Free Astronomy Magazine November-December 2022 ARABIC VERSION

or billions of years, the Milky Way’s largest satellite galaxies – the Large and Small Magel- lanic Clouds – have followed a per- ilous journey. Orbiting one another as they are pulled in toward our home galaxy, they have begun to unravel, leaving behind trails of gaseous debris. And yet – to the puzzlement of astronomers – these dwarf galaxies remain intact, with ongoing vigorous star formation. “A lot of people were struggling to explain how these streams of mate- rial could be there,” said Dhanesh Krishnarao (pictured above), assis- tant professor at Colorado College. “If this gas was removed from these galaxies, how are they still forming stars?” With the help of data from NASA’s Hubble Space Telescope and a re- tired satellite called the Far Ultravi- olet Spectroscopic Explorer (FUSE), a team of astronomers led by Krish- narao has finally found the answer: the Magellanic system is sur- rounded by a corona, a protective shield of hot supercharged gas. This cocoons the two galaxies, prevent- ing their gas supplies from being si- phoned off by the Milky Way, and therefore allowing them to con- tinue forming new stars. This discovery, recently published in Nature , addresses a novel aspect of galaxy evolution. “Galaxies enve- lope themselves in gaseous co- coons, which act as defensive shields against other galaxies,” said co-investigator Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland. Astronomers predicted the corona’s existence several years ago. “We dis- covered that if we