Counting the Unseen: Massive Black Hole Demographics from Tidal Disrution Events

过去20年的重大科学发现之一是，大型星系和它们的中心超大质量黑洞(BH)一起进化，每个星系都直接影响对方的可观测特性。较小质量的星系是否与中心黑洞类似地共同进化，或者实际上，拥有它们的比例是多少，仍然是一个悬而未决的问题，因为很难探测到中等质量(100,000个太阳质量)的黑洞。一种很有希望的探测和量化这些天体的方法是利用潮汐扰乱事件(TDE)期间发出的短暂光，即BH强大的引力潮汐力量将距离它太近的恒星撕裂。该项目的主要目标是利用现有的20Mpc内低质量星系的颜色、恒星质量和中心恒星密度测量数据，对即将到来的维拉·C·鲁宾天文台预计将探测到的TDEs的预期频率和亮度进行建模。这些观测将揭示拥有黑洞的低质量星系的比例、它们的质量，以及更广泛地说，中心黑洞的主要形成机制。该项目将支持研究生和本科生外展实习生。当中等质量的BHS无论是从运动学上还是通过它们的吸积信号都非常难以检测到的地方，TDEs代表了一种强大的替代技术。然而，使用观测到的TDEs来限制黑洞的“人口统计”，需要根据星系的性质对这些事件进行准确的预测。首先，黑洞附近恒星的秒尺度密度是准确预测TDE速率的关键参数，而这种空间尺度只能在~20Mpc以内的星系中旋转。在质量小于银河系的星系中，这些尺度上的中心密度(因此TDE速率)由核星团主导。该项目将使用核密度测量结合目前的恒星质量函数来限制一系列BH质量分布和占有率的TDE速率。然后，这些预测可以与兹维基瞬变工厂(ZTF)和即将到来的维拉·C·鲁宾天文台的数据进行比较，首次确定低至1亿太阳质量的星系中的BH人口统计数据。另外两个项目还将预测大质量星系周围剥离的核中的TDE率，并试图解释恒星爆炸后星系中TDEs的明显“过剩”(大约每三个中就有一个)。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

One of the major scientific discoveries of the last two decades is that large galaxies and their central super-massive black holes (BH) have evolved together, with each directly influencing observable properties of the other. Whether less massive galaxies have similarly coevolved with central BHs, or indeed, what fraction even possess them, is still an open question due to the difficulty in detecting intermediate mass (100,000 solar masses) BHs. A promising approach to detect and quantify these objects utilizes the brief outbursts of light emitted during a tidal disruption event (TDE), where a BH's strong gravitational tidal forces shred a star passing too close to it. The primary aim of this project is to use existing color, stellar mass, and central stellar density measurements of low mass galaxies within 20 Mpc to model the expected frequency and luminosities of TDEs that the upcoming Vera C. Rubin Observatory are expected to detect by the thousands. These observations will reveal the fraction of low-mass galaxies that host BHs, their masses, and more broadly the primary formation mechanism of central BHs. The project will support a graduate student as well as undergraduate outreach interns.Whereas intermediate mass BHs are exceedingly difficult to detect either kinematically or through their accretion signatures, TDEs represent a robust alternative technique. However, using observed TDEs to constrain black hole “demographics” requires accurate predictions of these events as a function of galaxy properties. To first order, the parsec scale density of stars in the immediate vicinity of a BH is the key parameter for accurately predicting TDE rates, and such spatial scales can only be revolved for galaxies within ~20 Mpc. In galaxies less massive than the Milky Way the central densities on these scales (and thus TDE rates) are dominated by nuclear star clusters. This project will use nuclear density measurements combined with present-day stellar mass functions to constrain the TDE rates for a range of BH mass distributions and occupation fractions. These predictions can then be compared to data from the Zwicky Transient Factory (ZTF) and the upcoming Vera C. Rubin Observatory to determine the BH demographics in galaxies as low as 100-million solar masses for the first time. Two additional projects will also predict TDE rates in stripped nuclei surrounding massive galaxies and attempt to explain the apparent “overabundance” (roughly one of every three) of TDEs in post-starburst galaxies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.