GRS 1915+105

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, Granat 1915+105, V1487 Aql and NOVA Aql 1992.

• Mass, in M☉ (the Sun's mass): 12.4 +2.0/−1.8 M☉, from the companion star's orbit, with the parallax distance. M. J. Reid et al., “A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass”, The Astrophysical Journal 796, 2 (2014). doi:10.1088/0004-637X/796/1/2, arXiv:1409.2453
• Spin, a* (0 is still, 1 is the fastest a hole can turn): > 0.98, from continuum fitting. J. E. McClintock et al., “The Spin of the Near-Extreme Kerr Black Hole GRS 1915+105”, The Astrophysical Journal 652, 518 (2006). doi:10.1086/508457, arXiv:astro-ph/0606076
• Spin: 0.86 +0.13/−0.46 (best fit 0.86; 0.4 to 0.99 allowing for the errors in its mass, tilt and distance), from continuum fitting with the parallax mass, tilt and distance. B. S. Mills, S. W. Davis and M. J. Middleton, “The black hole spin in GRS 1915+105, revisited”, The Astrophysical Journal (2021). doi:10.3847/1538-4357/abf2b7, arXiv:2101.11655
• Spin: 0.56 ± 0.02, from reflection, from Suzaku in its hard state, fitting below 10 keV. J. L. Blum et al., “Measuring the Spin of GRS 1915+105 with Relativistic Disk Reflection”, The Astrophysical Journal 706, 60 (2009). doi:10.1088/0004-637X/706/1/60, arXiv:0909.5383
• Spin: 0.98 ± 0.01, from the same data fitted over the whole band. J. L. Blum et al., “Measuring the Spin of GRS 1915+105 with Relativistic Disk Reflection”, The Astrophysical Journal 706, 60 (2009). doi:10.1088/0004-637X/706/1/60, arXiv:0909.5383
• Spin: 0.976 +0.018/−0.056, from reflection, refitting every NuSTAR observation. Where a spin has several published values, each one is listed with its method. The picture is drawn at the middle of the range of published values. P. A. Draghis et al., “Systematically Revisiting All NuSTAR Spins of Black Holes in X-Ray Binaries”, The Astrophysical Journal 969, 40 (2024). doi:10.3847/1538-4357/ad43ea, arXiv:2311.16225
• Spin drawn: 0.699, the middle of the range of published values (spin assumed).
• Feed: From 10% to 100% of the Eddington rate in X-rays from 1992 to 2018. Since 2018 it has been far fainter, about 1% in its hard state, which may be because gas now hides it. K. I. I. Koljonen and T. Hovatta, “ALMA/NICER observations of GRS 1915+105 indicate a return to a hard state”, Astronomy & Astrophysics (2021), §3.1. doi:10.1051/0004-6361/202039581, arXiv:2102.00693 and S. E. Motta et al., “Observations of a radio-bright, X-ray obscured GRS 1915+105”, Monthly Notices of the Royal Astronomical Society 503, 152 (2021). doi:10.1093/mnras/stab511, arXiv:2101.01187
• Angle: 60 ± 5°, from the jet's angle to our line of sight, from blobs thrown out in both directions, at the parallax distance; the inner disc's tilt from X-ray reflection is 60 ± 8. M. J. Reid et al., “A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass”, The Astrophysical Journal 796, 2 (2014). doi:10.1088/0004-637X/796/1/2, arXiv:1409.2453 and P. A. Draghis et al., “Systematically Revisiting All NuSTAR Spins of Black Holes in X-Ray Binaries”, The Astrophysical Journal 969, 40 (2024). doi:10.3847/1538-4357/ad43ea, arXiv:2311.16225
• Distance: 28 049 +6 523/−5 218 light years (8.6 +2.0/−1.6 kpc, kiloparsecs, each a thousand parsecs of 3.26 light years), from radio parallax. M. J. Reid et al., “A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass”, The Astrophysical Journal 796, 2 (2014). doi:10.1088/0004-637X/796/1/2, arXiv:1409.2453
• The companion star's orbit, once round: 33.85 ± 0.16 days, from the star's radial velocities (§3). D. Steeghs et al., “The not-so-massive black hole in the microquasar GRS 1915+105”, The Astrophysical Journal 768, 185 (2013). doi:10.1088/0004-637X/768/2/185, arXiv:1304.1808
• Its distance from the hole, halfway between nearest and farthest: 0.48 au, from Kepler's third law, from the period and the two masses, 12.4 and 0.47 suns. D. Steeghs et al., “The not-so-massive black hole in the microquasar GRS 1915+105”, The Astrophysical Journal 768, 185 (2013). doi:10.1088/0004-637X/768/2/185, arXiv:1304.1808 and M. J. Reid et al., “A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass”, The Astrophysical Journal 796, 2 (2014). doi:10.1088/0004-637X/796/1/2, arXiv:1409.2453
• Its eccentricity (0 is a circle): 0 (assumed: a circle fits the velocities), from a sine wave fitted to the star's radial velocities (§3). D. Steeghs et al., “The not-so-massive black hole in the microquasar GRS 1915+105”, The Astrophysical Journal 768, 185 (2013). doi:10.1088/0004-637X/768/2/185, arXiv:1304.1808
• How it lies on our sky: not measured, since only the star's speed towards and away from us is known. The zoomed-out orbit is drawn with its rising node due north, going round anticlockwise, and with the star in front of the hole on 19 September 2010 (± 0.06 days), from the velocity fit's phase zero, which the paper calls the star's conjunction without saying which one, taken here as the star passing in front of the hole. D. Steeghs et al., “The not-so-massive black hole in the microquasar GRS 1915+105”, The Astrophysical Journal 768, 185 (2013). doi:10.1088/0004-637X/768/2/185, arXiv:1304.1808
• The companion star's mass: 0.47 ± 0.27 M☉, from the mass ratio, from how fast the star spins and how fast it orbits. D. Steeghs et al., “The not-so-massive black hole in the microquasar GRS 1915+105”, The Astrophysical Journal 768, 185 (2013). doi:10.1088/0004-637X/768/2/185, arXiv:1304.1808
• The companion star's radius: not published
• The companion star's surface temperature: not published; the star is a K-type giant M. J. Reid et al., “A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass”, The Astrophysical Journal 796, 2 (2014). doi:10.1088/0004-637X/796/1/2, arXiv:1409.2453
• Jet speed: between 0.65 and 0.81 times the speed of light, changing from one ejection to the next, from blobs thrown out in both directions at the parallax distance. An earlier study, which assumed a larger distance, found 0.98 M. J. Reid et al., “A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass”, The Astrophysical Journal 796, 2 (2014). doi:10.1088/0004-637X/796/1/2, arXiv:1409.2453 and R. P. Fender et al., “MERLIN observations of relativistic ejections from GRS 1915+105”, Monthly Notices of the Royal Astronomical Society 304, 865 (1999). doi:10.1046/j.1365-8711.1999.02364.x, arXiv:astro-ph/9812150

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.