NSF-BSF: Stellar Collisions in Extreme Environments

在银河系的中心，恒星的数量级比太阳系附近的恒星密集，导致高速恒星碰撞。 同样的剧烈事件也发生在其他星系的中心。Metzger和Stone将使用计算机模拟来研究这些碰撞。他们将研究：（1）潮汐破坏事件（TDE）冒名顶替者，其中恒星-恒星碰撞模仿真实的TDE事件（当一颗星星靠近超大质量黑洞（SMBH）时，被潮汐力拉开）;（2）在SMBH周围的吸积盘中发生碰撞，并在盘中产生耀斑，以及（3）如何利用碰撞率来预测激光干涉引力波天文台（LIGO）可能探测到多少个引力波源。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，以进一步加强两国天体物理界之间的合作。Metzger和Stone将招募研究生和博士后学者参加为期一周的时域引力波天体物理学国际暑期班。模拟将用于精确量化1）掠射，高超音速恒星-恒星碰撞的流体动力学结果和电磁特征：Metzger和Stone首次提出的新型瞬态; 2）高超音速星星-活动星系核盘碰撞，这对解释极端的变化尾部具有重要的希望，即，变貌活动星系核从这项工作中做出的预测将直接为尖端的时域调查提供信息，例如，ASASSN、ZTF和eROSITA。 相关的分析工作将模拟和量化大范围的“碰撞”场景，以进一步了解密集星星团中引力波源的形成。修改连续极限，“n-sigma-v”碰撞率处方可能会强烈影响球状和核星星集群的LIGO/Virgo源生产的可扩展性。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.