סמינר באסטרונומיה ובאסטרופיזיקה: The Chaotic Origins of LIGO's Binary Black Holes
Nick Stone, HUJI
The detection of GW150914 in late 2015 inaugurated the era of gravitational wave (GW) astronomy. After several years of detector upgrades, and the expansion of the LIGO network to include Virgo, GW sources are now detected on a regular basis, with binary black holes (BBHs) dominating the detection rate. However, we still cannot answer the most basic astronomical question about the GWs we observe: what astrophysical process is responsible for bringing the majority of detected BBHs close enough in separation so that they can merge due to GW emission? I will survey the major theoretical mechanisms for producing LIGO-band BBH mergers, before focusing on two that are of particular interest to me. First, I will discuss the "AGN Channel," in which wide BBHs embedded in the dense gas of an AGN accretion disk are driven hydrodynamically to merger. This channel is unique in that it may possess both direct and indirect electromagnetic counterparts (though the former will be very challenging to detect), and also in the large fraction of multiple mergers it may produce. Second, I will discuss how dense star clusters, such as globulars, can synthesize hard BBHs through repeated binary-single scatterings, which produce short-lived, metastable triple systems. The evolution of these non-hierarchical triples is chaotic, preventing deterministic analytic solutions. However, the presence of chaos allows us to derive a simple statistical solution by invoking the ergodic hypothesis. This statistical solution to the generic 3-body problem agrees well with numerical experiments, and will greatly simplify the study of BBH synthesis in dense star clusters.
מארגן הסמינר: ד"ר עומר ברומברג