M87*

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. NED is NASA's catalogue of objects beyond our Galaxy. Known as: in SIMBAD, M 87 (the galaxy's name, which SIMBAD uses for the hole), M 87*, NGC 4486, Virgo A and 3C 274; in NED, Messier 087.

• Mass, in M☉ (the Sun's mass): 6.5 × 10⁹ ± 7 × 10⁸ M☉ (6.5 billion, ± 0.2 billion from the measurement and ± 0.7 billion from the method; the motion of its gas gives a lighter 3.5 +0.9/−0.7 billion), from the size of the ring in the Event Horizon Telescope image, at the distance below. Event Horizon Telescope Collaboration, “First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole”, The Astrophysical Journal Letters 875, L6 (2019). doi:10.3847/2041-8213/ab1141, arXiv:1906.11243 and J. L. Walsh et al., “The M87 Black Hole Mass from Gas-dynamical Models of Space Telescope Imaging Spectrograph Observations”, The Astrophysical Journal 770, 86 (2013). doi:10.1088/0004-637X/770/2/86, arXiv:1304.7273
• Spin, a* (0 is still, 1 is the fastest a hole can turn): 0.90 ± 0.05, from the twist in the light of the Event Horizon Telescope image, at about 95% confidence. F. Tamburini, B. Thidé and M. Della Valle, “Measurement of the spin of the M87 black hole from its observed twisted light”, Monthly Notices of the Royal Astronomical Society Letters (2020). doi:10.1093/mnrasl/slz176, arXiv:1904.07923
• Spin: > 0.8 (about 0.8, which the authors say is probably a lower limit), from how fast the inner gas turns, about 0.14 times the speed of light, read from the Event Horizon Telescope image. M. Drew et al., “New estimates of the spin and accretion rate of the black hole M87*”, The Astrophysical Journal Letters 984, L31 (2025). doi:10.3847/2041-8213/adc90e, arXiv:2505.17035
• Spin: No value. Models of the Event Horizon Telescope image with no spin make jets too weak to match. 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. Event Horizon Telescope Collaboration, “First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring”, The Astrophysical Journal Letters 875, L5 (2019). doi:10.3847/2041-8213/ab0f43, arXiv:1906.11242
• Spin drawn: 0.899, the middle of the range of published values (spin assumed).
• Feed: 2 × 10⁻⁵ (a feeding rate rather than a measure of its light; models that fit the image span 2 × 10⁻⁷ to 4 × 10⁻⁴), from the rate gas falls in, estimated from the density and size of the glowing region, over the rate that would make it shine at the Eddington limit. Event Horizon Telescope Collaboration, “First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring”, The Astrophysical Journal Letters 875, L5 (2019). doi:10.3847/2041-8213/ab0f43, arXiv:1906.11242
• Angle: 17.2 ± 3.3°, from the jet's angle to our line of sight, from the speeds and brightness of the jet and the fainter jet on the far side; another study puts it under 18.6°. F. Mertens et al., “Kinematics of the jet in M87 on scales of 100–1000 Schwarzschild radii”, Astronomy & Astrophysics 595, A54 (2016), eq. 4. doi:10.1051/0004-6361/201628829, arXiv:1608.05063 and R. C. Walker et al., “The Structure and Dynamics of the Sub-parsec Scale Jet in M87 Based on 50 VLBA Observations Over 17 Years at 43 GHz”, The Astrophysical Journal 855, 128 (2018). doi:10.3847/1538-4357/aaafcc, arXiv:1802.06166
• Distance: 5.48 × 10⁷ +2.61 × 10⁶/−2.28 × 10⁶ light years (16.8 +0.8/−0.7 Mpc, megaparsecs, each a million parsecs of 3.26 light years), from the distance the Event Horizon Telescope adopted from earlier measurements. Event Horizon Telescope Collaboration, “First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole”, The Astrophysical Journal Letters 875, L6 (2019). doi:10.3847/2041-8213/ab1141, arXiv:1906.11243
• Jet speed: 0.92 times the speed of light (the fast stream at its centre; a slower outer layer moves at about 0.5), from the motion of features in radio images of the jet within a parsec of the hole, at 43 GHz. F. Mertens et al., “Kinematics of the jet in M87 on scales of 100–1000 Schwarzschild radii”, Astronomy & Astrophysics 595, A54 (2016), eq. 4. doi:10.1051/0004-6361/201628829, arXiv:1608.05063

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.