Free Astronomy Magazine May-June 2024 ARABIC VERSION

W neticwhitedwarfWD0816-310,whereastronomers hebackgroundartist’simpressionshowsthemag- havefoundascarimprintedonitssurfaceasaresultof havingingestedplanetarydebris.Thevideoabovesum- marisesthediscovery.[ESO/L.Calçada] hen a star like our Sun reachestheendofitslife, itcaningestthesur- roundingplanetsandasteroidsthat were born with it. Now, using the EuropeanSouthernObservatory’s VeryLargeTelescope(ESO’sVLT)in Chile,researchershavefounda uniquesignatureofthisprocessfor thefirsttime—ascarimprintedon the surface of a white dwarf star. “It is well known that some white dwarfs — slowly cooling embers of starslikeourSun—arecannibalis- ingpiecesoftheirplanetarysystems. Now we have discovered that the star’smagneticfieldplaysakeyrole in this process, resulting in a scar onthewhitedwarf’ssurface,” says Stefano Bagnulo, an astronomer at ArmaghObservatoryand Planetarium in Northern Ire- land,UK,andleadauthorof the study. Thescartheteamobservedis aconcentrationofmetalsim- printedonthesurfaceofthe white dwarf WD 0816-310, theEarth-sizedremnantofa starsimilarto,butsomewhat moremassivethan,ourSun. “Wehavedemonstratedthat thesemetalsoriginatefroma planetaryfragmentaslarge as or possibly larger than Vesta, which is about 500 kilometresacrossandthesec- ond-largestasteroidintheSolarSys- tem,” says Jay Farihi, a professor at University College London, UK, and co-authoronthestudy.Theobserva- tions also provided clues to how the stargotitsmetalscar.Theteamno- ticed that