NGC 5466

NGC 5466 is a globular cluster of stars in the constellation Boötes. It was discovered by German-British astronomer William Herschel on May 17, 1784, and catalogued as H VI.9.^[8] This large, dim cluster has an apparent visual magnitude of 9.2 and spans an angular size of 9.0′.^[4] It is relatively distant from the Sun,^[3] about 52 thousand light-years (16.0 kpc) away,^[3][9] and 53 thousand light-years (16.3 kpc) from the Galactic Center.^[10]

NGC 5466
NGC 5466 by Hubble Space Telescope; 3.5′ view
Observation data (J2000 epoch)
Class	XII[1]
Constellation	Boötes
Right ascension	14h 05m 27.29s[2]
Declination	+28° 32′ 04.0″[2]
Distance	4.91 ± 0.12 kpc (16.0 ± 0.4 kly)[3]
Apparent magnitude (V)	9.2[4]
Apparent dimensions (V)	9.0′[4]
Physical characteristics
Absolute magnitude	−6.98[3]
Mass	1.79×105[5] M☉
Tidal radius	238.0 ly (72.98 pc)[3]
VHB	16.47
Metallicity	${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = –1.95±0.02[6] dex
Estimated age	12.15±0.11 Gyr[6]
Notable features	Tidal stream
Other designations	NGC 5466, C 1403+287, GCl 27, GC 3776, h 1746, H 6[7]
See also: Globular cluster, List of globular clusters

Observations

The Shapley–Sawyer Concentration Class of NGC 5466 is XII.^[1] This is a loose cluster with an unusually low central density compared to other globulars with similar luminosity.^[11] It is located at a high galactic latitude and thus displays negligible reddening from interstellar dust.^[11] The cluster has a core radius of 1.43′±0.10′ and a half-light radius of 2.3′±0.07′. The King tidal radius is 238.0 ly (72.98 pc).^[3]

Observation of the distribution of stars in the cluster shows the impact of mass segregation, with heavier objects sinking toward the center. This is a dynamically young cluster that is just starting to evolve.^[12] An isochrone fit to the cluster yields an age estimate of 12.15±0.11 billion years.^[6] Other age estimates range from 12.2±0.9 to 13.57 Gyr, depending on the method.^[9][13] It has an extremely low metallicity.^[6]

In 2006, a long tidal stream was detected stretching from this cluster,^[14] perhaps reaching as far as 45° to 60° across the sky.^[15][16] It has a combined mass estimated as 4.0×10³ M_☉.^[3] The width dispersion of the stream is 1.31°±0.24°, corresponding to a physical width of 1,200 ± 220 ly (367 ± 67 pc) at the distance of the cluster.^[3] The presence of a tidal tail suggests the cluster has been strongly disrupted due to gravitational interactions with the Milky Way galaxy.^[11] At some point, this stream may have been tidally disrupted by the Large Magellanic Cloud.^[16]

A total of 97 blue straggler stars have been identified in this cluster, which show a mild central peak in distribution.^[17] In 2019, it was reported that a candidate hot white dwarf had been discovered orbiting a blue straggler star in the outskirts of NGC 5466. This was the second such pair discovered in a globular cluster.^[18] Three short period eclipsing binaries have been found along with six SX Phoenicis variables.^[19][20] This was the first globular where a blue straggler eclipsing variable was found.^[12] The cluster is host to the brightest-known anomalous Cepheid variable, designated V19.^[21][22]

Gallery

• 
  The location of NGC 5466 (circled in red)
• 
  NGC 5466 imaged with a 32-inch telescope

See also

• List of stellar streams