H1821+643

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

Supermassive Black Hole

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

The Schwarzschild diameter of this black hole is between Template:Convert and Template:Convert, 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, $\sim 1\mathrm{\%}$ the density of air at sea level on Earth.

External links

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

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