Stars, Planets, and ISM Seminar

Harriet Dinerstein, The University of Texas at Austin

An Organic Harvest: Carbon Macromolecules from Planetary Nebulae

Asymptotic Giant (AGB) stars are known to be major suppliers of dust to the ISM. We are now learning that, through the planetary nebulae (PNe) they expel, they are also sources of large C-bearing molecules such as Polycyclic Aromatic Hydrocarbons (“PAHs”), fullerenes (pure-carbon “soccer balls”), and similar structures. It is unclear whether these molecules form early on the AGB, or are created later in the PN, when UV radiation from the central star impinges upon the stellar ejecta, driving ISM-like chemistry. I will report on the efforts of the “ESSENcE” team, an informal international collaboration, to elucidate the formation processes of PAHs, fullerenes, etc., by observing spatially-resolved PNe with JWST. Our recent targets included the Ring Nebula, the Butterfly Nebula (NGC 6302), and Tc 1, the first astronomical source in which fullerenes were detected. We find that PAHs can form in O-rich material despite a widespread assumption that they require C > O, and that PNe can serve as useful testbeds for probing the origin and evolution of PAHs under nebular conditions in general including those in high-redshift galaxies.

Jesse Han, Harvard University

A Supermassive Black Hole in the LMC and How Roman Can Find It

Supermassive black holes can produce hypervelocity stars via the Hills mechanism. We directly trace a population of hypervelocity stars to the LMC, indicating the presence of an SMBH. We model the Hills mechanism to estimate its mass to be ~1e6 Msun; this mass lies precisely on the M-sigma relation expected for the LMC. We further discuss how an all-sky Roman survey can constrain the proper motion of faint stars such as hypervelocity stars, which can pinpoint where the SMBH resides.