the strength of the metal detection changed as the star ro- tated, suggesting that the metalsare concentrated on a specific area on the white dwarf’s surface, rather thansmoothlyspreadacrossit.They also found that these changes were synchronised with changes in the white dwarf’s magnetic field, indi- catingthatthismetalscarislocated on one of its magnetic poles. Put to- gether,thesecluesindicatethatthe magnetic field funneled metals onto the star, creating the scar. “Surprisingly, the material was not evenlymixedoverthesurfaceofthe star,aspredictedbytheory.Instead, this scar is a concentrated patch of planetary material, held in place by thesamemagneticfieldthathas guidedtheinfallingfragments,” saysco -authorJohnLandstreet,a professoratWesternUniversity, Canada, who is also affiliated with the Armagh Observatory and Plane- tarium. “Nothing like this has been seenbefore.” Toreachtheseconclu- sions, the team used a ‘Swiss-army knife’ instrument on the VLT called FORS2, which allowed them to de- tectthemetalscarandconnectitto the star’s magnetic field. “ESO has the unique combination of capabili- ties needed to observe faint objects suchaswhitedwarfs,and sensitivelymeasurestellar magneticfields,” saysBag- nulo.Intheirstudy,theteam also relied on archival data from the VLT’s X-shooter instrument to confirm their findings. Harnessing the power of observations like these, astronomers can re- vealthebulkcompositionof exoplanets, planets orbiting other stars outside the Solar System. This unique study alsoshowshowplanetarysys- temscanremaindynamically active,evenafter‘death’.     