Free Astronomy Magazine September-October 2024

A Hubble finds surprises around a nova called HM Sagittae byNASA/ESA Ray Villard stronomers have used new data from NASA’s Hubble SpaceTelescopeandthere- tiredSOFIA(StratosphericObserva- toryforInfraredAstronomy)aswell asarchivaldatafromothermissions torevisitoneofthestrangestbinary starsystemsinourgalaxy–40years after it burst onto the scene as a bright and long-lived nova. A nova isastarthatsuddenlyincreasesits brightness tremendously and then fadesawaytoitsformerobscurity, usually in a few months or years. BetweenAprilandSeptember1975, the binary system HM Sagittae (HM Sge)grew250timesbrighter.Even moreunusual,itdidnotrapidlyfade awayasnovaecommonlydo,but has maintained its luminosity for decades.Recently,observationsshow that the system has gotten hotter, but paradoxically faded a little. HM Sge is a particular kind of sym- bioticstarwhereawhitedwarfand a bloated, dust-producing giant companion star are in an eccentric orbit around each other, and the white dwarf ingests gas flowing from the giant star. That gas forms ablazinghotdiskaroundthewhite dwarf,whichcanunpredictablyun- dergo a spontaneous thermonu- clear explosion as the infall of hy- drogenfromthegiantgrowsdenser on the surface until it reaches a tipping point. These fireworks