NSF-BSF: Stellar Collisions in Extreme Environments

在银河系的中心，恒星群的密度比太阳附近高一个数量级，导致了高速的恒星碰撞。同样的暴力事件也发生在其他星系的中心。梅茨格和斯通将使用计算机模拟来研究这些碰撞。他们将研究：(1)潮汐扰动事件(TDE)，其中恒星与恒星的碰撞模拟了真正的TDE事件(恒星靠近超大质量黑洞(SMBH)，并被潮汐引力拉开)；(2)围绕超大质量黑洞(SMBH)的吸积盘中的碰撞，以及在盘中产生的耀斑；(3)如何使用碰撞速率来预测激光干涉仪引力波天文台(LIGO)可能探测到的引力波来源。该项目得到了美国国家科学基金会和美国-以色列两国科学基金会的支持，以进一步促进两国天体物理学界的合作。梅茨格和斯通将招募研究生和博士后学者参加为期一周的国际时域引力波天体物理学暑期班。这些模拟将被用来精确量化1)掠过的高超音速恒星-恒星碰撞：一种由梅茨格和斯通首先提出的新型瞬变现象；2)高超声速恒星-活动星系核的盘碰撞，这对解释变异性的极端尾巴，即改变外观的活动星系核具有重要的前景。这项工作做出的预测将直接为前沿的时间域调查提供信息，例如ASASSN、ZTF和eROSITA。相关的分析工作将模拟和量化各种“碰撞”情景，以加深我们对致密星团中引力波源形成的理解。对连续谱极限、“n-sigma-v”碰撞速率公式的修改可能会强烈影响球状星团和核星团用于LIGO/室女座震源生产的可能性。这一裁决反映了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。

In the center of the Milky Way, stellar populations are orders of magnitude denser than in the Solar neighborhood, leading to high-velocity stellar collisions. The same violent events occur in the centers of other galaxies. Metzger and Stone will study these collisions using computer simulations. They will study: (1) tidal disruption event (TDE) impostors, where a star-star collision mimics a true TDE event (where a star passes close to a supermassive black hole (SMBH) and is pulled apart by tidal forces); (2) collisions in an accretion disk around a SMBH, and resulting flares in the disk, and (3) how to use the rate of collisions to predict how many gravitational wave sources are likely to be detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO). This project is supported by both the National Science Foundation and the US-Israel Binational Science Foundation to further collaborations between the astrophysical communities in the two countries. Metzger and Stone will recruit graduate students and postdoctoral scholars to attend a week-long international summer school on time-domain gravitational wave astrophysics.The simulations will be used to precisely quantify the hydrodynamic outcomes and electromagnetic signatures of 1) grazing, hypersonic star-star collisions: a new type of transient first proposed by Metzger and Stone; 2) hypersonic star – AGN disk collisions, which holds significant promise for explaining the extreme tail of variability, i.e., changing-look AGN. The predictions made from this work will directly inform cutting-edge time-domain surveys, e.g., ASASSN, ZTF, and eROSITA. Related analytic work will simulate and quantify a wide range of “collision” scenarios to further our understanding of the formation of gravitational wave sources in dense star clusters. Modifications to continuum-limit, “n-sigma-v” collision rate prescriptions could strongly affect the plausibility of globular and nuclear star clusters for LIGO/Virgo source production.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.