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12 Apr 2019

Are brown dwarfs failed stars or super-planets?

    Artist conception of a brown dwarf (Image credit: NASA/JPL-Caltech)

    Artist conception of a brown dwarf (Image credit: NASA/JPL-Caltech)

    Brown dwarfs are celestial bodies that are less massive than stars and more massive than planets. It remains unclear whether they all form like stars in interstellar gas clouds or they can also form like planets in disks of gas and dust around young stars. A team of astronomers that includes Dr Man Hoi Lee from the Department of Physics and Department of Earth Sciences and former postdoctoral fellow Dr Trifon Trifonov in his team discovered that the star v Ophiuchi is orbited by two brown dwarfs in a 6:1 orbital resonance configuration. The orbital periods of the two brown dwarfs are 530 and 3185 days, which means that the brown dwarf closer to v Ophiuchi orbits its star six times while the more distant brown dwarf completes one orbit. This system is the first to have two brown dwarfs in orbital resonance, and the period ratio of the resonance is also the largest discovered so far for a pair of brown dwarfs or planets orbiting a star. This 6:1 resonant configuration strongly indicates that these brown dwarfs formed like planets in a disk around the star and underwent migration due to interactions with the disk. The finding has just been published as a highlighted paper in the 2019 April issue of the journal Astronomy & Astrophysics




    棕矮星是一類質量在較重的恆星和較輕的行星之間的天體,目前尚不清楚它們是否都像恆星一樣在星際氣體雲中形成,或者它們也可能像行星一樣在圍繞原恆星的氣體和塵埃盤中形成。一個包括來自香港大學的李文愷博士和前任博士後研究員 Trifon Trifonov的天文學家團隊發現了圍繞蛇夫座v恆星的兩顆棕矮星是在一個6:1共振軌道結構。這兩顆棕矮星的公轉周期分別為530和3185天,意味著當靠近蛇夫座v星的棕矮星繞其恆星運行六次,較遠的棕矮星便完成一個軌道運行。這個系統是第一個有一對棕矮星在軌道共振中,並且共振的周期比率也是在已知的圍繞恆星的棕矮星或行星中最大的一對。這種6:1的共振軌道結構強烈地表明這兩顆棕矮星像行星一樣在圍繞原恆星的氣體和塵埃盤中形成,並且由於與原行星盤的相互作用而進行遷移。這一結果剛剛在2019年4月的《天文和天體物理》期刊上作為重點論文發表。