Abell 665

Abell 665
300px Chandra X-ray image of Abell 665 Credit: NASA
Observation data (Epoch J2000)
Constellation(s)	Ursa Major
Right ascension	08h 30m 45.2s
Declination	+65° 52′ 55″
Brightest member	2MASX J08305736+6550299
Richness class	5
Bautz-Morgan classification	III
Velocity dispersion	1 390+120 −110 km/s
Redshift	0.1819
Distance (co-moving)	720 Mpc (2,348 Mly) h−1 0.73
ICM temperature	7.7 ± 0.4 keV (r ≲ 100 h−1 0.73 kpc)
Binding mass	~1015 h−1 0.75 M☉
X-ray flux	(11.8 ± 15.6%)×10−12 erg s−1 cm−2 (0.1—2.4 keV)
See also: Galaxy groups, Galaxy clusters, List of galaxy clusters

Abell 665 is a galaxy cluster in the Abell catalogue in the constellation Ursa Major. It is also known as the only cluster in his 1989 catalog to receive Abell's highest richness class of 5. This means that it contains at least 300 galaxies in the magnitude range of m₃ to m₃+2, where m₃ is the magnitude of the 3rd brightest member of the cluster. The clusters in all other richness classes contain less than 300 such galaxies. Abell 665's combination of high brightness and large distance, made it an excellent candidate along with 37 other clusters to help determine the Hubble constant using the Sunyaev–Zel'dovich effect in 2006.

Member velocity, cluster velocity dispersion, and X-ray data suggest that Abell 665 is composed of 2 similar-mass clusters which are at or very close to core crossing, give or take ≲ 0.5 Gyr.

See also

• List of Abell clusters