My research interests include supermassive black holes in low-mass galaxies, nuclear star clusters, and transient and variable astrophysical phenomena. You can read more about these areas below.

Black holes in low mass galaxies

Observations have shown that every massive galaxy (roughly the size of our Milky Way and larger) contains a massive black hole at the center. However, the population of massive black holes at the centers of dwarf galaxies remains relatively elusive. My primary research interests involve searching for and studying black holes in the smallest galaxies to better understand massive black hole formation and growth over cosmic time. I am particularly focused on using photometric variability to identify AGN in low mass galaxies that are missed by other selection techniques.

Papers on AGN variability in low-mass galaxies

• “A search for optical AGN variability in 35,000 low-mass galaxies with the Palomar Transient Factory” (Baldassare, Geha & Greene 2020)

• “Identifying AGNs in Low-mass Galaxies via Long-term Optical Variability” (Baldassare, Geha & Greene 2018)

Papers on properties of AGN in low-mass galaxies

• “Populating the low-mass end of the M-sigma relation” (Baldassare et al. 2020b)

• “Hubble Space Telescope Imaging of the Active Dwarf Galaxy RGG 118” (Baldassare et al. 2017b)

• “X-ray and Ultraviolet Properties of AGNs in Nearby Dwarf Galaxies” (Baldassare et al. 2017a)

• “Multi-epoch Spectroscopy of Dwarf Galaxies with AGN Signatures: Identifying Sources with Persistent Broad Hα Emission” (Baldassare et al. 2016)

• “A 50,000 Solar Mass Black Hole in the Nucleus of RGG 118” (Baldassare et al. 2015)

Transient and variable phenomena

Through my work on variability of active galactic nuclei, I have become interested in other transient and variable phenomena discovered through repeat imaging surveys, including “changing state” AGN and stellar transients. Recently, collaborators and I studied an unusually long lived stellar transient in the extremely metal poor dwarf galaxy PHL 293B. I am also a member of the Young Supernova Experiment, a time domain survey using the Pan-STARRS telescopes.

Paper: “The Curious Case of PHL 293B: A Long-Lived Transient in a Metal-Poor Blue Compact Dwarf Galaxy” (Burke, Baldassare et al. 2020)

Nuclear star clusters

Dense nuclear star clusters are often found at the centers of low-mass galaxies, but there are many open questions relating to their formation and possible links to massive black holes. It has even been proposed that nuclear star clusters can lead to the formation of massive black holes. I am interested in the using the properties of nuclear star clusters to constrain possible formation pathways, as well as studying their co-existence with massive black holes.

Paper: “Massive black hole formation in dense stellar environments: Enhanced X-ray detection rates in high velocity dispersion nuclear star clusters” (Baldassare et al. 2022)

Paper: “AGN Activity in Nucleated Galaxies as Measured by Chandra” (Foord et al. 2017)

Paper: “Nucleation of Early-type Galaxies in the Field versus Cluster Environment” (Baldassare et al. 2014)