探测朝向Local Group星系的月下质量致密天体
Detecting Sub-lunar Mass Compact Objects toward the Local Group Galaxies
摘要：
通过监测本星系群中的大量恒星，我们可以检测到月球下质量致密天体（SULCO）的纳米透镜事件，如银河系晕中的原始黑洞（PBH）和流氓（自由浮动）矮行星。与恒星质量天体的微透镜效应相比，有限源尺寸效应变得重要，透镜持续时间变短（$\sim 10^{1-4}\,\textrm{s}$）。以M33中含有$V<26$的恒星为源，进行一夜观测，如果SULCO构成了所有暗物质成分，我们将能够探测到银河系晕中质量为$10^{-9}M_{\odot}$至$10^{-7}M_{\odot}$的SULCO引起的$10^{3-4}$纳米透镜事件，其中源的S/N为$>5$。此外，我们预计$10^{1-2}$事件中，由于质量范围为$10^{-11}M_{\odot}$到$10^{-9}M_{\odot}$的SULCO的透镜效应，具有S/N $>100$的明亮蓝色恒星被微弱放大。因此，该方法将为银河系晕中的SULCO打开一个新的窗口，否则将无法观察到。
英文摘要：
By monitoring a large number of stars in the Local Group galaxies, we can detect nanolensing events by sub-lunar mass compact objects (SULCOs) such as primordial black holes (PBHs) and rogue (free-floating) dwarf planets in the Milky Way halo. In contarst to microlensing by stellar-mass objects, the finite-source size effect becomes important and the lensing time duration becomes shorter ($\sim 10^{1-4}\,\textrm{s}$). Using stars with $V<26$ in M33 as sources, for one-night observation, we would be able to detect $10^{3-4}$ nanolensing events caused by SULCOs in the Milky Way halo with a mass of $10^{-9}M_{\odot}$ to $10^{-7}M_{\odot}$ for sources with S/N$>5$ if SULCOs constitute all the dark matter components. Moreover, we expect $10^{1-2}$ events in which bright blue stars with S/N$>100$ are weakly amplified due to lensing by SULCOs with a mass range of $10^{-11}M_{\odot}$ to $10^{-9}M_{\odot}$. Thus the method would open a new window on SULCOs in the Milky Way halo that would otherwise not be observable.
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