included a co- rona in the simulations of the Mag- ellanic Clouds falling onto the Milky Way, we could explain the mass of extracted gas for the first time,” ex- plained Elena D’Onghia, a co-inves- tigator at the University of Wis- consin–Madison. “We knew that the Large Magellanic Cloud should be massive enough to have a co- rona.” But although the corona stretches more than 100,000 light-years from the Magellanic clouds and covers a huge portion of the southern sky, it is effectively invisible. Mapping it required scouring through 30 years of archived data for suitable meas- urements. Researchers think that a galaxy’s corona is a remnant of the primordial cloud of gas that col- lapsed to form the galaxy billions of years ago. Although coronas have been seen around more distant dwarf galaxies, astronomers had never before been able to probe one in as much detail as this. NOVEMBER-DECEMBER 2022 رﺻﺪ وﺟﻮدﻫﺎﻟﺔ ﺣﻮل ﻣﺎ ﺳﺤﺎ ﺟﻼن : ﻘﻠﻢ ﻣﺎرﻏﺮﺖ و . ﺎروﺛﺮز و ﺎﻟﺔ ﻧﺎﺳﺎ / و ﺎﻟﺔ اﻟﻔﻀﺎء اﻷوروﺑ ﺔ ﻠﻴﺎرات اﻟﺴﻨ ﻋﺎﺷﺖ أﻛـﱪ ا ﺠـﺮات اﻟﺘﺎﺑﻌــﺔ ﺠــﺮة درب اﻟﺘﺒﺎﻧــﺔ - ﺘﻲ ﺳــﺤﺎﺑ ﻣﺎﺟﻼن اﻟﻜﱪى واﻟﺼﻐﺮى - رﺣﻠﺔ ﻣﺤﻔﻮﻓﺔ ﺑﺎ ﺨﺎﻃﺮ . ﺗﺪور ﻛـﻞ واﺣـﺪة ﺣـﻮل اﻷﺧـﺮى ﺑﻴﻨﻤﺎ ﻳﺘﻢ ﺳـﺤﺒﻬﺎ ﻧﺤـﻮ ﻣﺠﺮﺗﻨـﺎ ، ﰲ ﺑـﺪأﺗﺎ اﻻﻧﻬﻴﺎر ﺗﺎرﻛ وراءﻫﻤ ﺎ آﺛﺎرًا ﻣـﻦ اﻟﺤﻄـﺎم اﻟﻐﺎزي . وﻣﻊ ذﻟﻚ - ﻣﻤﺎ ﻳﺜ ﺣـ ة ﻋﻠﻤـﺎء اﻟﻔﻠﻚ - ﺗﻈﻞ ﻫﺬه ا ﺠﺮات اﻟﻘﺰﻣﺔ ﺳـﻠﻴﻤﺔ ، ﻣﻊ اﺳﺘﻤﺮار ﺗﺸﻜﻞ ﻧﺠﻤﻲ ﻗﻮي ﻗﺎ . ل داﻧﻴﺶ ﻛﺮﻳﺸـﻨﺎراو ) ﰲ اﻟﺼـﻮرة أﻋـﻼه ( ، اﻷﺳـﺘﺎذ ا ﺴﺎﻋﺪ ﰲ ﻛﻠﻴﺔ ﻛﻮﻟﻮرادو " : ﻛـﺎن اﻟﻜﺜـ ﻳﻦ ﻣﻦ اﻟﻨﺎس ﻳﺠﺎﻫﺪون ﻟﴩح ﻛﻴﻒ ﻳﻤﻜـﻦ أن ﺗﻜﻮن ﻫﺬه اﻟﺘﺪﻓﻘﺎت ﻣﻦ ا ـﻮاد ﻣﻮﺟـﻮدة ." " إذا ﺗﻤﺖ إزاﻟﺔ ﻫﺬا اﻟﻐﺎز ﻣﻦ ﻫﺬه ا ﺠـﺮات ، ﻓﻜﻴﻒ ﻻ ﺗﺰال ﺗﺘﺸﻜﻞ اﻟﻨﺠـﻮم؟ " ﺑﻤﺴـﺎﻋﺪة اﻟﺒﻴﺎﻧﺎت ﻣﻦ ﺗﻠﺴﻜﻮب ﻫﺎ ﺑﻞ اﻟﻔﻀﺎﺋﻲ اﻟﺘﺎﺑﻊ ﻟﻮﻛﺎﻟﺔ ﻧﺎﺳﺎ وﻗﻤﺮ ﺻﻨﺎﻋﻲ ﻣﺘﻘﺎﻋﺪ ﻳﺴـﻤﻰ ﻣﺴﺘﻜﺸﻒ اﻷﺷﻌﺔ ﻓﻮق اﻟﺒﻨﻔﺴﺠﻴﺔ اﻟﻄﻴﻔﻲ ـــ ﺗﻮﺻـﻞ ﻓﺮﻳــﻖ ﻣـﻦ ﻋﻠﻤــﺎء اﻟﻔﻠـﻚ ﺑﻘﻴـﺎدة ﻛﺮﻳﺸﻨﺎو أﺧ ًا إﱃ اﻹﺟﺎﺑـﺔ : ﻧﻈـﺎم ﻣـﺎﺟﻼن ﻣﺤﺎط ﺑﻬﺎﻟﺔ ، وﻫ ﻲ ﻋﺒﺎرة ﻋﻦ درع ﻣﻦ اﻟﻐﺎز ا ﺸﺤﻮن اﻟﺴﺎﺧﻦ . وﻳﺆدي ﻫـﺬا إﱃ ﴍﻧﻘـﺔ ا ﺠﺮﺗ ، ﻣﻤﺎ ﻳﺤﻮل دون ﻋﺰل ﻣﺠـﺮة درب اﻟﺘﺒﺎﻧﺔ إﻣﺪادات ﻏﺎزﻫﻤـﺎ ، وﺑﺎﻟﺘـﺎﱄ ﻳﺴـﻤﺢ ﻟﻬﻤﺎ ﺑﺎﻻﺳﺘﻤﺮار ﰲ ﺗﻜﻮﻳﻦ ﻧﺠﻮم ﺟﺪﻳﺪة . ﻫﺬا اﻻﻛﺘﺸـﺎف ، اﻟـﺬي ﻧُﴩـ ﻣـﺆﺧﺮًا ﰲ ﻣﺠﻠـﺔ اﻟﻄﺒﻴﻌﺔ ، ﻳﻌﺎﻟﺞ ﺟﺎﻧﺒًـﺎ ﺟﺪﻳـﺪًا ﻣـﻦ ﺗﻄـﻮر ا ﺠﺮات . ﻗﺎل اﻟﺒﺎﺣﺚ ا ﺸﺎرك أﻧﺪرو ﻓـﻮﻛﺲ ﻣﻦ ﻣﻌﻬـﺪ ﻋﻠـﻮم اﻟﺘﻠﺴـﻜﻮب اﻟﻔﻀـﺎﺋﻲ ﰲ ﺑﺎﻟﺘﻴﻤﻮر ﺑﻮﻻﻳﺔ ﻣﺎرﻳﻼﻧﺪ " : ﺗﺤـﻴﻂ ا ﺠـﺮات ﻧﻔﺴﻬﺎ ﰲ ﻣﺠﻤﻮﻋﺎت ﻏﺎزﻳﺔ ﺗﻌﻤـﻞ ﻛـﺪروع دﻓﺎﻋﻴﺔ ﺿﺪ ا ﺠﺮات اﻷﺧﺮى ." ﻟﻘﺪ ﺗﻮﻗﻊ ﻋﻠﻤﺎء اﻟﻔﻠﻚ وﺟﻮد اﻟﻬﺎﻟﺔ ﻣﻨﺬ ﻋﺪ ة . ﺳﻨﻮات اﻛﺘﺸﻔﻨﺎ أﻧﻪ إذا ﻗﻤﻨﺎ ﺑﺘﻀﻤ ﻫﺎﻟﺔ ﰲ ﻣﺤﺎﻛ ـﺎة ﺣﺎﺳ ـﻮﺑﻴﺔ ﻻﻧ ـﺪﻓﺎع ﺳ ـﺤﺎﺑﺘﻲ ﻣــﺎﺟﻼن ﻧﺤــﻮ ﻣﺠﺮﺗﻨــﺎ درب اﻟﺘﺒﺎﻧـــﺔ . ـــــــــ ﻓ ﻌﲆ ﺳﺒﻴﻞ ا ﺜﺎل ، ﻳﻤﻜﻨﻨﺎ ﴍح ﻛﺘﻠـﺔ اﻟﻐـﺎز ا ﺴﺘﺨﺮج ﻷول ﻣﺮة " ، أوﺿﺤﺖ إﻳﻠﻴﻨﺎ دوﻧﻐﻴﺎ ا ﺤﻘﻖ ا ﺸـﺎرك ﰲ ﺟﺎﻣﻌـﺔ وﻳﺴﻜﻮﻧﺴـﻦ - ﻣﺎدﻳﺴﻮن " . ﻛﻨﺎ ﻧﻌﻠـﻢ أن ﺳـﺤﺎﺑﺔ ﻣـﺎﺟﻼن اﻟﻜﱪى ﻳﺠﺐ أ ن ﺗﻜﻮن ﺿـﺨﻤﺔ ﺑﻤـﺎ ﻳﻜﻔـﻲ ﻟﺤﺪوث اﻟﻬﺎﻟﺔ ". وﻟﻜﻦ ﻋـﲆ اﻟـﺮﻏﻢ ﻣـﻦ أن اﻟﻬﺎﻟﺔ ﺗ ﻤﺘﺪ ﻷﻛﺜﺮ ﻣﻦ ﻣﺎﺋﺔ أﻟﻒ ﺳﻨﺔ ﺿﻮﺋﻴﺔ ﻣﻦ ﺳﺤﺎﺑﺘﻲ ﺗ ﻣﺎﺟﻼن و ﻐﻄﻲ ﺟﺰءًا ﻛﺒ ًا ﻣﻦ اﻟﺴﻤﺎء اﻟﺠﻨﻮﺑﻴﺔ ، إﻻ أﻧﻬ ﺎ ﺔ ﻏ ﻣﺮﺋﻴ . ﻓﻌﻠﻴًﺎ ﻟﻘﺪ ﺗﻄﻠﺐ رﺳﻢ اﻟﺨﺮاﺋﻂ اﻟﺒﺤﺚ ﻋﻦ ﺑﻴﺎﻧﺎت ﻣﺆرﺷﻔﺔ ـﺪة ٣٠ ﻋﺎﻣًـﺎ ﻹﺟـﺮاء ﻗﻴﺎﺳـﺎت . ﺳﺒﺔ ﻣﻨﺎ ﻳﻌﺘﻘﺪ اﻟﺒﺎﺣﺜﻮن أن اﻟﻬﺎﻟﺔ ﰲ ا ﺠﺮة ﻫﻲ ﺑﻘﺎﻳﺎ ﺳﺤﺎﺑﺔ اﻟﻐﺎز اﻟﺒﺪاﺋﻴﺔ اﻟﺘﻲ اﻧﻬﺎرت ﻟﺘﺸﻜﻞ ا ﺠﺮة ﻣﻨﺬ ﻣﻠﻴﺎرات اﻟﺴﻨ ﺑـ. ﺎﻟﺮﻏﻢ ﻣﻦ أن اﻟﻬﺎﻟﺔ رﺻﺪت ﺣﻮل ا ﺠﺮات اﻟﻘﺰﻣـﺔ اﻟﺒﻌﻴﺪة ، إﻻ أن اﻟ ﻌﻠﻤﺎء ﻟﻢ ﻳﺘﻤﻜﻨﻮا ﺳﺎﺑﻘﺎ ﻣﻦ ﻫﺎ ﺳﱪ ﺑﻤﺜﻞ ﻫﺬا اﻟﻘﺪر ﻣﻦ اﻟﺘﻔﺎﺻـﻴﻞ ﻗﺒـﻞ . ذﻟـﻚ ﻗـﺎل ﻛﺮﻳﺸـﻨﺎ راو ﻳﻮﺟـﺪ اﻟﻜﺜـ ﻣـﻦ ــــــ ﻟﻤﻠ ﺎرات ٢٨ ﻫﺎﻟﺔ در اﻟﺘ ﺎﻧﺔ ﻧﻮﻓﻤ دﻳﺴﻤ 2022