Free Astronomy Magazine November-December 2023 ARABIC VERSION

M Stellar layers of a galactic onion by NOIRLab Josie Fenske uch like humans, galaxies are shaped by the environment in which they form. While no two are exactly alike, they can be divided into three main types: spiral, elliptical and irregular. Of these types, elliptical galaxies are the largest and are thought to evolve out of galactic collisions and mergers between spirals. About one-tenth of ellip- tical galaxies are classified as shell galaxies, charac- terized by the concentric shells that make up their galactic halos. A striking example of this type of galaxy is NGC 3923, with its onion-like layers beautifully show- cased in this image taken with the DOE-built Dark Energy Camera (DECam) on the Víctor M. Blanco 4- meter Telescope at Cerro Tololo Inter-American Ob- servatory (CTIO), a Program of NSF’s NOIRLab. Located in the constellation Hydra, NGC 3923 is about 70 million light-years away from Earth and 150,000 light-years across, making it about 50% larger than our Milky Way. As is thought to be the story of all shell galaxies, the layered structure seen in NGC 3923 likely developed as a consequence of a merger with another, smaller spiral galaxy in the past. As they merged, the larger galaxy’s gravitational field slowly peeled off stars NOVEMBER-DECEMBER 2023 ﻣﺠﻠﺔ FreeAstronomy ﺎﻟﻌﺮ ﺔ 24 ﻃ ﻘﺎت ﻧ ﻤ ﺔ ﻣﻦ اﻟ ﺼﻞ اﻟﻤﺠﺮي : ﻘﻠﻢ ﺟﻮزيﻓﻨﺴﻜﻲ – ﻣﺨﺘ ﻧﻮﻳﺮﻻب ال ا ﺠﺮات ﺗﺘﺸﻜﻞ ﻣﺜﻞ اﻟﺒﴩ ﺣﺴﺐ اﻟﺒﻴﺌﺔ اﻟﺘﻲ ﺗﺘﺸﻜﻞ ﻓﻴﻬﺎ . ﻋﲆ اﻟﺮﻏﻢ ﻣﻦ أﻧﻪ ﻻ ﻳﻮﺟﺪ اﺛﻨﺎن ﻣﺘﺸﺎﺑ ﻬﺎن ﺗﻤﺎﻣًﺎ، إﻻ أﻧﻪ ﻳﻤﻜﻦ ﺗﻘﺴﻴﻤﻬ ﺎ إﱃ ﺛﻼﺛﺔ أﻧﻮاع رﺋﻴﺴﻴﺔ : اﻟﺤﻠﺰوﻧﻴﺔ واﻟﺒﻴﻀﺎوﻳﺔ وﻏـ ا ﻨﺘﻈﻤﺔ . ﻣﻦ ﺑ ﻫﺬه اﻷﻧﻮاع، ﺗﻌﺪ ا ﺠـﺮات اﻹﻫﻠﻴﻠﺠﻴـﺔ ﻫـﻲ اﻷﻛﱪ وﻳُﻌﺘﻘـﺪ أﻧﻬـﺎ ﺗﻄـﻮرت ﻧﺘﻴﺠـﺔ اﻻﺻـﻄﺪاﻣﺎت ا ﺠﺮﻳـﺔ واﻻﻧﺪﻣﺎﺟﺎت ﺑ ا ﺠﺮات اﻟﺤﻠﺰوﻧﻴﺔ . ﻳﺘﻢ ﺗﺼﻨﻴﻒ ﺣﻮاﱄ ﻋُﴩ ا ﺠﺮات اﻹﻫﻠﻴﻠﺠﻴﺔ ﻋﲆ أﻧﻬـﺎ ﻣﺠـﺮات ﺻﺪﻓﻴﺔ وﺗﺘﻤﻴﺰ ﺑﺄﺻﺪاف ﻣﺘﺤﺪة ا ﺮﻛﺰ ﺗﺸﻜﻞ ﻫﺎﻻﺗﻬﺎ ا ﺠﺮﻳﺔ . ﻣﻦ اﻷﻣﺜﻠﺔ اﻟﻮاﺿﺤﺔ ﻋﲆ ﻫﺬا اﻟﻨﻮع ﻣﻦ ا ﺠـﺮات ﻫـﻲ ﻣﺠـﺮة NGC 3923 ﻣﻊ ﻃﺒﻘﺎﺗﻬﺎ اﻟﺸﺒﻴﻬﺔ ﺑﺎﻟﺒﺼﻠﺔ ا ﻌﺮوﺿـﺔ ﺑﺸـﻜﻞ ﺟﻤﻴﻞ ﰲ ﻫﺬه اﻟﺼﻮرة ا ﻠﺘﻘﻄﺔ ﺑﻜﺎﻣ ا اﻟﻄﺎﻗـﺔ ا ﻈﻠﻤـﺔ دي ) ( ﻛﺎم اﻟﺘﻲ ﺻﻨﻌﺘﻬﺎ وزارة اﻟﻄﺎﻗﺔ ﺑﺘ وا ﺘﺼﻠﺔ ﻠﺴﻜﻮب ﻓﻴﻜﺘﻮر إم ﺑﻼﻧﻜﻮ اﻟﺒﺎﻟﻎ 4 أﻣﺘﺎر ﰲ ﻣﺮﺻﺪ ﺳ و ﺗﻮﻟﻮﻟـﻮ ، وﻫـﻮ ﺑﺮﻧـﺎﻣﺞ ﻟ ﻠﻤﺨﺘﱪ اﻟﻮﻃﻨﻲ ﻷﺑﺤﺎث ﻋﻠﻢ اﻟﻔﻠﻚ اﻟﺒﺼ ـ ﺮي واﻷﺷـﻌﺔ ﺗﺤـﺖ اﻟﺤﻤﺮاء ) ﻧﻮﻳﺮﻻب ( اﻟﺘﺎﺑﻊ ﺆﺳ ﺴﺔ اﻟﻌﻠﻮم اﻟﻮﻃﻨﻴﺔ اﻷﻣﺮﻳﻜﻴﺔ . ﻧﻮﻓﻤﺒﺮ - ﺩﻳﺴﻤﺒﺮ 2 0 2 3 إن