be- tweencompanionstarsfascinateas- ﻣﺠﻠﺔ FreeAstronomy ﺎﻟﻌﺮ ﺔ 48 ﺸﻒﻜ" ﻫﺎﺑﻞ " ﻣﻔﺎﺟﺂت ﺣﻮل اﻟ ﻤﺴﺘﻌﺮ it ae : ﻘﻠﻢ راي ﻓ ﻼرد و ﺎﻟﺔ ﻧﺎﺳﺎ / و ﺎﻟﺔ اﻟﻔﻀﺎء اﻷوروﺑ ﺔ - ﺳﺒﺘﻤﺒﺮ ﺃﻛﺘﻮﺑﺮ 2 0 2 4 اﺳـﺘﺨﺪم ﻋﻠﻤﺎء اﻟﻔﻠﻚ ﺑﻴﺎﻧﺎت ﺟﺪﻳﺪة ﻣـﻦ ﺗﻠﺴﻜﻮب ﻫﺎﺑﻞ اﻟﻔﻀﺎﺋﻲ اﻟﺘﺎﺑﻊ ﻟ ﻮﻛﺎﻟﺔ ﻧﺎﺳﺎ وﻛـــﺬﻟﻚ ﺑﻴﺎﻧـــﺎت ﺻـــﻮﻓﻴﺎ ) ﻣﺮﺻـــﺪ اﻟﺴﱰاﺗﻮﺳﻔ ﻟﻌﻠﻢ اﻟﻔﻠﻚ ﺑﺎﻷﺷـﻌﺔ ﺗﺤـﺖ اﻟﺤﻤﺮاء ﺬﻟﻚ ﻛ( ﺑﻴﺎﻧﺎت أرﺷﻴﻔﻴﺔ ﻣﻦ ﺑﻌﺜﺎت أﺧﺮى ﻹﻋﺎدة اﻟﻨﻈﺮ ﰲ أﺣـﺪ أﻏـﺮب أﻧﻈﻤـﺔ اﻟﻨﺠﻮم اﻟﺜﻨﺎﺋﻴﺔ ﰲ ﻣﺠﺮﺗﻨﺎ ﺑﻌﺪ 40 ﺎﻋﺎﻣ ﻣﻦ ﻇﻬﻮرﻫﺎ ﻋﲆ اﻟﺴـﺎﺣﺔ ﻛﻤﺴـﺘﻌﺮ ﴩق ـﻣـ وﻃﻮﻳﻞ اﻷ .ﻣـﺪ ا ﺴـﺘﻌﺮ ﻫـﻮ ﻧﺠـﻢ ﻳـﺰداد ﺳﻄﻮﻋﻪ ﻓﺠﺄة ﺑﺸﻜﻞ ﻛﺒ ﺛـﻢ ﻳـﺘﻼﳽ إﱃ ﺧﻔﻮﺗﻪ اﻟﺴﺎﺑﻖ، ﻋـﺎدة ﰲ ﻏﻀـﻮن ﺑﻀـﻌﺔ أﺷـﻬﺮ أو ﺳـﻨﻮات . ﺑـ أﺑﺮﻳـﻞ و ﺳـﺒﺘﻤﱪ 1975 زاد ﺳﻄﻮع اﻟﻨﻈﺎم اﻟﺜﻨـﺎﺋﻲ ا ﺴـﻤﻰ HM Sagittae (HM Sge) ﺑﻤﻘ ـﺪار 250 ﻣﺮة واﻷﻣﺮ اﻷﻛﺜﺮ ﻏﺮاﺑﺔ ﻫﻮ أﻧﻪ ﻟﻢ ﻳـﺘﻼﳽ ﺑﴪﻋﺔ ﻛﻤﺎ ﺗﻔﻌﻞ ا ﺴـﺘﻌﺮات ﻋـﺎدة ﻟﻜﻨـﻪ ــــ ﺣﺎﻓﻆ ﻋﲆ ﻌﺎﻧﻪ ﻟﻌﻘﻮد . ﰲ اﻵوﻧﺔ اﻷﺧـ ة ﺗﻈﻬـﺮ اﻷ رﺻـﺎد أن اﻟﻨﻈــﺎم أﺻــﺒﺢ أﻛﺜــﺮ ﺳﺨﻮﻧﺔ وﻟﻜﻦ ﻣﻦ ا ﻔﺎرﻗﺔ أﻧﻪ ﺧﻔﺖ ﻗﻠـﻴﻼ HM Sge ﻫـﻮ ﻧـﻮع ﻣﻌـ ﻣـﻦ اﻟﻨﺠـﻮم اﻟﺘﻜﺎﻓﻠﻴﺔ ﺣﻴﺚ ﻳﻮﺟـﺪ ﻗـﺰم أﺑـﻴﺾ وﻧﺠـﻢ ﻣﺮاﻓﻖ ﻋﻤﻼق ﻣﻨﺘﻔﺦ ﻣﻨﺘﺞ ﻟﻠﻐﺒﺎر ﰲ ﻣـﺪار ﺷﺪﻳﺪ اﻻﺳﺘﻄﺎﻟﺔ ﺣـﻮل ﺑﻌﻀـﻬﻤﺎ اﻟـﺒﻌﺾ واﻟﻘﺰم اﻷﺑﻴﺾ ﻳﺒﺘﻠـﻊ اﻟﻐـﺎز ا ﺘـﺪﻓﻖ ﻣـﻦ اﻟﻨﺠﻢ اﻟﻌﻤﻼق وﻳﺸﻜﻞ ﻫـﺬا اﻟﻐـﺎز ﺎً ﻗﺮﺻـ ﺳﺎﺧﻨًﺎ ﻣﺸﺘﻌﻼً ﺣﻮل اﻟﻘﺰم اﻷﺑﻴﺾ واﻟـﺬي ﻳﻤﻜـﻦ أن ﻳﺘﻌـﺮض ﺑﺸـﻜﻞ ﻏـ ﻣﺘﻮﻗــﻊ ﻻ ﻧﻔﺠﺎر ﻧﻮوي ﺣﺮاري ﺗﻠﻘﺎﺋﻲ ﻋﻨﺪﻣﺎ ﺰداد ﺗـ ﻛﺜﺎﻓﺔ ﺳﻘﻮط اﻟﻬﻴﺪروﺟ ﻣﻦ اﻟﻌﻤﻼق ﻋﲆ اﻟﺴﻄﺢ ﺣﺘﻰ ﻳﺼﻞ إﱃ ﻧﻘﻄﺔ اﻟﺘﺤﻮل . ﺗﺒﻬﺮ ﻫﺬه اﻷﻧﺸﻄﺔ ﺑ اﻟﻨﺠـﻮم ا ﺼـﺎﺣﺒﺔ ﻋﻠﻤﺎء اﻟﻔﻠﻚ ﻣﻦ ﺧﻼل ﺗﻘﺪﻳﻢ ﻧﻈـﺮة ﺛﺎﻗﺒـﺔ ـــ