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The only way to detect black holes is through their influence on their surroundings. Black holes can be detected when their extreme gravity effects nearby luminous gas and stars. They can also be detected from the gravitational waves generated when two black holes merge. Both of these methods require that the black hole is in close proximity to other objects - gas, stars, or another black hole in a binary system. None of these methods can be used to find free-floating, isolated black holes. Luckily, general relativity gives us another way that these dark objects can be detected.
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Finding Black Holes with Gravitational Lensing
We are searching for black holes in the Milky Way using gravitational lensing. Our Galaxy likely contains 100 million stellar-mass black holes. The number and mass statistics of black holes can provide important constraints on the star formation history, the stellar mass function, supernova physics and how BHs form, the equation of state of nuclear matter, and the existence of primordial black holes. To date, isolated stellar-mass black holes have never been definitively detected and only two dozen black holes in our Galaxy have measured masses – all in binaries.
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DOS: Distance between the observer and the source.
Easy math inline
Einstein Radius (θE): Angular radius of the circular image created when the source and lens are aligned along the line of sight of the observer.
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Where G is the gravitational constant, ML is mass of the lens, and c is the speed of light.
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tE: Einstein crossing time. The time it takes for the lens to traverse the Einstein radius
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$$\theta_E = \mu_{rel} t_E$$ |
Microlensing with ZTF
Members: Michael Medford, Jessica Lu,
Collaborators: Will Dawson (LLNL)
60 Microlensing Events from the Three Years of Zwicky Transient Facility Phase One (Medford, Abrams et al. 2023)
Gravitational Microlensing Event Statistics for the Zwicky Transient Facility (Medford et al. 2020)
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Members: Jessica Lu, Casey Lam, Natasha Abrams
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, Jeff Chen
A re-analysis of the isolated black hole candidate OGLE-2011-BLG-0462/MOA-2011-BLG-191 (Lam et al. 2023)
An Isolated Mass-gap Black Hole or Neutron Star Detected with Astrometric Microlensing (Lam et al. 2022)
Supplement: "An Isolated Mass-gap Black Hole or Neutron Star Detected with Astrometric Microlensing" (2022, ApJL, 933, L23) (Lam et al. 2022)
From Stars to Compact Objects: The Initial-Final Mass Relation (Lu et al. 2019)
A Search for Stellar-Mass Black Holes via Astrometric Microlensing (Lu et al. 2016)
Finding Black Holes with Photometric Microlensing
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Collaborators: Matt Hosek (UCLA)
The Impact of Initial-Final Mass Relations on Black Hole Microlensing (Rose et al., 2022)
PopSyCLE: A New Population Synthesis Code for Compact Object Microlensing Events (Lam et al. 2020)
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Members: Jessica Lu, Casey Lam, Kingsley Ehrich, Matt Ortiz, Theophilus Pedapolu, Sean Terry
Collaborators: Keming Zhang, Josh Bloom, Scott Gaudi (OSU), Francois Lanusse (U Paris-Saclay)
Other Microlensing and Compact Object Work
This work is generally led out of other groups with muLab members collaborating on the work.
A Search for Predicted Astrometric Microlensing Events by Nearby Brown Dwarfs (Luberto et al. 2022)
Adaptive Optics Imaging Can Break the Central Caustic Cusp Approach Degeneracy in High-magnification Microlensing Events (Terry et al. 2022)
Searching for a Hypervelocity White Dwarf SN Ia Companion: A Proper-motion Survey of SN 1006 (Shields et al. 2022)
MOA-2007-BLG-400 A Super-Jupiter-mass Planet Orbiting a Galactic Bulge K-dwarf Revealed by Keck Adaptive Optics Imaging (Bhattacharya et al. 2021)
MOA-2009-BLG-319Lb: A Sub-Saturn Planet inside the Predicted Mass Desert (Terry et al. 2021)