Gaia BH3

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, LS II +14 13 (the companion star's name, which SIMBAD uses for the pair), Gaia DR3 4318465066420528000 and 2MASS J19391872+1455542.

• Mass, in M☉ (the Sun's mass): 32.70 ± 0.82 M☉, from the giant star's astrometric orbit in pre-release Gaia data, with radial velocities. Gaia Collaboration, P. Panuzzo et al., “Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry”, Astronomy & Astrophysics Letters (2024). doi:10.1051/0004-6361/202449763, arXiv:2404.10486
• 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: No measurement was checked for this hole; nothing is seen falling in.
• Angle: 110.6 ± 0.1°, from the star's orbital inclination (Table 2; the two fits give 110.58 ± 0.10 and 110.66 ± 0.11). The angle is the tilt of the companion star's orbit, drawn as if it were the disc's plane; over 90° means the star goes round clockwise as we see it, so the view is 69° from face-on. Gaia Collaboration, P. Panuzzo et al., “Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry”, Astronomy & Astrophysics Letters (2024). doi:10.1051/0004-6361/202449763, arXiv:2404.10486
• Distance: 1 920 light years (590 pc), from Gaia parallax. Gaia Collaboration, P. Panuzzo et al., “Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry”, Astronomy & Astrophysics Letters (2024). doi:10.1051/0004-6361/202449763, arXiv:2404.10486
• The companion star's orbit, once round: 4 253.1 ± 98.5 days, from the combined solution (Table 2). Gaia Collaboration, P. Panuzzo et al., “Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry”, Astronomy & Astrophysics Letters (2024). doi:10.1051/0004-6361/202449763, arXiv:2404.10486
• Its distance from the hole, halfway between nearest and farthest: 16.55 ± 0.28 au, from the star's orbit round the pair's centre, 16.17 ± 0.27 au (Table 2), scaled up by the total mass over the hole's, (32.70 + 0.76) / 32.70. Gaia Collaboration, P. Panuzzo et al., “Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry”, Astronomy & Astrophysics Letters (2024). doi:10.1051/0004-6361/202449763, arXiv:2404.10486
• Its eccentricity (0 is a circle): 0.7291 ± 0.0048, from the combined solution (Table 2). Gaia Collaboration, P. Panuzzo et al., “Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry”, Astronomy & Astrophysics Letters (2024). doi:10.1051/0004-6361/202449763, arXiv:2404.10486
• How it lies on our sky: its rising node 136.236 ± 0.128° east of north, its nearest point 77.34 ± 0.76° on from that, reached on 27 February 2018 (± 0.88 days), from the combined solution (Table 2). Gaia Collaboration, P. Panuzzo et al., “Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry”, Astronomy & Astrophysics Letters (2024). doi:10.1051/0004-6361/202449763, arXiv:2404.10486
• The companion star's mass: 0.76 ± 0.05 M☉, from stellar models fitted to its spectrum and brightness (Table 3). Gaia Collaboration, P. Panuzzo et al., “Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry”, Astronomy & Astrophysics Letters (2024). doi:10.1051/0004-6361/202449763, arXiv:2404.10486
• The companion star's radius: 4.936 ± 0.016 solar radii, from its brightness and temperature (Table 3). Gaia Collaboration, P. Panuzzo et al., “Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry”, Astronomy & Astrophysics Letters (2024). doi:10.1051/0004-6361/202449763, arXiv:2404.10486
• The companion star's surface temperature: 5 212 ± 80 K, from its spectrum (Table 3). Gaia Collaboration, P. Panuzzo et al., “Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry”, Astronomy & Astrophysics Letters (2024). doi:10.1051/0004-6361/202449763, arXiv:2404.10486

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.