H1821+643 is an extraordinarily luminous, radio-quiet quasar in the constellation of Draco. ^[1] The associated Active Galactic Nucleus (AGN) is situated in the Brightest Central Galaxy (BCG) of a massive (${\displaystyle \sim 6.3\times 10^{14}M_{\odot ))$), strong cooling flow cluster, CL 1821+64.^[2] Russel et al (2010) spatially isolated its X-ray signal from the surrounding cluster in Chandra X-ray observatory observations and computed ${\displaystyle L_{\odot }=10^{47}erg/s}$ from the observed X-ray luminosity. ^[2]

The SMBH centred in CL 1821+64 is believed to be among the most massive in the known Universe.^[2] A variety of techniques have found different values for the mass. 5 studies found values ${\displaystyle M_{BH}\sim 10^{9}M_{\odot ))$. Kim et al (2004) and Floyd et al (2008) used galactic bulge luminosity fits derived from Hubble data to find ${\displaystyle 10^{9}M_{\odot ))$ and ${\displaystyle 3\times 10^{9}M_{\odot ))$ respectively. Russell et al (2010) provided a rough estimate of ${\displaystyle M_{BH}\sim 3\times 10^{9))$M_☉.^[2] This was an underestimate with ${\displaystyle \log(\Delta M_{BH}/M_{\odot })\geq 1}$. Kolman et al (1991) and Shapovalova (2016) independently modelled the quasar UV spectrum to find ${\displaystyle M_{BH}\sim 3\times 10^{9}M_{\odot ))$. Capellupo et al (2017) found ${\displaystyle M_{BH}\sim 3\times 10^{9))$ using ${\displaystyle H\beta }$ line emissions. 2 independent X-ray studies found significantly higher values. Reynolds et al (2014) found ${\displaystyle 6\times 10^{9}M_{\odot ))$ by modelling reflection from the accretion disc and Walker et al found ${\displaystyle 3\times 10^{10}M_{\odot ))$ by modelling the interaction of the black hole with the Intracluster medim (ICM) as a Compton-cooled feeding cycle. ${\displaystyle M_{BH))$ is in the range ${\displaystyle \log(M_{BH}/M_{\odot })\sim 9.2-10.5}$.^[2]

The Schwarzschild diameter of this black hole is between 9.4 terametres (63 AU) and 188 terametres (1,260 AU), which is about 16 times the diameter of Pluto's orbit. If the hole were a Euclidean sphere, the average density would be 18 g/m³, ${\displaystyle \sim 1\%}$ the density of air at sea level on Earth.^[a]

• Simbad, SIMBAD
• NED, NED, NASA/IPAC Extragalactic Database

v t e Constellation of Draco
List of stars in Draco Draco in Chinese astronomy
Stars	Bayer α (Thuban) β (Rastaban) γ (Eltanin) δ (Altais) ε (Tyl) ζ (Aldhibah) η (Athebyne) θ ι (Edasich) κ λ (Giausar) μ (Alrakis) ν (Kuma) ξ (Grumium) ο π ρ σ (Alsafi) τ υ φ χ ψ1 (Dziban) ψ2 ω Flamsteed 6 7 (Tianyi) 8 (Taiyi) 10 (i) 15 (A) 18 (g) 19 (h) 26 36 39 (b) 42 (Fafnir) 45 (d) 64 (e) 68 Variable TW AG BY CL CM CX DO V581 HR 3751 4126 4934 5811 6237 6618 (Alruba) 6817 7137 7783 HD 101364 156279 158259 176693 191939 Other 2MASS 1237+6526 2MASS J17554042+6551277 G 240-72 GD 356 Gliese 420 Gliese 625 Gliese 687 GRW +70 8247 Kepler-4 Kepler-10 Kepler-12 Kepler-90 Kepler-296 LP 71-82 Qatar-1 Struve 2398 TOI-1136 WISE 1647+5632
Exoplanets Orbitar HD 139357 b HD 167042 b Hypatia Kepler-4b Kepler-10b c Kepler-12b Kepler-90e f g h i TOI-1452 b TrES-2b
Star clusters LAMOST 1
Nebulae Abell 50 Cat's Eye Nebula
Galaxies	NGC 3147 4121 4125 4236 4319 4345 4513 4589 5678 5777 5866 5866B 5879 5906 5907 5949 5963 5965 5982 5985 6090 6248 6285 6286 6340 6365 6373 6394 6412 6503 6566 6621 6622 6670 6786 6789 Other 3C 249.1 3C 305 3C 319 3C 371 3C 390.3 3C 401 4C +72.26 H1821+643 HFLS3 KKR 25 PGC 39058 UGC 9391
Galaxy clusters Abell 2218 CL1358+62 Draco Supercluster
Astronomical events Swift J1644+57 SN 2005B SN 2016aps
Category