Gaia BH1

Where the numbers come from

There is no catalogue of black holes as such, as far as we know. A hole goes by the name of something we can see: the star orbiting it, the X-ray source, the galaxy around it. When two black holes merge into one, the new hole is named for the date the ripple in space from the merger (its gravitational waves) reached the detectors on Earth that listen for them. SIMBAD is astronomers' online catalogue of objects beyond the Solar System. Known as: in SIMBAD, GALEX J172841.0-003451 (the companion star's name, which SIMBAD uses for the pair), Gaia DR3 4373465352415301632 and 2MASS J17284110-0034514.

• Mass, in M☉ (the Sun's mass): 9.62 ± 0.18 M☉, from joint fit of the star's Gaia astrometric orbit and its radial velocities. K. El-Badry et al., “A Sun-like star orbiting a black hole”, Monthly Notices of the Royal Astronomical Society 518, 1057 (2023). doi:10.1093/mnras/stac3140, arXiv:2209.06833
• Spin, a* (0 is still, 1 is the fastest a hole can turn): No published measurement that we could find.
• Spin drawn: 0.6, the value the homepage picture starts on. We found no published value, so this is an assumption.
• Feed: < 2.1 × 10⁻¹⁰, from Chandra's X-ray upper limit, L_X < 10^29.4 erg/s, divided by the Eddington luminosity for this mass. A. C. Rodriguez et al., “The Quiescent X-ray and Radio Emission of Gaia BH1 and Gaia BH2”, Publications of the Astronomical Society of the Pacific 136, 024203 (2024). arXiv:2311.05685
• Angle: 126.6 ± 0.4°, from the star's orbital inclination, from the joint fit (Table 1). The angle is the tilt of the companion star's orbit, since no disc has been seen; the orbit is drawn as if it were the disc's plane. An inclination over 90° means the star goes round clockwise as we see it, so the view is 53° from face-on. K. El-Badry et al., “A Sun-like star orbiting a black hole”, Monthly Notices of the Royal Astronomical Society 518, 1057 (2023). doi:10.1093/mnras/stac3140, arXiv:2209.06833
• Distance: 1 570 light years (480 pc), from Gaia parallax. K. El-Badry et al., “A Sun-like star orbiting a black hole”, Monthly Notices of the Royal Astronomical Society 518, 1057 (2023). doi:10.1093/mnras/stac3140, arXiv:2209.06833
• The companion star's orbit, once round: 185.59 ± 0.05 days, from the joint fit (Table 1). K. El-Badry et al., “A Sun-like star orbiting a black hole”, Monthly Notices of the Royal Astronomical Society 518, 1057 (2023). doi:10.1093/mnras/stac3140, arXiv:2209.06833
• Its distance from the hole, halfway between nearest and farthest: 1.40 ± 0.01 au, from the joint fit (Table 1). K. El-Badry et al., “A Sun-like star orbiting a black hole”, Monthly Notices of the Royal Astronomical Society 518, 1057 (2023). doi:10.1093/mnras/stac3140, arXiv:2209.06833
• Its eccentricity (0 is a circle): 0.451 ± 0.005, from the joint fit (Table 1). K. El-Badry et al., “A Sun-like star orbiting a black hole”, Monthly Notices of the Royal Astronomical Society 518, 1057 (2023). doi:10.1093/mnras/stac3140, arXiv:2209.06833
• How it lies on our sky: its rising node 97.8 ± 1.0° east of north, its nearest point 12.8 ± 1.1° on from that, reached on 31 December 2015 (± 0.7 days), from the joint fit (Table 1). K. El-Badry et al., “A Sun-like star orbiting a black hole”, Monthly Notices of the Royal Astronomical Society 518, 1057 (2023). doi:10.1093/mnras/stac3140, arXiv:2209.06833
• The companion star's mass: 0.93 ± 0.05 M☉, from stellar models fitted to its spectrum and brightness. K. El-Badry et al., “A Sun-like star orbiting a black hole”, Monthly Notices of the Royal Astronomical Society 518, 1057 (2023). doi:10.1093/mnras/stac3140, arXiv:2209.06833
• The companion star's radius: 0.99 ± 0.05 solar radii, from its spectrum and brightness. K. El-Badry et al., “A Sun-like star orbiting a black hole”, Monthly Notices of the Royal Astronomical Society 518, 1057 (2023). doi:10.1093/mnras/stac3140, arXiv:2209.06833
• The companion star's surface temperature: 5 850 ± 50 K, from its spectrum. K. El-Badry et al., “A Sun-like star orbiting a black hole”, Monthly Notices of the Royal Astronomical Society 518, 1057 (2023). doi:10.1093/mnras/stac3140, arXiv:2209.06833

Every number on this page is quoted from a published paper or a catalogue, with the method it came from. No image or data file from these sources is loaded, so there is nothing to licence; the figure is our own drawing from their numbers.