Astrophysics Brown Bag Lunch Talk 11/8/2021: Speakers: Simone Bavera (University Of Geneva) And Shreyas Vissapragada (CalTech)

Monday November 8, 2021 12:00 pm
TBA in person or via Zoom

Monday, November 8, 2021

12:00 – 12:30pm

Simone Bavera, University of Geneva

Probing the progenitors of spinning binary black-hole mergers with long gamma-ray burst observations

Abstract: Long duration gamma-ray ray bursts (LGRBs) are thought to be associated with the collapse of massive, rapidly spinning stars and the formation of compact objects. Developments in asteroseismology and gravitational wave detections point towards efficient angular momentum transport inside stars, which implies that the core of massive stars slows down after they expand to become super-giants and lose any significant initial angular momentum via stellar winds or binary mass transfer. On the other hand, tidal interactions in close binary systems can maintain a star tidally locked to short orbital periods leading to the formation of spinning black holes. I will discuss how the formation of fast-spinning binary black hole (BBH) mergers, originating from the evolution of isolated binaries, are associated with luminous LGRBs. Using population synthesis studies that employ detailed stellar structure and binary evolution calculations, we find that ~10% of the GWTC-2 reported BBHs had a luminous LGRB associated with their formation. Because of the short merger timescale of these highly spinning BBHs, LGRBs can probe their formation throughout cosmic time outside current gravitational waves detectors’ horizons.

Bio: I am a Ph.D. student working on gravitational-wave astrophysics with Tassos Fragos at the University of Geneva. In particular, I study the origin of black hole spin in the formation of merging binary black holes in the context of isolated binary evolution. As a member of the POSYDON collaboration (, I am currently working on bringing detailed MESA stellar and binary simulations to population synthesis of double compact objects.


12:30 – 1:00pm

Shreyas Vissapragada, CalTech

Observing the Evaporating Atmospheres of Exoplanets in Metastable Helium

Abstract: A majority of the extrasolar planets discovered by transit surveys reside surprisingly close to their host stars, and their atmospheres are so intensely irradiated that they can escape altogether. This critical evolutionary process may play a key role in clearing out the Neptune desert (a dearth of Neptune-mass planets on orbits shorter than five days), but it is relatively unconstrained observationally. The recent discovery of the planetary metastable helium line, which probes tenuous gas near the wind-launching radius, allows us to place some of the first observational constraints on photoevaporation. In this talk, I will first discuss a novel narrowband photometric technique for studying atmospheric outflows using the Wide-field InfraRed Camera (WIRC) at Palomar Observatory. I will then mention some initial results from our survey of atmospheric escape in gas giant planets on the edge of the Neptune desert, and finally I will propose some future directions for atmospheric escape studies with the exciting new sample of TESS planets.

Bio: I am a fifth-year PhD student at Caltech working with Professor Heather Knutson in the Planetary Science department. I primarily study transiting exoplanets with the Hale 200-inch telescope at Palomar
Observatory, and have worked on observations of planetary orbital dynamics (with transit-timing variations) and atmospheric evolution (with the metastable helium line).


Event Contact

Josh Borrow