Stars that evolve near the Galactic massive black hole show strange behaviors. The spectroscopic features of these stars show that they must be old. But their luminosities are much higher than the amounts that are predicted by the current stellar evolutionary models, which means that they must be active and young stars. In fact this group of stars shows signatures of old and young stars, simultaneously. This is a paradox known as the "paradox of youth problem" (PYP). Some people tried to solve the PYP without supposing dark matter effects on stars. But, in this work, we implemented Weakly Interacting Massive Particles (WIMPs) annihilation as a new source of energy inside such stars. This implementation is logical for stars that evolve at high dark matter density environments. The new source of energy causes stars to follow different evolutionary paths on the H-R diagram in comparison with classical stellar evolutionary models. Increasing dark matter density in stellar evolutionary simulations causes the deviations from the standard H-R diagrams becomes more pronounced. By investigating the effects of WIMPs density on stellar structures and evolutions, we concluded that by considering dark matter effects on stars at the Galactic center, it is possible to solve the PYP. In addition to dark matter effect, complete solutions to PYP must consider all extreme and unique physical conditions that are present near the Galactic massive black hole.
A solution to the paradox of youth in the Galactic centre
Universidade de Coimbra（科英布拉大学）；Universidade do Porto（波尔图大学）；Universidade de Lisboa（里斯本大学）；Observatoire de Paris, Université PSL, Sorbonne Université（巴黎天文台，巴黎文理研究大学，索邦大学）；University of Amsterdam（阿姆斯特丹大学）
Making massive stars in the Galactic Centre via accretion onto low-mass stars within an accretion disc
在银河系中心超大质量黑洞的$\sim 0.4$ pc内观测到的超大质量恒星的起源是一个谜。来自黑洞的潮汐力可能会抑制{ \it in situ}恒星的形成，而年轻的大质量恒星似乎会排除在其他地方形成，然后（以某种方式）进入银河系中心。在这里，我们考虑第三种方法来产生这些大质量的恒星，从低质量的恒星包含在核星团，围绕着超大质量黑洞。一个经过的气体云可以被超大质量黑洞潮汐般撕碎，在黑洞周围形成一个吸积盘。嵌入吸积盘中的恒星会通过邦迪-霍伊尔吸积从盘中吸积气体，其中吸积速率为$\dot{M}_\star \propto M_\star^2$。这种超指数增长的吸积可以导致恒星质量的急剧增加，在某些情况下达到所需的40-50 M $_\odot$。质量增长率敏感地依赖于恒星的轨道偏心率及其倾角。当恒星被圆盘捕获时，轨道倾角和/或它们的偏心率的演变，以及它们的轨道被圆化，将增加产生的大质量恒星的数量。因此，吸积到低质量恒星上会导致银河系中心和其他星系核的超重恒星质量函数。产生的大质量恒星将通过超新星爆炸污染环境，并可能产生紧凑的双星，其合并可能被LIGO-VIRGO引力波天文台检测到。
The Solar Neighborhood LV: Spectral Characterization of an Equatorial Sample of 580 K Dwarfs
Agnes Scott College（阿格尼丝·斯科特学院）；RECONS Institute（RECONS研究所）；Georgia State University（佐治亚州立大学）；Steward Observatory and Department of Astronomy, The University of Arizona（亚利桑那大学斯图尔德天文台和天文学系）；Wesleyan University（卫斯理安大学）；The Ohio State University（俄亥俄州立大学）
