Speaker: Emily Griffith
The Impact of Black Hole Formation on Population Averaged Supernova Yields
The landscape of black hole (BH) formation -- which massive stars explode as core-collapse supernovae (CCSN) and which implode to BHs -- profoundly affects the IMF-averaged nucleosynthetic yields of a stellar population. Building on the work of Sukhbold et al. (2016), I will discuss IMF-averaged yields at solar metallicity for a wide range of assumptions, including neutrino-driven engine models with extensive BH formation, models with a simple mass threshold for BH formation, and a model in which all stars from 8-120 solar masses explode. I will discuss the range in elemental yields achieved by varying degrees of explodability and which abundance ratios may be useful diagnostics in constraining the Galactic BH landscape. While no landscape choice achieves across-the-board agreement with observed abundance ratios, the discrepancies offer empirical clues to aspects of massive star evolution or explosion physics still missing from the models.
Speaker: Tharindu Jayasinghe Arachchilage
"The Unicorn": Discovery of a nearby, mass gap black hole candidate
Our knowledge of compact object binaries is very biased. Historically, we have only identified them if they are accreting in mass transfer systems, contain pulsars or through the gravitational waves from merging systems. To fully understand their numbers, properties, formation mechanisms and evolutionary paths, new discoveries of non-interacting compact binaries are necessary. We discovered the closest known black hole candidate as a binary companion to V723 Mon. V723 Mon is a nearby (~460 pc), bright (V~8.3 mag), evolved (T_eff~4440 K, and L~173 L☉) red giant in a high mass function, f(M)=1.72 ± 0.01 M☉, nearly circular binary (P~59.9 days, e~0). V723 Mon has previously been classified as an eclipsing binary, but its ASAS, KELT, and TESS light curves are those of a nearly edge-on ellipsoidal variable. Detailed models of the light curves constrained by the period, radial velocities and stellar temperature give an inclination of 87.0±2°, a mass ratio of q=0.33 ± 0.02, a companion mass of M_comp=3.04 ± 0.06 M☉, the radius of the giant as R=24.9 ± 0.7 R☉, and the giant’s mass as M_giant=1.00 ± 0.07 M☉. The simplest explanation for the massive companion is a single compact object, most likely a black hole in the "mass gap".