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Peer-reviewedCC BY 4.0The Astrophysical Journal Supplement Series

Black Hole Astrometric Binaries in the Roman Galactic Bulge Time Domain Survey

  • Casey Y. Lam1
  • Jessica R. Lu2
  • Kareem El-Badry2
  • Anil Seth3
  • Joshua D. Simon1
  • Natasha S. Abrams2
  • Andrea Bellini4
  • Matthew W. Hosek5
  • Peter McGill6
6 affiliations
  1. 1Observatories of the Carnegie Institution for Science
  2. 2Department of Astronomy
  3. 3Department of Physics and Astronomy
  4. 4Space Telescope Science Institute
  5. 5UCLA Department of Physics and Astronomy
  6. 6Space Science Institute
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Abstract

The Nancy Grace Roman Space Telescope (Roman), NASA’s newest flagship mission, launched 2026 August 30. As part of its mission, Roman will conduct the Galactic Bulge Time Domain Survey (GBTDS), which will generate ∼50,000 epochs of high-precision photometric and astrometric data for ∼10 ⁸ sources across 1.7 deg ² in the Galactic bulge. Roman GBTDS astrometry is comparable to Gaia Data Release 4 in terms of number of stars, astrometric precision, and time baseline, and is highly complementary in terms of wavelength and sky location. In this paper, we investigate a synthetic population of GBTDS sources to characterize the detectability of unresolved astrometric binaries, in particular those with compact object companions. Assuming the occurrence rate of black holes (BHs) and neutron stars (NSs) in astronomical-unit-scale orbits around stars is 10 ⁻⁷ and 10 ⁻⁶ , respectively, and that Roman achieves an astrometric precision of 1% of a pixel, O ( 10 ) BH+star and O ( 10 ) NS+star detached binaries will be detectable. The BHs will have median mass measurement uncertainties of ∼25%, increasing the existing sample of detached astrometric BH binaries by a factor of 3. Together with the O ( 1 0 2 ) isolated BHs expected to be discovered by microlensing in the Roman GBTDS and an additional O ( 10 ) detached BH binaries in Gaia DR4, this will provide a representative view of the quiescent Galactic stellar-mass BH population.

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Cite

BibTeXRIS
BibTeX
@article{lam2026black,
  title = {{Black Hole Astrometric Binaries in the Roman Galactic Bulge Time Domain Survey}},
  author = {Casey Y. Lam and Jessica R. Lu and Kareem El-Badry and Anil Seth and Joshua D. Simon and Natasha S. Abrams and Andrea Bellini and Matthew W. Hosek and Peter McGill},
  journal = {The Astrophysical Journal Supplement Series},
  year = {2026},
  month = nov,
  doi = {10.3847/1538-4365/aeae25},
  url = {https://iopscience.iop.org/article/10.3847/1538-4365/aeae25},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Black Hole Astrometric Binaries in the Roman Galactic Bulge Time Domain Survey
AU  - Casey Y. Lam
AU  - Jessica R. Lu
AU  - Kareem El-Badry
AU  - Anil Seth
AU  - Joshua D. Simon
AU  - Natasha S. Abrams
AU  - Andrea Bellini
AU  - Matthew W. Hosek
AU  - Peter McGill
PY  - 2026
DA  - 2026/11/02
JO  - The Astrophysical Journal Supplement Series
DO  - 10.3847/1538-4365/aeae25
UR  - https://iopscience.iop.org/article/10.3847/1538-4365/aeae25
AB  - The Nancy Grace Roman Space Telescope (Roman), NASA’s newest flagship mission, launched 2026 August 30. As part of its mission, Roman will conduct the Galactic Bulge Time Domain Survey (GBTDS), which will generate ∼50,000 epochs of high-precision photometric and astrometric data for ∼10 ⁸ sources across 1.7 deg ² in the Galactic bulge. Roman GBTDS astrometry is comparable to Gaia Data Release 4 in terms of number of stars, astrometric precision, and time baseline, and is highly complementary in terms of wavelength and sky location. In this paper, we investigate a synthetic population of GBTDS sources to characterize the detectability of unresolved astrometric binaries, in particular those with compact object companions. Assuming the occurrence rate of black holes (BHs) and neutron stars (NSs) in astronomical-unit-scale orbits around stars is 10 ⁻⁷ and 10 ⁻⁶ , respectively, and that Roman achieves an astrometric precision of 1% of a pixel, O ( 10 ) BH+star and O ( 10 ) NS+star detached binaries will be detectable. The BHs will have median mass measurement uncertainties of ∼25%, increasing the existing sample of detached astrometric BH binaries by a factor of 3. Together with the O ( 1 0 2 ) isolated BHs expected to be discovered by microlensing in the Roman GBTDS and an additional O ( 10 ) detached BH binaries in Gaia DR4, this will provide a representative view of the quiescent Galactic stellar-mass BH population.
SN  - 0067-0049
SN  - 1538-4365
ER  -