﺠﻢ ﻧﻴﻮﺗﺮوﻧﻲ ﴎﻳﻊ اﻟﺪوران ﺗﻜﻮّن ﻋﻨﺪﻣﺎ اﻧﻬﺎر ﻧﺠﻢ ﺿﺨﻢ وﻣﻦ ا ﺤﺘﻤﻞ أن ﺗﻘـﻮم رﻳﺎﺣـﻪ اﻟﻨﺠﻤﻴ ـﺔ وﺿـﻐﻄﻪ اﻹﺷـﻌﺎﻋﻲ ﻳﺸــﻜﻼن اﻟﻜﺮﻳﺎت اﻟﻘﺮﻳﺒﺔ وﰲ ﻫـﺬه اﻟﺼـﻮرة أﻳﻀـﺎ ﻳﺒﺪو ﻛﻤﺎ ﻟـﻮ أن CG4 ﻋـﲆ وﺷـﻚ اﻟﺘﻬـﺎم ا ﺠﺮة اﻟﺤﻠ ﺰوﻧﻴـﺔ اﻟﺤﺎﻓـﺔ (ESO 257-19 (PGC 21338 واﻟﺘﻲ ﻳﺒﺪو أﻧﻬـﺎ ﻣﻮﺿـﻮﻋﺔ ﺑﻼ ﺣ ﻤﺎﻳﺔ أﻣﺎﻣﻬﺎ ﻟﻜﻦ ﰲ اﻟﻮاﻗﻊ ﺗﺒﻌﺪ ﻫـﺬه ا ﺠﺮة أﻛﺜﺮ ﻣﻦ ﻣﺎﺋﺔ ﻣﻠﻴﻮن ﺳـﻨﺔ ﺿـﻮﺋﻴﺔ ﻋﻦ CG4 وﻳﺒﺪو أﻧﻬﺎ ﻗﺮﻳﺒـﺔ ﻓﻘـﻂ ﺑﺴـﺒﺐ اﻧﺘﻈﺎﻣﻬﺎ ﰲ ﻧﻔﺲ ﺧﻂ اﻟﺮؤﻳﺔ .