Binary Compact Objects and their Progenitors

恒星内部核反应产生的热量会产生压力，防止星星在自身引力作用下坍缩。然而，所有的恒星最终都会耗尽核燃料。当这种情况发生时，星星会在自身重量的作用下坍缩，核心将形成一个非常致密、紧凑的残余物。根据星星的质量，残余物可能是黑洞，中子星星或白色矮星。许多恒星形成于双星系统中--两颗恒星彼此受到引力的束缚。如果一个双星系统中的两颗恒星都演化成致密天体，那么这个系统就被称为“致密天体双星”。在最近的巡天观测中，螺旋形和合并的致密天体双星被观测到为明亮的瞬变，并被探测为引力波的来源。来自加州理工学院（Caltech）的一个团队将研究这些紧凑双星系统的形成途径。他们的结果将限制影响这些系统演化的物理过程，这些过程决定了它们的引力波和电磁特征。该团队将致力于各种项目，旨在留住STEM领域的代表性不足的少数民族（URM）本科生。特别是，首席研究员（PI）将指导来自加州理工学院和邻近机构的URM本科生和研究生。PI还将参加加州理工学院新的FUTURE Ignited计划，旨在帮助有色人种学生为研究生院做准备，包括帮助申请过程和加州理工学院的研究机会。最后，PI将参加几次公共外联活动。该团队将使用先进的计算技术来模拟二进制紧凑对象的形成途径。他们将专注于了解轨道角动量（AM）是如何丢失的，以使两个残留物能够螺旋并合并。特别是，它们将：（1）对具有一定范围的白色矮（WD）质量、初始轨道周期和氢壳质量的WD模型进行演化计算，以确定观测到的WD双星的后公共包络条件。(2)通过拉格朗日-2（L2）点将额外的AM损失应用到双星演化模型中，以考虑到如果质量转移速率足够高，物质可以通过更高的拉格朗日点逃逸的事实。(3)运行包括氦（情况BB）转移的二元模型，包括由于L2质量损失而导致的额外AM损失。(4)模拟由经历Case BB氦质量转移的恒星产生的严重剥离的Ib/c型超新星的光变曲线。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估而被认为值得支持。

Heat from nuclear reactions inside stars creates pressure that prevents the star from collapsing under its own gravity. However, all stars will ultimately run out of nuclear fuel. When this happens, the star collapses under its own weight and the core will form a very dense, compact remnant. Depending on the mass of the star, the remnant will either be a black hole, neutron star or white dwarf. Many stars are formed in binary systems – two stars that are gravitationally bound to each other. If both stars in a binary evolve to form compact objects, the resulting system is known as a “compact object binary”. Compact object binaries that in-spiral and merge have been observed in recent sky surveys as bright transients and detected as sources of gravitational waves. A team from the California Institute of Technology (Caltech) will study the formation pathways of these compact binary systems. Their results will constrain the physical processes affecting the evolution of these systems, which determine their gravitational wave and electromagnetic signatures. The team will work on a variety of projects designed to retain under-represented minority (URM) undergraduates in STEM fields. In particular, the Principal Investigator (PI) will mentor URM undergraduate and graduate students from Caltech and neighboring institutions. The PI will also participate in Caltech's new FUTURE Ignited program designed to help students of color to prepare for graduate school, including help with the application process and research opportunities at Caltech. Finally, the PI will participate in several public outreach events. The team will use advanced computational techniques to model the formation pathways of binary compact objects. They will focus on understanding how orbital angular momentum (AM) is lost to enable the two remnants to in-spiral and merge. In particular, they will: (1) Perform evolutionary calculations for binary White Dwarf (WD) models with a range of WD masses, initial orbital periods, and hydrogen shell masses to determine the post common envelope conditions of observed WD binaries. (2) Implement extra AM loss via the Lagrangian-2 (L2) point into binary stellar evolution models for a range of progenitor mass, companion mass, and initial orbital period to account for the fact that material can escape through the higher Lagrangian points if the mass transfer rate is high enough. (3) Run binary models that include helium (Case BB) transfer, including extra AM loss due to L2 mass loss. (4) Model the light curves of heavily stripped type Ib/c supernovae produced by stars undergoing Case BB helium mass transfer.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.