MAY-JUNE2024 ﻣﺠﻠﺔ FreeAstronomy ﺎﻟﻌﺮ ﺔ 31 ﻋﻨﺪﻣﺎ ﻳﺼ ﻞ ﻧﺠـﻢ ﻣﺜـﻞ ﺷﻤﺴـﻨﺎ إﱃ ﻧﻬﺎﻳـﺔ ﺣﻴﺎﺗﻪ ﻳﻤﻜﻨـﻪ أن ﻳﺒﺘﻠـﻊ اﻟﻜﻮاﻛـﺐ ا ﺤﻴﻄـﺔ واﻟﻜﻮﻳﻜﺒﺎت اﻟﺘﻲ وﻟﺪت ﻣﻌﻪ . اﻵن ﺑﺎﺳﺘﺨﺪام اﻟﺘﻠﺴ ـﻜﻮب اﻟﻜﺒــ ﺟ ـﺪ اً اﻟﺘــﺎﺑﻊ ﻟﻠﻤﺮﺻ ـﺪ اﻷوروﺑﻲ اﻟﺠﻨﻮﺑﻲ ﰲ ﺗﺸﻴ ﲇ وﺟـﺪ اﻟﺒـﺎﺣﺜﻮن ﻷول ﻣﺮة ﺗﻮﻗﻴﻌﺎً اً ﻓﺮﻳﺪ ﻟﻬﺬه اﻟﻌﻤﻠﻴـﺔ - ﻧﺪﺑـﺔ ﻣﻄﺒﻮﻋﺔ ﻋﲆ ﺳﻄﺢ ﻧﺠﻢ ﻗﺰم أﺑﻴﺾ . " ﻣﻦ ا ﻌﺮوف أن ﺑﻌﺾ اﻷﻗﺰام اﻟﺒﻴﻀﺎء - اﻟﺘﻲ ﺗﱪد ﺑﺒﻂء ﺟﻤﺮات اﻟﻨﺠـﻮم ﻣﺜـﻞ ﺷﻤﺴـﻨﺎ - ﺗﻘﻮم ﺑﺘﻔﻜﻴﻚ أﺟﺰاء ﻣﻦ أﻧﻈﻤﺘﻬﺎ اﻟﻜﻮﻛﺒﻴـﺔ . ﻳﻘﻮل ﺳﺘﻴﻔﺎﻧﻮ ﺑﺎﺟﻨﻮﻟﻮ ﻋﺎﻟﻢ اﻟﻔﻠﻚ ﰲ ﻣﺮﺻﺪ أرﻣﺎغ واﻟﻘﺒ ﺔ اﻟﺴﻤﺎوﻳﺔ ﰲ أﻳ ﺮﻟﻨـﺪا اﻟﺸـﻤﺎﻟﻴﺔ ﺑﺎ ﻤﻠﻜﺔ ا ﺘﺤﺪة وا ﺆﻟﻒ اﻟﺮﺋﻴ ـ : ﴘ ﻟﻠﺪراﺳـﺔ " ﻟﻘﺪ اﻛﺘﺸـﻔﻨﺎ اﻵن أن ا ﺠـﺎل ا ﻐﻨﺎﻃﻴـ ﴘ ـ ﻟﻠﻨﺠﻢ ﻳﻠﻌﺐ دورا رﺋﻴﺴﻴﺎ ﰲ ﻫﺬه اﻟﻌﻤﻠﻴﺔ ﻣﻤﺎ ﻳﺆدي إﱃ ﻧﺪﺑـﺔ ﻋـﲆ ﺳـﻄﺢ اﻟﻘـﺰم اﻷﺑﻴﺾ ." اﻟﻨﺪﺑﺔ اﻟﺘﻲ رﺻﺪﻫﺎ اﻟﻔﺮﻳﻖ ﻫﻲ ﻋﺒﺎرة ﻋﻦ ﺗﺮﻛﻴـﺰ ﻣـﻦ ا ﻌـﺎدن ﻣﻄﺒﻮع ﻋﲆ ﺳﻄﺢ اﻟﻘـﺰم اﻷﺑـﻴﺾ WD 0816-310 وﻫـﻮ ﺑﻘﺎﻳـﺎ ﻧﺠـﻢ ﻣﻤﺎﺛﻞ ﺑﺤﺠﻢ اﻷرض وﻟﻜﻨﻪ أﻛـﱪ إﱃ ﺣﺪ ﻣﺎ ﻣـﻦ ﺷﻤﺴـﻨﺎ . ﻳﻘـﻮل ﺟـﺎي ﻬﻲ ﻓﺮﻳ اﻷﺳﺘﺎذ ﰲ ﺟﺎﻣ ﻌـﺔ ﻛﻮﻟﻴـﺪج ﻟﻨــﺪن، ا ﻤﻠﻜــﺔ ا ﺘﺤــﺪة وا ﺆﻟــﻒ ا ﺸﺎرك ﰲ اﻟﺪراﺳ :"ﺔ ﻟﻘﺪ أﺛﺒﺘﻨـﺎ أن ﻫﺬه ا ﻌﺎدن ﺗﻨﺸﺄ ﻣﻦ ﺟـﺰء ﻛـﻮﻛﺒﻲ ﻛﺒ ﻣﺜﻞ أو رﺑﻤﺎ أﻛﱪ ﻣﻦ ﻴﺴـﺘﺎ ﻓ" " اﻟــﺬي ﻳﺒﻠــﻎ ﻋﺮﺿــﻪ ﺣــﻮاﱄ 500 ـــــــ ﻛﻴﻠﻮﻣﱰ وﻫﻮ ﺛﺎﻧﻲ أﻛـﱪ ﻛﻮﻳﻜـﺐ ﰲ اﻟﻨﻈـﺎم اﻟﺸﻤﴘ ﺪﻗ". ﻣﺖ اﻷرﺻﺎد أ ﻳﻀـ ﺎ أدﻟـﺔ ﺣـﻮل ﻛﻴﻔﻴﺔ ﺣ ﺼـﻮل اﻟـﻨﺠﻢ ﻋـﲆ ﻧﺪﺑـﺔ ﻣﻌﺪﻧﻴـﺔ . رﺻﺪ و اﻟﻔﺮﻳﻖ أن ﻗﻮة اﻟﻜﺸـﻒ ﻋـﻦ ا ﻌـﺎدن ﺗﺘﻐـ ﻣـﻊ دوران اﻟـﻨﺠﻢ ﻣﻤـﺎ ﻳﺸـ إﱃ أن ا ﻌﺎدن ﺗﱰﻛﺰ ﰲ ﻣ ﻨﻄﻘﺔ ﻣﺤﺪدة ﻋـﲆ ﺳـﻄﺢ اﻟﻘﺰم اﻷﺑﻴﺾ ﺑـﺪﻻ ﻣـﻦ اﻧ ﺘﺸـﺎرﻫﺎ ﻋـﱪ و ه وﺟﺪوا أﻳﻀًﺎ أن ﻫﺬه اﻟﺘﻐﻴ ات ﻛﺎﻧﺖ ﻣﺘﺰاﻣﻨﺔ ﻣﻊ ﺗﻐـ ات ﰲ ا ﺠـﺎل ا ﻐﻨﺎﻃﻴـ ـ ﴘ ﻟﻠﻘـﺰم اﻷﺑﻴﺾ ﻣﻤﺎ ﻳﺸ إﱃ أن ﻫﺬه اﻟﻨﺪﺑﺔ ا ﻌﺪﻧﻴـﺔ ﺗﻮﺟﺪ ﻋﲆ أﺣﺪ أﻗﻄﺎﺑـﻪ ا ﻐﻨﺎﻃﻴﺴـﻴﺔ . ﺗﺸـ ﻫﺬه اﻷدﻟﺔ ﻣﺠﺘﻤﻌﺔ إﱃ أن ا ﺠﺎل ا ﻐﻨﺎﻃﻴ ﴘ ﻗﺎم ﺑﺘﻮﺟﻴﻪ ا ﻌـﺎدن إﱃ اﻟـﻨﺠﻢ ﻣﻤـﺎ أدى إ ﱃ ﺗﺸﻜﻞ اﻟﻨﺪﺑﺔ . ا ﺜ أن ﻛﺬﻟﻚ ا ـﺎدة ﻟـﻢ ﺗﻜـﻦ ﻣﺨﺘﻠﻄﺔ ﺑﺎﻟﺘﺴﺎوي ﻋﲆ ﺳـﻄﺢ اﻟـﻨﺠﻢ ﻛﻤـﺎ ــــ ﺗﻨﺒﺄت اﻟﻨﻈﺮﻳﺔ ." ﺑﺪﻻً ﻣﻦ ذﻟـﻚ ﻫـﺬه اﻟﻨﺪﺑـﺔ ﻋﺒﺎرة ﻋﻦ رﻗﻌﺔ ﻣﺮﻛﺰة ﻣـﻦ ﻣـﺎدة ﻛﻮﻛﺒﻴـﺔ، ﻣﺜﺒﺘـﺔ ﰲ ﻣﻜﺎﻧﻬـﺎ ﺑﻮاﺳـﻄﺔ ﻧﻔــﺲ ا ﺠـﺎل ا ﻐ ـ ﻨﺎﻃﻴ ﴘ اﻟﺬي وﺟﻪ اﻟﺸﻈﺎﻳﺎ ا ﺘﺴﺎﻗﻄﺔ " ﻛﻤﺎ ﻳﻘﻮل ا ﺆﻟﻒ ا ﺸﺎرك ﺟـﻮن ﻻﻧﺪﺳـﱰﻳﺖ اﻷﺳﺘﺎذ ﰲ ﺟﺎﻣﻌﺔ وﻳﺴـﱰن ﺑﻜﻨـﺪا ا ﻨﺘﺴـﺐ أﻳﻀًﺎ إﱃ ﻓﺮﻳﻖ اﻟﺒﺤﺚ و ﻣﺮﺻﺪ أرﻣـﺎغ واﻟﻘﺒـﺔ اﻟﺴﻤﺎوﻳﺔ . " ﻟﻢ ﺗﺘﻢ رؤﻳﺔ ﳾء ﻣﺜﻞ ﻫـﺬا ﻣـﻦ ." ﻗﺒــﻞ وﻟﻠﻮﺻ ـﻮل إﱃ ﻫ ـﺬه اﻻﺳ ـﺘﻨﺘﺎﺟﺎت، اﺳــﺘﺨﺪم اﻟﻔﺮﻳــﻖ أداة " ﺳــﻜ اﻟﺠــﻴﺶ ـاﻟ ﻋـﲆ " ﺴﻮﻳﴪي اﻟﺘﻠﺴـﻜﻮب اﻟﻜﺒـ ﺟـﺪاً ﺗﺴﻤﻰ FORS2 واﻟﺘﻲ ﺳﻤﺤﺖ ﻟﻬﻢ ﺑﺎﻛﺘﺸﺎف اﻟﻨﺪﺑﺔ ا ﻌﺪﻧﻴﺔ ورﺑﻄﻬﺎ ﺑﺎ ﺠﺎل ا ﻐﻨﺎﻃﻴـ ﴘ ـ ﻟﻠ ـﻨﺠﻢ . ﻳﻘ ـﻮل ﺑــﺎﺟﻨﻮﻟﻮ " : ﻳﻤﺘﻠ ـﻚ ا ﺮﺻــﺪ اﻻوروﺑﻲ اﻟﺠﻨﻮﺑﻲ ﺎ ﻓﺮﻳﺪ ﺠـﻣﺰﻳ ا ﻣﻦ اﻟﻘﺪرات اﻟﻼزﻣﺔ ﻟﺮﺻﺪ اﻷﺟﺴ ﺎم اﻟﺨﺎﻓﺘﺔ ﻣﺜﻞ اﻷﻗﺰام اﻟﺒﻴﻀـﺎء وﻗﻴـﺎس ا ﺠـ ﺎﻻت ا ﻐﻨﺎﻃﻴﺴﻴﺔ اﻟﻨﺠﻤﻴﺔ . ﰲ دراﺳﺘﻬﻢ اﻋﺘﻤﺪ اﻟﻔﺮﻳﻖ أﻳﻀ ﺎً ﻋـﲆ اﻟﺒﻴﺎﻧـﺎت اﻷرﺷﻴﻔﻴﺔ ﻣﻦ أداة اﻛﺲ" - "ﺷﻮﺗﺮ ﻟﺘﺄﻛﻴﺪ ﻧﺘﺎﺋﺠﻬﻢ وﻣﻦ ﺧﻼل ﺗﺴـﺨ ﻣﺜــﻞ ﻫــﺬه اﻷرﺻــﺎد ﻳﺴــﺘﻄﻴﻊ اﻟﻔﻠﻜﻴــﻮن اﻟﻜﺸ ـﻒ ﻋــﻦ ﺗﺮﻛﻴ ـﺐ ا ﻟﻜﻮاﻛـﺐ اﻟﻨﺠﻤﻴـﺔ وﻫـﻲ ﻛﻮاﻛـﺐ ﺗﺪور ﺣﻮل ﻧﺠﻮم أﺧﺮى . ﺗﻈﻬﺮ ﻫـﺬه اﻟﺪراﺳـﺔ أن اﻷﻧﻈﻤـﺔ اﻟﻜ ﻮﻛ ﺒﻴـﺔ ﻳﻤﻜـﻦ أن ﺗﻈـﻞ ﻧﺸـﻄﺔ دﻳﻨﺎﻣﻴﻜﻴﺎ ا ﻮت" ﺣﺘﻰ ﺑﻌﺪ ." - ﻣﺎﻳﻮ ﻳﻮﻧﻴﻮ 2 0 2 4 ﻫﺬا اﻟﺮﺳﻢ اﻟﺘﺨ ﻠﻲ اﻟﻘﺰم اﻷﺑ ﺾاﻟﻤﻐﻨﺎﻃ ﺴﻲ WD0816- 310 ــــﺚ وﺟــــﺪ ﻋﻠﻤــــﺎء اﻟﻔﻠــــﻚ ﺼــــﻤﺔ ﻣﻄﺒﻮﻋــــﺔ ﻋﻠــــﻰﺳــــﻄﺤﮫ ﻧﺘﻴﺠــــﺔ ، ﺣ ا ـــــــــــــﻮﻛ ـــــــــــــﺘﻼع ﺣﻄـــــــــــــﺎم . ـــــــــــــﺪﻳﻮ أﻋـــــــــــــﻼﻩ اﻟﻔ ﻳ ﻮﺿـــــــــــــﺢ ﻃﺒ ﻌـــــــــــــﺔ ﻫــــــــــــــﺬا اﻻﻛﺘﺸﺎف ]. ESO/L.Calçada [