About
After receiving a Master-equivalent degree in Physics from the Universita' Statale degli Studi di Milano (Italy), Gallo moved to the Netherlands to complete her graduate studies in Astronomy at the Universiteit van Amsterdam (PhD 2005). She is currently a Professor of Astronomy at the University of Michigan, and was previously a Hubble Postdoctoral Fellow at the MIT Kavli Institute (2008−2010), and a Chandra Postdoctoral Fellow at the University of California, Santa Barbara (2005−2008). Gallo's primary field of research is observational high energy astrophysics, with a main focus on the properties of accreting black holes. More recently, she became interested in the effects of high-energy stellar irradiation in the context of atmospheric escape from exoplanets.
Research Areas
Compact objects: Gallo's research work has contributed substantially in shaping the current paradigm for the so-called jet-accretion coupling in galactic X-ray binaries. The analysis carried out in “Hard state neutron star and black hole X-ray binaries in the radio:X-ray luminosity plane” strengthens decade-old claims and cements black holes as more radio-powerful than neutron star X-ray binaries, by a factor of about 20. For the first time, Gallo and collaborators are able to conclude that this discrepancy can not be fully accounted for by the mass gap between the two classes of objects (stellar black holes are more massive than neutron stars by a factor of five at least), nor by the excess X-ray emission arising from the boundary region between the neutron star surface and the impinging accretion inflow and is thus likely to reflect physical differences in the inflow efficiency or the jet powering mechanism.
Supermassive black holes: Gallo's extragalactic research spurs from the outstanding question whether indeed all galaxies host supermassive black holes. More specifically, it is still unclear whether galaxies less than one tenth the size of the Milky Way (that is, the bulk of the population by number) host supermassive black holes. While interesting in its own right, this question is intertwined with a more profound query: the origin of supermassive black holes. In “X-ray constraints on the local supermassive black hole occupation fraction” Gallo's group laid out a robust methodology to infer the local occupation fraction leveraging Chandra X-ray Telescope imaging observations of nearby galaxies. The preferred occupation fraction in the low-mass regime is constrained above 40% with high confidence, with no upper bound. This result tentatively disfavors heavy black holes as the predominant seeding mechanism at very high redshift.
Exoplanets: Gallo's work in this area concerns in the effect that the prolonged and/or variable high-energy stellar irradiation has on upper planetary atmospheres. Stellar extreme-UV and X-ray irradiation could severely impact planetary evolution, causing severe heating, thermally-driven escape, and possible evaporation of the original hydrogen-helium envelope. The recent surge in the number of known exoplanets, together with the imminent deployment of new ground and space-based facilities for exoplanet discovery and characterization require a prompt and efficient assessment of the most promising targets for intensive follow-up spectroscopic studies. Gallo has been worked on the development of ATES - a numerical code that is specifically designed to compute the temperature, density, velocity and ionization fraction profiles of highly irradiated planetary atmospheres of primordial composition, along with the instantaneous atmospheric mass loss rate. The latest applications of ATES involve modeling metastable helium absorption during transits and studying the effects of a rapidly cooling white dwarf spectrum on the upper atmospheres of any close-in planets.
Publications
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