View source for H1821+643

{{Short description|Quasar in the
constellation Draco}}
{{Infobox quasar
| name = H1821+643
| image =File:H1821+643.jpg 
| caption=[[Chandra X-ray Observatory]] image of H1821+643
| epoch = J2000.0
| ra = {{RA|18|21|57.2365}} <!-- or {{Deg2HMS|0.0000|sup=yes}} -->
| dec = {{DEC|+64|20|36.226}}
| constellation name = [[Draco (constellation)|Draco]]
| z = 0.2970
| dist_ly = {{convert|3.4|Gly|Gpc}}
| type = [[Quasar]]
| appmag_v = 14.24
| size_v =
| notes =
| names =
| luminosity_specify
}}

'''H1821+643''' is an extraordinarily luminous, radio-quiet [[quasar]] in the [[constellation]] of [[Draco (constellation)|Draco]].
<ref name=joe>
{{cite journal 
|doi=10.1093/mnras/stu1067
| arxiv=1405.7522 
|last1 = Walker 
|first1 = S. A. 
|title = The effect of the quasar H1821+643 on the surrounding intracluster medium: Revealing the underlying cooling flow 
| journal=Monthly Notices of the Royal Astronomical Society 
| volume=442 
| issue=3 
| pages=2809 
|last2 =  Fabian 
|first2 = A. C. 
|last3 =  Russell 
|first3 = H. R. 
|last4 =  Sanders 
|first4 = J. S. 
|year = 2014 
| doi-access=free 
| bibcode=2014MNRAS.442.2809W 
}}
</ref>
The associated Active Galactic Nucleus (AGN) is situated in the Brightest Central Galaxy (BCG) of a massive (<math>\sim 6.3 \times 10^{14} M_\odot</math>), strong [[cooling flow]] cluster, CL 1821+64.<ref name="J S-R"/> Russel et al (2010) spatially isolated its X-ray signal from the surrounding cluster in Chandra X-ray observatory observations and computed <math>L_\odot = 10^{47} erg/s</math> from the observed X-ray luminosity. 
<ref name="J S-R">
{{cite arXiv 
<!--|doi=10.1093/mnras/stu1067-->
| arxiv=1405.7522 
|last1 = Sisk-Reynés
|first1 = J. 
|title = Evidence for a moderate spin from X-ray reflection of the high-mass supermassive black hole in the cluster-hosted quasar H1821+643
<!--
| journal=Monthly Notices of the Royal Astronomical Society 
| volume=
| issue= 
| pages=
| bibcode=
-->
|last2 =  Reynolds 
|first2 = C. S. 
|last3 =  Matthews
|first3 = J. H. 
|last4 =  Smith 
|first4 = R. N. 
|year = 2022
}}
</ref>

==Supermassive Black Hole==
The SMBH centred in CL 1821+64 is believed to be among the most massive in the known Universe.<ref name="J S-R"/> A variety of techniques have found different values for the mass. 5 studies found values <math>M_{BH} \sim 10^9 M_\odot</math>. Kim et al (2004) and Floyd et al (2008) used galactic bulge luminosity fits derived from Hubble data to find <math>10^9 M_\odot</math> and <math>3 \times 10^9 M_\odot</math> respectively. Russell et al (2010) provided a rough estimate of <math>M_{BH} \sim 3 \times 10^9</math>[[Solar mass|{{solar mass}}]].<ref name="J S-R"/> This was an underestimate with <math>\log(\Delta M_{BH}/M_\odot) \geq 1</math>. Kolman et al (1991) and Shapovalova (2016) independently modelled the quasar UV spectrum to find <math>M_{BH} \sim 3 \times 10^9 M_\odot</math>. Capellupo et al (2017) found <math>M_{BH} \sim 3 \times 10^9</math> using <math>H\beta</math> line emissions. 2 independent X-ray studies found significantly higher values. Reynolds et al (2014) found <math>6\times10^9 M_\odot</math> by modelling reflection from the accretion disc and Walker et al found <math>3\times10^{10} M_\odot</math> by modelling the interaction of the black hole with the Intracluster medium (ICM) as a Compton-cooled feeding cycle. <math>M_{BH}</math> is in the range <math>\log(M_{BH}/M_\odot) \sim 9.2 - 10.5</math>.<ref name="J S-R"/>

The [[Schwarzschild radius|Schwarzschild diameter]] of this black hole is between {{convert|9.4|Tm|AU|lk=on}} and {{convert|188|Tm|AU|lk=on}}, 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/m<sup>3</sup>, <math>\sim 1 \%</math> the density of [[Atmosphere of Earth|air at sea level on Earth]].<ref group="lower-alpha">Mass 3.0×10<sup>10</sup> * [[Solar mass|2.0×10<sup>30</sup>]]=6.0×10<sup>40</sup> kg. [[Sphere#Enclosed volume|Volume]] at radius 8.6×10<sup>13</sup> m is 2.66×10<sup>42</sup> m<sup>3</sup>.</ref>

==Footnotes==
{{notelist}}

==References==
{{Reflist}}

==External links==
* [https://simbad.u-strasbg.fr/simbad/sim-id?Ident=H1821%2B643 Simbad], [[SIMBAD]]
* [https://ned.ipac.caltech.edu/byname?objname=H1821%2B643&hconst=67.8&omegam=0.308&omegav=0.692&wmap=4&corr_z=1 NED], [[NASA/IPAC Extragalactic Database | NED]], NASA/IPAC Extragalactic Database

{{Draco (constellation)|state=collapsed}}

{{DEFAULTSORT:H1821 643}}
[[Category:Draco (constellation)]]
[[Category:Quasars]]
[[Category:Supermassive black holes]]


{{Quasar-stub}}